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Myxozoa represent a diverse group of microscopic cnidarian endoparasites alternating between invertebrate and vertebrate hosts. Of the approximately 2,600 species described predominantly from teleost fish, only 1.8% have been reported from cartilaginous fishes (Elasmobranchii). As ancestral vertebrate hosts of myxozoans, elasmobranchs may have played an important role in myxozoan evolution, however, they are also some of the largest vertebrate hosts known for this group of parasites. We screened 50 elasmobranchs belonging to nine species and seven families, from various geographical areas, for myxozoan infection. We found a 22% overall prevalence of myxozoans in elasmobranchs and describe five species new to science. We investigated, for the first known time, the evolution of spore size within three phylogenetic clades, Ceratomyxa, Sphaerospora sensu stricto and Parvicapsula. We found that spores from elasmobranch-infecting myxozoans were on average 4.8× (Ceratomyxa), 2.2× (Parvicapsula clade) and 1.8× (Sphaerospora sensu stricto except polysporoplasmic Sphaerospora spp.) larger than those from teleosts. In all analysed clades, spore size was correlated with phylogenetic position. In ceratomyxids, it was further strongly positively correlated with fish body size and habitat depth, independent of cellular composition of the spores and phylogenetic position in the tree. While in macroparasites a host size-correlated increase in parasite size occurs on a large scale and is often related to improved exploitation of host resources, in microscopic parasites size ranges vary at the scale of a few micrometres, disproportionate to the available additional space in a large host. We discuss the ecological role of these changes with regard to transmission under high pressure and an invertebrate fauna that is adapted to deeper marine habitats.

Sloths and ground sloths (Xenarthra: Tardigrada) are among the most conspicuous mammals in the Cenozoic faunas of South America. During the late Pleistocene and the early Holocene, all the megafaunal xenarthrans became extinct. While much attention has been paid to understanding the causes of megafauna extinction, less attention has been given to understanding the impacts of the loss of the megafauna on other organisms with whom they interacted. Paleoparasitology offers the opportunity to look back into the past and observe directly how parasites responded to environmental change and host decline events. The present work is the first paleoparasitological study on megaherbivores dung from the archaeological site Cueva Huenul 1 (northwestern Patagonia, Argentina). Twenty one dung samples were examined for parasites. Samples were processed by rehydration in a 0.5% water solution of trissodium phosphate, followed by homogenization, filtered and processed by spontaneous sedimentation. Additionally, microhistological analyses of three samples were made. The dung samples were identified as belonging to a ground sloth. Ground sloths from northwestern Patagonia were infected by the nematodes Trichostrongylus sp., Nematodirus sp., at least three Strongylida-type species, Trichuris sp., one ascaridid and one unidentified nematode. Also, the results indicated that the diet was mainly based on shrub species (Schinus johnstonii, Prosopis sp., Berberis empetrifolia, Ephedra chilense and Retanilla patagonica), typical of the Monte vegetation. Also, the cacti Maihuenia and the grasses Festuca kurtziana, Hordeum comosum, Stipa speciosa and Poa sp. (Family Poaceae) were found but in less frequency. The host-parasite-environment interactions, the potential parasitic diseases and ecological consequences of the ground sloth extinction are discussed. This study shows the potential of paleoparasitological studies of ancient feces to contribute to the understanding of the evolutionary histories of parasites and hosts.

Several foodborne diseases have been described in coastal populations from the past, many of them including parasitic infections related to marine diets. Considering this background, the strong relationship between hunter-gatherers from Patagonia and the marine species implies a possible source of parasitic infections and zoonotic risk. However, marine parasitic species have not been identified in archaeological sites from Patagonia so far. The aim of this paper is to propose the potential parasitic infections produced by the consumption of marine molluscs, fishes, birds and sea mammals by human populations from Patagonia during the Holocene, considering the current parasitic species identified in the Southern Atlantic Ocean. We searched in journal articles and book chapters for references of archaeological remains of molluscs, fishes, seabirds and marine mammals recorded in archaeological sites from the Atlantic coast below the 42nd parallel South. Afterwards, we surveyed all the macroparasites of marine origin identified by current parasitological research in the same species found in the archaeological record. We found that most of the marine species in the zooarchaeological record of Patagonia are currently hosts of many parasites. Some species of molluscs, fishes and pinnipeds are highly infected by larvae that are potentially hazardous for human health. Some of them are responsible for acute or chronic zoonotic diseases, with severe consequences depending on how the food was cooked, the amount of consumed parasites and the immune response of the host, in this case, humans. Fishes are host of several parasites related to anisakidosis and corynosomiasis. Sea lions species were also a potential source of the same zoonosis but also diphyllobothriasis. Molluscs are hosts of several parasitic species, but with less severe consequences for human health. On the other hand, birds are infected by adult parasites, without direct zoonotic importance. These findings, although limited by temporal and environmental variability, can provide a speculative overview about the potential influence of marine diets in the health of past hunter-gatherers of Patagonia, particularly if fishes, molluscs or marine mammals were consumed inadequately cooked.

Mistletoes, lianas, vines, and epiphytes fulfill many of the population dynamic criteria of animal macroparasites. A new study illustrates elegant ways to quantify cost to the host and how this impacts competition between mistletoe species. It opens the door to a much fuller consideration of plant parasites as macroparasites.

Intraspecific competition between co-infecting parasites can influence the amount of virulence, or damage, they do to their host. Kin selection theory dictates that infections with related parasite individuals should have lower virulence than infections with unrelated individuals, because they benefit from inclusive fitness and increased host longevity. These predictions have been tested in a variety of microparasite systems, and in larval stage macroparasites within intermediate hosts, but the influence of adult macroparasite relatedness on virulence has not been investigated in definitive hosts. This study used the human parasite Schistosoma mansoni to determine whether definitive hosts infected with related parasites experience lower virulence than hosts infected with unrelated parasites, and to compare the results from intermediate host studies in this system. The presence of unrelated parasites in an infection decreased parasite infectivity, the ability of a parasite to infect a definitive host, and total worm establishment in hosts, impacting the less virulent parasite strain more severely. Unrelated parasite co-infections had similar virulence to the more virulent of the two parasite strains. We combine these findings with complementary studies of the intermediate snail host and describe trade-offs in virulence and selection within the life cycle. Damage to the host by the dominant strain was muted by the presence of a competitor in the intermediate host, but was largely unaffected in the definitive host. Our results in this host-parasite system suggest that unrelated infections may select for higher virulence in definitive hosts while selecting for lower virulence in intermediate hosts.

