Helminth infections in Apodemus sylvaticus in southern England: interactive effects of host age, sex and year on the prevalence and abundance of infections.

Helminth parasites were studied in the wood mouse, Apodemus sylvaticus, in southern England in September of each of four successive years (1994-1997). Nine species of helminths were recorded: five nematodes (Heligmosomoides polygyrus, Syphacia stroma, Pelodera strongyloides, Trichuris muris, Capillaria murissylvatici), two cestodes (Microsomacanthus crenata, Taenia taeniaeformis) and two trematodes (Corrigia vitta, Brachylaemus recurvum). In total, 134 mice were examined and 91.8% carried at least one species of helminth. The majority of mice carried two to three species (60.5%) and the highest combination was six of the nine species recorded in the study. The patterns of between-year variations in the prevalence and abundance of infection were different for each of the six species for which sufficient quantitative data were available to enable statistical analysis. For H. polygyrus, the most important source of variation arose from between-year differences, host age and the interaction of these factors: abundance increased with host age but in 1995 the age pattern was markedly different from that in the remaining years. The abundance of C. vitta also varied significantly between years but additionally there was a strong independent age effect. For M. crenata, the year x age interaction was significant, indicating that abundance among different age cohorts varied from year to year but there was also a weak significant main effect of age arising from the youngest age cohort carrying no parasites and the oldest age cohort the heaviest infections. For P. strongyloides the only significant factor was between-year variation with 1995 being a year of exceptionally low prevalence and abundance of infection. No significant between-year variation was detected for S. stroma but there was a strong sex effect (males carrying heavier infections) and an age effect (older mice of both sexes carrying heavier infections). The abundance of Trichuris muris varied only in relation to host age, worm burdens growing in intensity with increasing age, but there was also a significant interaction between year and host sex with respect to prevalence. For the remaining three species, the prevalence of infections was too low (< 8.2%) to enable any meaningful interpretation. This analysis emphasizes the need for carefully controlled statistical procedures in aiding the interpretation and the prioritization of the factors affecting worm burdens in wild rodents.     

Local variation in helminth burdens of Egyptian spiny mice (Acomys cahirinus dimidiatus) from ecologically similar sites: relationships with hormone concentrations and social behaviour

Populations of Egyptian spiny mice (Acomys cahirinus dimidiatus) in a fragmented montane wadi system in the Sinai showed significant differences in the abundance of gut helminths. Differences in parasite load between populations were positively associated with measures of androgen activity but showed no significant relationship with glucocorticoid activity. Social discrimination tests with adult males from different wadis showed that those from sites with greater helminth abundance were less likely to investigate odours from other males and were less aggressive when subsequently interacting with the odour donors. Subjects showed markedly more investigation towards the odours of males from distant wadis compared with those from their own or immediately neighbouring wadi, but were less aggressive when confronted with odour donors from distant wadis. Despite this, there was a positive relationship between the amount of investigation towards distant male odour and subsequent aggression towards the male. While aggressiveness was positively associated with measures of androgen and glucocorticoid activity, no significant relationship emerged with individual helminth infection. Thus aggressiveness appeared to relate to overall local population levels of infection rather than individual challenge.     

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.     

Helminth community structure in birds of prey (Accipitriformes and Falconiformes) in southern Italy

