Multi-host Parasite Research Articles

The biogeography of the caribou lungworm, Varestrongylus eleguneniensis (Nematoda: Protostrongylidae) across northern North America.

Varestrongylus eleguneniensis (Nematoda; Protostrongylidae) is a recently described species of lungworm that infects caribou (Rangifer tarandus), muskoxen (Ovibos moschatus) and moose (Alces americanus) across northern North America. Herein we explore the geographic distribution of V. eleguneniensis through geographically extensive sampling and discuss the biogeography of this multi-host parasite. We analyzed fecal samples of three caribou subspecies (n = 1485), two muskox subspecies (n = 159), and two moose subspecies (n = 264) from across northern North America. Protostrongylid dorsal-spined larvae (DSL) were found in 23.8%, 73.6%, and 4.2% of these ungulates, respectively. A portion of recovered DSL were identified by genetic analyses of the ITS-2 region of the nuclear rDNA or the cytochrome oxidase c subunit I (COI) region of the mtDNA. We found V. eleguneniensis widely distributed among caribou and muskox populations across most of their geographic prange in North America but it was rare in moose. Parelaphostrongylus andersoni was present in caribou and moose and we provide new geographic records for this species. This study provides a substantial expansion of the knowledge defining the current distribution and biogeography of protostrongylid nematodes in northern ungulates. Insights about the host and geographic range of V. eleguneniensis can serve as a geographically extensive baseline for monitoring current distribution and in anticipating future biogeographic scenarios under a regime of accelerating climate and anthropogenic perturbation.

Disease mortality in domesticated animals is predicted by host evolutionary relationships

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.

Long-term prevalence data reveals spillover dynamics in a multi-host (Artemia), multi-parasite (Microsporidia) community

In the study of multi-host parasites, it is often found that host species contribute asymmetrically to parasite transmission. Yet in natural populations, identifying which hosts contribute to parasite transmission and maintenance is a recurring challenge. Here, we approach this issue by taking advantage of natural variation in the composition of a host community. We studied the brine shrimps Artemia franciscana and Artemia parthenogenetica and their microsporidian parasites Anostracospora rigaudi and Enterocytospora artemiae. Previous laboratory experiments had shown that each host can transmit both parasites, but could not predict their actual contributions to the parasites’ maintenance in the field. To resolve this, we gathered long-term prevalence data from a metacommunity of these species. Metacommunity patches could contain either or both of the Artemia host species, so that the presence of the hosts could be linked directly to the persistence of the parasites. First, we show that the microsporidian A. rigaudi is a spillover parasite: it was unable to persist in the absence of its maintenance host A. parthenogenetica. This result was particularly striking, as A. rigaudi displayed both high prevalence (in the field) and high infectivity (when tested in the laboratory) in both hosts. Moreover, the seasonal presence of A. parthenogenetica imposed seasonality on the rate of spillover, causing cyclical pseudo-endemics in the spillover host A. franciscana. Second, while our prevalence data was sufficient to identify E. artemiae as either a spillover or a facultative multi-host parasite, we could not distinguish between the two possibilities. This study supports the importance of studying the community context of multi-host parasites, and demonstrates that in appropriate multi-host systems, sampling across a range of conditions and host communities can lead to clear conclusions about the drivers of parasite persistence.

The relative contributions of host density and genetic diversity on prevalence of a multi-host parasite in bumblebees

The relative contributions of host density and genetic diversity on prevalence of a multi-host parasite in bumblebees

Carrying a selfish genetic element predicts increased migration propensity in free-living wild house mice.

Life is built on cooperation between genes, which makes it vulnerable to parasitism. Selfish genetic elements that exploit this cooperation can achieve large fitness gains by increasing their transmission relative to the rest of the genome. This leads to counter-adaptations that generate unique selection pressures on the selfish genetic element. This arms race is similar to host-parasite coevolution, as some multi-host parasites alter the host's behaviour to increase the chance of transmission to the next host. Here, we ask if, similarly to these parasites, a selfish genetic element in house mice, the t haplotype, also manipulates host behaviour, specifically the host's migration propensity. Variants of the t that manipulate migration propensity could increase in fitness in a meta-population. We show that juvenile mice carrying the t haplotype were more likely to emigrate from and were more often found as migrants within a long-term free-living house mouse population. This result may have applied relevance as the t has been proposed as a basis for artificial gene drive systems for use in population control.