Cerastoderma edule (edible cockle) is among the most exploited bivalves in Europe playing an important socio-economic role. Cockles live in estuaries and lagoons where their population is controlled by several environmental factors including parasitism. Parasites represent an important part of the world known biodiversity but are often neglected. Trematodes are the most prevalent macroparasites of cockles being able to exert an impact both at the individual and population levels. Therefore, it is of prime relevance to recognize and understand the parasite-host system dynamics in order to better predict potential conservation threats to bivalve populations and to maximize the success of stock and disease episodes management. Cockle monitoring was conducted in 2012 and 2016, in six and eight stations, respectively, at the Ria de Aveiro coastal lagoon, Portugal. Cockles were sampled in one single occasion in 2012 and seasonally in 2016. The tested hypothesis is that the trematode community in cockles was spatially and seasonally heterogeneous but stable over time. The main result showed that despite a relative homogeneity of the parasite community structure in cockles, the among-years heterogeneity of trematode communities was higher than among-stations and among-seasons heterogeneity rejecting the postulated hypothesis. Results demonstrated that trematode communities from the Ria de Aveiro are characterized by low abundance, which resulted in a spatial and seasonal trematode homogeneity (despite an overall channel difference and a slight downstream-upstream gradient). The interannual analysis showed a worrisome loss of trematode diversity and prevalence which consequently indicates an important loss of overall diversity and/or environmental conditions reflecting the negative effects of global change (mean temperature rise and overharvesting, among others). The present study highlighted the importance of trematodes in characterising their associated environment and respective biodiversity which might be helpful to assess ecosystem ecological status and to identify threatened areas.

Archaeoparasitology provides a unique perspective on the health and habits of ancient cultures through the identification of parasite remains in archaeological materials. We identified eggs of the human whipworm, Trichuris trichiura, in coprolites recovered from Late Archaic (1926–1751 cal. BCE) and Ancestral Puebloan (1039–1163 cal. CE) sites in Chaco Canyon, New Mexico. Our findings represent the earliest record of T. trichiura in North America, the first record of the species from Chaco Canyon, and the first record of a macroparasite from a Late Archaic site (Atlatl Cave) on the Colorado Plateau. T. trichiura is common in the global archaeoparasitology record, but until now it was not known to have infected Ancestral Puebloans. Environmental barriers to transmission and lack of contact with infected Mesoamerican cultures have previously been used to explain the absence of this species from the Southwest. The new evidence of T. trichiura presented here raises questions about the cultural context which led to the arrival and persistence of this parasite in both a Late Archaic cave and an Ancestral Puebloan great house at Chaco Canyon. We propose that the moisture requirements of T. trichiura transmission may have been met through anthropogenic modification of the local environment, and that the presence of this species at Chaco Canyon suggests contact with infected Mesoamerican cultures. We also report the presence of the pinworm, Enterobius vermicularis, and unidentified larval nematodes in the Chaco Canyon archaeological record.

Highlights • Simple, yet flexible, model of human movement patterns. • Analytic formalism which can be used to derive important spatial scales. • Introduces a novel drift–diffusion approximation for stochastic reservoirs. • A new critical spatial scale predicted for helminth reservoirs of infection. • The necessary data needed to test these predictions is outlined in detail., The life cycle of parasitic organisms that are the cause of much morbidity in humans often depend on reservoirs of infection for transmission into their hosts. Understanding the daily, monthly and yearly movement patterns of individuals between reservoirs is therefore of great importance to implementers of control policies seeking to eliminate various parasitic diseases as a public health problem. This is due to the fact that the underlying spatial extent of the reservoir of infection, which drives transmission, can be strongly affected by inputs from external sources, i.e., individuals who are not spatially attributed to the region defined by the reservoir itself can still migrate and contribute to it. In order to study the importance of these effects, we build and examine a novel theoretical model of human movement between spatially-distributed focal points for infection clustered into regions defined as ‘reservoirs of infection’. Using our model, we vary the spatial scale of human moment defined around focal points and explicitly calculate how varying this definition can influence the temporal stability of the effective transmission dynamics – an effect which should strongly influence how control measures, e.g., mass drug administration (MDA), define evaluation units (EUs). Considering the helminth parasites as our main example, by varying the spatial scale of human movement, we demonstrate that a critical scale exists around infectious focal points at which the migration rate into their associated reservoir can be neglected for practical purposes. This scale varies by species and geographic region, but is generalisable as a concept to infectious reservoirs of varying spatial extents and shapes. Our model is designed to be applicable to a very general pattern of infectious disease transmission modified by the migration of infected individuals between clustered communities. In particular, it may be readily used to study the spatial structure of hosts for macroparasites with temporally stationary distributions of infectious focal point locations over the timescales of interest, which is viable for the soil-transmitted helminths and schistosomes. Additional developments will be necessary to consider diseases with moving reservoirs, such as vector-born filarial worm diseases.

Biological invasions have the capacity to introduce non-native parasites. This study aimed to determine whether the invasive green crab population, Carcinus spp., on the Southwestern Atlantic coast of Argentina harbours any symbionts, and whether these may spillover or spillback between native crabs, Cyrtograpsus altimanus and C. angulatus. Macroscopy, histology, and molecular analyses of some parasites were used to describe and compare their diversity across the three species of crab. We also evaluated the susceptibility of invasive Carcinus spp. to a native digenean, Maritrema madrynense, via experimental infections (exposure and cohabitation). Our results revealed that the green crab pathobiome included similar symbiotic groups to native crabs. This included putative viral, bacterial, and protozoan parasites. Haplosporidium-like observations were recorded in all crab species, and a single green crab was found to be parasitized by an Agmasoma-like microsporidium. Metagenomic analysis of one individual revealed additional symbiotic diversity (46 bacteria, 5 eukaryotic species). The green crabs were infected by more microparasite taxa than the native crabs (5:3). Wild populations of Carcinus spp. were free of metazoan parasites and are shown not to be susceptible to M. madryense under experimental conditions. Our results suggest a reduction/escape of macroparasites (trematode Maritrema madrynense; acanthocephalan Profilicollis chasmagnathi) in invasive Carcinus spp. compared to their native competitors.

Parasite virulence is a key trait in host-parasite interactions and plays a crucial role in infection dynamics. Our study system offers the rare opportunity to study the virulence of an individual macroparasite (Schistocephalus solidus) in its vertebrate fish host (Gasterosteus aculeatus). The size of the tapeworm in the fish can be regarded as a good proxy for individual parasite virulence, as parasite size correlates negatively with fitness traits of the stickleback host (i.e. the bigger the parasite, the lower the host's reproductive success) as well as directly with the number of parasite offspring to be expected. To investigate how virulence is inherited, laboratory bred, parasite-naïve stickleback were infected with a cross of two S. solidus populations of either high or low virulence, as well as one hybrid cross between the two. The relative weight of the parasite as expressed in the parasite index served as a measure of virulence. Furthermore, we measured several condition and immune related traits in the fish host to assess parasite impact on the stickleback. We hypothesized that parasite virulence is to a large extent genetically determined and correlated with several fitness traits in the stickleback host. We found that virulence is inherited additively in S. solidus, with hybrids of high and low virulence parasites displaying intermediate levels. However, contrary to expectation, infection rate of S. solidus in three-spined stickleback is not related to virulence. Even though the presence of the parasite caused differences in host condition, these were indistinguishable between the different levels of virulence in this experiment. Fish immune traits also showed a response to infection but had no correlation with level of parasite virulence. With this experiment we have taken the first step towards understanding how virulence is inherited and how it is driven in the Schistocephalus-stickleback system, even though virulence, as measured here, does not directly translate into cost for the host. A better understanding of the costs inflicted on the host by S. solidus infection is needed to understand this interaction in greater detail.

