Search

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.

Rodents play an important role in the transmission of zoonotic diseases since they serve as reservoirs of these infections. A survey of ecto and intestinal parasites of the African giant rat (Cricetomys gambianus) was carried out between January and May, 2018 in Il-orin to access their potential as reservoirs of zoonoses. A total of 60 African giant rats were caught live using single catch rat traps which were set around bushes, near human habitation. The giant rats were euthanized with chloroform and thoroughly examined for ectoparasites. The giant rats were dissected and the alimentary canal removed. Direct smear floatation and sedimentation methods were used to detect endoparasites in the animals. The prevalence of different types of endoparasites were: Hymenolepis nana (33.3 %), Hymenolepis diminuta (25.0 %), Aspicularis tetraptera (29.2 %), and Acanthocephala spp. (12.5 %), while the ectoparasites were: Ixodes rasus (37.9 %), Xenopsylla cheopis (44.8 %) and Ornithonyssus bacoti (17.2 %). African giant rats harbour quite a number of infections that can be spread to humans especially in developing countries where most communities are economically disadvantaged, thus the need to properly enlighten the populace.

The paper reports the study of macroparasite load and aggressiveness of the European perch Perca fluviatilis juveniles of different size captured in the Rybinsk Reservoir (Volga River). A total of 13 macroparasite species have been identified with the Tylodelphys sp. and Ichthyocotylurus sp. trematodes and the Triaenophorus nodulosus cestode being the most abundant ones. A statistically significant correlation between the invasion intensity and fish size and aggressiveness has been found only for T. nodulosus. The possible mechanisms underlying T. nodulosus plerocercoid effects on the size and behavior of their fish hosts, the parasite transmission to the final host, and phenotypic differentiation in perch populations are discussed.

Functional roles of the rich microbiota of the skin are not fully understood, but include protection against microbial diseases and other environmental challenges. In experimental studies, we show that reducing the microbiota from cane toad (Rhinella marina) skin by gently wiping with absorptive gauze resulted in threefold higher rates of infection by lungworms (Rhabdias pseudosphaerocephala) following standardised exposure to infective skin-penetrating larvae. Higher concentrations of microbial DNA were associated with lower rates of lungworm entry. Our data suggest that microbial activity on the anuran skin comprises an important line of defence against attack by macroparasites as well as by fungi and other microbes., Highlights • Reduced microbiota on toad skin resulted in higher rates of infection by lungworms. • Higher concentrations of microbial DNA were associated with lower infection rates. • Microbes on skin may be first line of defence against parasites as well as disease.

The purpose of the research is to study the parasite fauna of the common frog (Rana temporaria Linnaeus, 1758) inhabiting the vicinity of the Visim Nature Biosphere Reserve.Materials and methods. The species composition, dominance structure and endoparasite infection of 32 individuals of R. temporaria caught along the banks of the upper reaches of the Sulem Riverwere assessed according to the following indicators: the prevalence and intensity of infection and abundance index.Results and discussion. The species composition of parasites in a common frog from the vicinity of the Visim Nature Biosphere Reserve is presented for the first time. Five species of macroparasites have been identified, classified as Nematoda: Oswaldocruzia filiformis (Goeze, 1782), Neoraillietnema praeputiale (Skrjabin, 1916), Cosmocerca ornata (Dujardin, 1845), Rhabdias bufonis (Schrank, 1788) and as Platyhelminthes: Haplometra cylindracea (Zeder, 1800). One species of endosymbiotic protozoa of Chromista, Opalina ranarum was recorded (Purkinje et Valentin, 1835). The prevalence of the infection of common frogs by helminths reaches 100%, the abundance index is 11.06, and protozoa is 93.8% and 62.16, respectively. Nematodes O. filiformis (the prevalence of infection 96.9%, and abundance index 7.97) and R. bufonis (the prevalence of infection 46.9%, abundance index 2.28) predominate. It was shown that nematode N. praeputiale was not found in the parasitocenosis of immature amphibians, and trematode H. cylindracea was not found in adult animals. The proportion of O. filiformis and C. ornata increases with age in common frogs. It was found that the animals of the July population are infected with nematode R. bufonis largely. Regardless of the age of R. temporaria, the probability of colonization by O. ranarum in spring will be higher.

