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Morphological, gene sequence, host tissue tropism, and life cycle characteristics were utilized to describe the myxozoan, Myxobolus rasmusseni n. sp. from fathead minnow, Pimephales promelas, collected from reservoirs in southern Alberta. Results from serial histological sections of whole heads showed that myxospores were contained within irregular-shaped and sized coelozoic capsules (=plasmodia). Clusters of membrane-bound, myxospore-filled plasmodia filled the head cavities of juvenile fathead minnows, leading to the development of large, white, disfiguring lesions in mid to late summer. Bilateral exopthalmia (pop-eye disease) was a common outcome of M. rasmusseni n. sp. development. BLASTn search of a 1974 bp sequence of the 18S rDNA gene isolated from myxospores indicated that M . rasmusseni n. sp. was distinct from other coelozoic and histozoic Myxobolus spp. cataloged in GenBank. 18S rDNA gene sequences from triactinomyxon spores released from the oligochaete Tubifex were 100% identical to sequences from myxospores collected from syntopic fathead minnows. Results from a longitudinal survey of the 2020 cohort of fathead minnows showed that young-of-the-year are exposed at 1-5 mo and that 60-90% of these had developed myxospore-filled lesions approximately one year later. Data regarding potential sources and timing of M. rasmusseni n. sp. emergence in fathead minnow populations are needed., (© 2024 The Authors.)

Individual hosts are often co-infected with multiple parasite species. Evidence from theoretical and empirical studies supports the idea that co-occurring parasites can impact each other and their hosts via synergistic or antagonistic interactions. The fundamental aim of understanding the consequences of co-infection to hosts and parasites requires an understanding of patterns of species co-occurrence within samples of hosts. We censused parasite assemblages in 755 adult, male fathead minnows collected from 7 lakes/ponds in southern Alberta, Canada between 2018 and 2020. Fifteen species of endoparasites infected fathead minnows, 98% of which were co-infected with between 2 and 9 parasite species (mean species richness: 4.4 ± 1.4). Non-random pairwise associations were detected within the overall parasite community. There were particularly strong, positive associations in the occurrences and intensities of the 2 congeneric larval trematodes Ornithodiplostomum sp. and Ornithodiplostomum ptychocheilus that comprised >96% of the 100 000+ parasites counted in the total sample of minnows. Furthermore, the occurrence of Ornithodiplostomum sp. was a strong predictor of the occurrence of O. ptychocheilus , and vice versa. Positive covariation in the intensities of these 2 dominants likely arises from their shared use of physid snails as first intermediate hosts in these waterbodies. These 2 species represent a predictable and non-random component within the complex assemblage of parasites of fathead minnows in this region.

Most trematodes and some cestodes have obligate life history features that include an asexual developmental stage that can produce genetically-identical individuals (clonemates) followed by an adult stage with sexual reproduction. These life history features can influence the evolutionary mechanism of inbreeding in parasites, especially among self-compatible hermaphroditic endoparasites whose mating opportunities are restricted to within hosts. As clonemate mating in hermaphroditic species produces a genetic inbreeding signature identical to that of self-mating, it is important to understand how clonemates are transmitted through their life stages. A handful of prior studies compared clone richness (number of clones) across life cycle stages to infer transmission processes and to characterize clone abundance distributions (CADs) among hosts. Here we illustrate the use of the proportion of clonemate dyads (PC) within hosts to describe the CADs. PC has several advantages as an ecological metric in that it is unbiased by sample size, takes into account relative parasite burdens, and has a direct transmission interpretation, i.e., the probability of cotransmitting clonemates. Moreover, PC is also an evolutionary metric as it can be used to estimate a potential clonemate mating rate. We demonstrate the use of PC in comparing CADs within and across 2 trematode developmental stages in the lancet fluke Dicrocoelium dendriticum. Also, we show how genetic estimates of apparent selfing (true selfing plus clonemate mating) at larval and juvenile stages can be compared to PC estimated at the adult stage to assess the contribution of clonemate mating to apparent selfing. The eco-evolutionary links presented are generalizable to assess sibling cotransmission as well. Thus, the framework presented herein will facilitate future field-based studies on the transmission and mating systems of parasitic flatworms., (© American Society of Parasitologists 2022.)

The dilution effect describes the negative association between host biodiversity and the risk of infectious disease. Tests designed to understand the relative roles of host species richness, host species identity, and rates of exposure within experimental host communities would help resolve ongoing contention regarding the importance and generality of dilution effects. We exposed fathead minnows to infective larvae of the trematode, Ornithodiplostomum ptychocheilus in minnow-only containers and in mixed containers that held 1-3 other species of fish. Parasite infection was estimated as the number of encysted worms (i.e., brainworms) present in minnows following exposure. The results of exposure trials showed that nonminnow fish species were incompatible with O. ptychocheilus larvae. There was no reduction in mean brainworm counts in minnows in mixed containers with brook sticklebacks or longnose dace. In contrast, brainworm counts in minnows declined by 51% and 27% in mesocosms and aquaria, respectively, when they co-occurred with emerald shiners. Dilution within minnow + shiner containers may arise from shiner-induced alterations in minnow or parasite behaviors that reduced encounter rates between minnows and parasite larvae. Alternatively, shiners may act as parasite sinks for parasite larvae. These results highlight the role of host species identity in the dilution effect. Our results also emphasize the complex and idiosyncratic effects of host community composition on rates of parasite infection within contemporary host communities that contain combinations of introduced and native species., Competing Interests: The authors have no conflicting interests., (© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

Host manipulation by parasites is a fascinating evolutionary outcome, but adaptive scenarios that often accompany even iconic examples in this popular field of study are speculative. Kin selection has been invoked as a means of explaining the evolution of an altruistic-based, host-manipulating behavior caused by larvae of the lancet fluke Dicrocoelium dendriticum in ants. Specifically, cotransmission of larval clonemates from a snail first host to an ant second host is presumed to lead to a puppeteer parasite in the ant's brain that has clonemates in the ant abdomen. Clonal relatedness between the actor (brain fluke) and recipients (abdomen flukes) enables kin selection of the parasite's host-manipulating trait, which facilitates transmission of the recipients to the final host. However, the hypothesis that asexual reproduction in the snail leads to a high abundance of clonemates in the same ant is untested. Clonal relationships between the manipulator in the brain and the nonmanipulators in the abdomen are also untested. We provide empirical data on the lancet fluke's clonal diversity within its ant host. In stark contrast to other trematodes, which do not exhibit the same host-manipulating behavioral trait, the lancet fluke has a high abundance of clonemates. Moreover, our data support existing theory that indicates that the altruistic behavior can evolve even in the presence of multiple clones within the same ant host. Importantly, our analyses conclusively show clonemate cotransmission into ants, and, as such, we find support for kin selection to drive the evolution and maintenance of this iconic host manipulation., Competing Interests: The authors declare no competing interest.