Parasitic castration is an adaptive strategy where parasites usurp the hosts' reproductive physiology to complete their life cycle. The alterations in the host traits vary in their magnitude, from subtle changes in the host morpho-physiology and behaviour to the production of complex aberrant phenotypes, which often depend on the host gender. The strepsipteran macroparasite Xenos vesparum induces dramatic behavioural and physiological changes in its female host, the paper wasp Polistes dominula, while its effect on the male phenotype is largely unknown. In this study we investigated how a single X. vesparum parasite influences the functional morphology of P. dominula male reproductive apparatus. We performed morphometry and ultrastructure characterization of corpora allata, testes, seminal vesicles and accessory glands in parasitized and unparasitized males, and also in young and old males to control for the effect of age on the natural deterioration of these organs. Our results show that age significantly affects the development of male reproductive apparatus. A low parasite load - one parasite per host is the common prevalence in the field - has only a marginal impact on the reproductive morphology of P. dominula males, affecting quantitatively but not qualitatively the protein content of male accessory glands. Thus, in male P. dominula wasps, X. vesparum appears to behave as a true "parasite", in clear opposition to the role of "parasitoid" that it takes in female hosts where castration causes the reproductive death.

Infection with the abomasal nematode Haemonchus contortus is responsible for considerable production loss in small ruminants globally, and especially in warm, summer-rainfall regions. Previous attempts to predict infection levels have followed the traditional framework for macroparasite models, i.e . tracking parasite population sizes as a function of host and climatic factors. Targeted treatment strategies, in which patho-physiological indices are used to identify the individuals most affected by parasites, could provide a foundation for alternative, incidence-based epidemiological models. In this paper, an elaboration of the classic susceptible-infected-recovered (SIR) model framework for microparasites was adapted to haemonchosis and used to predict disease in Merino sheep on a commercial farm in South Africa. Incidence was monitored over a single grazing season using the FAMACHA scoring system for conjunctival mucosal coloration, which indicates high burdens of H. contortus , and used to fit the model by estimating transmission parameters. The model predicted force of infection (FOI) between sequential FAMACHA monitoring events in groups of dry, pregnant and lactating ewes, and related FOI to factors including climate (temperature, rainfall and rainfall entropy), using a random effects model with reproductive status group as the cluster variable. Temperature and rainfall in the seven days prior to monitoring significantly predicted the interval FOI (p ≤ 0.002), while rainfall entropy did not (p = 0.289). Differences across the three groups accounted for approximately 90% of the variability in the interval FOI over the period of investigation. Maintained FOI during targeted treatment of cases of haemonchosis suggests strong underlying transmission from sub-clinically infected animals, and/or limited impact on pre-existing pasture contamination by removal of clinical worm burdens later in the grazing season. The model has the potential to contribute to the sustainable management of H. contortus by predicting periods of heightened risk, and hence to focus and optimise limited resources for monitoring and treatment. SIR-type model frameworks are an alternative to classic abundance-based compartmental models of macroparasite epidemiology, and could be useful where incidence data are available. Significant challenges remain, however, in the ability to calibrate such models to field data at spatial and temporal scales that are useful for decision support at farm level.

Host–parasite coevolution has rarely been observed in natural systems. Its study often relies on microparasitic infections introducing a potential bias in the estimation of the evolutionary change of host and parasite traits. Using biological invasions as a tool to study host–parasite coevolution in nature can overcome these biases. We demonstrate this with a cross-infection experiment in the invasive macroparasite Mytilicola intestinalis and its bivalve host, the blue mussel Mytilus edulis. The invasion history of the parasite is well known for the southeastern North Sea and is characterised by two separate invasion fronts that reached opposite ends of the Wadden Sea (i.e. Texel, The Netherlands and Sylt, Germany) in a similar time frame. The species’ natural history thus makes this invasion an ideal natural experiment to study host–parasite coevolution in nature. We infected hosts from Texel, Sylt and Kiel (Baltic Sea, where the parasite is absent) with parasites from Texel and Sylt, to form sympatric, allopatric and naïve infestation combinations, respectively. We measured infection rate, host condition and parasite growth to show that sympatric host–parasite combinations diverged in terms of pre- and post-infection traits within

Numerous marine populations experience parasite pressure. This is the case of the cockles Cerastoderma edule which are often highly infected by trematode macroparasites. These parasites display a complex life cycle, with a succession of free-living and parasitic stages. Climate, and in particular temperature, is an important modulator of the transmission dynamics of parasites. Consequently, global change is thought to have implications for the epidemiology of infectious diseases. Using Himasthla quissetensis , a dominant parasite of cockles as 2nd intermediate host in Arcachon Bay (France), we used mathematical models of parasite emergence (cercariae) and parasite infection (metacercariae) in cockles as a function of water temperature, in order to study different scenarios of temperature increases. Globally, with a + 0.5 °C to + 6.0 °C simulation, cumulated emergence of cercariae and accumulation of metacercariae tended to decrease or stagnate, respectively. This is the consequence of a trade-off between sooner (spring) and later (autumn) cercariae emergence/infestation on one hand, and a longer inhibition period of cercariae emergence/infestation during the hottest days in summer. Using sea water temperature in Oualidia (Morocco) where mean annual sea temperature is 3 °C higher than in Arcachon Bay, our model predicted infestation all year long (no seasonality). The model gave a correct estimation of the total number of parasites that was expected in cockles. Conversely, observed infestation in Oualidia followed a seasonal pattern like in Arcachon Bay. These results suggest that, if temperature is a strong driver of parasite transmission, extrapolation in the framework of climate change should be performed with caution.

Marine environmental conditions are naturally changing throughout the year, affecting life cycles of hosts as well as parasites. In particular, water temperature is positively correlated with the development of many parasites and pathogenic bacteria, increasing the risk of infection and diseases during summer. Interannual temperature fluctuations are likely to alter host–parasite interactions, which may result in profound impacts on sensitive ecosystems. In this context we investigated the parasite and bacterial Vibrionaceae communities of four common small fish species (three-spined stickleback Gasterosteus aculeatus, Atlantic herring Clupea harengus, European sprat Sprattus sprattus and lesser sand eel Ammodytes tobianus) in the Northern Wadden Sea over a period of two years. Overall, we found significantly increased relative diversities of infectious species at higher temperature differentials. On the taxon-specific level some macroparasite species (trematodes, nematodes) showed a shift in infection peaks that followed the water temperatures of preceding months, whereas other parasite groups showed no effects of temperature differentials on infection parameters. Our results show that even subtle changes in seasonal temperatures may shift and modify the phenology of parasites as well as opportunistic pathogens that can have far reaching consequences for sensitive ecosystems.

