Helminth parasites of the wild rabbit Oryctolagus cuniculus near Malham Tarn, Yorkshire, UK

Between 1992 and 1996, 95 rabbits from the immediate locality of Malham Tarn, North Yorkshire, UK were examined for the presence of helminth parasites. All the examinations took place in late September or October. Three species of nematodes, Graphidium strigosum, Passalurus ambiguus and Trichostrongylus retortaeformis and two species of cestodes, Taenia pisiformis and Cittotaenia pectinata were identified. There were no associations between helminth species richness and year of sampling, host weight or sex. A logistic model was fitted to the prevalence data from these helminths as was an over-dispersed Poisson model to the worm burden data. Graphidium strigosum was the most frequently identified species with an average prevalence of 78%. The mean prevalence and intensity of Graphidium infection were significantly effected by sampling year. The lower than normal rainfall recorded at the Tarn during the years 1995 and 1996 may have be one reason for this pattern. The worm burden of G. strigosum was significantly positively associated with rabbit body weight. The intensity of infection with P. ambiguus was significantly higher in female rabbits. There was a significant non-linear relationship between P. ambiguus worm burden and rabbit weight (P = 0.002) with worm burdens being highest in the 1000 g to 1499 g weight cohort. Trichostrongylus retortaeformis was only identified in 1994 and male rabbits harboured significantly higher worm burdens than females (48 vs. 7, P = 0.022). Over the five years, the average Taenia pisiformis prevalence was 31% and there was a significant positive association between worm burden and rabbit weight (P = 0.001). Cittotaenia pectinata had a prevalence of 37% over the whole study period with no interactions between prevalence or intensity and body weight, year of sampling or rabbit sex. All five helminths showed an overdispersed distribution with k values less than 1.     

Helminths of the wild rabbit (Oryctolagus cuniculus) in Macaronesia

Two hundred and four rabbits from 8 Macaronesian islands (Pico, San Jorge, San Miguel, Terceira, and Flores from Azores Archipelago; Tenerife and Alegranza from Canary Islands; and Madeira from Madeira Archipelago) were examined for helminth parasites between 1995 and 2000. Three species of cestodes, Taenia pisiformis (larvae), Andrya cuniculi, and Mosgovoyia ctenoides, and 5 species of nematodes, Trichuris leporis, Graphidium strigosum, Trichostrongylus retortaeformis, Passalurus ambiguus, and Dermatoxys hispaniensis, were identified. Only 3 species (M. ctenoides, T. retortaeformis, and P. ambiguus) were regularly distributed over the 3 archipelagos. Taenia pisiformis was not collected in Madeira, nor was A. cuniculi in the Azores and G. strigosum in the Canary Islands. Trichuris leporis and D. hispaniensis were only found in Madeira. Significant differences in the general prevalence of the nematodes G. strigosum and T. retortaeformis were detected between Azores and Madeira. The prevalence of T. retortaeformis differs significantly between the Azores and the Canaries and that of P. ambiguus was higher in Madeira than in Azores and Canaries. The helminth richness found in the wild rabbit in these Macaronesian archipelagos was very low compared with the Palearctic helminth fauna of this host. The wild rabbit was introduced from the Iberian Peninsula into different Macaronesian islands. Helminths introduced with Oryctolagus cuniculus into these islands also are commonly found in Iberian wild rabbits, which are excellent colonizers, as demonstrated in this study.     