Background: The biodiversity and distributions of terrestrial snails at local and regional scales are influenced by their low vagility and microhabitat specificity. The accessibility of large-bodied species and their characteristically high levels of genetic polymorphism make them excellent ecological and evolutionary models for studies on the phylogeography, phylogenetics, and conservation of organisms in fragmented populations. This study aims to elucidate the biodiversity, systematics, and distributions of genetic lineages within the genus Oreohelix at the northern and western periphery of their range., Results: We found four mitochondrial clades, three of which are putative subspecies of Oreohelix subrudis. One clade was geographically widespread, occurring within numerous sites in Cypress Hills and in the Rocky Mountains, a second was geographically restricted to the Rocky Mountains in Alberta, and a third was restricted to the Cypress Hills region. A fourth clade was the small-bodied species, O. cooperi. ITS2 sequence and screening data revealed three genetic clusters, of which one was O. cooperi. Cluster 1 contained most individuals in COI clade X and some from clade B and cluster 2 was predominantly made up of individuals from COI clades B and B' and a few from clade X. ITS2 alleles were shared in a narrow contact zone between two COI clades, suggestive of hybridization between the two., Conclusions: A sky island known as Cypress Hills, in southeastern Alberta, Canada, is a biodiversity hotspot for terrestrial land snails in the genus Oreohelix. The observed phylogeographic patterns likely reflect reproductive isolation during the Last Glacial Maximum, followed by secondary contact due to passive, long-range dispersal resulting from low vagility, local adaptation, and complex glacial history.

The control of emerging parasites requires a fundamental knowledge of where and when rates of transmission are high. Data on spatiotemporal patterns of infection are challenging to obtain, particularly for complex life cycle parasites that involve transmission into multiple obligate hosts. The lancet liver fluke, Dicrocoelium dendriticum, has a long history of colonization outside its native host and geographical range in continental Europe. Infection patterns involving adult and metacercarial stages have been characterized for this trematode in a region of emergence in western Canada within co-grazing herbivores and ants, but infection patterns in snail intermediate hosts in this region are unknown. We combined spatiotemporal prevalence surveys with sequence analyses of the cytochrome c oxidase subunit 1 ( COI) barcoding gene from samples of sporocyst tissue in infected snails to confirm that D. dendriticum utilizes 3 sympatric species of Oreohelid land snail ( Oreohelix subrudis, Oreohelix sp., and Oreohelix cooperi) as first intermediate host. Mean prevalence within a total sample of 900 adult snails collected over 1 field season from 6 sites was 9.9 ± 2.4%. For each species of snail, prevalence ranged between 5-30% within monthly samples, with peaks in mid-summer followed by declines in fall. Between-site variation in prevalence was low and non-significant, implying that rates of transmission of D. dendriticum miracidia from domestic stock and wildlife into snails are similar within localized sites, despite high variation in local habitat characteristics and in the structure of the definitive host community.

Some parasites are able to manipulate the behaviour of their hosts to their own advantage. One of the most well-established textbook examples of host manipulation is that of the trematode Dicrocoelium dendriticum on ants, its second intermediate host. Infected ants harbour encysted metacercariae in the gaster and a non-encysted metacercaria in the suboesophageal ganglion (SOG); however, the mechanisms that D. dendriticum uses to manipulate the ant behaviour remain unknown, partly because of a lack of a proper and direct visualisation of the physical interface between the parasite and the ant brain tissue. Here we provide new insights into the potential mechanisms that this iconic manipulator uses to alter its host's behaviour by characterising the interface between D. dendriticum and the ant tissues with the use of non-invasive micro-CT scanning. For the first time, we show that there is a physical contact between the parasite and the ant brain tissue at the anteriormost part of the SOG, including in a case of multiple brain infection where only the parasite lodged in the most anterior part of the SOG was in contact with the ant brain tissue. We demonstrate the potential of micro-CT to further understand other parasite/host systems in parasitological research.

Hippoboscid flies (Diptera: Hippoboscidae) include species that are ectoparasites of birds in the Northern Hemisphere, but little is known regarding their taxonomy, parasites, avian host associations, or geographical distribution in North America. In late August of 2013 and 2014, we collected hippoboscid flies from live birds trapped in mist nets as part of a banding study in Cypress Hills Interprovincial Park in southeastern Alberta, Canada. A total of 113 birds comprising 9 species was examined in 2013. Of these, 18 individuals were infested with 1-3 Ornithomya anchineuria Speiser (n = 22 flies; prevalence = 15.9%). Eight of these flies carried 1-8 adult female epidermoptid mites anchored to their ventral, posterior abdomens. Each female was associated with clusters of up to 30 stalked eggs. The first pair of tarsi on adult female mites was highly modified as anchors, indicating permanent attachment through the host cuticle. Morphological traits identified these mites as Myialges cf. borealis Mironov, Skirnisson, Thorarinsdottier and Nielsen. Cytochrome c oxidase subunit 1 ( COX1) gene sequences obtained for 2 mites were distinct from those previously reported for species of Myialges, being most similar to Myialges trinotoni Cooreman. The paucity of available gene sequences for Myialges and related genera of epidermoptid mites prevents any further conclusions regarding taxonomy. These findings extend previous reports of O. anchineuria from Pacific and Atlantic coasts of Canada inland to the central migratory flyway of the Northern Great Plains and expand the limited information available for Myialges spp.