Fedorov's lumpsucker, Eumicrotremus fedorovi Mandrytsa, 1991, is native to the Kuril Islands area. Two sets of 69 and 30 adult specimens of E. fedorovi caught on the continental shelf and slope of Simushir Island in the Pacific Ocean were dissected and studied for macroparasites. The studied specimens were heavily infected with plerocercoids of Nybelinia surmenicola and Ascarophis pacifica. For the first time, 15 parasite taxa were recorded for E. fedorovi. None of the parasites found are solely specific to the E. fedorovi or to the representatives of the family Cyclopteridae. The infection of E. fedorovi could be dramatically different in different parts of the Simushir Island area in terms of parasite species composition and intensity of infection.

Parasites can significantly impact animal populations by changing host behaviour, reproduction and survival. Detecting and quantifying these impacts is critical for understanding disease dynamics and managing wild animal populations. However, for wild hosts infected with macroparasites, it is notoriously difficult to quantify the fatal parasite load and number of animals that have died due to disease. When ethical or logistical constraints prohibit experimental determination of these values, examination of parasite intensity and distribution data may offer an alternative solution. In this study we introduce a novel method for using intensity data to detect and quantify parasite-induced mortality in wildlife populations. We use simulations to show that this method is more reliable than previously proposed methods while providing quantitative estimates of parasite-induced mortality from empirical data that are consistent with previously published qualitative estimates. However this method, and all techniques that estimate parasite-induced mortality from intensity data alone, have several important assumptions that must be scrutinised before applying those to real-world data. Given that these assumptions are met, our method is a new exploratory tool that can help inform more rigorous studies of parasite-induced host mortality.

Many of the challenges which face modellers of directly transmitted pathogens also arise when modelling the epidemiology of pathogens with indirect transmission – whether through environmental stages, vectors, intermediate hosts or multiple hosts. In particular, understanding the roles of different hosts, how to measure contact and infection patterns, heterogeneities in contact rates, and the dynamics close to elimination are all relevant challenges, regardless of the mode of transmission. However, there remain a number of challenges that are specific and unique to modelling vector-borne diseases and macroparasites. Moreover, many of the neglected tropical diseases which are currently targeted for control and elimination are vector-borne, macroparasitic, or both, and so this article includes challenges which will assist in accelerating the control of these high-burden diseases. Here, we discuss the challenges of indirect measures of infection in humans, whether through vectors or transmission life stages and in estimating the contribution of different host groups to transmission. We also discuss the issues of “evolution-proof” interventions against vector-borne disease.

Seasonal forcing represents a pervasive source of environmental variability in natural systems. Whilst it is reasonably well understood in interacting populations and host-microparasite systems, it has not been studied in detail for host-macroparasite systems. In this paper we analyse the effect of seasonal forcing in a general host-macroparasite system with explicit inclusion of the parasite larval stage and seasonal forcing applied to the birth rate of the host. We emphasise the importance of the period of the limit cycles in the unforced system on the resulting dynamics in the forced system. In particular, when subject to seasonal forcing host-macroparasite systems are capable of multi-year cycles, multiple solution behaviour, quasi-periodicity and chaos. The host-macroparasite systems show a larger potential for multiple solution behaviour and a wider range of periodic solutions compared to similar interacting population and microparasite systems. By examining the system for parameters that represent red grouse and the macroparasite nematode Trichostrongylus tenuis we highlight how seasonality could be an important factor in explaining the wide range of seemingly uncorrelated cycle periods observed in grouse abundance in England and Scotland.

The overdispersion in macroparasite infection intensity among host populations is commonly simulated using a constant negative binomial aggregation parameter. We describe an alternative to utilising the negative binomial approach and demonstrate important disparities in intervention efficacy projections that can come about from opting for pattern-fitting models that are not process-explicit. We present model output in the context of the epidemiology and control of soil-transmitted helminths due to the significant public health burden imposed by these parasites, but our methods are applicable to other infections with demonstrable aggregation in parasite numbers among hosts.

Graphical abstract, Highlights • Parasites are extremely diverse and ubiquitous in natural ecosystems. • They have critical roles in ecological and evolutionary processes. • Many parasite species are believed to be threatened or already extinct. • All arguments for the conservation of any species apply equally well to parasites. • Parasite conservation can be a very challenging endeavor., Parasites appropriate host resources to feed and/or to reproduce, and lower host fitness to varying degrees. As a consequence, they can negatively impact human and animal health, food production, economic trade, and biodiversity conservation. They can also be difficult to study and have historically been regarded as having little influence on ecosystem organization and function. Not surprisingly, parasitic biodiversity has to date not been the focus of much positive attention from the conservation community. However, a growing body of evidence demonstrates that parasites are extremely diverse, have key roles in ecological and evolutionary processes, and that infection may paradoxically result in ecosystem services of direct human relevance. Here we argue that wildlife parasites should be considered meaningful conservation targets no less relevant than their hosts. We discuss their numerical and functional importance, current conservation status, and outline a series of non-trivial challenges to consider before incorporating parasite biodiversity in conservation strategies. We also suggest that addressing the key knowledge gaps and communication deficiencies that currently impede broad discussions about parasite conservation requires input from wildlife parasitologists.

The occurrence of macroparasites was studied from 543 stray cats in four urban cities from the west (Kuala Lumpur), east (Kuantan), north (Georgetown) and south (Malacca) of Peninsular Malaysia from May 2007 to August 2010. Five ectoparasites species were recovered namely, Ctenocephalides felis, Felicola subrostratus, Haemaphysalis bispinosa, Heterodoxus spiniger and Lynxacarus radovskyi. Two cats from Georgetown were infested with the dog louse, H. spiniger and this represented the first host record for this species in Malaysia. Up to nine species of helminths were recovered with overall high prevalences of infection of 83% in Kuantan, followed by 75.1% in Kuala Lumpur, 71.6% in Georgetown and 68% in Malacca. The helminth species comprised five nematodes, Toxocara malaysiensis, Toxocara cati, Ancylostoma braziliensis, Ancylostoma ceylanicum, Physaloptera praeputialis, two cestodes Taenia taeniaeformis, Dipylidium caninum and one trematode, Playtnosomum fastosum. The majority of helminths were present in the four study sites except for the absence of P. praeputialis in Kuala Lumpur. The prevalence and abundance of infections were analysed taking intrinsic (host age and sex) and extrinsic (season) factors into consideration. Levels of infection and infestation were mainly influenced by host age and to a lesser extent sex and season, whereas four nematode species exhibited significant interactions within the intestine of the cat host. The potential for transmission of some macroparasite species from stray cats to the human population in urban areas is discussed.