Major Histocompatibility Complex (MHC) genes code for proteins that recognize foreign protein antigens to initiate T‐cell‐mediated adaptive immune responses. They are often the most polymorphic genes in vertebrate genomes. How evolution maintains this diversity remains of debate. Three main hypotheses seek to explain the maintenance of MHC diversity by invoking pathogen‐mediated selection: heterozygote advantage, frequency‐dependent selection, and fluctuating selection across landscapes or through time. Here, we use a large‐scale field parasite survey in a stickleback metapopulation to test predictions derived from each of these hypotheses. We identify over 1000 MHC IIβ variants (alleles spanning paralogous genes) and find that many of them covary positively or negatively with parasite load, suggesting that these genes contribute to resistance or susceptibility. However, despite our large sample‐size, we find no evidence for the widely cited stabilizing selection on MHC heterozygosity, in which individuals with an intermediate number of MHC variants have the lowest parasite burden. Nor do we observe a rare‐variant advantage, or widespread fluctuating selection across populations. In contrast, we find that MHC diversity is best predicted by neutral genome‐wide heterozygosity and between‐population genomic divergence, suggesting neutral processes are important in shaping the pattern of metapopulation MHC diversity. Thus, although MHC IIβ is highly diverse and relevant to the type and intensity of macroparasite infection in these populations of stickleback, the main models of MHC evolution still provide little explanatory power in this system.

As global trade of live animals expands, there is increasing need to assess the risks of invasive organisms, including pathogens, that can accompany these translocations. The movement and release of live baitfish by recreational anglers has been identified as a particularly high-risk pathway for the spread of aquatic diseases in the United States. To provide risk-based decision support for preventing and managing disease invasions from baitfish release, we developed a hazard identification and ranking tool to identify the pathogens that pose the highest risk to wild fish via this pathway. We created a screening protocol and semi-quantitative stochastic risk ranking framework, combining published data with expert elicitation (n = 25) and applied the framework to identify high-priority pathogens for the bait supply in Minnesota, USA. Normalized scores were developed for seven risk criteria (likelihood of transfer, prevalence in bait supply, likelihood of colonization, current distribution, economic impact if established, ecological impact if established and host species) to characterize a pathogen's ability to persist in the bait supply and cause impacts to wild fish species of concern. The generalist macroparasite Schizocotyle acheilognathi was identified as presenting highest overall threat, followed by the microsporidian Ovipleistophora ovariae, and viral haemorrhagic septicaemia virus. Our findings provide risk-based decision support for managers charged with maintaining both the recreational fishing industry and sustainable, healthy natural resources. Particularly, the identification of several high-risk but currently unregulated pathogens suggests that focusing risk management on pathogens of concern in all potential host species could reduce disease introduction risk. The ranking process, implemented here for a single state case study, provides a conceptual framework for integrating expert opinion and sparse available data that could be scaled up and applied across jurisdictions to inform risk-based management of the live baitfish pathway.

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.

Parasite aggregation is a frequently occurring phenomenon where majority of the parasites accumulate in the smaller fraction of the host population while many individual hosts have low parasite load. One of the mechanisms of parasite aggregation is heterogeneity in the host-parasite interaction. Here, we aim to develop and analyze a spatiotemporal model to explain the details of this mechanism. We construct an agent-based simulation involving fish hosts that forage on zooplanktons harboring macroparasites. In this study, we restrict our simulations to a lentic ecosystem, i.e., still, closed freshwater environment. Our simulations show that (i) the initial sizes of the population of both the fish and zooplanktons have minimal effect on the aggregation of parasites; (ii) increasing the probabilities of reproduction of both fish and zooplankton lead to parasite aggregation among fish hosts; and (iii) aggregation occurs either by decreasing the size of the infection area or increasing the size of the zooplankton-free area in the lentic ecosystem. Our results can be used to provide insights and visualization of the underlying processes leading to aggregation. These can also be used to aid experimentalists in determining the statistical distribution of parasites in hosts for disease prevention and control.

