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1. It is well known that gastrointestinal nematodes can have a significant impact on the growth of farmed ruminants. The clinical signs of these parasites are often subtle, with production losses mainly due to reductions in host appetite and gut function. However, little is known about the impact of this widespread group of parasites on wild ruminants. We use experiments and cross-sectional data to investigate the effects of gastrointestinal nematodes on a wild host, the Svalbard reindeer. 2. Individually marked reindeer were treated for parasites. Their body mass, back fat depth and fecundity were compared with the control group one year later. The effect of treatment on worm burdens was investigated in a subsample of animals that were culled 3 and 6 months after treatment. Also, the relationship between the intensity of infection and body mass, back fat depth and host pregnancy rates was investigated in cross-sectional data from culled reindeer. 3. The anthelmintic treatment caused an increase in the body mass, back fat depth and fecundity of the reindeer. Treatment depressed the abundance of adult parasites of Ostertagia gruehneri for at least 6 months, but had no significant effect on the abundance of adults of the other dominant parasite species, Marshallagi marshalli, or the abundance of larval stages of either species. 4. In the cross-sectional study, the probability of a reindeer being pregnant in late winter was negatively related to the abundance of adult O. gruehneri when controlling for host body mass. However, no clear evidence were found for an effect of parasitism on host condition in the cross-sectional study. 5. Our experimental results show for the first time in a natural ruminant host population that gastrointestinal nematodes can have a significant effect on host condition and fecundity. However, effects of infection on host condition was not detectable in the cross-sectional study. Also, we show that the experimental effects on host condition and fecundity is most likely to be due to a negative effect of O. gruehneri, while the experimental design did not allow detection of potential negative effects of M. marshalli.

The present study was carried out to determine the prevalence of gastrointestinal helminthiasis in ruminants in an irrigated area of lower Punjab (Pakistan). For this purpose, 100 faecal samples were collected from sheep, goats, cattle and buffaloes. Parasitological procedures including direct and indirect methods (sedimentation and floatation) and coproculture were used for the identification of helminths. The overall prevalence of helminthiasis was 51% in cattle, 47% in buffaloes, 62% in sheep and 52% in goats, with nematodes being the most common helminths. The prevalence of helminths was higher in young animals compared with adults in cattle (P < 0.0001), buffaloes (P < 0.0001), sheep (P < 0.059) and goats (P = 0.010). The prevalence of different species of helminths also varied in different age groups, with Toxocara vitulorum being higher in calves than adults both in cattle (P = 0.017) and buffaloes (P < 0.0001). Sex-wise prevalence of helminths was higher in males than females for buffaloes (P < 0.0001) and sheep (P = 0.014) in contrast to cattle and goats.

Human schistosomiasis—or bilharzia—is a parasitic disease caused by trematode flukes of the genus Schistosoma. By conservative estimates, at least 230 million people worldwide are infected with Schistosoma spp. Adult schistosome worms colonise human blood vessels for years, successfully evading the immune system while excreting hundreds to thousands of eggs daily, which must either leave the body in excreta or become trapped in nearby tissues. Trapped eggs induce a distinct immune-mediated granulomatous response that causes local and systemic pathological effects ranging from anaemia, growth stunting, impaired cognition, and decreased physical fitness, to organ-specific effects such as severe hepatosplenism, periportal fibrosis with portal hypertension, and urogenital inflammation and scarring. At present, preventive public health measures in endemic regions consist of treatment once every 1 or 2 years with the isoquinolinone drug, praziquantel, to suppress morbidity. In some locations, elimination of transmission is now the goal; however, more sensitive diagnostics are needed in both the field and clinics, and integrated environmental and health-care management will be needed to ensure elimination.