Contrasting consequences of different defence strategies in a natural multihost–parasite system

Hosts counteract infections using two distinct defence strategies, resistance (reduction in pathogen fitness) and tolerance (limitation of infection damage). These strategies have been minimally investigated in multi-host systems, where they may vary across host species, entailing consequences both for hosts (virulence) and parasites (transmission). Comprehending the interplay among resistance, tolerance, virulence and parasite success is highly relevant for our understanding of the ecology and evolution of infectious and parasitic diseases. Our work investigated the interaction between an insect parasite and its most common bird host species, focusing on two relevant questions: (i) are defence strategies different between main and alternative hosts and, (ii) what are the consequences (virulence and parasite success) of different defence strategies? We conducted a matched field experiment and longitudinal studies at the host and the parasite levels under natural conditions, using a system comprising Philornis torquans flies and three bird hosts – the main host and two of the most frequently used alternative hosts. We found that main and alternative hosts have contrasting defence strategies, which gave rise in turn to contrasting virulence and parasite success. In the main bird host, minor loss of fitness, no detectable immune response, and high parasite success suggest a strategy of high tolerance and negligible resistance. Alternative hosts, on the contrary, resisted by mounting inflammatory responses, although with very different efficiency, which resulted in highly dissimilar parasite success and virulence. These results show clearly distinct defence strategies between main and alternative hosts in a natural multi-host system. They also highlight the importance of defence strategies in determining virulence and infection dynamics, and hint that defence efficiency is a crucial intervening element in these processes.

In Vitro Antileishmanial Activity of a Black Morel, Morchella importuna (Ascomycetes).

We studied the anti-Leishmania activity of a fractionated extract from the mushroom Morchella importuna in an in vitro system. Leishmaniasis is an important infectious disease caused by a range of Leishmania species, which are multihost protozoa parasites transmitted to humans by the sand fly and infecting macrophages. Leishmaniasis is an increasing worldwide health problem, including in the Mediterranean basin. Current chemotherapy treatments are limited by their toxic effects, the need for long-term treatment, and the increasing development of resistance by the parasite cells. Thus, alternative therapies are being considered, including herbal and mushroom products. We studied the effect of extracts from M. importuna on L. tropica promastigote cell proliferation and survival, and on their toxicity against human macrophages. The aqueous mushroom extract was compared with 3 successive extracted fractions: an 80% ethanol fraction, a water-soluble polysaccharide fraction, and a polyphenolic fraction. All 4 extracts showed anti-Leishmania activity; the aqueous extract was most active. The inhibition activity was dose dependent in killing Leishmania. No cell recovery was recorded after exposure to the mushroom extract. Microscopic observation showed morphological changes and the loss of flagella on the parasites. No cytotoxic activity was recorded against human macrophages at the same extract concentrations. The findings suggest the potential use of extracts of an edible Morchella mushroom against the Leishmania parasite in humans.

A novel B- and helper T-cell epitopes-based prophylactic vaccine against Echinococcus granulosus

Introduction: In this study, we targeted the worm stage of Echinococcus granulosus to design a novel multi-epitope B- and helper T-cell based vaccine construct for immunization of dogs against this multi-host parasite. Methods: The vaccine was designed based on the local Eg14-3-3 antigen (Ag). DNA samples were extracted from the protoscoleces of the infected sheep’s liver, and then subjected to the polymerase chain reaction (PCR) with 14-3-3 specific forward and reverse primers. For the vaccine designing, several in silico steps were undertaken. Three-dimensional (3D) structure of the local Eg14-3-3 Ag was modeled by EasyModeller software. The protein modeling accuracy was then analyzed via various validation assays. Potential transmembrane helix, signal peptide, post-translational modifications and allergenicity of Eg14-3-3 were evaluated as the preliminary measures of B-cell epitopes (BEs ) prediction. Having used many web-servers, a well-designed process was carried out for improved prediction of BEs. High ranked linear and conformational BEs were utilized for engineering the final vaccine construct. Possible T-helper epitopes (TEs) were identified by the molecular docking between 13-mer fragments of the Eg14-3-3 Ag and two high frequent dog class II MHC alleles (i.e., DLA-DRB1*01101 and DRB1*01501). The epitopes coverage was evaluated by Shannon’s variability plot. Results: The final designed construct was analyzed based on different physicochemical properties, which was then codon optimized for high-level expression in Escherichia coli k12. This minigene construct is the first dog-specific epitopic vaccine construct that is established based on TEs with high-binding affinity to canine MHC alleles. Conclusion: This in silico study is the first part of a multi-antigenic vaccine designing work that represents as a novel dog-specific vaccine against E. granulosus. Here, we present key data on the step-by-step methodologies used for designing this de novo vaccine, which is under comprehensive in vivo investigations.