Parasite distributions are constantly changing due to climate change, local and global movement of animals and humans, as well as land use and habitat change. The trematode Dicrocoelium dendriticum is a relatively recent invader of Canada, being first reported in eastern Canada in the 1930s and western Canada in the 1970s. However, historical records are scarce and its emergence is poorly understood. The establishment of this parasite in Canada provides an interesting opportunity to explore the use of population genetic approaches to help elucidate the invasion history of a relatively recently established helminth parasite. In this study, we compare the genetic diversity and population structure of a number of D. dendriticum populations from western and eastern Canada, and compare these with much longer established European populations. Two independent genetic marker systems were used; a microsatellite marker panel and a cytochrome c oxidase 1 (cox1) mitochondrial (mt)DNA sequence marker. We found distinct differences in both genetic diversity and population structure of the different Canadian populations that provide insights into their invasion histories compared with the European populations. Two populations from British Columbia, Canada - Salt Spring and Vancouver Islands - are of low diversity, show evidence of a population bottleneck and are closely related to each other, suggesting a shared recent history of establishment. These west coast populations are otherwise most closely related to those from eastern Canada and western Europe, and in contrast are genetically divergent from those in Cypress Hills, Alberta, Canada. Although the Alberta parasite population is the most recently reported in Canada, being first identified there in the early 1990s, it was the most genetically diverse of those examined and showed a strong pattern of admixture of genotypes present in western and eastern Europe. Overall, our results are consistent with a model in which western Europe is likely the source of flukes on the east coast of Canada, which were then subsequently translocated to the west coast of Canada. The most recently reported D. dendriticum population in Canada appears to have a different history and likely has multiple origins., (Copyright © 2017 Australian Society for Parasitology. All rights reserved.)

Portable user-friendly diagnostic tests can benefit detection and surveillance of wildlife diseases. Here, the performance of a compact POCKIT™ Nucleic Acid Analyzer for detection of Ambystoma tigrinum virus (ATV), an emerging Iridovirus that is associated with high host mortality in the western tiger salamander (Ambystoma mavortium) in North America was assessed. Tissue samples from 188 larval tiger salamanders collected from sites in Alberta, Canada were tested by both iiPCR and by conventional PCR. Results of the two assays showed 96.3% agreement. All 176 samples that tested positive by conventional PCR were also positive by iiPCR, while 12 of the samples that were negative by conventional PCR were positive by iiPCR. Comparison of the limits of detection of the two assays shows that the iiPCR assay was more sensitive than conventional PCR and had a LOD95 of 20 copies per reaction. The instrument automatically analyzes and displays results within 40min following nucleic acid extraction. The novel technology could enhance detection of, and response to, wildlife pathogens, particularly those that occur sporadically, cause rapid outbreaks, and/or occur within isolated geographical regions., (Crown Copyright © 2017. Published by Elsevier B.V. All rights reserved.)

The expansion of parasite distributions outside of their native host and geographical ranges has occurred repeatedly over evolutionary time. Contemporary examples include emerging infectious diseases (EIDs), many of which pose threats to human, domestic animal, and wildlife populations. Theory predicts that parasites with complex life cycles will be rare as EIDs due to constraints imposed by host specialization at each life-cycle stage. In contrast to predictions of this theory, we report 2 new intermediate hosts in the 3-host life cycle of the liver fluke Dicrocoelium dendriticum in Cypress Hills Provincial Park, Alberta, Canada. Results of sequence analysis of the cytochrome oxidase 1 (cox1) mitochondrial gene identified the terrestrial snail Oreohelix subrudis and the ant Formica aserva as first and second intermediate hosts, respectively, in the region. Neither of these intermediate hosts, nor their suite of domestic and wild mammalian grazers used in the life cycle, occurs within the native range of D. dendriticum in Europe. Our results from host surveys show that the prevalence of D. dendriticum in samples of O. subrudis varied between 4% and 10%, whereas mean metacercariae intensity in F. aserva varied between 33 and 41 (n = 163, mean ± SD = 38 ± 35). These results are the first to describe the complete life cycle of emerging lancet fluke in western North America. The process of multi-level ecological fitting, in which the lancet fluke possesses pre-existing traits to utilize host resources, rather than host species, at each life-cycle stage provides a mechanism for the establishment of this complex life cycle in a novel habitat and in novel hosts.

Parasites residing within the central nervous system of their hosts have the potential to reduce various components of host performance, but such effects are rarely evaluated. We assessed the olfactory acuity of fathead minnows (Pimephales promelas) infected experimentally with the monogenean Dactylogyrus olfactorius, the adults of which live within the host's olfactory chambers. Olfactory acuity was compared between infected and uninfected hosts by assessing electro-olfactography (EOG) neural responses to chemical stimuli that indicate the presence of food (L-alanine) or the presence of conspecifics (taurocholic acid). We also compared differences in gross morphology of the olfactory epithelium in infected and uninfected minnows. Differences in EOG responses between infected and uninfected minnows to both cue types were non-significant at 30 days post-exposure. By days 60 and 90, coincident with a two times increase in parasite intensity in the olfactory chambers, the EOG responses of infected minnows were 70-90% lower than controls. When infected fish were treated with a parasiticide (Prazipro), olfactory acuity returned to control levels by day 7 post-treatment. The observed reduction in olfactory acuity is best explained by the reduced density of cilia covering the olfactory chambers of infected fish, or by the concomitant increase in the density of mucous cells that cover the olfactory chambers. These morphological changes are likely due to the direct effects of attachment and feeding by individual worms or by indirect effects associated with host responses. Our results show that infection of a commonly occurring monogenean in fathead minnows reduces olfactory acuity. Parasite-induced interference with olfactory performance may reduce a fish's ability to detect, or respond to, chemical cues originating from food, predators, competitors or mates., (© 2017 The Authors. Journal of Animal Ecology © 2017 British Ecological Society.)

Dactylogyrus olfactorius n. sp. (Monogenea) is described from the olfactory chamber of the fathead minnow Pimephales promelas Rafinesque in Alberta, Canada. The new species resembles Dactylogyrus bychowskyi Mizelle, 1937, D. bifurcatus Mizelle, 1937 and D. simplexus Mizelle, 1937, all parasites of Pimephales spp. in North America, in overall size and shape of the anchors and hooks, and in having a male copulatory complex with a tapered tubular penis and bifurcate accessory piece. Diagnostically, D. olfactorius n. sp. has relatively small anchors, hooks of anchor length, and a thin, long dorsal bar and no apparent ventral bar nor 4A hooks. Scanning electron microscopy revealed the body tegument of D. olfactorius n. sp. to be microvillous and in shallow annular folds, while that of D. bifurcatus, occurring on host gills of the same fish, was avillous and in gill-like folds dorsally and ventrally. Partial 28S rDNA sequences revealed significant differences between the two species, supporting establishment of D. olfactorius n. sp. and dispelling the possibility of ecophenotypic effects of site of attachment on morphology.

