Host population density and body mass as determinants of species richness in parasite communities: comparative analyses of directly transmitted nematodes of mammals

Epidemiological theory predicts positive correlations between host population density or body mass and species richness among parasite communities. Here I test these predictions by a comparative study of communities of directly transmitted mammalian parasites, gastrointestinal strongylid nematodes. I use data from 45 species of mammals, representing examination of 17 200 individual hosts. The variable studied was the average number of gastrointestinal strongylid nematode species per host population, and three different methods were used to obtain estimates of parasite species richness that are unbiased by number of host individuals examined. Analyses were done using the phylogenetically independent contrast method. Host population density and parasite species richness were strongly positively correlated when the effects of host body weight had been controlled for. Controlling for other variables did not change this, and the relationship was found regardless of method used to correct for uneven sampling effort among host species. A positive relationship between parasite species richness and host body weight was also found, but the effect of host densities had to be controlled for to see this. These relationships between host traits and species richness of directly transmitted parasites are stronger than patterns found using data on indirectly transmitted mammalian parasites, and suggests that links between host traits and parasite species richness are stronger than previously suggested. The results are consistent with parasite species richness being positively linked to pathogen transmission rates and reductions in transmission rates possibly increasing extinction probabilities in parasite populations. The results also suggest that parasites may exert a cost of increases in rate of population energy usage, and thus show that pathogens may be important in generating independence between body mass and rate of population energy usage among host species.     

Generalist nematodes dominate the nemabiome of roe deer in sympatry with sheep at a regional level

The growth of livestock farming and the recent expansion of wild ungulate populations in Europe favor opportunities for direct and/or indirect cross-transmission of pathogens. Comparatively few studies have investigated the epidemiology of gastro-intestinal nematode parasites, an ubiquitous and important community of parasites of ungulates, at the wildlife/livestock interface. In this study, we aimed to assess the influence of livestock proximity on the gastrointestinal nematode community of roe deer in a rural landscape located in southern France. Using ITS-2 rDNA nemabiome metabarcoding on fecal larvae, we analysed the gastrointestinal nematode communities of roe deer and sheep. In addition, we investigated Haemonchus contortus nad4 mtDNA diversity to specifically test parasite circulation among domestic and wild host populations. The dominant gastrointestinal nematode species found in both the roe deer and sheep were generalist species commonly found in small ruminant livestock (e.g. H. contortus), whereas the more specialised wild cervid nematode species (e.g. Ostertagia leptospicularis) were only present at low frequencies. This is in marked contrast with previous studies that found the nemabiomes of wild cervid populations to be dominated by cervid specialist nematode species. In addition, the lack of genetic structure of the nad4 mtDNA of H. contortus populations between host species suggests circulation of gastrointestinal nematodes between roe deer and sheep. The risk of contact with livestock only has a small influence on the nemabiome of roe deer, suggesting the parasite population of roe deer has been displaced by generalist livestock parasites due to many decades of sheep farming, not only for deer grazing close to pastures, but also at a larger regional scale. We also observed some seasonal variation in the nemabiome composition of roe deer. Overall, our results demonstrate significant exchange of gastrointestinal nematodes between domestic and wild ungulates, with generalist species spilling over from domestic ungulates dominating wild cervid parasite communities.     

Evaluating the Effects of Ivermectin Treatment on Communities of Gastrointestinal Parasites in Translocated Woylies (<Emphasis Type="Italic">Bettongia penicillata</Emphasis>)