We compared helminth communities in 6 species of birds of prey from the Calabria region of southern Italy. In total, 31 helminth taxa, including 17 nematodes, 9 digeneans, 3 acanthocephalans, and 2 cestodes, were found. All helminth species were observed in the gastrointestinal tract, except for 3 spirurid nematodes. Most of the parasite species were detected in at least 2 hosts, but 13 helminth species were found in only 1 host. At the infracommunity level, the overall species richness and Brillouin's index of diversity varied by host, with the highest values in a generalist feeder, the Eurasian buzzard (Buteo buteo), and the lowest in a specialist, the western honey buzzard (Pernis apivorus). Species richness was gender dependent only in the sparrow hawk (Accipiter nisus). The helminth communities were characterized by different dominant species, namely, Centrorhynchus spp. (Acanthocephala) in the Eurasian buzzard and common kestrel (Falco tinnunculus), Parastrigea intermedia (Digenea) in the marsh harrier (Circus aeruginosus), Physaloptera alata (Nematoda) in the sparrow hawk, Serratospiculum tendo (Nematoda) in the peregrine falcon (Falco peregrinus), and Strigea falconis (Digenea) in the western honey buzzard. Statistical analyses confirmed a highly significant difference of helminth infracommunity structure among host species. We conclude that in the Calabria region of southern Italy, each of the raptor species studied is distinct in terms of its helminth communities, and more diverse feeding habits of the host correspond with richer helminth communities.     

Structure in parasite component communities in wild rodents: predictability, stability, associations and interactions .... or pure randomness?

Experimental data establish that interactions exist between species of intestinal helminths during concurrent infections in rodents, the strongest effects being mediated through the host's immune responses. Detecting immune-mediated relationships in wild rodent populations has been fraught with problems and published data do not support a major role for interactions in structuring helminth communities. Helminths in wild rodents show predictable patterns of seasonal, host age-dependent and spatial variation in species richness and in abundance of core species. When these are controlled for, patterns of co-infection compatible with synergistic interactions can be demonstrated. At least one of these, the positive relationship between Heligmosomoides polygyrus and species richness of other helminths has been demonstrated in three totally independent data-sets. Collectively, they explain only a small percentage of the variance/deviance in abundance data and at this level are unlikely to play a major role in structuring helminth communities, although they may be important in the more heavily infected wood mice. Current worm burdens underestimate the possibility that earlier interactions through the immune system have taken place, and therefore interactions may have a greater role to play than is immediately evident from current worm burdens. Longitudinal studies are proposed to resolve this issue.     

Paraspiralatus sakeri n. g., n. sp. (Nematoda: Spiruroidea, Spirocercidae) from saker falcons, Falco cherrug in Saudi Arabia and the first report of larvae from the subcutaneous tissues of houbara bustards, Chlamydotis undulata macqueeni in Pakistan

A new nematode genus and species, Paraspiralatus sakeri, is described from the stomach of a wild-caught, female saker falcon in Saudi Arabia. This spirurid differs from the nearest genus and species Spiralatus baeri Chabaud, Brygoo & Durette, 1963 in the shape of the pseudolabia, shape of the buccal capsule and absence of a large cephalic vesicle. In addition, third stage spirurid larvae were recovered for the first time from subcutaneous tissues of two houbara bustards. These had died in the Rahim Yar Khan Rehabilitation Center (Houbara Foundation International, Lahore, Pakistan) in Pakistan and were examined at the National Avian Research Center in the United Arab Emirates. The morphology of the larvae and host pathology are described. Comparative studies with the adult spirurids from the saker falcon showed each to have similar cephalic and pharyngeal morphological features to the adults described indicating they are probably the same species. Spirurid nematodes of the suborder Spirurina normally have an arthropod intermediate host. In view of the host, the site from which the larvae were recovered and the fact that this is a rare occurrence, the houbara bustard is considered to be a paratenic host.     

Seasonal and site specific variation in the component community structure of intestinal helminths in Apodemus sylvaticus from three contrasting habitats in south-east England

Seasonal fluctuations in the prevalence and abundance of infection with intestinal helminths were studied in Apodemus sylvaticus (wood mouse, n = 399), from three contrasting habitats in southern England, to test the hypothesis that both intrinsic (host sex, age) and extrinsic (season, site) factors influence parasite species richness and abundance. Five species of helminths were recovered but only one of these (Capillaria murissylvatici) was site-specific (Dungeness). Total species richness was therefore 5 at Dungeness and 4 at the other two sites. Mean species richness was 1.4, but in adult mice there was a pronounced difference between the sites, and an independent highly significant effect of season. Syphacia stroma and Corrigia vitta both showed marked differences between sites in respect of prevalence and abundance of infection. Capillaria murissylvatici was encountered at Dungeness mostly in the spring whereas seasonal changes in abundance of S. stroma were consistent across all three sites. Seasonal fluctuations in the abundance of Catenotaenia pusilla were compounded by differences between sites. Host sex was not a significant factor in any species, although a posteriori analysis of S. stroma worm burdens for the Isle of Wight site revealed a moderate local sex effect. Overall the principal determinants of variation in helminth burdens were the extrinsic factors, site and season.     