This study characterizes polymorphic microsatellite loci from adults of the liver fluke Dicrocoelium dendriticum sampled from a population of sympatric beef cattle and wapiti in a region of emergence in southern Alberta, Canada. We also scrutinized the markers to validate their use in studying the population genetics of this complex life cycle parasite. Among the nine loci described, four deviated significantly from Hardy Weinberg Equilibrium (HWE) due to technical artefacts. The remaining five loci were in HWE. These five provided sufficient resolution to identify clonemates produced from the obligate asexual reproduction phase of the life cycle in snails and to assess the impact of non-random transmission of clonemates on measures of FIS, FST and genotypic disequilibrium. Excluding clonemates, we show that the sub-population of worms was in HWE, that average FIS within hosts was 0.003 (p=0.4922) and that there was no population genetic structure among hosts FST=0.001 (p=0.3243). These markers will be useful for studies of Dicrocoelium dendriticum ecology, transmission, and evolution., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Gyrodactylus salmonis is a common ectoparasite on the fins and body of North American salmonids in fresh water. In this study, the spatial distribution of G. salmonis on 60 captive hatchery-reared rainbow trout, Oncorhynchus mykiss , is reported. The highest parasite densities occurred on 5 × 5-mm(2) sections of the dorsal fin followed by the trunk, other fins, and the olfactory chamber, with the lowest densities on the head. The finding of infections within the olfactory chamber of 93% of the fish was unexpected. One possibility is that such infections represented spillover from high-density infrapopulations that occur on the skin and fins. However, this possibility is unlikely, because worm densities at various sites along the body surface of infected fish did not correlate with densities within the olfactory chamber. The parasite conceivably enters the chamber either via water incurrent or by crawling in from the head and subsequently remaining at this site to feed and reproduce. Results from scanning electron microscopy are consistent with physical modification to the olfactory epithelium associated with the attachment/reattachment of the opisthaptor and epithelial grazing.

Epidemiological rate parameters of host generalist parasites are difficult to estimate, especially in cases where variation in parasite performance can be attributed to host species. Such cases are likely common for generalist parasites of sympatric grazing mammals. In this study, we combined data from experimental exposures in cattle and sheep and natural infections in elk to compare the recruitment, morphology and reproduction of adult Dicrocoelium dendriticum, a generalist trematode that has emerged in sympatric grazing hosts in Cypress Hills Provincial Park, Alberta. Overall, there were no significant differences in the recruitment of metacercariae and in the pre-patency period of adults in experimentally exposed cattle and sheep. All flukes reached reproductive maturity and the degree of reproductive inequality between individual flukes within each infrapopulation was moderate and approximately equal among the three host species. Neither fluke size nor per capita fecundity was constrained by density dependence. Thus, fitness parameters associated with growth and reproduction were approximately equivalent among at least three species of definitive host, two of which are sympatric on pastures in this Park. The generalist life-history strategy of this trematode, which is known to extend to other stages of its life cycle, has likely contributed to its invasion history outside its native range in Europe.

Background: Gastrointenstinal nematodes (GIN) present a serious challenge to the health and productivity of grazing stock around the globe. However, the epidemiology of GIN transmission remains poorly understood in northern climates. Combining use of serological diagnostics, GIS mapping technology, and geospatial statistics, we evaluated ecological covariates of spatial and temporal variability in GIN transmission among bovine calves pastured in Alberta, Canada., Methods: Sera were collected from 1000 beef calves across Alberta, Canada over three consecutive years (2008-2010) and analyzed for presence of anti-GIN antibodies using the SVANOVIR Ostertagia osteragi-Ab ELISA kit. Using a GIS and Bayesian multivariate spatial statistics, we evaluated the degree to which variation in specific environmental covariates (e.g. moisture, humidity, temperature) was associated with variation in spatial and temporal heterogeneity in exposure to GIN (Nematodirus and other trichostrongyles, primarily Ostertagia and Cooperia)., Results: Variation in growing degree days above a base temperature of 5 °C, humidity, air temperature, and accumulated precipitation were found to be significant predictors of broad-scale spatial and temporal variation in serum antibody concentrations. Risk model projections identified that while transmission in cattle from southeastern and northwestern Alberta was relatively low in all years, rate of GIN transmission was generally higher in the central region of Alberta., Conclusions: The spatial variability in risk is attributed to higher average humidity, precipitation and moderate temperatures in the central region of Alberta in comparison with the hot, dry southeastern corner of the province and the cool, dry northwestern corner. Although more targeted sampling is needed to improve model accuracy, our projections represent an important step towards tying treatment recommendations to actual risk of infection.

Sera from calves originating on a 17,000 ha ranch in southeastern Alberta, were collected over three consecutive years (2008-2010) at weaning and analysed for the presence of anti-Ostertagia antibodies using the SVANOVIR(®)Ostertagia ostertagi-Ab ELISA kit. Faecal samples taken at the same time were analysed for presence of nematode eggs using the modified Wisconsin faecal flotation technique. Mean optical density ratio (ODR) values for all calves were similar in 2008 and 2010 while the 2009 values were significantly higher. Similar cumulative frequency distribution profiles were found for 2008 and 2010 while the 2009 profile had an increased number of values in the higher bin categories. This pattern indicates higher nematode transmission on pasture in 2009. There was no significant difference in ODR values between egg positive and egg-negative calves and no significant correlation was detected between individual ODR values and faecal egg output. Significantly higher ODR values in 2009 appear contradictory to general assumptions about the ecological requirements of larval development, as 2009 was a relatively dry year. However, examination of weather data identified 5-6 rainfall events that may have resulted in episodic enhanced survival of nematode larvae., (Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.)