Cockles ( Cerastoderma edule ) are among the most exploited bivalves in Europe. They live in lagoons and estuaries where they undergo many stressors including parasites. Trematodes are the most prevalent macroparasites of cockles and can exert a significant impact on their host populations depending on parasite species and infection intensity. Monitoring these parasite–host systems in order to predict potential host mortalities require a correct knowledge of the spatio-temporal variation of infection. A yearly monitoring of cockles from six stations around Ile aux Oiseaux, Arcachon Bay (France) was conducted between 1998 and 2005. Distance between two stations was ca. 1 km. Nine trematode species were identified. Despite a relative homogeneity of the parasite community structure in cockles, between three and six clusters were identified by Hierarchical Ascendant Classification showing that among-sites heterogeneity of trematode communities in cockles was higher than within-site heterogeneity. At the scale of 8 years, and for 2-year old cockles, these patterns remained stable in four out of six stations. Spatial aggregation disappeared with cockle age, since parasite communities in 3-year cockles did not reflect any particular station(s): with age, cockles eventually accumulated most trematode species and lost the site signature. On the other hand, we demonstrated that the commonly accepted theory stating that older/larger cockles accumulate more trematode larvae was not verified and that there could exist a vulnerable age/size that doesn’t correspond to largest values. This study provided a new insight in the parasite community heterogeneity in their host, and in the significance of samples in relation with space and time.

Theoretical demographic models with accompanying experimental programs provide an important framework to study the life history of organisms. In this paper we examine the fitness characteristics of gregarine parasites (Apicomplexa) and how these evolutionary long-lived parasites are shaped by their own life cycle stages inside and outside a definitive insect host. Although gregarines have been investigated in experimental works, their fitness and population characteristics have not been subject to modeling efforts to help understand their longevity or interactions with their host species. We develop a dynamic, mechanistic population model represented by a system of two differential equations for two of the parasite stages: the mature parasite, or trophont, inside a definitive insect host, and the infectious oocyst stage in the water environment of the host. In contrast to many classical macroparasite models, the force of infection between oocysts and hosts is of sigmoid type. Inside the host, production of the water borne infectious state is modeled by linear production rate in the trophont population with a density-independent trophont mortality. We examine stability of model's equilibria for different parameter values and different host populations. This leads to the definition of a fitness parameter that acts as a bifurcation parameter for the model. The model shows good cause for the establishment and long-time persistence of this common, widespread parasite. It is parameterized by extensive data gathered at Cedar Point Biological Station, and numerical calculations based on those parameters illustrate the dynamics. Possible applications include parasite control in aquacultures.

Multiple analytical techniques were used to evaluate the impact of multiple parasite species on the mortality of threatened juvenile coho salmon (Oncorhynchus kisutch) from the West Fork Smith River, Oregon, USA. We also proposed a novel parsimonious mathematical representation of macroparasite distribution, congestion rate, which (i) is easier to use than traditional models, and (ii) is based on Malthusian parameters rather than probability theory. Heavy infections of Myxobolus insidiosus (Myxozoa) and metacercariae of Nanophyetus salmincola and Apophallus sp. occurred in parr (subyearlings) from the lower mainstem of this river collected in 2007 and 2008. Smolts (yearlings) collected in 2007–2010 always harboured fewer Apophallus sp. with host mortality recognised as a function of intensity for this parasite. Mean intensity of Apophallus sp. in lower mainstem parr was 753 per fish in 2007 and 856 per fish in 2008, while parr from the tributaries had a mean of only 37 or 13 parasites per fish, respectively. Mean intensity of this parasite in smolts ranged between 47 and 251 parasites per fish. Over-dispersion (variance to mean ratios) of Apophallus sp. was always lower in smolts compared with all parr combined or lower mainstem parr. Retrospective analysis based on smolt data using both the traditional negative binomial truncation technique and our proposed congestion rate model showed identical results. The estimated threshold level for mortality involving Apophallus sp. was at 400–500 parasites per fish using both analytical methods. Unique to this study, we documented the actual existence of these heavy infections prior to the predicted mortality. Most of the lower mainstem parr (approximately 75%) had infections above this level. Heavy infections of Apophallus sp. metacercariae may be an important contributing factor to the high over-wintering mortality previously reported for these fish that grow and develop in this section of the river. Analyses using the same methods for M. insidiosus and N. salmincola generally pointed to minimal parasite-associated mortality.

Parasites and parasitism is common. Worm macroparasites have evolved life-history traits that allow them to successfully transmit between spatially and temporally separated patches of host resource and to survive within these environments. Macroparasites have common life-history strategies to achieve this, but these general themes are modified in a myriad of ways related to the specific biology of their hosts. Parasite life histories are also dynamic, responding to conditions inside and outside of hosts, and they continue to evolve, especially in response to our attempts to control them and the harm that they cause.

There is a growing awareness that cyclic population dynamics in vertebrate species are driven by a complex set of interactions rather than a single causal factor. While theory suggests that direct host–parasite interactions may destabilise population dynamics, the interaction between host and parasite may also influence population dynamics through indirect effects that result in delayed responses to either density or to life-history traits. Using empirical data on mountain hares (Lepus timidus) infected with a nematode parasite (Trichostrongylus retortaeformis), we developed an individual-based model (IBM) that incorporated direct effects and delayed life-history effects (DLHEs) of a macroparasite, alternative transmission mechanisms and seasonality in host population dynamics. The full model describes mean characteristics of observed mountain hare time series and parasite abundance, but by systematically removing model structure we dissect out dynamic influences of DLHEs. The DLHEs were weakly destabilising, increasing the propensity for cyclic dynamics and suggesting DLHEs could be important processes in host–parasite systems. Further, by modifying model structure we identify a strong influence of parasite transmission mechanism on host population stability, and discuss the implications for parasite aggregation mechanisms, host movement and natural geographical variation in host population dynamics. The effect of T. retortaeformis on mountain hares likely forms part of a complex set of interactions that lead to population cycles.

In the present study, the macroparasite assemblage infecting Helicolenus dactylopterus (Delaroche, 1809) in three different areas off the Portuguese coast was evaluated in order to assess their use as biological tags in stock identification. Fish were obtained from commercial landings in Azores, Madeira and mainland Portugal (Peniche), and were examined for macroparasites infections according to standard procedures. Parasite assemblage composition and the prevalence and mean abundance of each macroparasite taxa within each area were calculated. Amongst the 20 taxa found, 13 were selected as good biological tags, presenting statistically different infection levels between areas. Anisakidae larvae, which presented different prevalence and mean abundance levels between the three areas, were further identified according to the restriction fragment length polymorphism (RFLP) pattern on TaqI, HinfI and HhaI. The multivariate discriminant analysis applied to the macroparasites species present in more than one area and showing prevalence higher than 10% revealed a high differentiation among the three sampled areas suggesting at least three different bluemouth stocks in Portuguese waters.