Opportunities and challenges for modelling epidemiological and evolutionary dynamics in a multihost, multiparasite system: Zoonotic hybrid schistosomiasis in West Africa.

Multihost multiparasite systems are evolutionarily and ecologically dynamic, which presents substantial trans‐disciplinary challenges for elucidating their epidemiology and designing appropriate control. Evidence for hybridizations and introgressions between parasite species is gathering, in part in line with improvements in molecular diagnostics and genome sequencing. One major system where this is becoming apparent is within the Genus Schistosoma, where schistosomiasis represents a disease of considerable medical and veterinary importance, the greatest burden of which occurs in sub‐Saharan Africa. Interspecific hybridizations and introgressions bring an increased level of complexity over and above that already inherent within multihost, multiparasite systems, also representing an additional source of genetic variation that can drive evolution. This has the potential for profound implications for the control of parasitic diseases, including, but not exclusive to, widening host range, increased transmission potential and altered responses to drug therapy. Here, we present the challenging case example of haematobium group Schistosoma spp. hybrids in West Africa, a system involving multiple interacting parasites and multiple definitive hosts, in a region where zoonotic reservoirs of schistosomiasis were not previously considered to be of importance. We consider how existing mathematical model frameworks for schistosome transmission could be expanded and adapted to zoonotic hybrid systems, exploring how such model frameworks can utilize molecular and epidemiological data, as well as the complexities and challenges this presents. We also highlight the opportunities and value such mathematical models could bring to this and a range of similar multihost, multi and cross‐hybridizing parasites systems in our changing world.

Modelling the influence of host community composition in a sylvatic Trypanosoma cruzi system.

Species composition of wild reservoir hosts can influence the transmission and maintenance of multi-host vector borne pathogens. The 'pace of life' hypothesis proposes that the life history strategy of reservoir hosts can influence pathogen transmission of vector borne generalist pathogens. We use empirical data to parameterize a mathematical model that investigates the impacts of host life history traits on vector transmission dynamics of the vector-borne multi-host parasite Trypanosoma cruzi in habitats characterized by different degrees of deforestation and varying host community structure. The model considers susceptible and infected vector and host populations. When comparing the proportion of vectors infected with T. cruzi predicted by the model with empirical data, we found a trend of increasing vector infection as anthropogenic landscape disturbance increases for both data and model output. The model's vector infection rates were significantly lower than empirical results, but when incorporating host congenital transmission in the model, vector infection approaches field data. We conclude that intervened habitats associated with r-selected host species communities predict higher proportions of infected vectors.

Integrating phylogenetic and ecological distances reveals new insights into parasite host specificity.

The range of hosts a pathogen infects (host specificity) is a key element of disease risk that may be influenced by both shared phylogenetic history and shared ecological attributes of prospective hosts. Phylospecificity indices quantify host specificity in terms of host relatedness, but can fail to capture ecological attributes that increase susceptibility. For instance, similarity in habitat niche may expose phylogenetically unrelated host species to similar pathogen assemblages. Using a recently proposed method that integrates multiple distances, we assess the relative contributions of host phylogenetic and functional distances to pathogen host specificity (functional-phylogenetic host specificity). We apply this index to a data set of avian malaria parasite (Plasmodium and Haemoproteus spp.) infections from Melanesian birds to show that multihost parasites generally use hosts that are closely related, not hosts with similar habitat niches. We also show that host community phylogenetic ß-diversity (Pßd) predicts parasite Pßd and that individual host species carry phylogenetically clustered Haemoproteus parasite assemblages. Our findings were robust to phylogenetic uncertainty, and suggest that phylogenetic ancestry of both hosts and parasites plays important roles in driving avian malaria host specificity and community assembly. However, restricting host specificity analyses to either recent or historical timescales identified notable exceptions, including a 'habitat specialist' parasite that infects a diversity of unrelated host species with similar habitat niches. This work highlights that integrating ecological and phylogenetic distances provides a powerful approach to better understand drivers of pathogen host specificity and community assembly.