Epidemiological parameters such as transmission rate, rate of parasite-induced host mortality, and rate of development of host defenses can be assessed indirectly by characterizing the manner in which parasite burdens change with host age. For parasites that are host generalists, estimates of these important parameters may be host-species dependent. In a cross-sectional study, we determined age-abundance profiles of infection in samples of sympatric free-ranging elk and domestic cattle infected with the lancet liver fluke, Dicrocoelium dendriticum. This parasite was introduced into Cypress Hills Provincial Park in southeastern Alberta, Canada in the mid 1990s, and now occurs in 60-90% of co-grazing elk and beef cattle examined at necropsy. The livers of 173 elk were made available by hunters during the 1997-2011 hunting seasons and livers from 35 cattle were purchased from ranchers. In elk, median worm abundance peaked in 6-24 month-olds (median = 72, range = 0-1006) then significantly declined to <10 worms/host in 10-16 year olds. The decline in fluke burden with age is not consistent with an age-related decline in exposure to metacercariae in intermediate hosts and high rates of fluke-induced host mortality are unlikely. Rather, the pattern of peak fluke burdens in elk calves and juveniles, followed by a decline in older animals is consistent with the development of a protective immune response in older hosts. There was no pattern of worm accumulation or decline in sympatric cattle, although statistical power to detect a significant effect was low. These results highlight the complexity and context-dependent nature of epidemiological processes in multi-host systems.

1. Individuals that live in groups benefit from increased foraging success and decreased predation. Protection from some types of parasites may provide an additional benefit of group-living. For fish, the extent to which shoaling can reduce an individual's risk of exposure to the infective stages of parasites is unknown. 2. We tested for antiparasite benefits of shoaling in fathead minnows exposed to larvae (cercariae) of two of their most common species of trematode, Ornithodiplostomum ptychocheilus and Posthodiplostomum minimum. As developing stages (metacercariae) of these trematodes cause reductions in minnow activity, growth and survival, natural selection should favour the evolution of cercariae-avoidance behaviours. 3. We evaluated shoal dimensions in groups of minnows exposed to O. ptychocheilus and to other chemical/physical stimuli within aquaria. To compare risk of exposure in shoaling vs. non-shoaling fish, we confined groups of minnows into mesh cages in outdoor mesocosms, exposed them to cercariae, then compared mean worm numbers in grouped vs. solitary fish. Lastly, we tested whether fish located within the centre of an artificial shoal reduced their risk of cercariae exposure compared with those along peripheral edges. 4. Minnows distinguished infective cercariae from other potential aquatic threats and responded with activity that reduced the 2-dimensional area of their shoals 15-fold compared with water-only controls. Fish confined within artificial shoals had 3-fold fewer worms than single fish and minnows located within the centre of artificial shoals had significantly fewer worms than those without peripheral minnows. 5. These results show that shoaling reduces a minnows' risk of exposure to cercariae, either directly via detection of cercariae in the water column followed by behavioural avoidance or indirectly via behaviour-mediated differences in exposure between shoaling vs. non-shoaling fish., (© 2012 The Authors. Journal of Animal Ecology © 2012 British Ecological Society.)

Although results from field surveys have linked parasites to oxidative stress in their fish hosts, direct evidence involving experimentally infected hosts is lacking. We evaluated the effects of experimental infections with larval trematodes on induction of oxidative stress in fathead minnows, Pimephales promelas. Juvenile fish were exposed in the laboratory to the larvae (cercariae) of 2 species of trematode: Ornithodiplostomum sp. that develops in the liver, and O. ptychocheilus that develops in the brain. For Ornithodiplostomum sp., lipid peroxidation concentration in liver tissue increased 5 days after exposure and remained higher than controls until the end of the experiment at 28 days. For O. ptychocheilus, liver lipid peroxidation concentration was higher than controls at 5 days, but not thereafter. Sustained elevation in lipid peroxidation concentration for the liver trematode may be explained by direct tissue damage caused by developing larvae in the liver, or by an immune response. These experimental results support those from field studies, indicating that the lipid peroxidation assay may be an effective biomonitor for parasite-induced oxidative stress in fish, and that the nature of the oxidative stress response is species and/or tissue specific.

Apparent changes in the distribution of Dicrocoelium dendriticum in western Canada and the absence of other liver flukes in the area prompted an examination of the humoral responses in naturally infected cattle sharing pasture with heavily infected wild cervids. Western blots using sera from the infected cattle indicated that the cattle had antibodies to various fluke antigens, however the pattern of response varied among isotypes. Isotype analysis indicated that Dicrocoelium-infected cattle produced IgG1, and IgM antibodies, but not IgG2 antibodies. Subsequent comparison of the efficiency of coprological and serological approaches for diagnosis showed that while 43.5% of a separate group of 26 yearlings had eggs in their faeces, the immunoblots indicated that all had detectable antibodies. A group of cattle necropsied for confirmation of fluke status was used to evaluate humoral immune responses and to provide baseline information in the preliminary development of an indirect ELISA for detection of anti-fluke antibodies., (Crown Copyright © 2010. Published by Elsevier B.V. All rights reserved.)

The metacercarial stage of trematodes is typically considered an encysted, developmentally quiescent, resting stage. Yet the metacercariae of some species of strigeoid trematode undergo extravagant development within specific tissues of their second intermediate host. Our understanding of patterns of migration, site selection and development of these types of metacercariae is known for only a few species. In this study, we characterize the invasion and development of Ornithodiplostomum sp. metacercariae in their second intermediate host, the fathead minnow, Pimephales promelas. Diplostomules completed their migration into the abdominal cavity between 15 min and 48 h p.i. Most diplostomules migrated along muscular and connective tissue then penetrated the peritoneal lining of the abdominal cavity en route to the liver or pancreas. Alternatively, some diplostomules migrated within the host's circulatory system, including the heart and arteries of the hepatic portal system. Metacercarial development in the liver and pancreas involved distinct growth, encystment and consolidation phases. Metacercarial volume increased 15-fold between 48 h and 4 weeks p.i., presumably due to absorptive and/or ingestive feeding activities within host tissues. By 2 weeks p.i., metacercariae were enveloped within a cyst wall and they were found loosely attached to the surfaces of internal tissues or unattached within the body cavity. These results emphasize the complex nature of metacercarial migration and growth and demonstrate that their growth and encystment phases occur within different habitats within their intermediate hosts., (Copyright © 2010 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