A variety of symbionts inhabit colonies of scleractinian corals, the main component of coral reef ecosystems. Obligate symbionts spend almost their whole lives (except the pelagic larvae stage) on or in the host, while facultative symbionts are less tightly associated with the host and easily leave them when food becomes scarce and competition and predation increase. The influence of parasites on the life traits of obligate and facultative symbionts has not yet been studied. The first step in this direction is the study of basic parameters of parasite infracommunities associated with coral symbionts. It was suggested that obligate symbionts that are tightly associated with their hosts and their symbiotic communities are more often infected. An alternative hypothesis suggests that facultative symbionts are more frequently infected because they easily change habitats and consume a broad food spectrum. For several years, we studied parasites of obligate and facultative symbionts (fish, decapods crustaceans, mollusks) associated with the corals Acropora and Pocillopora in the Nha Trang Bay (South China Sea). The highest abundance and diversity of macroparasites (Monogenea, Cestoda, Trematoda, Nematoda, Copepoda) were found in facultative symbionts of corals, fish-parabionts. Obligate fish-inbionts were infected much less often (Cestoda, Trematoda, Nematoda). Obligate symbionts predominated in the invertebrate symbionts, which were also weakly infected. The low abundance and diversity of parasites in obligate symbionts suggest that there should be significant investments in antiparasitic defense, which, together with efficient antipredation defense, minimize the mortality of obligate symbionts. Their fecundity and population number are usually low. Facultative symbionts presumably suffer higher mortality than obligate symbionts, but a more intensive use of resources and higher population numbers may compensate for this. A significant increase in the infection rate with an increase in host body size is typical of facultative symbionts, which are less protected than obligate symbionts. The latter showed low infection levels in all size groups. The results suggest that the role of parasites in shaping the life strategies of symbionts is no less important than the role of predators.

The enemy release hypothesis (ERH) postulates that during the invasion process an introduced species is released from the natural enemies that regulate its populations, promoting its invasion success in the new environment. Callosciurus erythraeus is a sciurid native to Southeast Asia that has been successfully introduced into Argentina and other Asian and European countries. The aim of this study was to provide new parasitological data on this species and to compare it with studies in native and other introduced ranges under the framework of the ERH. We proposed two working hypotheses: (1) an analysis at the community level to compare the prevalence, abundance and identity of parasites of C. erythraeus and sympatric native mammals in the main invasion focus of Argentina, and (2) an analysis at the biogeographical level to compare parasite richness in native and introduced ranges of C. erythraeus and parasite prevalence and richness among introduced regions with different invasion success (using population density and spread as proxy variables). The community analyses indicated that C. erythraeus has lost its specific parasites in Argentina and that it has a lower level of parasitism than other native mammals. The biogreographical analyses indicated a lower macroparasite richness of C. erythraeus in introduced ranges compared to its native range. However, parasite richness in introduced ranges was not associated with population density and spread. The negative correlation between parasite prevalence and population parameters was mainly due to the low parasite prevalence of C. erythraeus in Argentina where this species shows high density and spread. The release of parasites of C. erythraeus in comparison to its native and other introduced ranges, the low acquisition of generalist parasites and the high population density and spread reached in Argentina are mostly in agreement with the expected outcomes based on the ERH. Further studies are needed to better understand the role of the ERH in the invasion success of this species., Centro de Estudios Parasitológicos y de Vectores

For the first time, information about the entire parasitofauna of the the so-iuy mullet Planiliza haematocheila has been summarized on the basis of published and personal data. Features of its similarities and differences in the native Pacific region and in the areas of invasion, the Black and Azov Seas, have been identified. Potentially pathogenic parasites for the host’s health have been identified. It is assumed that the cases of death of the so-iuy mullet caused by them are due to the youth of parasite–host relationships, because all these species were acquired by the so-iuy mullet during the introduction into the Sea of Azov. Known practical recommendations are given to reduce the negative impact of one of the groups of macroparasites, trematodes, on the population of the so-iuy mullet in the Azov basin.