Parasite co-infection and interaction as drivers of host heterogeneity

We examined the hypothesis that the interaction between concomitant infecting parasites modifies host susceptibility, parasite intensity and the pattern of parasite distribution within the host population. We used a 26 year time series of three common parasites in a natural population of rabbits: two gastrointestinal nematodes (Trichostrongylus retortaeformis and Graphidium strigosum) and the immunosuppressive myxoma virus. The frequency distribution of nematodes in the host population and the relationship between host age and nematode intensity were explored in rabbits with either single or dual nematode infections and rabbits infected with the nematodes and myxoma virus. The aggregation of T. retortaeformis and G. strigosum among the rabbits varied with the nature of the co-infection both in male and female hosts. The two nematodes exhibited different age-intensity profiles: G. strigosum intensity increased exponentially with host age while T. retortaeformis intensity exhibited a convex shape. The presence of a secondary infection did not change the age-intensity profile for G. strigosum but for T. retortaeformis co-infection (either both nematodes or myxoma-nematodes) resulted in significantly greater intensities in adult hosts. Results suggest that multi-species infections contributed to aggregation of parasites in the host population and to seasonal variation in intensity, but also enhanced differences in parasitism between sexes. This effect was apparent for T. retortaeformis, which appears to elicit a strong acquired immune response but not for G. strigosum which does not produce any evident immune reaction. We concluded that concomitant infections mediated by host immunity are important in modifying host susceptibility and influencing heterogeneity amongst individual hosts.     

The occurrence and abundance of helminth parasites of the mountain hare Lepus timidus (L.) and the wild rabbit Oryctolagus cuniculus (L.) in Aberdeenshire, Scotland

Mountain hares were collected each month between April 1984 and March 1985 and their intestines examined for helminths. 26 rabbits were also collected between July and December 1984 and examined for gastro-intestinal helminths. Three nematode and two cestode species were found in the hares while only two nematode and one cestode species were found in the rabbits. Trichostrongylus retortaeformis was recorded from 88% of the 193 hares and 92% of the rabbits while comparable figures for Passalurus ambiguus were 0.5% and 54% and for Mosgovoyia pectinata 14% and 81%. Seasonal fluctuations were observed in the T. retortaeformis populations in the hare; numbers tended to be low during the winter months and high throughout the summer. Paranoplocephala wimerosa was reported for the first time from the British Isles and Trichostrongylus axei was recorded for the first time in the mountain hare.     

The helminth parasites of the wild rabbit Oryctolagus cuniculus and their effect on host condition in Dunas de Mira, Portugal

The present study focuses on the helminth parasite community of the wild rabbit in a sand dune area in Portugal over a 5-year period. The influence of host sex and year on the composition of the helminth community is assessed, along with the potential effect of the detected helminths on host body condition. The basic structure of the helminth community comprises Mosgovoyia ctenoides, Graphidium strigosum, Trichostrongylus retortaeformis, Nematodiroides zembrae and Passalurus ambiguus. Mean intensities of G. strigosum varied between years. General G. strigosum intensities were also found to vary according to both year and host sex, but not according to the interaction of both factors. When assessing the effect of helminths on rabbit body condition (expressed by the kidney fat index), higher burdens of M. ctenoides, a cestode that presents a relatively large body mass, were found to induce a reduction in rabbit condition.     

Patterns of parasite aggregation in the wild European rabbit (Oryctolagus cuniculus)

Understanding the factors controlling the distribution of parasites within their host population is fundamental to the wider understanding of parasite epidemiology and ecology. To explore changes in parasite aggregation, Taylor's power law was used to examine the distributions of five gut helminths of the wild rabbit. Aggregation was found to be a dynamic process that varied with year, season, host sex, age class, and myxomatosis. Yearly and seasonal changes are thought, in the main, to be the result of variations in weather conditions acting upon infectious stages (or intermediate hosts). Evidence in support of this was the comparatively low degree of fluctuation in the aggregation of the pinworm, Passalurus ambiguus, as the infectious stage of this parasite is likely to be less susceptible to environmental variation. Host age had a marked effect on the level of aggregation of all parasites, but this effect varied between parasite species. P. ambiguus, Trichostrongylus retortaeformis and Cittotaenia denticulata aggregation were lower in adult than juvenile rabbits whilst Graphidium strigosum and Mosgovoyia pectinata aggregation tended to increase with age. Host immunity is thought to be responsible for these differences. Differences in aggregation for different parasites were also seen when the rabbit population was split into males and females. Myxomatosis had a marked effect on helminth distribution with substantially less aggregation in rabbits showing clinical signs of the disease.     