Wildlife species are often treated with anti-parasitic drugs prior to translocation, despite the effects of this treatment being relatively unknown. Disruption of normal host–parasite relationships is inevitable during translocation, and targeted anti-parasitic drug treatment may exacerbate this phenomenon with inadvertent impacts on both target and non-target parasite species. Here, we investigate the effects of ivermectin treatment on communities of gastrointestinal parasites in translocated woylies (Bettongia penicillata). Faecal samples were collected at three time points (at the time of translocation, and 1 and 3 months post-translocation) and examined for nematode eggs and coccidian oocysts. Parasite prevalence and (for nematodes) abundance were estimated in both treated and untreated hosts. In our study, a single subcutaneous injection of ivermectin significantly reduced Strongyloides-like egg counts 1 month post-translocation. Strongyle egg counts and coccidia prevalence were not reduced by ivermectin treatment, but were strongly influenced by site. Likewise, month of sampling rather than ivermectin treatment positively influenced body condition in woylies post-translocation. Our results demonstrate the efficacy of ivermectin in temporarily reducing Strongyloides-like nematode abundance in woylies. We also highlight the possibility that translocation-induced changes to host density may influence coinfecting parasite abundance and host body condition post-translocation.     

Strongylids (Nematoda: Strongylidae) of domestic horses in Ukraine: modern state of Fauna and structure of the parasite community

Species composition and structure of the strongylid community was studies on helminthological material collected from 162 domestic horses from 11 regions of Ukraine by the in vivo method. Animals were treated with anthelmintic drug "Univerm" (0.2% aversectin C, Russia). Faecal samples (200 g each) were collected from every horse at 24, 36, 48 and 60 hours after treatment; all nematodes expelled (90.851 specimens) were collected and identified. Thirty-three strongylid species from 12 genera (8 species of subfamily Strongylinae and 25--of Cyathostominae) were found in domestic horses in Ukraine. Cyathostominae dominated in the strongylid community; they were found in 100 % horses and composed 98.21% of community. "Core" of the strongylid community was composed by 7 cyathostome species. Decreasing of proportion of Strongylinae in the community for last 40 years was registered; strongylines were found in 37.6% of horses and composed 1.25% of community. Maximal prevalence was 20.98% (Strongylus vulgaris). Bray-Curtis cluster analysis revealed high similarity of strongylid communities in horses from various regions of Ukraine. Difference in general structure of strongylid communities of horses from different horse-keeping conditions was established. Horses from farms with stable-paddock keeping conditions had bimodal strongylid community structure; while horses from stable-pasture keeping conditions possessed multimodal community structure.     

Three surface antigens dominate the mucosal antibody response to gastrointestinal L3-stage strongylid nematodes in field immune sheep

Although gastrointestinal nematode parasites are a major human and veterinary health problem, little is known about how the host is sometimes able to mount an effective immune rejection response. In previous work, we identified a carbohydrate larval surface antigen (CarLA) as the target of mucosal antibodies that can elicit rejection of Trichostrongylus colubriformis L3s in sheep. Here we characterise the natural mucosal antibody responses to L3s from three major strongylid gastrointestinal parasites of sheep, Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia circumcincta. The mucosal antibody repertoire of naturally field-immune sheep was displayed on bacteriophage as single-chain antibodies (scFvs) and phage were selected for the ability to bind to the surface of living L3s of the three nematode species. All nematode-binding scFvs were found to recognize one of three different antigen classes that are each found in the three strongylid species. These three antigen classes appear to represent all of the major antigens recognized on Western blots by pooled mucosal antibodies from field-immune sheep. One of the antigen classes is a heterogeneous, high molecular weight molecule that is protease-sensitive. The scFvs recognizing this surface antigen also recognize a similar antigen in all strongylids tested. A second antigen class is a protease-insensitive, low molecular weight antigen found only in sheaths and scFvs recognizing this antigen cross-react with a similar molecule found in all strongylids tested. The third surface antigen class is CarLA and all of the anti-CarLA scFvs obtained from the field-immune sheep repertoire were specific to L3s of only one species and often recognized only a subset of the worms. Thus three different L3-stage surface antigens, two that lack a protein component, dominate the natural mucosal antibody response to L3-stage gastrointestinal strongylid nematodes in sheep.     