Parasites and pathogens can influence the survivorship, behavior, and very structure of their host species. For example, experimental studies have shown that trematode parasites can cause high frequencies of severe limb malformations in amphibians. In a broad-scale field survey covering parts of California, Oregon, Washington, Idaho, and Montana, we examined relationships between the frequency and types of morphological abnormalities in amphibians and the abundance of trematode parasite infection, pH, concentrations of 61 pesticides, and levels of orthophosphate and total nitrate. We recorded severe malformations at frequencies ranging from 1% to 90% in nine amphibian species from 53 aquatic systems. Infection of larvae by the trematode Ribeiroia ondatrae was associated with, and functionally related to, higher frequencies of amphibian limb malformations than found in uninfected populations (≤5%). Parasites were concentrated around the basal tissue of hind limbs in infected anurans, and malformations associated with infection included skin webbings, supernumerary limbs and digits, and missing or malformed hind limbs. In the absence of Ribeiroia, amphibian populations exhibited low (0-5%) frequencies of abnormalities involving missing digits or distal portions of a hind limb. Species were affected differentially by the parasite, and Ambystoma macrodactylum, Hyla regilla, Rana aurora, R. luteiventris, and Taricha torosa typically exhibited the highest frequencies of abnormalities. None of the water-quality variables measured was associated with malformed amphibians, but aquatic snail hosts (Planorbella spp.) were significant predictors of the presence and abundance of Ribeiroia infection. Morphological comparisons of adult specimens of Ribeiroia collected from different sites and raised in experimental definitive hosts suggested that all samples represented the same species-R. ondatrae. These field results, coupled with experimental research on the effects of Ribeiroia on amphibians, demonstrate that Ribeiroia infection is an important and widespread cause of amphibian limb malformations in the western United States. The relevance of trematode infection to declines of amphibian populations and the influence of habitat modification on the pathology and life cycle of Ribeiroia are emphasized as areas requiring further research.

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.

Corridor disease is an acute, fatal disease of cattle caused by buffalo-adapted Theileria parva. This is a nationally controlled disease in South Africa and strict control measures apply for the movement of buffalo, which includes mandatory testing for the presence of T. parva and other controlled diseases. Accurate diagnosis of the T. parva carrier state in buffalo using the official real-time hybridization PCR assay (Sibeko et al. 2008), has been shown to be affected by concurrent infection with T. sp. (buffalo)-like parasites. We describe the Hybrid II assay, a real-time hybridization PCR method, which compares well with the official hybridization assay in terms of specificity and sensitivity. It is, however, not influenced by mixed infections of T. sp. (buffalo)-like parasites and is as such a significant improvement on the current hybridization assay.

Widespread reports of malformed amphibians are of growing conservation concern. Although accounts of mass malformations (>5%) in North American amphibian populations date back to the 1940s, they are often poorly documented and are rarely explained. We reviewed available information for nine historical accounts from California, Colorado, Idaho, Mississippi, Montana, Ohio, and Texas reported between 1946 and 1988. We then asked the following questions: (1) Which of these cases were associated with Ribeiroia (Trematoda: Digenea) infection? (2) Are malformations still occurring at these sites? And (3) if so, have the frequency or types of abnormalities changed? Each site was resurveyed between 1999 and 2002, and original voucher specimens were redescribed and examined for trematode infection. Direct identification and classification by discriminant function analysis indicated that historical malformations at six of eight sites were associated with infection by Ribeiroia, dating back as far as 1946. Malformations recorded historically at these sites were consistent with the documented effects of Ribeiroia infection, including extra limbs, cutaneous fusion, and bony triangles. Of the six sites that still supported amphibians upon resurvey, three continued to support severe limb malformations at frequencies of 7-50% in one or more species. Although no pesticides were detected, amphibians from each of these sites were infected with Ribeiroia metacercariae. Taken together, these results suggest that Ribeiroia infection has historically been an important cause of mass malformations in amphibians. We conclude that although parasite-induced malformations are not a new phenomenon, there is qualitative evidence suggesting that their prevalence has increased recently, and we highlight the need for long-term research to evaluate the impacts of malformations on amphibian population viability.