Accurate diagnosis of parasites within individual hosts remains a difficult task. Incorrect and/or inaccurate diagnosis restricts the potential for targeted treatment of individuals and limits our understanding of key epidemiological characteristics of potential pathogens of domestic stock. In this study, we compared the specificity and sensitivity of four diagnostic methods for determination of the presence and intensity of the cestode Anoplocephala perfoliata in horses. Over 400 horses from an abattoir in south-central Alberta were evaluated for the presence and number of cestodes. Thirty one horses were infected with 1 to >1000 worms. Diagnosis based upon faecal egg counts of horses with known numbers of worms was least accurate in detecting worm presence. Detection of circulating antibodies to the cestode was most sensitive using Western blot analysis (100%), but had lower specificity (87%). A serum-based ELISA had a lower sensitivity (70%) for detection of antibodies. A coproantigen ELISA had 74% sensitivity and 92% specificity, and there was a positive correlation between antigen concentration and tapeworm intensity. The coproantigen ELISA may have the potential as a diagnostic tool for determining the presence and intensity of this potentially pathogenic cestode.

The migration of subadult parasites to preferred sites within final hosts is well characterized. In contrast, the migration of larval stages of trematodes to specific sites within their second intermediate hosts is poorly understood. We used a serial necropsy approach to characterize the migration of Ornithodiplostomum ptychocheilus diplostomules from the point of cercarial penetration, to encystment within the outermost tissues of the brain of fathead minnows. Diplostomules utilized peripheral nerves to access the central nerve cord, or they used specific cranial nerves to directly access the brain. Within 3 h of exposure to cercariae, 46% of all diplostomules were observed within the medulla of the brain. Diplostomules subsequently utilized specific neural tracts to reach lateral regions of the outermost tissue layer of the optic lobes, the stratum marginale. Diplostomules remained in this layer during their 4-week growth phase, then shifted site to the adjacent meninges for encystment. Characterization of a habitat shift for developing versus encysted metacercariae helps explain the results of previous ecological studies that document transient changes in the effects of metacercariae on the surivival, behaviour, and anti-parasite defences of infected fish.

Evidence for the presumed linkage between the enigmatic rodlet cells of fish and exposure to helminths is anecdotal and indirect. We evaluated the proliferation and development of rodlet cells in the optic lobes of fathead minnows exposed to cercariae of Ornithodiplostomum ptychocheilus. Mean rodlet cell densities (ca. 10/mm(2)) in the optic lobes were similar between unexposed controls and minnows with 1- and 2-week old infections. Rodlet cell densities increased at 4 weeks p.i., reaching maxima (ca. 200/mm(2)) at 6 weeks p.i., followed by a decline at 9 weeks. This temporal pattern of proliferation and maturation paralleled the development of metacercariae within the optic lobes. Unencysted metacercariae develop rapidly within tissues of the optic lobes for approximately 4 weeks after penetration by cercariae, then shift to the adjacent meninges to encyst. The former stage is associated with tissue damage, the latter with massive inflammation of the meninges. Thus, peak densities and maturation of rodlet cells correspond to the period when inflammation of the meninges caused by the large metacercarial cysts is at a maximum. Our results support recent contentions that rodlet cells comprise part of the host inflammatory defence response., (2009 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

We examined tegumental development of the diplostomulum of Ornithodiplostomum ptychocheilus, with respect to structural transformations that have functional relevance to the invasion, migration, and site establishment processes in the brain of the fish second-intermediate host, Pimephales promelas. Using a combination of brightfield, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal microscopy (CM), we demonstrated that the diplostomula become established in the outer region of the optic lobes within 24-48 hr of penetration and continue to grow and transform over a period of 4-14 days. During this period, the J-shaped body consists of 2 distinct regions: (1) a highly motile prosoma with distinctive tegumental spines and (2) an opisthosoma, the tegument of which is elaborated into a dense uniform layer of long, thin microvilli. The prosoma is alternately invaginated into and everted from the opisthosoma, thus constituting a protrusible proboscis. By day 14 postinfection (PI), the body has lost this bipartite structure and has taken on the uniformly flattened form characteristic of metacercariae. The transitory complex structure of the diplostomula appears to be well suited to burrowing through host tissues (primarily by action of the prosoma), followed by rapid dissociation of host tissue and nutrient accumulation (primarily by action of the opisthosoma) in preparation for metacercaria encystment.

Many fishes possess specialized epidermal cells that are ruptured by the teeth of predators, thus reliably indicating the presence of an actively foraging predator. Understanding the evolution of these cells has intrigued evolutionary ecologists because the release of these alarm chemicals is not voluntary. Here, we show that predation pressure does not influence alarm cell production in fishes. Alarm cell production is stimulated by exposure to skin-penetrating pathogens (water moulds: Saprolegnia ferax and Saprolegnia parasitica), skin-penetrating parasites (larval trematodes: Teleorchis sp. and Uvulifer sp.) and correlated with exposure to UV radiation. Suppression of the immune system with environmentally relevant levels of Cd inhibits alarm cell production of fishes challenged with Saprolegnia. These data are the first evidence that alarm substance cells have an immune function against ubiquitous environmental challenges to epidermal integrity. Our results indicate that these specialized cells arose and are maintained by natural selection owing to selfish benefits unrelated to predator-prey interactions. Cell contents released when these cells are damaged in predator attacks have secondarily acquired an ecological role as alarm cues because selection favours receivers to detect and respond adaptively to public information about predation.

Previous surveys of wild ungulates indicate that the liver fluke, Dicrocoelium dendriticum, was rare in the Cypress Hills area of southeastern Alberta. However, 41 of 59 wapiti (Cervus elaphus) sampled during the 2003 and 2004 hunting seasons from this region were infected, with 7 hosts containing >1,000 worms. Prevalence and mean intensity were similarly high in sympatric beef cattle and mule deer. Worm abundance in wapiti was age related, with calves containing significantly higher numbers of worms (mean +/- SD abundance = 825 +/- 1098) than adults (107 +/- 259). This pattern with host age was not evident in beef cattle, although the smaller sample sizes may be a contributing factor. These results indicate that D. dendriticum is now well established in Cypress Hills Park, circulating between at least 3 species of sympatric ungulates, including beef cattle.