Nematode community structure in the brush-tailed rock-wallaby, Petrogale penicillata: Implications of captive breeding and the translocation of wildlife

Despite an increasing appreciation of the disease risks associated with wild-life translocations, the effects which captive breeding programs exert on parasite communities remain understudied. This may be attributed, in part, to the current lack of rapid and cost-effective techniques for comparing parasite assemblages between host populations. Terminal restriction fragment length polymorphism (T-RFLP) analysis of the rDNA region encompassing the internal transcribed spacers (ITS-1 and ITS-2) and 5.8S rRNA gene was used to characterise bursate nematode communities (suborder Strongylida) across two captive and two non-captive colonies of the threatened brush-tailed rock-wallaby, Petrogale penicillata. A clone library was constructed and a restriction enzyme selected to differentiate the predominant operational taxonomic units (OTUs) by the unique peak profiles they generated. The prevalence, intensity of infection and comparative structure of strongylid assemblages was evaluated for each of the host colonies. Compared to wild conspecifics, captive wallabies exhibited a reduced prevalence of infection and significantly lower faecal egg counts. T-RFLP revealed that a high proportion of the OTUs co-occurred across three of the four study locations. Despite this, the composition of strongylid assemblages was significantly different between the colonies, even when host translocation events had occurred. These results suggest that captive breeding programs may exert a profound impact on parasitic helminth assemblages. Developing efficient techniques for characterising community dynamics in potentially pathogenic organisms is critical to the long term success of species recovery efforts worldwide.     

Evaluating the Effects of Ivermectin Treatment on Communities of Gastrointestinal Parasites in Translocated Woylies (Bettongia penicillata)

Wildlife species are often treated with anti-parasitic drugs prior to translocation, despite the effects of this treatment being relatively unknown. Disruption of normal host–parasite relationships is inevitable during translocation, and targeted anti-parasitic drug treatment may exacerbate this phenomenon with inadvertent impacts on both target and non-target parasite species. Here, we investigate the effects of ivermectin treatment on communities of gastrointestinal parasites in translocated woylies (Bettongia penicillata). Faecal samples were collected at three time points (at the time of translocation, and 1 and 3 months post-translocation) and examined for nematode eggs and coccidian oocysts. Parasite prevalence and (for nematodes) abundance were estimated in both treated and untreated hosts. In our study, a single subcutaneous injection of ivermectin significantly reduced Strongyloides-like egg counts 1 month post-translocation. Strongyle egg counts and coccidia prevalence were not reduced by ivermectin treatment, but were strongly influenced by site. Likewise, month of sampling rather than ivermectin treatment positively influenced body condition in woylies post-translocation. Our results demonstrate the efficacy of ivermectin in temporarily reducing Strongyloides-like nematode abundance in woylies. We also highlight the possibility that translocation-induced changes to host density may influence coinfecting parasite abundance and host body condition post-translocation.

     

A repeatable and quantitative DNA metabarcoding assay to characterize mixed strongyle infections in horses

Horses are ubiquitously infected by a diversity of gastro-intestinal parasitic helminths. Of particular importance are nematodes of the family Strongylidae, which can significantly impact horse health and performance. However, knowledge about equine strongyles remains limited due to our inability to identify most species non-invasively using traditional morphological techniques. We developed a new internal transcribed spacer 2 (ITS2) DNA metabarcoding ‘nemabiome’ assay to characterise mixed strongyle infections in horses and assessed its performance by applying it to pools of infective larvae from fecal samples from an experimental herd in Kentucky, USA and two feral horse populations from Sable Island and Alberta, Canada. In addition to reporting the detection of 33 different species with high confidence, we illustrate the assay’s repeatability by comparing results generated from aliquots from the same fecal samples and from individual horses sampled repeatedly over multiple days or months. We also validate the quantitative potential of the assay by demonstrating that the proportion of amplicon reads assigned to different species scales linearly with the number of larvae present. This new tool significantly improves equine strongyle diagnostics, presenting opportunities for research on species-specific anthelmintic resistance and the causes and consequences of variation in mixed infections.     