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.     

Intestinal helminths of capybaras, Hydrochoerus hydrochaeris, from Venezuela

Quantitative parameters of intestinal helminth species and their potential relations to host characteristics in a population of capybaras (Hydrochoerus hydrochaeris) from Venezuela are reported for the first time. The intestines of 40 capybaras were collected during the 1992-annual harvest at Hato El Cedral. Six helminth species were found: 2 cestodes (Monoecocestus macrobursatum, M. hagmanni), 2 nematodes (Viannella hydrochoeri, Protozoophaga obesa), and 2 trematodes (Hippocrepis hippocrepis, Taxorchis schistocotyle). This is the first report for M. macrobursatum in Venezuela. Helminth abundance did not differ between sexes or age classes. Although patterns of distribution for all helminth species were overdispersed, the high prevalence found for all species (over 70%) and the high abundance observed for nematodes made it difficult to assess the effect that these helminths may produce on capybaras. Nevertheless, the negative associations found between the body condition of capybaras and helminth intensity for M. macrobursatum and V. hydrochoeri, might be pointing out potential host population regulatory role for these parasites which require further research.     

Phenotypic analysis of host-parasite interactions in lambs infected with Teladorsagia circumcincta

Female Blackface lambs expected to exhibit genetic variability for resistance to gastrointestinal nematodes, were either exposed to continuous experimental infections of Teladorsagia circumcincta or were sham-dosed to monitor phenotypic responses to infection. As a measure of parasitism and host response, worm-eggs in faeces (faecal egg count, FEC) were counted over a 3-month period and worm burdens were ascertained at post-mortem. The host response to the infection was also measured by differential counts of white blood cells, anti-T. circumcincta IgA antibody levels and body weight. Results suggest that nematode abundance (mean number of parasites per host) and prevalence (proportion of infected animals) were maximal shortly after the beginning of infection (21 days p.i.) when virtually all the infected animals were shedding worm eggs. Increasing anti-T. circumcincta IgA antibody and eosinophil concentrations were associated with a reduction in total numbers of adult worms and an increase in the frequency of early L4s. The data also suggest that genetic selection for an enhanced anti-T. circumcincta IgA response might complement selection based on a reduced FEC as a strategy to select for resistance to gastrointestinal nematodes.     

The helminth community of the wood mouse, Apodemus sylvaticus, in the Sierra Espuna, Murcia, Spain

The helminth community of the wood mouse, Apodemus sylvaticus, in the Sierra Espuna was characterized after a complete analysis of its helminth community component and infracommunity structure relative to host age, sex and year of capture. The helminth community comprised 13 species: one trematode, four cestodes and eight nematodes. The cestode Pseudocatenotaenia matovi and the nematode Syphacia frederici were the most prevalent and abundant helminth species, respectively. Sixty four percent of mice analysed presented helminths with a direct cycle and 42% presented helminths with an indirect cycle. The helminth community presents a low diversity with infracommunities usually made up of only one or two helminth species. Host age and year of capture seem to play a major role in determining species richness and helminth diversity, but not in determining the abundance of helminths. Host sex does not seem to affect the infection rate nor the diversity. Further studies on more samples of wood mice and other small mammal species in this regional park are needed to explore any possible interactions between helminth communities in the host populations.     