Influence of host weight, sex and reproductive status on helminth parasites of the wild rabbit, Oryctolagus cuniculus, in Navarra, Spain.

A study was carried out in Navarra (northern Spain) on the influence of the weight, sex and reproductive status (lactant, pregnant or lactant + pregnant females and testicular weight for males) of the wild rabbit (Oryctolagus cuniculus) on two cestodes species: Andrya cuniculi and Mosgovoyia ctenoides and four intestinal nematodes: Graphidium strigosum, Trichostrongylus retortaeformis, Nematodiroides zembrae and Dermatoxys hispaniensis. A significantly higher prevalence of A. cuniculi was detected in lactant + pregnant females compared with non-breeding females. Trichostrongylus retortaeformis and N. zembrae showed a significantly higher mean intensity in lactant and lactant + pregnant females than in non-reproductive females. Trichostrongylus retortaeformis presented a higher mean intensity in females than in males, and the mean intensity of the same parasite species was significantly lower in active and inactive males compared with lactant and lactant + pregnant females. There were no significant differences between sexes in the prevalence of helminth parasites. No significant correlation was detected between host weight and the intensity (of infection) of helminths studied. No significant differences in the prevalence and mean intensity of the two cestode species were observed in the three weight categories studied (kittens, juveniles and adults). The prevalence of G. strigosum and mean intensity of T. retortaeformis were significantly higher in older heavier animals than in juveniles.     

Observations on the seasonal incidence of myxomatosis and its interactions with helminth parasites in the European rabbit (Oryctolagus cuniculus)

European rabbits (Oryctolagus cuniculus) were collected monthly over a 10-yr period and the incidence of myxomatosis and the size of helminth populations were recorded. Myxomatosis occurred annually, always as an epidemic in the latter half of the year and was associated with both an increase in the percentage of animals infected and the size of the infections of the nematodes Trichostrongylus retortaeformis and Passalurus ambiguus and the cestode Mosgovoyia pectinata. It is suggested that myxomatosis had the effect of reducing the rabbits' overall immune response to infection and that due to the regular annual occurrence of myxomatosis, the resulting increase in the size of helminth infections must be considered an integral part of the population dynamics of these parasites.     

Seasonal variation in gut morphology in wild rabbits (Oryctolagus cuniculus)

It is shown experimentally that diet composition affected the sizes of several digestive organs in juvenile rabbits collected from the wild. Stomach weight, small intestine volume and colon length were larger in rabbits reared on diets higher in fibre. Small intestine weight, however, was lower.
Analysis of natural variation in wild adult rabbits showed that all digestive organs (except for the appendix) were larger in rabbits living on chalk soils than in those living on sand or clay. Seasonal variation was more marked in males than in females, probably because of the sexes' different breeding requirements. Thus most male digestive organs were smaller between December and June than at other times of year. Female digestive organs did not show this pattern, and were largest in May/June, when the demands of pregnancy and lactation are highest. However, food quality may have been important too. Food quality is probably highest in April, and most digestive organs were then smallest (both sexes). The dry weights of stomach and small intestine did not fit these patterns. Stomach weight increased with the presence of the nematode parasite Graphidium strigosum and small intestine and caecal volumes with the presence of cestodes. Numbers of nematodes (Trichostrongylus retortaeformis and Passalurus ambiguus) in the caecum or colon, however, had no effects on organ sizes.
Data are presented on variation in intensity and prevalence of these helminth parasites with season and soil type.     

Prevalence, intensity and aggregation of intestinal parasites in mountain hares and their potential impact on population dynamics

Mountain hare Lepus timidus populations show unstable dynamics and since hares carry a significant helminth infection and host-parasite interactions are known to be destabilising, they have been proposed as a possible causal mechanism for the observed instability. We assessed the prevalence, intensity of infection and aggregation of the helminth parasites Graphidium strigosum and Trichostrongylus retortaeformis recovered from 589 mountain hares culled from 30 Scottish sporting estates in 1999 and 2000. Graphidium strigosum showed low prevalence and intensity of infection and was highly aggregated. In contrast, T. retortaeformis showed high prevalence and intensity of infection and a low degree of aggregation. Differences in body condition of the hares were best explained by a model including sex and month of collection and interaction terms for sex-month and intensity of infection of T. retortaeformis-month. The low degree of aggregation of T. retortaeformis and the significant negative effect of intensity of infection on body condition are in accordance with the hypothesis that the host-parasite interaction is the causative destabilising mechanism for mountain hare dynamics.     