A 4 year observation of gastrointestinal nematode egg counts,nemabiomes and the benzimidazole resistance genotypes of Teladorsagia circumcincta on a Scottish sheep farm

Anthelmintic resistance threatens the sustainability of sheep production globally. Advice regarding strategies to reduce the development of anthelmintic resistance incorporates the outcomes of modelling exercises. Further understanding of gastrointestinal nematode species diversity, and population dynamics and genetics (which may vary between species) is required to refine these models; and field studies combining faecal egg outputs, species composition and resistance genetics are needed to calibrate them. In this study, faecal samples were taken from ewes and lambs on a commercial farm in south-eastern Scotland at approximately 3 t-4 week intervals between spring and autumn over a period of 4 years. Faecal egg counts were performed on these samples, and L₃ were collected from pooled coprocultures. Deep amplicon sequencing was used to determine both the species composition of these L₃ and the proportions of benzimidazole-resistant single nucleotide polymorphisms in the isotype-1 β-tubulin locus of the predominant species, Teladorsagia circumcincta L₃. Despite consistent management throughout the study, the results show variation in gastrointestinal nematode species composition with time and between age groups, that was potentially associated with weather conditions. The F200Y benzimidazole resistance mutation is close to genetic fixation in the T. circumcincta population on this farm. There was no evidence of variation in isotype-1 β-tubulin single nucleotide polymorphisms frequency between age groups, and no genetic evidence of reversion to benzimidazole susceptibility, despite targeted benzimidazole usage. This study highlights the need to include speciation when investigating gastrointestinal nematode epidemiology and anthelmintic resistance, and serves as an example of how genetic data may be analysed alongside species diversity and faecal egg counts, when markers for other anthelmintic classes are identified.     

Possible Influence of B Chromosomes on Genes Included in Immune Response and Parasite Burden in Apodemus flavicollis

Genetic background underlying wild populations immune response to different parasites is still not well understood. We studied immune response to multiple infections and to competition between different parasite species at different developmental stages in population of yellow-necked mouse, Apodemus flavicollis. Quantitative real-time PCR was used to investigate associations of MHC II-DRB, IL-10 and Tgf-β genes expressions with presence of intestinal parasites at different developmental stages. Furthermore, we were interested whether the host related characteristics (sex, age, body condition, presence of B chromosomes or expression of other genes) or characteristics of present parasites (number of adult parasites of each identified species, egg count of each parasite genus, total number of nematode individuals) affect differential expression of the studied genes. A significant invert association between the expression of MHC II-DRB and Tgf-β gene was found, which together with absence of IL-10 association confirmed modified Th2 as the main type of immune response to nematode infections. Effect of recorded parasites and parasite life-cycle stage on expression levels of MHC II-DRB gene was detected only through interactions with host-related characteristics such as sex, age, and the presence of B chromosomes. The presence of B chromosomes is associated with lower expression level of Tgf-β gene. Although the influence of host genetic background on parasite infection has already been well documented, this is the first study in mammals that gave presence of B chromosomes on immune response full consideration.     

Host densities as determinants of abundance in parasite communities

Several epidemiological models predict a positive relationship between host population density and abundance of directly transmitted macroparasites. Here, we generalize these, and test the prediction by a comparative study. We used data on communities of gastrointestinal strongylid nematodes from 19 mammalian species, representing examination of 6670 individual hosts. We studied both the average abundance of all strongylid nematodes within a host species, and the two components of abundance, prevalence and intensity. The effects of host body weight, diet, fecundity and age at maturity and parasite body size were controlled for directly, and the phylogenetically independent contrast method was used to control for confounding factors more generally. Host population density and average parasite abundance were strongly positively correlated within mammalian taxa, and across all species when the effects of host body weight were controlled for. Controlling for other variables did not change this. Even when looking at single parasite species occurring in several host species, abundance was highest in the host species with the highest population density. Prevalence and intensity showed similar patterns. These patterns provide the first macroecological evidence consistent with the prediction that transmission rates depend on host population density in natural parasite communities.     