The interaction of pathogens between wild and farmed aquatic animal populations is a concern that remains unclear and controversial. Ichthyophthirius multifiliis, a ciliated protozoan parasite, is a pathogen of freshwater finfish species with geographic and host range that causes significant economic losses in aquaculture. Flow-through farming systems may facilitate the transfer of such a parasite with free-living stages between farmed and wild stocks. Here, experimental and field study infection data are used to describe the infection dynamics of Ichthyophthirius multifiliis in rainbow trout using a simple macroparasite model by including host resistance. The study considered flow-through farming systems with a single or two age-class compartments and simulated the transfer of the parasite between farmed and wild fish populations. Results suggest that aquaculture can promote the prevalence of the resistance in wild stocks by increasing the parasite population in the wild environment. At the same time, acquired resistance in the farmed fish population may protect the wild fish population from lethal effects of the parasite by reducing the total parasite population. This study offers a promising mathematical basis for understanding the effects of freshwater aquaculture in disease spread in wildlife, developing risk assessment modeling, and exploring new ways of aquaculture management.

The study of intestinal parasite communities is an important aspect of conservation biology, disease ecology, and wildlife health. Researchers can use the presence of select micro- and macroparasites as an indicator of host health. Only two studies have sampled intestinal parasites in free-ranging Aotus monkeys despite their wide geographic distribution in Central and South America. We therefore conducted a survey of gastrointestinal parasites using 50 fecal samples from seven free-ranging black-headed night monkey (Aotus nigriceps) groups at three field sites in the Peruvian Amazon. We calculated an index of habitat quality using Gentry transects and compared this with parasite communities. We recovered seven intestinal parasite taxa: Strongyloides sp.; Balantioides sp.; Trypanoxyuris sp.; Entamoeba sp.; and unidentified species of ascarid, strongylid, and trematode. Two of these taxa have previously been described in captive Aotus nigriceps (Balantioides sp. and Strongyloides sp.). Parasite richness ranged from zero to five taxa with a mean of 0.8 parasite taxa (±1.0 SD) per fecal sample. Fifty-six percent of samples had at least one intestinal parasite taxon. We found all seven parasite taxa in the wet season but only Strongyloides sp. and Trypanoxyuris sp. in the dry season. Balantioides sp. was positively associated with both Entamoeba sp. and an unidentified trematode, while Entamoeba sp. was positively associated with the unidentified ascarid (P < 0.05). Extrapolations support the likelihood of recovering additional intestinal parasite taxa with increased sampling effort. Neither group size nor basal area was significantly associated with parasite richness. These results highlight the need for continued surveillance of Aotus parasites both temporally and across heterogeneous landscapes because several of the parasite taxa we found are pathogenic in nonhuman primates and people.

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.

Helminths are parasites that cause disease at considerable cost to public health and present a risk for emergence as novel human infections. Although recent research has elucidated characteristics conferring a propensity to emergence in other parasite groups (e.g. viruses), the understanding of factors associated with zoonotic potential in helminths remains poor. We applied an investigator-directed learning algorithm to a global dataset of mammal helminth traits to identify factors contributing to spillover of helminths from wild animal hosts into humans. We characterized parasite traits that distinguish between zoonotic and non-zoonotic species with 91% accuracy. Results suggest that helminth traits relating to transmission (e.g. definitive and intermediate hosts) and geography (e.g. distribution) are more important to discriminating zoonotic from non-zoonotic species than morphological or epidemiological traits. Whether or not a helminth causes infection in companion animals (cats and dogs) is the most important predictor of propensity to cause human infection. Finally, we identified helminth species with high modelled propensity to cause zoonosis (over 70%) that have not previously been considered to be of risk. This work highlights the importance of prioritizing studies on the transmission of helminths that infect pets and points to the risks incurred by close associations with these animals. This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.