Evaluation of the association of parasitism with mortality of wild European rabbits Oryctolagus cuniculus (L.) in southwestern Australia

Abundances of the parasitic nematodes Trichostrongylus retortaeformis and Passalurus ambiguus, and 8 Eimeria species were estimated by fecal egg and oocyst output in 12 discrete free-ranging populations of wild rabbits (Oryctolagus cuniculus) in southwestern Australia. Comparisons of parasite egg and oocyst counts were made between those rabbits known to have survived at least 2 mo after fecal samples were collected and those rabbits that did not survive. There were significant negative relationships between parasite egg and oocyst counts and survival when all age groups and collection periods were pooled for several species of coccidia and for T. retortaeformis. However, when the same comparisons were made within rabbit age groups and within collection periods, there were very few significant differences even where sample sizes were quite large. The differences indicated by the pooled analysis for coccidia were most likely due to an uneven host age distribution with respect to survival, combined with an uneven distribution of the oocyst counts with rabbit age. The result for T. retortaeformis was similarly affected but by a seasonal pattern. Parasitism by nematodes and coccidia did not appear to be an important mortality factor in these rabbit populations, at least at the range of host densities we examined. This suggests that other factors must have been responsible for the observed pattern of density-dependent regulation in these rabbits.     

The effect of dietary sainfoin ( Onobrychis viciifolia) on local cellular responses to Trichostrongylus colubriformis in sheep

The effect of sainfoin (Onobrychis viciifolia) hay consumption on the pathophysiology and local cellular responses of growing lambs during infection with Trichostrongylus colubriformis was investigated. Thirty-two lambs, 16 weeks of age, were allocated to 1 of 4 treatment groups (n=8) that were offered either grass (G) or sainfoin (S) hay while concurrently either infected (+), or not (-) with 12,000 L3 T. colubriformis larvae per week for 6 weeks. Liveweight gains were affected by diet (P=0.002) and reduced by infection (P<0.05). Faecal egg count was reduced in S+compared to G+ from days 35 to 42 (P=0.001); however, total egg output, worm burdens at day 42 and worm fecundity were similar between diets (P>0.05).Feeding sainfoin appeared to enhance immune cell development with tissue eosinophils, mast cells and pan T cells present in greater concentrations in S+ than in G+ animals. However, further studies are required to determine if the enhanced immune cell development is a consequence of a greater nutrient supply or a direct influence of sainfoin metabolites on local inflammatory responses to the gastrointestinal nematode T. colubriformis.     

Density-dependent effects on the survival and growth of the rodent stomach worm Protospirura muricola in laboratory mice

The spirurid nematode, Protospirura muricola, is of intrinsic interest as a rodent model of gastric nematode infections. Since worm burdens can be very heavy in nature, density dependent processes may constrain parasite growth. Laboratory mice (BKW) were exposed to varying doses of infective larvae of P. muricola in the range 5 to 40 third-stage larvae (L3), in four separate experiments in which progressively higher doses were utilized. All mice were culled 60 days after infection and a total of 518 worms (226 male and 292 female worms) was recovered, measured and weighed. Overall survival was 58.9%, but survival declined significantly with increasing dose by approximately 21% (from 66% at 5 L3 per mouse to 52% at 40 L3 per mouse). The length and weight of worms correlated positively in both sexes. Total worm biomass increased linearly with increasing numbers of worms. However, whilst the length and weight of male worms declined with increasing worm burden (8.4 and 24.6% respectively), female worms were less affected, only length showing a significant reduction with increasing parasite burden (16.0%). Therefore, increasing worm burdens impeded growth of P. muricola, but reduction in length and weight were relatively small in relation to the overall size of this nematode. Increasing worm burdens were associated with loss of host weight and reduction in stomach weight and worm burdens in excess of 20 exerted a measurable cost to the host, which in the field, may be associated with loss of overall host fitness.     