A combined parasitological molecular approach for noninvasive characterization of parasitic nematode communities in wild hosts

Most hosts are concurrently or sequentially infected with multiple parasites; thus, fully understanding interactions between individual parasite species and their hosts depends on accurate characterization of the parasite community. For parasitic nematodes, noninvasive methods for obtaining quantitative, species‐specific infection data in wildlife are often unreliable. Consequently, characterization of gastrointestinal nematode communities of wild hosts has largely relied on lethal sampling to isolate and enumerate adult worms directly from the tissues of dead hosts. The necessity of lethal sampling severely restricts the host species that can be studied, the adequacy of sample sizes to assess diversity, the geographic scope of collections and the research questions that can be addressed. Focusing on gastrointestinal nematodes of wild African buffalo, we evaluated whether accurate characterization of nematode communities could be made using a noninvasive technique that combined conventional parasitological approaches with molecular barcoding. To establish the reliability of this new method, we compared estimates of gastrointestinal nematode abundance, prevalence, richness and community composition derived from lethal sampling with estimates derived from our noninvasive approach. Our noninvasive technique accurately estimated total and species‐specific worm abundances, as well as worm prevalence and community composition when compared to the lethal sampling method. Importantly, the rate of parasite species discovery was similar for both methods, and only a modest number of barcoded larvae (n = 10) were needed to capture key aspects of parasite community composition. Overall, this new noninvasive strategy offers numerous advantages over lethal sampling methods for studying nematode–host interactions in wildlife and can readily be applied to a range of study systems.     

Establishment of a robotic,high-throughput platform for the specific diagnosis of gastrointestinal nematode infections in sheep

The accurate diagnosis of strongylid nematode infections is central to investigating their epidemiology and for parasite control. To overcome major limitations in sensitivity or specificity of traditional methods, including faecal egg count (FEC) and/or larval culture (LC), we evaluated and established a semi-automated, high throughput multiplexed-tandem PCR (MT-PCR) platform for the diagnosis of gastrointestinal strongylid nematode infections in sheep, and established its diagnostic sensitivity (100%) and specificity (87.5%) based on the testing of 100 faecal DNA samples from helminth-free sheep and 30 samples from sheep with infections confirmed by necropsy. Subsequently, the platform was employed to test 219 faecal samples from sheep with naturally acquired infections from various geographical localities within Australia and the results compared with those from conventional LC using 139 of the 219 samples. The results obtained using both MT-PCR and LC correlated significantly for most nematodes examined, but revealed that Oesophagostomum venulosum and Chabertia ovina (parasites of the large intestine) were significantly under-represented in the LC results. The results showed that Trichostrongylus spp. (87%), Teladorsagia circumcincta (80%) and Haemonchus contortus (67%) had the highest prevalences, followed by O. venulosum (51%) and C. ovina (12%). The molecular-diagnostic platform established can be used for species- or genus-specific diagnosis of patent nematode infections within 24 h (compared with 7–10 days for LC), and is a sensitive and cost effective tool for routine application in research and service laboratories.     

Exploring the Gastrointestinal “Nemabiome”: Deep Amplicon Sequencing to Quantify the Species Composition of Parasitic Nematode Communities

Parasitic helminth infections have a considerable impact on global human health as well as animal welfare and production. Although co-infection with multiple parasite species within a host is common, there is a dearth of tools with which to study the composition of these complex parasite communities. Helminth species vary in their pathogenicity, epidemiology and drug sensitivity and the interactions that occur between co-infecting species and their hosts are poorly understood. We describe the first application of deep amplicon sequencing to study parasitic nematode communities as well as introduce the concept of the gastro-intestinal “nemabiome”. The approach is analogous to 16S rDNA deep sequencing used to explore microbial communities, but utilizes the nematode ITS-2 rDNA locus instead. Gastro-intestinal parasites of cattle were used to develop the concept, as this host has many well-defined gastro-intestinal nematode species that commonly occur as complex co-infections. Further, the availability of pure mono-parasite populations from experimentally infected cattle allowed us to prepare mock parasite communities to determine, and correct for, species representation biases in the sequence data. We demonstrate that, once these biases have been corrected, accurate relative quantitation of gastro-intestinal parasitic nematode communities in cattle fecal samples can be achieved. We have validated the accuracy of the method applied to field-samples by comparing the results of detailed morphological examination of L3 larvae populations with those of the sequencing assay. The results illustrate the insights that can be gained into the species composition of parasite communities, using grazing cattle in the mid-west USA as an example. However, both the technical approach and the concept of the ‘nemabiome’ have a wide range of potential applications in human and veterinary medicine. These include investigations of host-parasite and parasite-parasite interactions during co-infection, parasite epidemiology, parasite ecology and the response of parasite populations to both drug treatments and control programs.     