Factors associated with the emergence and transmission of infectious diseases often do not follow the assumptions of traditional statistical models such as linearity and independence of outcomes. Transmission dynamics models are well suited to address infectious disease scenarios that do not conform to these assumptions. For example, these models easily account for changes in the incidence rates of infection as the proportions of susceptible and infectious persons change in the population. Fundamental concepts relating to these methods, such as the basic reproductive number, the effective reproductive number and the susceptible-infected-recovered compartmental models, are reviewed. In addition, comparisons and contrasts are made between the following concepts: microparasites and macroparasites, deterministic and stochastic models, difference and differential equations and homogeneous and heterogeneous mixing patterns. Finally, examples of how transmission dynamics models are being applied to factors associated with emerging infectious diseases, such as zoonotic origins, microbial adaption and change, human susceptibility and climate change, are reviewed.

Introduced pets released in natura can lead to sanitary risks for native fauna and humans. We analysed the macroparasite fauna of a total of 49 Pallas's squirrels, Callosciurus erythraeus, from two populations introduced into urbanised areas in Europe (n=16 female symbol and 13 male symbol from Antibes, France, 43 degrees 33'N-7 degrees 7'E; n=11 female symbol and 9 male symbol in from Dadizele, Belgium, 50 degrees 52'N-3 degrees 5'E). Of the 185 identified ectoparasites from Antibes, 183 were sucking lice Enderleinellus kumadai, with male squirrels 10 times more intensely infested than females. The flea Nosopsyllus fasciatus was found on two hosts. No hard ticks were recovered. Of the 131 arthropods specimens from Dadizele, 45 belonged to E. kumadai, with male squirrels three times more intensely infested than females. Eighty-six arthropods belonged to another sucking louse, Hoplopleura erismata, with males infested twice as intensely as females. No fleas or hard ticks were found. We only found 12 immature Hymenolepis sp. cestodes in the small intestine of three squirrels from Antibes and two immature Mastophorus sp. female nematodes in the stomach of a squirrel from Dadizele. We found no other helminths in the body cavity, heart, lung, liver, kidney or bladder. The macroparasite fauna of these two squirrel populations is consistent with what is expected from an introduced host, i.e., a few species dominated by specialist taxa imported with founders. The scarcity of other rodent species in the urbanized areas where Pallas's squirrels were sampled may explain the low variety of newly acquired macroparasites. The discrepancy in sucking lice infestations between males and females could be due to differences in either behaviour or physiology in this non-sexually dimorphic host. Based on the macroparasites found in this study, we expect minimal sanitary risks for both native fauna and humans in urbanized habitats such as those in our study.

In grazing systems, heterogeneous distributions of forage resources and faeces result in localised accumulations of nutrients and parasites (both macroparasites and microparasites), creating trade-offs between the costs of exposure to infestation or infection and the benefits of nutrient intake. Each contact between livestock and faeces in the environment is a potential parasite/pathogen transmission event. Thus, herbivores must make foraging decisions in complex environments which will affect their intake of both nutrients and parasites. However, the pattern of forage and faecal resources in agricultural environments will also be affected by the grazing management system in place. The aim of this study was to investigate the effect of grazing management on the risk of infection/infestation to livestock. We used a spatially explicit individual based stochastic foraging model to simulate livestock contact (both grazing and investigative) with faeces in the environment. The model was parameterised to simulate cattle grazing under three types of grazing management: set stock (i.e. where sward growth and cattle intake are in equilibrium in a single field); a two pasture rotation grazing system with increasing number of rotations; and a rotational grazing system with two rotations and increasing subdivisions of the pasture. Overall the amount of cattle contact with faecal-contaminated patches was similar in both set stocking and rotational grazing scenarios, suggesting no difference in the risk of infection or infestation between the different systems. However, the timing and absolute amounts of peak contact varied greatly indicating that different grazing management systems expose livestock to risks of different types of parasites at different times of the grazing season. Intensive rotational systems with small pasture blocks (especially the first grazing period) maximised livestock contact with fresh faeces, and thus exposure to microparasites (e.g. bacterial pathogens). Livestock re-entering pasture blocks in rotational systems and set stocked livestock had the highest contact with old faeces and thus have a greater risk of macroparasite transmission (gastrointestinal nematodes). This study highlights how livestock management affects the highly dynamic interaction between livestock and distributions of parasites in the environment and thus the levels of livestock exposure to parasites and pathogens via the faecal-oral route.

In this paper, we shall consider the nonlinear delay host macroparasite model with periodic coefficients (with common period ω). By means of a continuation theorem in coincidence degree theory, we establish a sufficient condition for the existence of a positive periodic solution M ¯ ( t ) with strictly positive components. Also, we establish some sufficient conditions for oscillation of all positive solutions about the positive periodic solution M ¯ ( t ) and establish a sufficient condition for the global attractivity of M ¯ ( t ) .

The population differentiation of seven flatfish species, Citharus linguatula , Lepidorhombus boscii , Platichthys flesus , Microchirus azevia , Solea lascaris , Solea senegalensis and Solea solea , widely distributed along the eastern north Atlantic and occurring in sympatry along the Portuguese coast was studied using morphological and parasitological data. Fish were obtained from commercial fishing vessels operating in three locations along the Portuguese coast (north, centre and south) between January 2003 and June 2005. Eleven morphometric and seven meristic characters were considered in morphological analyses. Size effect was removed from morphometric measurements by principal component analysis and a multivariate discriminant analysis was performed to investigate the differences between populations using both morphometric and meristic data, separately. Individuals were examined for macroparasites infections according to standard procedures, and a multivariate discriminant analysis was also applied to investigate population differences. Analyses of both types of data (morphological and parasitological) revealed a similar pattern of a generally low differentiation evidenced by the high overlap of individuals in the ordination diagrams. However, some differentiation was found between samples from the west (north and centre) and the south Portuguese coast evidencing the existence of an ecological differentiation along the Portuguese coast. Broad scale population studies should, therefore, take into account the information provided by such data, especially with regard to fisheries’ management policies and stock definition.

We assessed the effect of two pathogens (myxoma virus and Eimeria stiedae) and five macroparasites (gastrointestinal helminth species) of the wild rabbit (Oryctolagus cuniculus) upon total host body mass and abdominal fat level. Additionally, we assessed the effects of these organisms on the number of foetuses in adult females during the peak breeding period. Both mass of abdominal fat and total body mass of the rabbit were negatively associated with myxoma virus infection and increasing helminth species richness. Total body mass was also negatively associated with the protozoan parasite E. steidae. No relationship was found between any of the parasites/pathogens and the number of foetuses in adult females, although only relatively small sample sizes were available for this section of the analysis. Increasing host body mass was positively associated with number of foetuses and we propose that mass reduction caused by the pathogen and parasite species could also have the consequence of reducing foetal number.