With over 10000 species of Amphipoda currently described, this order is one of the most diverse groups of freshwater and marine Crustacea. Members of this group are globally distributed, and many are keystone species and ecosystem engineers within their respective ecologies. As with most organisms, disease is a key factor that can alter population size, behaviour, survival, invasion potential and physiology of amphipod hosts. This review explores symbiont diversity and pathology in amphipods by coalescing a range of current and historical literature to provide the first full review of our understanding of amphipod disease. The review is broken into 2 parts. The first half explores amphipod microparasites, which include data pertaining to viruses, bacteria, fungi, oomycetes, microsporidians, dinoflagellates, myxozoans, ascetosporeans, mesomycetozoeans, apicomplexans and ciliophorans. The second half reports the metazoan macroparasites of Amphipoda, including rotifers, trematodes, acanthocephalans, nematodes, cestodes and parasitic Crustacea. In all cases we have endeavoured to provide a complete list of known species that cause disease in amphipods, while also exploring the effects of parasitism. Although our understanding of disease in amphipods requires greater research efforts to better define taxonomic diversity and host effects of amphipod symbionts, research to date has made huge progress in cataloguing and experimentally determining the effects of disease upon amphipods. For the future, we suggest a greater focus on developing model systems that use readily available amphipods and diseases, which can be comparable to the diseases in other Crustacea that are endangered, economically important or difficult to house.

Parasitism can represent a potent agent of selection, and introduced parasites have the potential to substantially alter their new hosts' ecology and evolution. While significant impacts have been reported for parasites that switch to new host species, the effects of macroparasite introduction into naïve populations of host species with which they have evolved remain poorly understood. Here, we investigate how the estuarine white‐fingered mud crab (Rhithropanopeus harrisii) has adapted to parasitism by an introduced rhizocephalan parasite (Loxothylacus panopaei) that castrates its host. While the host crab is native to much of the East and Gulf Coasts of North America, its parasite is native only to the southern end of this range. Fifty years ago, the parasite invaded the mid‐Atlantic, gradually expanding through previously naïve host populations. Thus, different populations of the same host species have experienced different degrees of historical interaction (and thus potential evolutionary response time) with the parasite: long term, short term, and naïve. In nine estuaries across this range, we examined whether and how parasite prevalence and host susceptibility to parasitism differs depending on the length of the host's history with the parasite. In field surveys, we found that the parasite was significantly more prevalent in its introduced range (i.e., short‐term interaction) than in its native range (long‐term interaction), a result that was also supported by a meta‐analysis of prevalence data covering the 50 years since its introduction. In controlled laboratory experiments, host susceptibility to parasitism was significantly higher in naïve hosts than in hosts from the parasite's native range, suggesting that host resistance to parasitism is under selection. These results suggest that differences in host–parasite historical interaction can alter the consequences of parasite introductions in host populations. As anthropogenically driven range shifts continue, disruptions of host–parasite evolutionary relationships may become an increasingly important driver of ecological and evolutionary change.

The peculiarities of infection with the parasitic bopyrid isopods Gyge ovalis and Progebiophilus sp. and the rhizocephalan Sacculina upogebiae among the mud shrimp Upogebia major population in Vostok Bay (Peter the Great Bay, Sea of Japan) were investigated in April–November 2017. Parasites were found from spring to late autumn. The prevalence of isopod infection in U. major was 5.42%, females and males were equally infected. The prevalence of Sacculina upogebiae was 1.26%; this parasite was more common on the female hosts. Isopods were found on mud shrimp larger than 42 mm; rhizocephalan externae occurred in individuals larger than 57 mm. The highest prevalence of parasites was observed in the summer (7.44%). No cases of simultaneous infection with different species of parasites were noted in U. major.