Factors influencing the fecal egg and oocyst counts of parasites of wild European rabbits Oryctolagus cuniculus (L.) in Southern Western Australia

Abundance of intestinal parasites was monitored by fecal egg and oocyst counts for samples of wild rabbits Oryctolagus cuniculus with different levels of imposed female sterility from 12 populations in southwestern Australia. Differences in egg counts of Trichostrongylus retortaeformis between seasons and age groups were dependent on the sex of the host. Pregnancy may have been responsible for these differences because egg counts were consistently higher in intact females than in females surgically sterilized by tubal ligation. Egg counts for Passalurus ambiguus were influenced by season and host age but there were no differences between sexes or between intact and sterilized female rabbits. No differences were detected in the oocyst counts of the 8 species of Eimeria between male and female rabbits or between intact and sterilized females. Seasonal differences were detected in oocyst counts of Eimeria flavescens and Eimeria stiedai. The overwhelming determinant of coccidian oocyst counts was host age, with 6 species being much more abundant in rabbits up to 4 mo of age. There was a suggestion that egg counts of T. retortaeformis and oocyst counts of several species of Eimeria were reduced in populations where rabbit numbers had been depressed for at least 2 yr, but there was no evidence that short-term variations in rabbit numbers had a measurable effect on parasite abundance.     

Observations on the epidemiology and interactions between myxomatosis, coccidiosis and helminth parasites in a wild rabbit population in Scotland

A study of the epidemiology of myxomatosis and the protozoan liver parasite, Eimeria stiedae, in a population of wild rabbits in Scotland from 1977 to 2010 is reported. Rabbits were collected on a monthly basis resulting in a total of 5,337 animals examined for the infections. The investigation showed that within any 1 year over the 34 years of the investigation the percentage of rabbits with myxomatosis varied between 0 and 24 %, while for E. stiedae infections fluctuated between 3 and 42 %. There were strong seasonal trends in the prevalence of myxomatosis with over 16 % being infected in September and October, and for E. stiedae, peaks of over 40 % of livers infected were recorded in July. From 2007 to 2010, faeces were also examined for coccidia oocysts and parasitic nematode eggs. Rabbits infected with the myxoma virus had mean oocyst counts of 73,665 per gram faeces, while rabbits not infected with the myxoma virus had counts of 31,952 oocysts per gram. Comparable figures for nematode faecal egg counts were 911 per gram in myxomatosis-infected animals and 427 per gram in uninfected animals. The elevated nematode faecal egg counts in rabbits with myxomatosis reflects increased worm burdens already reported, but the elevated counts of coccidial oocysts have not previously been reported. This would suggest that myxomatosis could compromise rabbit immunity to nematodes and coccidia.     

Induction of immunity in sheep to Fasciola hepatica with mimotopes of cathepsin L selected from a phage display library

An M13 phage random 12-mers peptide library was used to screen cathepsin L mimotopes of Fasciola hepatica and to evaluate their immunogenicity in sheep. Seven clones showed positive reactivity to a rabbit anti-cathepsin L1/L2 antiserum in ELISA, and their amino acid sequences deduced by DNA sequencing were tentatively mapped on the protein. Twenty sheep were randomly allocated into 4 groups of 5 animals each, for immunization with 1x10(14) phage particles of clones 1, 20, a mixture of 7 clones and PBS, without adjuvant at the beginning, and 4 weeks later. All groups were challenged with 300 metacercariae at week 6 and slaughtered 16 weeks later. The mean worm burdens after challenge were reduced by 47.61% and 33.91% in sheep vaccinated with clones 1 and 20, respectively; no effect was observed in animals inoculated with the clone mixture. Also, a significant reduction in worm size and burden was observed for those sheep immunized with clone 1. Animals receiving clone 20, showed a significant reduction in egg output. Immunization induced a reduction of egg viability ranging from 58.92 to 82.11%. Furthermore, vaccinated animals produced clone-specific antibodies which were boosted after challenge with metacercariae of F. hepatica.     