Gastrointestinal helminths of little blue penguins,Eudyptula novaehollandiae (Stephens), from Otago,New Zealand

Data regarding helminth communities can provide insights into health, feeding interactions, behaviour and evolution of their host organisms. Penguins (Spheniscidae) are important components of marine food webs and tracking their helminth communities can be indicative of ecosystem health. New Zealand is home to 5 of the world's 19 penguin species and little is known about their gastrointestinal helminths. Here, we provide the first study on the gastrointestinal helminths of little blue penguins from south-eastern South Island, New Zealand. The helminth community consisted of two species of tapeworm; Tetrabothrius lutzi and Tetrabothrius sp.; three nematode species, Contracaecum eudyptulae, Capillaria sp. and Stegophorus macronectes; two acanthocephalans, Andracantha sigma and Bolbosoma balaenae; and one trematode, Galactosomum otepotiense. The most prevalent parasites were T. lutzi, A. sigma, and C. eudyptulae. This work includes three new host records and five new geographic records. This is the first report of B. balaenae occurring in a host other than a marine mammal. This study adds to our knowledge about the helminth community of New Zealand little blue penguins, and includes new genetic data on helminth species, providing a baseline against which future studies may be compared.     

An ecological law and its macroecological consequences as revealed by studies of relationships between host densities and parasite prevalence

Epidemiological models predict a positive relationship between host population density and abundance of macroparasites. Here I lest these by a comparative study. I used data on communities of four groups of parasites inhabiting the gastrointestinal tract of mammals, nematodes of the orders Oxyurida. Ascarida. Enoplida and Spirurida. respectively. The data came from 44 mammalian species and represent examination of 16886 individual hosts. I studied average prevalence of all nematodes within an order in a host species, a measure of community level abundance, and considered the potential confounding effects of host body weight, fecundity, age at maturity and diet. Host population density was positively correlated with parasite prevalence within the order Oxyurida, where all species have direct life cycles. Considering the effects of other variables did not change this. This supports the assumption that parasite transmission rate generally is a positive function of host population density_: It also strengthens the hypothesis that host densities generally act as important determinants of species richness among directly transmitted parasites and suggests that negative influence of such parasites on host population growth rate increase with increasing host population density among host species. Within the other three nematode orders, where a substantial number of the species have indirect life cycles, no relationships between prevalence and host population density were seen, Again. considering the effects of other variables did not affect this conclusion. This suggests that host population density is a poor predictor of species richness of indirectly transmitted parasites and that effects of such parasites on host population dynamics do not scale with host densities among species of hosts.     

Horses grazing with cattle have reduced strongyle egg count due to the dilution effect and increased reliance on macrocyclic lactones in mixed farms