Infectious diseases of domesticated animals impact human well-being via food insecurity, loss of livelihoods, and human infections. While much research has focused on parasites that infect single host species, most parasites of domesticated mammals infect multiple species. The impact of multihost parasites varies across hosts; some rarely result in death, whereas others are nearly always fatal. Despite their high ecological and societal costs, we currently lack theory for predicting the lethality of multihost parasites. Here, using a global dataset of >4,000 case-fatality rates for 65 infectious diseases (caused by microparasites and macroparasites) and 12 domesticated host species, we show that the average evolutionary distance from an infected host to other mammal host species is a strong predictor of disease-induced mortality. We find that as parasites infect species outside of their documented phylogenetic host range, they are more likely to result in lethal infections, with the odds of death doubling for each additional 10 million years of evolutionary distance. Our results for domesticated animal diseases reveal patterns in the evolution of highly lethal parasites that are difficult to observe in the wild and further suggest that the severity of infectious diseases may be predicted from evolutionary relationships among hosts.

Cane toads (Rhinella marina) are notoriously successful invaders: from 101 individuals brought to Australia in 1935, poisonous toads now cover an area >1.2 million km2 with adverse effects on native fauna. Despite extensive research on the role of macroparasites in cane toad invasion, viral research is lagging. We compared viral prevalence and diversity between toads in their native range (French Guiana, n=25) and two introduced ranges: Australia (n=151) and Hawai’i (n=10) with a metatranscriptomic and metagenomic approach combined with PCR screening. Australian toads almost exclusively harbor one of seven viruses detected globally. Rhimavirus-A (Picornaviridae) exhibited low genetic diversity and likely actively infected 9% of sampled Australian toads extending across ~2,000km of Northern Australia and up to the current invasion front. In native range cane toads, we identified multiple phylogenetically distinct viruses (Iridoviridae, Picornaviridae, Papillomaviridae, and Nackedna-like virus). None of the same viruses was detected in both ranges, suggesting that Australian cane toads have largely escaped the viral infection experienced by their native range counterparts. The novel native range viruses described here are potential biocontrol agents, as Australian toads likely lack prior immunological exposure to these viruses. Overall, our evidence suggests that there may be differences between viruses infecting cane toads in their native vs. introduced ranges, which lays the groundwork for further studies on how these viruses have influenced the toads’ invasion history.

The adaptive immune system is critical to an effective, long-lasting ability to respond to infection in vertebrates and T-helper (Th) cells play a key role in orchestrating the adaptive immune response. Laboratory studies show that functionally distinct Th responses provide protection against different kinds of parasites (i.e., Th1 responses against microparasites and Th2 against macroparasites).Natural populations must deal with challenges from a wide range of infectious agents and co-infection with different types of parasite is the norm, so different Th responses are likely to play an important and dynamic role in maintaining host health and fitness. However, the relationship between T helper immune phenotypes and infection with different types of parasites remains poorly understood in wild animals.In this study, we characterised variation in functionally distinct Th responses (Th1, Th2, Th17 and regulatory responses) in a wild population of Soay sheep using flow cytometry to detect Th-subset specific transcription factors, and ex vivo lymphocyte stimulation to quantify release of Th-associated cytokines. We specifically tested the prediction that raised Th1 and Th2 responses should predict reduced apicomplexan (coccidian) and helminth (nematode) parasite burdens, respectively.Cell counts of different Th subsets measured by flow cytometry did not vary with age or sex. However, all measures of Th-associated ex vivo cytokine production increased with age, and Th17- and regulatory Th-associated cytokine production increased more rapidly with age in males than females.Independent of age and sex, Th2-associated immune measures negatively predicted gastro-intestinal strongyle nematode faecal egg count, while production of the Th1-associated cytokine IFN-γ negatively predicted coccidian faecal oocyst count.Our results provide important support from outside the laboratory that Th1 and Th2 responses confer resistance to different kinds of parasites (micro- and macro-parasites, respectively). They also add to mounting evidence from wild populations that Th1/Th2 trade-offs often observed in controlled laboratory experiments may not readily translate to more complex natural systems.Our study illustrates that harnessing more specific reagents and tools from laboratory immunology has the potential to illuminate our understanding of epidemiology and host-parasite co-evolution in the wild.