Effective population size (N(e)) is a crucial parameter in evolutionary biology because it controls genetic drift and the response to selection. Thus, N(e) influences evolutionary processes in parasites, such as speciation, host-race formation, local host adaptation and the evolution of drug resistance. However, N(e) is a parameter that is ignored almost completely in parasitology. Our goal is to provide a conceptual framework that facilitates future studies of the N(e) of macroparasites. The key feature of macroparasite populations is that breeders are subdivided into infrapopulations. We use a model of subdivided breeders to show how some basic demographic factors that control N(e) in all species could be estimated for macroparasites. An important conclusion is that several features of parasite life cycles probably function in concert to reduce N(e) below that expected in a single free-living population of equivalent census size.

Multihost parasites have been implicated in the emergence of new diseases in humans and wildlife, yet little is known about factors that influence the host range of parasites in natural populations. We used a comprehensive data set of 415 micro- and macroparasites reported from 119 wild primate hosts to investigate broad patterns of host specificity. The majority (68%) of primate parasites were reported to infect multiple host species, including animals from multiple families or orders. This pattern corresponds to previous studies of parasites found in humans and domesticated animals. Within three parasite groups (viruses, protozoans and helminths), we examined parasite taxonomy and transmission strategy in relation to measures of host specificity. Relative to other parasite groups, helminths were associated with the greatest levels of host specificity, whereas most viruses were reported to infect hosts from multiple families or orders. Highly significant associations between the degree of host specificity and transmission strategy arose within each parasite group, but not always in the same direction, suggesting that unique constraints influence the host range of parasites within each taxonomic group. Finally characteristics of over 100 parasite species shared between wild primates and humans, including those recognised as emerging in humans, revealed that most of these shared parasites were reported from multiple host orders. Furthermore, nearly all viruses that were reported to infect both humans and non-human primates were classified as emerging in humans.

Host resistance to parasites and parasite infectivity may be subject to significant genetically determined variation within species. However, relatively little is known of how this variability is structured in natural vertebrate populations and their macroparasites. A laboratory experiment on host susceptibility–parasite infectivity variation in a wildlife host–parasite system (subspecies of the anuran X. laevis and their polystome flatworms), including 33 pairwise allopatric and sympatric host–parasite combinations (three parasite geographical isolates×11 host full-sibling families, n=600), revealed a complex pattern of infection success. Results amongst host sibships from different localities suggested that infection success was subject to a highly significant locality×parasite isolate interaction. Within localities, a highly significant sibship×isolate interaction also occurred in one of two groups of sibships examined. The existence of such interactions suggests a potential for frequency-dependent, Red Queen-like selection. Interaction between locality and isolate was partly due to higher infection levels in sympatric combinations, consistent with a general pattern of host-specific adaptation. However, some allopatric combinations produced unpredictably high infection levels, resulting in very asymmetrical cross-infectivity patterns (where the reciprocal cross-infections produced negligible infection). This phylogeographically structured host–parasite system may, therefore, sometimes generate local parasite strains with high infectivity to allopatric hosts. Secondary contact between populations could thus result in significant, and unequal, transfer of parasites.

Recent advances in ecology have improved our understanding of the role of parasites in the dynamics of wildlife populations. However, conditions that prevail in many wildlife systems, such as host movement, contact with livestock, and heterogeneity in the environment of the parasite outside of the host, have largely been ignored in existing models of macroparasite transmission. We need to refine these models if we are to stand a chance of developing effective parasite control strategies. New quantitative approaches enable us to address key complexities and make better use of scarce data, and these should enhance our efforts to understand and control emerging problems of interspecific parasite transmission.

A primary difference between predators and parasites is the number of victims that an individual attacks throughout a life-history stage. A key division within natural enemies is whether a successful attack eliminates the fitness of the prey or the host. A third distinctive axis for parasites is whether the host must die to further parasite development. The presence or absence of intensity-dependent pathology is a fourth factor that separates macroparasites from microparasites; this also distinguishes between social and solitary predators. Combining these four dichotomies defines seven types of parasitism, seven corresponding parasites, three forms of predation and, when one considers obligate and facultative combinations of these forms, four types of predator. Here, we argue that the energetics underlying the relative and absolute sizes of natural enemies and their victims is the primary selective factor responsible for the evolution of these different trophic strategies.

Kurtz, J., van der Veen, I. T., and Christen, M. 2001. Fluorescent vital labeling to track cestodes in a copepod intermediate host. Experimental Parasitology100, 36–43. In experimental studies of host-parasite interactions, it is often important to track parasites in their hosts and to discriminate between individual parasites. We used the fluorescent tracer dyes 7-amino-4-chloromethylcoumarin (CMAC) and, 5-chloromethylfluorescein diacetate (CMFDA) for vital labeling of Schistocephalus solidus (Cestoda) coracidia larvae. Labeling was fast and easy to perform and enabled microscopic detection of parasites appearing as procercoids in the hemocoel of the copepod intermediate host at 3 h after exposure. The label was still visible after 14 days. Extensive controls showed that CMAC (20 μM) labeling did not harm tapeworms or copepods. CMFDA (2 μM) reduced host survival, but the dye concentration can be decreased to avoid this in future studies. The new labeling method presented here has been very useful to track S. solidus parasites. It can be valuable for other parasites also and may be particularly suitable for visualization of individual live macroparasites in invertebrate hosts, for which we are not aware of any other appropriate method.

Amongst the potential biotic factors affecting bivalve population dynamics, parasitism has received little attention. Examination of the three dominant bivalves (the edible cockle Cerastoderma edule, the blue mussel Mytilus edulis , and the Manila clam Tapes philippinarum ) on an intertidal sandflat in the Bay of Arcachon (French Atlantic coast) revealed the occurrence of a rich community of macroparasites. These parasites belong to digenean trematodes (ten species), turbellarians (one species), cestodes (one species) and copepods (one species). The mean number of parasite species increased with shell length and reached 4 in cockles (maximum = 7 per ind.), 2.6 in mussels (max. = 5 per ind.) and only 1.7 in clams (max. = 4 per ind.). Total parasite prevalence was higher in cockles and mussels (84.9 and 72.3 %, respectively) than in clams (49.7 %). Host specificity was much higher for non-encysted larvae than for encysted metacercariae or non digenes. The occurrence of sporocysts of the digene Labratrema minimus in cockles seems to induce a lower infection by other parasite. The youngest bivalves (less than 10 mm in shell size) were nearly free of parasites. From the ‘shell size/parasite intensity’ relationship, the macroparasites are highly suspected to increase the mortality of recruits and adult bivalves. © 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS bivalves / parasites / recruitment / mortality / species richness

The impact of a macroparasite on a host population which can exhibit highly complex dynamics is considered. We focus on the case where the host reproduces annually, in which case we couple within-season density dependent interactions with a discrete-time pulse to reflect seasonal reproduction. Results from analytic arguments, supported by extensive numerical simulations, indicate that within season parasite-induced host mortality is potentially capable of stabilising and simplifying host dynamics. Moreover, the interaction of demographic processes occurring on different time-scales is, in some cases, stabilising. In particular, parasite reduction in host fecundity, which is a destabilising process in the May & Anderson continuous time model, is found to stabilise host macroparasite interactions under certain conditions. These results are discussed in an ecological context.