Anuran parasites from three biotopes in Rivers State, Nigeria

The parasitic infections of anurans from three biotopes (lowland forest, freshwater swamp and brackish water swamp) in Rivers State, Nigeria were investigated. A total of 94 anuran specimens were examined; 32 from the lowland forest, 28 from the freshwater swamp and 34 from the brackish water environment. Of the three biotopes, amphibians from the lowland forest harboured more parasite species. In total, 24 parasite species were recovered, including a pentastomid; larval acanthocephala; one cestode; one monogenean; sevendigeneans and thirteen nematode species. Only five of the 24 parasite species recovered were common to anurans from the three biotopes. Others were either restricted to one ecological habitat or were also found in hosts from a second habitat. A form of association seems to exist between ciliates and the Cephalochlamys compactus recovered from Hoplobatrachus occipitalis collected from the lowland forest. Hymenochirus sp. is a new host record for Progonimodiscus colubrifer, having been previously described from Silurana tropicalis. Aplectana mackintoschi is both a new geographical record for Nigeria and a multi-host parasite. We suspect Hyperolius concolor to be a paratenic rather than a definitive host for the immature Camallanus sp. recovered from the frog. Other parasites using anurans as paratenic hosts were also encountered.Keywords: Anurans, parasites, ecological biotopes, Rivers State, Nigeria

Detection of Leishmania spp. in Bats from an Area of Brazil Endemic for Visceral Leishmaniasis.

The multihost parasites Leishmania spp. infect a broad range of wild mammalian species including bats. Several species of bats have adapted to a variety of food resources and shelters in urban areas. This study aimed to detect Leishmania spp. DNA in bats present in forest fragments located in metropolitan areas endemic for leishmaniasis in Campo Grande, Mato Grosso do Sul (MS), Brazil. Blood samples were obtained from 80 individuals, including eight species of Phyllostomidae and one species of Vespertilionidae. Thirty of the 80 bats were positive for Leishmania spp. using conventional PCR, all belonging to the family Phyllostomidae. Eighteen samples tested by real-time PCR (qPCR) using specific primers for the kDNA of Leishmania infantum were positive. To the best of our knowledge, this is the first report detecting Leishmania spp. in Platyrrhinus incarum in addition to being the first reported detection of L.infantum in the bat species Phyllostomus discolor, Platyrrhinus lineatus, Artibeus planirostris and Artibeus lituratus. Our results show that bats can host Leishmania spp. in areas endemic for leishmaniasis, which must be taken into account in disease control operations by public health authorities.

Multihost Bartonella parasites display covert host specificity even when transmitted by generalist vectors.

Summary Many parasites infect multiple sympatric host species, and there is a general assumption that parasite transmission between co‐occurring host species is commonplace. Such between‐species transmission could be key to parasite persistence within a disease reservoir and is consequently an emerging focus for disease control.However, while a growing body of theory indicates the potential importance of between‐species transmission for parasite persistence, conclusive empirical evidence from natural communities is lacking, and the assumption that between‐species transmission is inevitable may therefore be wrong.We investigated the occurrence of between‐species transmission in a well‐studied multihost parasite system. We identified the flea‐borne Bartonella parasites infecting sympatric populations of Apodemus sylvaticus (wood mice) and Myodes glareolus (bank voles) in the UK and confirmed that several Bartonella species infect both rodent species. However, counter to previous knowledge, genetic characterization of these parasites revealed covert host specificity, where each host species is associated with a distinct assemblage of genetic variants, indicating that between‐species transmission is rare.Limited between‐species transmission could result from rare encounters between one host species and the parasites infecting another and/or host–parasite incompatibility. We investigated the occurrence of such encounter and compatibility barriers by identifying the flea species associated with each rodent host, and the Bartonella variants carried by individual fleas. We found that the majority of fleas were host‐generalists but the assemblage of Bartonella variants in fleas tended to reflect the assemblage of Bartonella variants in the host species they were collected from, thus providing evidence of encounter barriers mediated by limited between‐species flea transfer. However, we also found several fleas that were carrying variants never found in the host species from which they were collected, indicating some degree of host–pathogen incompatibility when barriers to encounter are overcome.Overall, these findings challenge our default perceptions of multihost parasite persistence, as they show that despite considerable overlaps in host species ecology, separate populations of the same parasite species may circulate and persist independently in different sympatric host species. This questions our fundamental understanding of endemic transmission dynamics and the control of infection within natural reservoir communities.