The effects of immunization of sheep with Trichostrongylus colubriformis larvae on worm burdens acquired during grazing

The effects of immunization of sheep with Trichostrongylus colubriformis larvae on worm burdens acquired during grazing. International Journal for Parasitology 19: 177-181. Romney sheep, reared helminth-free in pens to 5 months of age, were immunized against Trichostrongylus colubriformis by giving two doses of 200,000 T. colubriformis infective larvae at 15 day intervals to assess protection from natural challenge during grazing. Five immunized sheep and five unimmunized sheep were grazed on infested pasture for 4 weeks, and were then returned to the pens for 4 weeks before slaughter. Worm burdens, gastrointestinal histology and mucus antiparasite activity were examined at slaughter. Faecal egg counts and haematological examinations were carried out at regular intervals throughout the trial. Significant protection (P less than 0.05) was afforded immunized sheep against adult T. colubriformis (87%), T. axei (67%), Nematodirus spathiger (91%) and Ostertagia spp. (42%). Greater numbers of immature Nematodirus spp. and Ostertagia spp. were present in immunized sheep Overall, a significant (P less than 0.05) 42% reduction in total nematode burdens was afforded by immunization of the sheep with T. colubriformis larvae. Immunized sheep had significantly (P less than 0.05) more globule leukocytes, mast cells and eosinophils in gastrointestinal tissue and significantly (P less than 0.05) higher levels of mucous antiparasite activity than unimmunized sheep. Haematological observations showed some sheep had transient eosinophilia during immunization or grazing. Both immunized and unimmunized sheep showed depressed (P less than 0.05) total leukocyte counts during grazing which returned to pre-grazing levels within 1 week of return of the sheep to the pens. Overall, haematological parameters reflected parasite challenge and were unrelated to worm burdens acquired.     

Vaccination of young lambs against infection with Nematodirus battus using gamma irradiated larvae

Helminthologically naIve 6-week-old Suffolk lambs were given 1-3 doses of 20000 gamma-irradiated infective larvae (L3) of the nematode Nematodirus battus at weekly intervals. Following an anthelmintic drench they were challenged with 50000 viable L3 at 10 weeks of age. Nematode worm burdens 14 days post-challenge showed a significant (P<0.01) 66% reduction in the single vaccine dose group. The two and three dose groups had mean worm burdens which were 30 and 42% lower than controls, respectively, although these were not statistically significant. There was little measurable stimulation of the immune system in the vaccinated lambs, suggesting that the repeatedly dosed animals may have developed immunological unresponsiveness to the parasite.     

Glutathione S-transferase. Novel vaccine against Fasciola hepatica infection in sheep

The potential of GST as a vaccine candidate against liver fluke infection in ruminants was studied by vaccinating sheep (n = 9) with GST purified from adult worms of Fasciola hepatica and challenging with 500 F. hepatica metacercariae. The immunization induced a high antibody response to GST in contrast to the poor or undetectable response to this Ag observed in naturally infected sheep. Throughout the trial, the progress of the fluke infection was monitored by measuring RBC hemoglobin levels, the extent of liver damage and the fecal egg output in the sheep. This analysis indicated that a subpopulation (n = 4) of the GST vaccinated animals exhibited no anemia, reduced liver damage and a lower mean fecal egg count relative to the infected control group suggesting a lower fluke burden in these animals. Worm burdens in the livers of the GST vaccine group (107 +/- 22) were 57% lower than in the infected control group (250 +/- 25). The subpopulation of the GST vaccine group demonstrated a 78% reduction in mean worm burdens relative to the control group. These results show that GST of adult F. hepatica is a novel Ag that can significantly protect sheep against liver fluke infection. The results suggest that the immune response to GST is directed to the juvenile worm reducing the number of worms that can establish in the liver of the vaccinated animals.