Mosquitoes are vectors of many vertebrate blood parasites. A large number of associations have evolved encompassing culicines and anophelines, micro- and macroparasites and most classes of vertebrate. Parasite life histories, host pathology and vector behaviour all vary, but all these relationships share at least one thing in common; the bloodsucking habit of female mosquitoes provides a mode of transmission between definitive host and vector. Bloodfeeding is the pivotal factor in the continuation of both parasite and vector generations. Here, Hilary Hurd, Jon Hogg and Melanie Renshaw review the links between bloodfeeding, mosquito egg production and infection, and discuss the degree to which each factor may influence the others.

A comparative analysis of the relationship between the spleen a major organ of immunity and helminths was undertaken with bird species, using the phylogenetic regression technique. Species in which many individuals are infected with nematodes relative to the number of individuals examined for the presence of helminths (termed relative nematode presence) have significantly larger spleens, for a given body weight, in females (though not in males). There was little indication that this relationship depends on incidental ecological indices, the weights of other organs, or the ‘relative presences’ of trematodes, cestodes or haematozoa. Combined with previous, experimental, work it suggests that the avian spleen is important in resisting nematodes. Body weight is correlated with the relative presence of helminths; but even after removing body size effects, bird species which tend to be infected with trematodes are also more likely to be infected with cestodes. This paper indicates that the spleens of wild bird species are associated with macroparasites in the natural environment.

Parasites and the Behavior of Animals (Oxford Series in Ecology and Evolution)by Janice Moore, Oxford University Press, 2002. US$45.00 (315 pages) ISBN 019 508441 1Parasites and the Behavior of Animals has something for everyone, including ethologists, evolutionary ecologists, parasitologists, and physiologists like myself who would like to know more about how parasites influence host behavior. Janice Moore has an energetic and engaging style with which she describes the plethora of behavioral changes seen in parasitized animals and sets them in the proper ecological perspective. As she notes in the introduction, host behavior can influence both parasite-transmission rates and parasite–host survival. This fact sets the backdrop for the following survey. Throughout the animal kingdom, Moore finds fascinating examples of how the evolutionary trade offs of parasite versus host survival are carefully balanced, in most instances, in favor of the parasite involved. The physiological mechanisms responsible for the induction of these changes continue to remain speculative in most cases, but Moore does address the mechanistic processes involved in eliciting these changes in several instances.The central theme of the book is the Anderson and May model focusing on R0 or the reproductive rate as a measure of parasite fitness, which is the number of reproductive offspring that a parasite can produce. Those authors distinguished between the strategies of microparasites (e.g. bacteria and viruses) which are small and have a short life span, and which reproduce directly within the host, versus macroparasites (e.g. helminths, arthropods) which have larger bodies and longer life spans, and which disperse offspring from the host. What follows this introduction are chapters on behavioral alterations and parasite transmission, behavioral alterations and avoiding parasites, and the fitness and longevity of infected hosts, which altogether constitute a comprehensive review of the subject, so Moore is to be commended for her thoroughness. Topics such as behavioral fever and parasitic castration are dealt with in detail, and the evolutionary impact of these phenomena on parasite fitness (as well as host longevity and survival) is emphasized. The interplay between parasite offense and host defense is dissected at the finest level. Much less is known about the mechanisms responsible for the induction of host behavioral changes, but this is sure to change in the next decade.The tour de force of the book is the appendix, which comprises several tables citing literature for hundreds of host–parasite combinations in which host behavioral anomalies are found. References dealing with effects on host-feeding behavior, tropisms, activity levels, substrate preferences, social interactions and a myriad of other behaviors are included in the extensive bibliography. The classical literature, as well as up-to-date references, is included in the tables, rendering the appendix a valuable reference work, in itself justifying a purchase of the book.I wish the publisher had spent more on artwork and illustrative color photos, but the figures that are included complement the text nicely. The book is suitable to be used as a textbook for classes in behavior, evolution and host–parasite relationships, providing the right combination of overview and detail necessary in a text. This book has a minimum amount of jargon, and is thus appropriate for upper division undergraduates and graduates; its modest price is another plus for classroom use. Moore notes in the preface: ‘And I hope you have a good time reading this book’ – I truly did, and learned much by the experience.

Whilst many empirical studies have quantified the negative impact of parasites on host vital rates (survival, fecundity, etc.), few have come close to demonstrating that macroparasites are capable of regulating wildlife host populations. Arguably the only convincing demonstration of the regulatory effect of macroparasites on a wildlife host comes from the red grouse–Trichostrongylus tenuis system in northern England, where the impact of macroparasites was demonstrated at both the individual and population levels. However, even this study is not without its critics. Now, a new study adds additional weight to the idea that macroparasites can be important regulating agents [1xThe role of parasites in the dynamics of a reindeer population. Albon, S.D. et al. Proc. R. Soc. Lond. Ser. B. 2002; 269: 1625–1632Crossref | PubMed | Scopus (148)See all References][1].Albon et al. [1xThe role of parasites in the dynamics of a reindeer population. Albon, S.D. et al. Proc. R. Soc. Lond. Ser. B. 2002; 269: 1625–1632Crossref | PubMed | Scopus (148)See all References][1] describe new analyses that suggest that gastrointestinal nematodes are the main regulatory influence on the population dynamics of Svalbard reindeer Rangifer tarandus plathyrynchus. They used a combination of long-term monitoring over a six-year period, experimental manipulations and sophisticated statistical analyses to show that, although parasites do not appear to have a major effect on host survival, they do have a significant negative impact on the probability of female reindeer becoming pregnant. As parasitism (and hence parasite-mediated fecundity reduction) is host density-dependent, the parasites have the potential to regulate the population dynamics of their hosts. To test this idea further, Albon and colleagues constructed a Leslie matrix model parameterized with field data. Simulations of this model predicted that, in the presence of the parasites, the reindeer population would exhibit stable population dynamics, whereas in their absence, the population would grow unchecked. These results are consistent with the idea that the nematode parasites are regulating the population dynamics of their hosts. Interestingly, this analysis suggests that population regulation is achieved via a relatively small density-dependent reduction in reindeer fecundity; removing gut parasites with anthelmintics increased calf production by just 5–14%. Albon et al. argue that this effect is possible only because of the inherently low population growth rate of the reindeer (1–5%), which is constrained by the negative impact of winter precipitation on the production of calves.This study has made a significant contribution to the debate concerning the role of macroparasites in regulating natural populations of wildlife hosts. Albon and colleagues have shown that the nematodes impact on their hosts at the individual level and this, in theory, is sufficient to regulate the host population dynamics. However, they recognize that they still have some way to go before they can demonstrate conclusively that macroparasites are necessary and sufficient for population regulation. Ultimately, of course, population-level experiments are required, but these are inherently difficult and expensive. However, it is only via long-term, large-scale studies that population-level questions such as these can be addressed adequately.