Strongyle infection is an important issue in horse breeding. It impairs horse health and performance, with young horses being the most sensitive. Strongyle control has long relied on the systematic use of chemical treatments. However, expanding anthelmintic resistance among strongyles calls for alternative options. Mixed grazing is assumed to reduce strongyle load on the pasture as the result of a dilution effect. This has been shown in small ruminants grazing with cattle, but the putative benefits of co-grazing between horses and cattle have not yet been evaluated. Here, we conducted field surveys and face-to-face interviews on 44 farms from two contrasted saddle-horse production areas, Normandy and northern Massif Central, to compare equine strongyle management practices between specialized systems and mixed horse-cattle systems. Our goals were (i) to quantify breeders’ awareness of the putative benefits associated with the co-grazing of horses and cattle, (ii) to establish whether mixed farming was associated with different strongyle management strategies and (iii) to test whether strongyle egg excretion was reduced in horses grazed with beef cattle. Every breeder relied on systematic calendar treatments, and only 8 out of the 23 mixed breeders were aware that co-grazing of horses with cattle could be used as part of their strongyle control strategy. Management practices were similar across both systems in Normandy. In Massif Central, mixed breeders formed a distinct cluster from their specialized counterparts: deworming was less frequent and stocking density was higher in mixed farms, while specialized breeders seemed more willing to integrate herd and plot management into control strategies. Faecal egg counts measured in horses from Massif Central were significantly reduced when horses were grazed with cattle. This was the result of an increased reliance on macrocyclic lactones in mixed farms (P < 0.01) and a significant dilution effect (P < 0.01). When considering a subsample of horses treated with macrocyclic lactones only, young horses grazed with cattle had 50% fewer strongyle eggs excreted in their faeces than horses grazed in equine-only pastures (P < 0.01). This is the first evidence of the benefits of mixed grazing with cattle as an alternative to control strongyle infection in horses, although this promising alternative remains largely unknown by horse breeders.     

Microhabitat distributions and species interactions of ectoparasites on the gills of cichlid fish in Lake Victoria,Tanzania

Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other’s effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host–parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host–parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.     

Host-parasite ecology of the helminths in mountain gorillas

To understand patterns of intestinal parasitism in healthy, undisturbed endangered mountain gorillas (Gorilla beringei), we regularly collected fecal samples from a group of 14 wild gorillas residing in Bwindi Impenetrable National Park (BINP), Uganda, for about 1 yr. The objectives of the study were to collect baseline data in order to document the helminth parasites infecting this group of gorillas and to examine the effects of season and host age-sex class on patterns of parasite infection. In addition to weekly surveys of feces from all group members, fecal samples from 4 identified individuals were examined almost daily. We identified the diagnostic stages of the following parasites: strongylids (Strongylida), Anoplocephala gorillae, Probstmayria sp., Strongyloides fuelleborni, and a trematode. Monthly and daily fluctuations in strongylid egg counts were observed. Infants had lower strongylid egg counts compared with other group members. Both of the silverbacks had higher mean egg counts in the wet season than in the dry season. Examination of fecal samples from identifiable gorillas revealed high day-to-day variation in strongylid egg counts. No evidence of anthropozoonotic transmission of intestinal helminths was found.     

The relationships between faecal egg counts and gut microbial composition in UK Thoroughbreds infected by cyathostomins

A growing body of evidence, particularly in humans and rodents, supports the existence of a complex network of interactions occurring between gastrointestinal (GI) helminth parasites and the gut commensal bacteria, with substantial effects on both host immunity and metabolic potential. However, little is known of the fundamental biology of such interactions in other animal species; nonetheless, given the considerable economic losses associated with GI parasites, particularly in livestock and equines, as well as the global threat of emerging anthelmintic resistance, further explorations of the complexities of host-helminth-microbiota interactions in these species are needed. This study characterises the composition of the equine gut commensal flora associated with the presence, in faecal samples, of low (Clow) and high (Chigh) numbers of eggs of an important group of GI parasites (i.e. the cyathostomins), prior to and following anthelmintic treatment. High-throughput sequencing of bacterial 16S rRNA amplicons and associated bioinformatics and statistical analyses of sequence data revealed strong clustering according to faecal egg counts (P?=?0.003). A trend towards increased populations of Methanomicrobia (class) and Dehalobacterium (genus) was observed in Clow in comparison with Chigh. Anthelmintic treatment in Chigh was associated with a significant reduction of the bacterial Phylum TM7 14?days post-ivermectin administration, as well as a transient expansion of Adlercreutzia spp. at 2?days post-treatment. This study provides a first known insight into the discovery of the intimate mechanisms governing host-parasite-microbiota interactions in equines, and sets a basis for the development of novel, biology-based intervention strategies against equine GI helminths based on the manipulation of the commensal gut flora.