A survey was conducted in 150 households owning 1756 pigs in the rural areas of Mayo-Danay division in the north of Cameroon. A questionnaire survey was carried out to collect information on the pig-farming system and to identify potential risk factors for Taenia solium cysticercosis infection in pigs. Blood samples were collected from 398 pigs with the aim of estimating the seroprevalence of T. solium cysticercosis. The results showed that 90.7% of the pigs are free roaming during the dry season and that 42.7% of households keeping pigs in the rural areas have no latrine facility. Seventy-six per cent of the interviewed pig owners confirmed that members of the household used open-field defecation. Enzyme-linked immunosorbent assay (ELISA) for antigen and antibody detection showed an apparent prevalence of cysticercosis of 24.6% and 32.2%, respectively. A Bayesian approach, using the conditional dependence between the two diagnostic tests, indicated that the true seroprevalence of cysticercosis in Mayo-Danay was 26.6%. Binary logistic regression analysis indicated that a lack of knowledge of the taeniasis–cysticercosis complex and the absence of a pig pen in the household were associated with pig cysticercosis.

Free-living Soay sheep (Ovis aries) on the island of Hirta, St Kilda, Scotland, are naturally parasitized by gastrointestinal nematodes, predominantly Teladorsagia circumcincta. In this paper we show that reduced faecal egg counts (FEC) are associated with an allele at a microsatellite locus located in the first intron of the interferon gamma gene (o(IFN)-γ) in Soay sheep lambs and yearlings, measured at approximately 4 and 16 months of age, respectively. The same allele was also associated with increased T. circumcincta-specific antibody (IgA) in lambs, but not associated significantly in yearlings. Flanking control markers failed to show a significant association with either FEC or IgA. These results suggest that a polymorphic gene conferring increased resistance to gastrointestinal nematode parasites is located at or near the interferon gamma gene, and support previous reports which have mapped a quantitative trait locus (QTL) for resistance to this region in domestic sheep. Our data are consistent with the idea that a functional polymorphism leading to reduced expression or efficacy of (IFN)-γ could enhance the immune response to gastrointestinal nematodes by favouring the activity of the Th2 cell subset and antibody associated immune mechanisms.

Food-borne trematodiases are a group of neglected tropical diseases caused by liver, lung, and intestinal parasitic fluke infections. As part of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD 2010 study) and a WHO initiative, we assessed the global burden of human food-borne trematodiasis, as expressed in disability-adjusted life years (DALYs) for the year 2005. We systematically searched electronic databases for reports about human food-borne trematodiasis without language restriction, between Jan 1, 1980, and Dec 31, 2008. We used a broad search strategy with a combination of search terms and parasite and disease names. The initial search results were then screened on the basis of title, abstract, and, finally, full text. Relevant quantitative and qualitative data on human prevalence, morbidity, and mortality of food-borne trematodiasis were extracted. On the basis of available information on pathological and clinical appearance, we developed simplified disease models and did meta-analyses on the proportions and odds ratios of specified sequelae and estimated the global burden of human food-borne trematodiasis. We screened 33 921 articles and identified 181 eligible studies containing quantitative information for inclusion in the meta-analyses. About 56·2 million people were infected with food-borne trematodes in 2005: 7·9 million had severe sequelae and 7158 died, most from cholangiocarcinoma and cerebral infection. Taken together, we estimate that the global burden of food-borne trematodiasis was 665 352 DALYs (lower estimate 479 496 DALYs; upper estimate 859 051 DALYs). Furthermore, knowledge gaps in crucial epidemiological disease parameters and methodological features for estimating the global burden of parasitic diseases that are characterised by highly focal spatial occurrence and scarce and patchy information were highlighted. Despite making conservative estimates, we found that food-borne trematodiases are an important cluster of neglected diseases. Swiss National Science Foundation; Institute for Health Metrics and Evaluation.