An optimised multi-host trematode life cycle: fishery discards enhance trophic parasite transmission to scavenging birds

Overlapping distributions of hosts and parasites are critical for successful completion of multi-host parasite life cycles and even small environmental changes can impact on the parasite’s presence in a host or habitat. The generalist Cardiocephaloides longicollis was used as a model for multi-host trematode life cycles in marine habitats. This parasite was studied to quantify parasite dispersion and transmission dynamics, effects of biological changes and anthropogenic impacts on life cycle completion. We compiled the largest host dataset to date, by analysing 3351 molluscs (24 species), 2108 fish (25 species) and 154 birds (17 species) and analysed the resultant data based on a number of statistical models. We uncovered extremely low host specificity at the second intermediate host level and a preference of the free-swimming larvae for predominantly demersal but also benthic fish. The accumulation of encysted larvae in the brain with increasing fish size demonstrates that parasite numbers level off in fish larger than 140mm, consistent with parasite-induced mortality at these levels. The highest infection rates were detected in host species and sizes representing the largest fraction of Mediterranean fishery discards (up to 67% of the total catch), which are frequently consumed by seabirds. Significantly higher parasite densities were found in areas with extensive fishing activity than in those with medium and low activity, and in fish from shallow lagoons than in fish from other coastal areas. For the first time, C. longicollis was also detected in farmed fish in netpens. Fishing generally drives declines in parasite abundance, however, our study suggests an enhanced transmission of generalist parasites such as C. longicollis, an effect that is further amplified by the parasite’s efficient host-finding mechanisms and its alteration of fish host behaviour by larvae encysted in the brain. The anthropogenic impact on the distribution of trophically-transmitted, highly prevalent parasites likely results in a strong effect on food web structure, thus making C. longicollis an ideal bioindicator to compare food webs in natural communities versus those impacted by fisheries and aquaculture.

Host and ecology both play a role in shaping distribution of digenean parasites of New Zealand whelks (Gastropoda: Buccinidae: Cominella).

Digenean parasites infecting four Cominella whelk species (C. glandiformis, C. adspersa, C. maculosa and C. virgata), which inhabit New Zealand's intertidal zone, were analysed using molecular techniques. Mitochondrial 16S and cytochrome oxidase 1 (COI) and nuclear rDNA ITS1 sequences were used to infer phylogenetic relationships amongst digenea. Host species were parasitized by a diverse range of digenea (Platyhelminthes, Trematoda), representing seven families: Echinostomatidae, Opecoelidae, Microphallidae, Strigeidae and three, as yet, undetermined families A, B and C. Each parasite family infected between one and three host whelk species, and infection levels were typically low (average infection rates ranged from 1·4 to 3·6%). Host specificity ranged from highly species-specific amongst the echinostomes, which were only ever observed infecting C. glandiformis, to the more generalist opecoelids and strigeids, which were capable of infecting three out of four of the Cominella species analysed. Digeneans displayed a highly variable geographic range; for example, echinostomes had a large geographic range stretching the length of New Zealand, from Northland to Otago, whereas Family B parasites were restricted to fairly small areas of the North Island. Our results add to a growing body of research identifying wide ranges in both host specificity and geographic range amongst intertidal, multi-host parasite systems.

Thermal Change and the Dynamics of Multi-Host Parasite Life Cycles in Aquatic Ecosystems

Altered thermal regimes associated with climate change are impacting significantly on the physical, chemical, and biological characteristics of the Earth’s natural ecosystems, with important implications for the biology of aquatic organisms. As well as impacting the biology of individual species, changing thermal regimes have the capacity to mediate ecological interactions between species, and the potential for climate change to impact host–parasite interactions in aquatic ecosystems is now well recognized. Predicting what will happen to the prevalence and intensity of infection of parasites with multiple hosts in their life cycles is especially challenging because the addition of each additional host dramatically increases the potential permutations of response. In this short review, we provide an overview of the diverse routes by which altered thermal regimes can impact the dynamics of multi-host parasite life cycles in aquatic ecosystems. In addition, we examine how experimentally amenable host–parasite systems are being used to determine the consequences of changing environmental temperatures for these different types of mechanism. Our overarching aim is to examine the potential of changing thermal regimes to alter not only the biology of hosts and parasites, but also the biology of interactions between hosts and parasites. We also hope to illustrate the complexity that is likely to be involved in making predictions about the dynamics of infection by multi-host parasites in thermally challenged aquatic ecosystems.