Members of the genus Crassicauda (Nematoda: Spirurida) are macroparasites infect the body tissues of whales and dolphins. However, limited information is available on morphological descriptions and phylogenetic studies of the worms. In present study, we report the first complete mitochondrial genome of Crassicauda magna from Neophocoena sunameri in Ningbo, Zhejiang Provence, China. The mitogenome has 13,605 base pairs (74.97% A + T content) and is made up of a total of 36 genes (12 protein-coding, 22 transfer RNAs, and 2 ribosomal RNAs). This study will provide useful molecular information for addressing taxonomic and evolutionary issues in Crassicauda sp..

Disgust is hypothesized to be an evolved emotion that functions to regulate the avoidance of pathogen-related stimuli and behaviors. Individuals with higher pathogen disgust sensitivity (PDS) are predicted to be exposed to and thus infected by fewer pathogens, though no studies have tested this directly. Furthermore, PDS is hypothesized to be locally calibrated to the types of pathogens normally encountered and the fitness-related costs and benefits of infection and avoidance. Market integration (the degree of production for and consumption from market-based economies) influences the relative costs/benefits of pathogen exposure and avoidance through sanitation, hygiene, and lifestyle changes, and is thus predicted to affect PDS. Here, we examine the function of PDS in disease avoidance, its environmental calibration, and its socioecological variation by examining associations among PDS, market-related lifestyle factors, and measures of bacterial, viral, and macroparasitic infection at the individual, household, and community levels. Data were collected among 75 participants (ages 5 to 59 y) from 28 households in three Ecuadorian Shuar communities characterized by subsistence-based lifestyles and high pathogen burden, but experiencing rapid market integration. As predicted, we found strong negative associations between PDS and biomarkers of immune response to viral/bacterial infection, and weaker associations between PDS and measures of macroparasite infection, apparently mediated by market integration-related differences. We provide support for the previously untested hypothesis that PDS is negatively associated with infection, and document variation in PDS indicative of calibration to local socioeconomic conditions. More broadly, findings highlight the importance of evolved psychological mechanisms in human health outcomes.

Host–parasite dynamics often vary over time, brought about by changes in the parasite’s virulence or the host’s ability to resist or tolerate the parasite. Although virulence evolution in microparasites is well studied, we know little about temporal change in the pathogenicity of macroparasites such as blood‐feeding insects. Using data collected over 35 yr, we report a reduction in pathogenicity of the hematophagous swallow bug (Cimex vicarius) on its Cliff Swallow (Petrochelidon pyrrhonota) host. Relative to experimentally fumigated, parasite‐free nests, the negative effects of bugs on nestling swallow body mass and survival were less in the later years of the study than in the earlier years, and the negative relationship between nestling body mass and bug abundance became weaker over time. The survival of adult birds exposed to swallow bugs increased throughout the study, while survival of birds from parasite‐free nests decreased over time. Swallow bug abundance per nest, bug body size, and bug age ratios did not change during the study. Between‐colony transmission of bugs showed less immigration into larger colonies than in earlier studies, but there was no net change in transmission. Cliff Swallows did not reduce their exposure to bugs over time by being more likely to avoid infested nest or colony sites. Parents increased the number of food deliveries to their offspring over time in the presence of parasites, but the total amount of food delivered was unchanged. The reduced cost of swallow bug ectoparasitism does not seem related to changes in parasite narrow‐sense virulence, the host’s avoidance of parasites, the presence of alternative hosts for bugs, or climate‐driven phenological mismatches. The results probably reflect the Cliff Swallow’s evolving of greater tolerance to swallow bugs, brought about by the bird’s shift from natural cliff nesting sites to artificial structures that may harbor more bugs than natural cliffs. This study shows that hosts can respond relatively rapidly to high levels of parasitism, and provides support for models that suggest the evolution of tolerance should be expected in some host–parasite systems.