Populations of hosts vary extensively in the types and numbers of parasites that the average individual contains. Understanding the factors that lead to this variation is an important goal for parasite ecologists. We characterized patterns of helminth component community structure in whitefish collected from a cluster of 7 lakes located on an isolated plateau in northern Alberta, Canada. Component communities were species rich (5-6 species per lake), high in mean helminth intensity (approximately 80-500 individuals/host), and high in between-lake similarity (50-100%), a pattern consistent with results from studies on whitefish sampled from other localities in Northern Canada and Europe. Multivariate analyses indicated that the structure of the component communities was associated with 2 opposing environmental gradients. One was defined primarily by water colour, the second by phosphorous concentration. Thus, 4 lakes were characterized by a combination of high colour, low productivity, low parasite intensities, and the absence of larval acanthocephalans. Habitat/species associations were less clear as intensities increased, but the 3 remaining lakes tended to have the opposite characteristics. These results provide evidence that variation in helminth component community structure in fish is associated with variation in physicochemical characteristics that are linked to aquatic productivity.

Trematode metacercariae typically are regarded as nonfeeding and metabolically inactive. However, the metacercariae of many trematode species undergo complex and prolonged periods of development within their intermediate hosts. In the present study, we used electron microscopy to document chronological changes in development of the tegument of Ornithodiplostomum ptychocheilus metacercariae recovered from the brains of experimentally infected fathead minnows (Pimephales promelas). Commencing at 4 days postinfection (PI), the smooth, thin, syncytial tegument transforms into a complex microlamellar and microvillar system that encircles the entire body surface. The microvilli are oriented in parallel in an extended pattern, reaching directly away from the parasite and toward the receding host tissue. The microvilli disappear at approximately 28 days PI, followed by deposition of the cyst wall and further transformation of the tegument into the spinose, a glandular structure typical of an immature adult. To our knowledge, the progressive disaggregation of host cells at the leading edge of elongating parasite microvilli has not been demonstrated previously for any trematode. These results provide morphological evidence that the metacercariae of some trematode species undergo complex developmental changes associated with feeding in their intermediate host.

The effect of cadmium (Cd) exposure on infectivity of cercariae of 2 trematode species (Ornithodiplostomum ptychocheilus and Posthodiplostomum minimum) to their second intermediate fish host was evaluated. Individual fathead minnows (Pimephales promelas) were exposed to cercariae that had been treated with Cd solutions at concentrations of 0, 2, 20, or 200 microg/L for 2 hr. Two weeks later, the numbers of encysted metacercariae in the brain (O. ptychocheilus) and body cavity (P. minimum) of the fish were evaluated. ANOVA analyses indicated a strong negative effect of Cd concentration on cercaria infectivity. The species x Cd concentration interaction was not significant, indicating that the magnitude of Cd-induced reduction in infectivity was similar between O. ptychocheilus and P. minimum. The results show that short-term exposure to Cd, even at low concentrations, interferes with transmission processes that affect the recognition and penetration of cercariae, the migration and survival of metacercariae within the second intermediate host, or both.

We monitored temporal changes in the magnitude of altered host behaviour in minnows (Pimephales promelas) experimentally infected with metacercariae of a brain-encysting trematode (Ornithodiplostomum ptychocheilus). This parasite develops and then encysts in a region of the brain that mediates the optomotor response (OMR), an innate behaviour that links visual stimuli with motor performance. The OMR of infected and uninfected minnows was evaluated between 0 and 10 weeks post-infection (p.i.), an interval spanning the development period of metacercariae to infectivity in birds. Trials involved monitoring the time an individual minnow spent following a spinning drum that had been painted with alternating black and white stripes. At 2 and 4 weeks p.i., infected minnows followed the drum 40% less often than controls. Differences between controls and infected fish declined thereafter, and were undetectable by 10 weeks p.i. Both control and infected fish habituated equally rapidly to the spinning drum. However, the difference in performance between controls and infected fish was 29% for experienced fish and 48% for fish that had never experienced the drum. Because maximum parasite-induced reduction in OMR coincided with the period of maximum parasite development, the behavioural effects are most likely due to unavoidable pathology in the brain associated with developing larvae.

A lack of comparative studies limits our understanding of interspecific variation in parasite life histories, especially for species that incorporate asexual and resting stages into their life cycles. Ornithodiplostomum ptychocheilus and Posthodiplostomum minimum are sympatric diplostomid trematodes that share the same first (pond snail, Physa gyrina) and second (fathead minnow, Pimephales promelas) intermediate hosts within lakes in Alberta, Canada. Interspecific differences in the body sizes of adults, cercariae, and metacercariae were evaluated from parasites recovered from laboratory-raised chickens, snails, and minnows, respectively. Differences in adult worm fecundity and cercariae production were estimated from chickens and snails exposed to known numbers of parasite larvae. Posthodiplostomum minimum adults, metacercariae, and eggs were 97, 86, and 5% larger than those of 0. ptychocheilus, respectively. The average numbers of eggs produced per day by P. minimum was 3 times higher than for O. ptychocheilus, and P. minimum produced approximately twice as many cercariae per day. Although the larger of the 2 species had higher egg and cercariae production, conclusions regarding covariation between adult worm size and the reproductive rates of other life cycle stages require further studies on related species.

Circulation of 24 macroparasite species among 12 species of fish was evaluated within samples of hosts collected from 9 lakes on an isolated plateau in northern Alberta, Canada. Twenty-seven parasite taxa (24 species plus the larval stages of Triaenophorus crassus, T. stizostedionis, and Raphidascaris acus) had the potential to be circulated among hosts. Sixteen parasite taxa were recovered from a single host species within a lake. Of the 11 remaining nonspecialist taxa, 4 were larval stages that matured in fish or birds and 7 were adults. Eight of the 11 cases of circulation among hosts involved lake whitefish, and this host was involved in the transmission of 5 species to piscivorous fishes. Despite evidence for the circulation of 7 taxa among the 4 species of sympatric Salmonidae, 60-99% of all worms were recovered from just 1 species of host. These results indicated that approximately 60% of the parasite taxa that infected fish in these lakes were absolute host specialists. The remaining 40% of parasite taxa had restricted host ranges, with most examples of parasite circulation limited to the 2 species of sympatric coregonid.