Testing epidemiological functional groups as predictors of avian haemosporidia patterns in southern Africa

AbstractUnderstanding the dynamics of multihost parasites and the roles of different host species in parasite epidemiology requires consideration of the whole animal community. Host communities may be composed of hundreds of interacting species, making it necessary to simplify the problem. One approach to summarizing the host community in a way that is relevant to the epidemiology of the parasite is to group host species into epidemiological functional groups (EpiFGs). We used EpiFGs to test our understanding of avian malaria (PlasmodiumandHaemoproteus) dynamics in four communities of wetland‐associated birds in southern Africa. Bird counts and captures were undertaken every 2–4 months over 2 yr and malaria was diagnosed by nestedPCR. One hundred and seventy‐six bird species were allocated to a set of EpiFGs according to their assumed roles in introducing and maintaining the parasite in the system. Roles were quantified as relative risks from avian foraging, roosting, and movement ecology and assumed interaction with vector species. We compared our estimated a priori risks to empirical data from 3414 captured birds from four sites and 3485 half‐hour point counts. After accounting for relative avian abundance, our risk estimates significantly correlated with the observed prevalence ofHaemoproteusbut notPlasmodium. Although avian roosting height (for both malarial genera) and movement ecology (forPlasmodium) separately influenced prevalence, host behavior alone was not sufficient to predictPlasmodiumpatterns in our communities. Host taxonomy and relative abundance were also important for this parasite. Although using EpiFGs enabled us to predict the infection patterns of only one genus of heamosporidia, our approach holds promise for examining the influence of host community composition on the transmission of vector‐borne parasites and identifying gaps in our understanding of host–parasite interactions.

One health - an ecological and evolutionary framework for tackling Neglected Zoonotic Diseases.

Understanding the complex population biology and transmission ecology of multihost parasites has been declared as one of the major challenges of biomedical sciences for the 21st century and the Neglected Zoonotic Diseases (NZDs) are perhaps the most neglected of all the Neglected Tropical Diseases (NTDs). Here we consider how multihost parasite transmission and evolutionary dynamics may affect the success of human and animal disease control programmes, particularly neglected diseases of the developing world. We review the different types of zoonotic interactions that occur, both ecological and evolutionary, their potential relevance for current human control activities, and make suggestions for the development of an empirical evidence base and theoretical framework to better understand and predict the outcome of such interactions. In particular, we consider whether preventive chemotherapy, the current mainstay of NTD control, can be successful without a One Health approach. Transmission within and between animal reservoirs and humans can have important ecological and evolutionary consequences, driving the evolution and establishment of drug resistance, as well as providing selective pressures for spill-over, host switching, hybridizations and introgressions between animal and human parasites. Our aim here is to highlight the importance of both elucidating disease ecology, including identifying key hosts and tailoring control effort accordingly, and understanding parasite evolution, such as precisely how infectious agents may respond and adapt to anthropogenic change. Both elements are essential if we are to alleviate disease risks from NZDs in humans, domestic animals and wildlife.

Ecology, Virulence, and Phylogeny of Blastulidium paedophthorum, a Widespread Brood Parasite of Daphnia spp.

Parasitism is now recognized as a major factor impacting the ecology and evolution of plankton, including Daphnia. Parasites that attack the developing embryos of daphniids, known as brood parasites, were first described in the early 1900s but have received relatively little study. Here, we link previous morphological descriptions of the oomycete brood parasite Blastulidium paedophthorum with information on its phylogenetic placement, ecology, and virulence. Based on the morphology and phylogenetic relationship with other members of the Leptomitales, we show that a brood parasite observed in daphniids in the Midwestern United States is B. paedophthorum. We used morphology, DNA sequences, and laboratory infection experiments to show that B. paedophthorum is a multihost parasite that can be transmitted between species and genera. A field survey of six hosts in 15 lakes revealed that B. paedophthorum is common in all six host taxa (present on 38.3% of our host species-lake-sampling date combinations; the maximum infection prevalences were 8.7% of the population and 20% of the asexual adult female population). Although B. paedophthorum was observed in all 15 lakes, presence and infection prevalence varied among lakes. Infection with B. paedophthorum did not reduce host life span but significantly impacted host fecundity. Theory predicts that parasites that affect host fecundity without affecting host life span should have the strongest impact on host population dynamics. Based on its virulence and commonness in natural populations and on the central role of daphniids in freshwater food webs, we predict that B. paedophthorum will influence daphniid ecology and evolution, as well as the larger food web.