We examined the relationship between the numbers of brain-encysting trematodes (Ornithodiplostomum ptychocheilus) and the magnitude of altered behaviors in fathead minnows (Pimephales promelas). Because cysts develop within a brain region that integrates visual stimuli with motor response. we evaluated the standard optomotor response (OMR). Monitoring this task involved recording the time minnows spent following a spinning drum, on which alternating black and white stripes had been painted. Minnows were exposed to 0, 5, 20, 120, and 300 cercariae and then their OMR was evaluated at 2-wk postinfection. Surprisingly, only minnows that had high numbers of parasites (155 +/- 31 worms/fish) or low numbers of parasites (3 +/- 3 worms/ fish) differed significantly in their optomotor performance compared with controls. Reduced OMR of heavily infected minnows was positively correlated with reduction in minnow activity. In contrast, reduced OMR in lightly infected minnows was independent of host activity and was likely associated with the rapid development of parasite larvae within the optic tecta. The nonlinear relationship between parasite intensity and effect on host behavior was consistent with an earlier study, but the underlying mechanisms producing this pattern are unknown.

Two trichostronglyes, Teladorsagia ostertagi and Nematodiru helvetianus, accounted for > 99% of nematodes recovered from gastrointestinal tracts of 47 lambs pastured in central Alberta during the summer of 2000. Their prevalence and mean intensity increased from < 10% and < 50 worms/host, in late June, to > 80% and approximately 1000 worms/host, by mid-July, respectively.

Annual, seasonal, and interlake variation in prevalence and intensity of Ornithodiplostomum ptychocheilus (Faust) metacercariae was assessed in populations of fathead minnows (Pimephales promelas) collected from 4 lakes in north-central Alberta. Mean metacercariae intensity in young-of-the-year minnows varied extensively (5-123 metacercariae/host) among year, month, and lakes. In 2 of the lakes, prevalence always reached 100%, and mean intensity always peaked in September or October. The high spatial and annual variation in metacercarial recruitment was partly attributable to variation in host size. but variation in water depth, temperature, snail densities, and bird visitation likely also played a role. A laboratory experiment demonstrated that host and metacercariae survival was intensity-independent during a period of simulated winter. Thus, metacercariae recruited in the fall survive until the following spring.

Metacercariae of the trematode Ornithodiplostomum ptychocheilus cause a conspicuous enlargement of the cranium of juvenile fathead minnows (Pimephales promelas). Minnows sampled from 2 naturally infected ponds in northern Alberta, Canada, had 12% higher and 7% wider craniums compared to fish from an adjacent, uninfected pond. We tested the prediction that cranial distortion was caused by encystment of metacercariae on the brains of slow-growing minnows in a factorial experiment. Juvenile fish were either exposed once to 120 cercariae or 3 times to 40 cercariae; they were then fed either a low- or high-quantity diet for 8 wk. Results showed that after controlling for host size, cranial heights were affected by infection regime and host diet but not by the infection x diet interaction. Cranial distortion was most prominent in minnows exposed once to cercariae, showing that the rapid, simultaneous growth of metacercariae interfered with the normal development of the cranium. Thus, the expression of the parasite-induced phenotype was context dependent, the result of factors associated with the dynamics of cercariae transmission and host growth rate.

Intensity-dependent development of Ornithodiplostomum ptychocheilus metacercariae was studied in fathead minnows (Pimephales promelas) exposed to 0, 20, or 120 cercariae. Subsamples of hosts were necropsied at 2-wk intervals to monitor parasite recruitment, growth, and time to encystment. The complex development of metacercariae within the cranium of minnows involved growth, encystment, and consolidation phases, each of which were affected by intensity. At the end of the growth phase, metacercariae from low-dose fish were 20% longer than those from high-dose fish and the latter took 2-4 wk longer to encyst. At the end of the postencystment consolidation phase (6-8 wk postinfection), the size of metacercariae decreased by approximately 50%. The rate of consolidation was slower in high-dose fish. Our results show that time, intensity, and temperature affect development of O. ptychocheilus. Because metacercariae development and differentiation are linked to infectivity, events occurring in intermediate hosts can potentially impact the structure and size of trematode suprapopulations.

The growth and survival of juvenile toads, Bufo bufo, infected with a common lung nematode, Rhabdias bufonis, were studied. Toads were raised from tadpoles in the laboratory and infected 2 months after metamorphosis. Individual toads were exposed to doses of 10, 40, 80 or 160 larvae, which enabled examination of the hypothesis that parasite-induced mortality is affected by worm numbers. Growth of infected toads began to diverge from that of uninfected controls at 6 weeks post infection (WPI) and by 12 WPI the most heavily infected toads were approximately half the mass of controls. No controls died throughout the experiment; however, mortality of infected toads was strongly affected by parasite density. A mechanism for mortality is suggested by the significant negative relationship between parasite density and dietary intake. This parasite-induced anorexia was detected at 3 WPI and persisted up to 9 WPI. Patterns of reduced host growth, survival and dietary intake provide experimental evidence of the negative consequences of parasitic infection in a natural parasite-host system which may also be present under natural conditions.

Density-dependence in worm establishment, numbers, biomass and larval production were examined in primary infections of 0, 10, 40, 80 and 160 larvae of the lung nematode, Rhabdias bufonis in the common toad, Bufo bufo. The infection procedure established 4 non-overlapping levels of infection which persisted until 6 weeks post-infection (p.i.), after which there was an overall decline up to 12 weeks p.i. Worm numbers had no direct effect on adult worm survival but temporal changes in worm weight were density-dependent. Adult worm establishment in the lungs declined significantly as the numbers of worms in the lungs increased. At the lowest exposure dose, 86% of the larvae administered reached maturity in the lungs while at the highest, only 37% did so. Also, the numbers of immature larvae outside the lungs increased as adult worm numbers increased. Both features provide evidence for a threshold limit to the numbers of worms maturing in the lungs. Worm numbers also affected larval output per host and per capita fecundity. A significant positive relationship between per capita fecundity and per capita worm weight suggested that density-dependence acted primarily to constrain the growth of individual worms. Finally, the constraints imposed on worm growth and fecundity were apparently relaxed when worm density decreased, providing evidence for density-dependent flexibility in per capita fecundity. Density-dependence in worm establishment and per capita fecundity are mechanisms which may potentially regulate this host-parasite interaction in the field. Both mechanisms may be functionally related to physical space limitations in the lungs, within which worms must compete for finite nutrients.