Effects of precipitation on parasite burden along a natural climatic gradient in southern Africa – implications for possible shifts in infestation patterns due to global changes

As a consequence of environmental change, it is expected that shifts in temperature and precipitation patterns will influence parasite communities and their hosts with unpredictable impact. Parasites play a vital role in ecosystems but there is only limited quantitative data which describe the effects of environmental parameters under natural conditions. We investigated the influence of rainfall, relative humidity and temperature on the prevalence, abundance and infection intensity of nematodes in southern Africa by studying the gastro‐intestinal helminth community of the striped mouse Rhabdomys pumilio. Along a precipitation gradient from the Cape of South Africa to northern Namibia we trapped 470 mice over a geographical distance of about 1400 km. Faecal egg counts of 439 sampled individuals and dissections of 161 gastro‐intestinal tracts revealed 15 different helminth species. The most abundant nematode species harboured in 62.6% of all infected mice were the oxyurid Syphacia obvelata followed jointly by two species (Heligmonina spira and Neoheligmonella capensis) of the subfamily Nippostrongylinae (43.7%). We found a significant positive correlation between mean annual precipitation (rainfall and relative humidity) and nematode infestation rates of animals and a negative correlation with temperature. In addition, we found associations between precipitation and different qualitative measurements of parasite burden (mean nematode species richness, mean number of nematode worms and infection intensity per individual host). The similarity in nematode species composition decreased with distance between all study sites. Our study indicates for the first time an association between climatic variables and parasite prevalence and abundance along a continuous natural climatic gradient in a small mammal. These results might be incorporated in the development of models which can predict possible threats for the balance of ecosystems and shifts in infestation patterns due to global changes.     

SEASONAL AND DEMOGRAPHICAL VARIATION IN INTESTINAL HELMINTH INFECTION OF GREYWING FRANCOLIN

Little, R.M., Verster, A. & Crowe, T.M. 1993. Seasonal and demographical variation in intestinal helminth infection of Greywing Francolin. Ostrich 64:178-181.

The proportion of the population carrying intestinal parasites (prevalence of infection) and the mean number of parasites per host within the host population (worm burden) for 312 Greywing Francolin Fran-colinus africanus were recorded on the Stormberg Plateau, eastern Cape Province, during April 1989-De-cember 1990. Most Greywing (86%) had helminths in their small intestine or caeca. Variation in levels of helminth infection (i.e. both prevalence and burdens) was independent of host sex. Nematodes were confined to the caeca where they were present in high numbers throughout the year with two peaks during June-August and November-January. The prevalence and worm burdens of nematodes were independent of host age Nematodes were more prevalent than cestodes. The prevalence and number of cestodes in the small intestine were highest during September-February and Faked during November-December. Levels of prevalence of cestodes were significantly higher in juvenile Greywing than in adults during the austral winter (May-July). The number of cestodes was consistently, but not significantly, higher in juveniles than in adults. Greywing body mass and population density were not significantly correlated with worm burdens.     

Helminth-modified pulmonary immune response protects mice from allergen-induced airway hyperresponsiveness

It has been shown that the presence of certain helminth infections in humans, including schistosomes, may reduce the propensity to develop allergies in infected populations. Using a mouse model of schistosome worm vs worm + egg infection, our objective was to dissect the mechanisms underlying the inverse relationship between helminth infections and allergies. We have demonstrated that conventional Schistosoma mansoni egg-laying male and female worm infection of mice exacerbates airway hyperresponsiveness. In contrast, mice infected with only schistosome male worms, precluding egg production, were protected from OVA-induced airway hyperresponsiveness. Worm-infected mice developed a novel modified type 2 cytokine response in the lungs, with elevated allergen-specific IL-4 and IL-13 but reduced IL-5, and increased IL-10. Although schistosome worm-only infection is a laboratory model, these data illustrate the complexity of schistosome modulation of host immunity by the worm vs egg stages of this helminth, with the potential of infections to aggravate or suppress allergic pulmonary inflammation. Thus, infection of mice with a human parasitic worm can result in reduced airway inflammation in response to a model allergen.     

Cyclic and non-cyclic dynamics in populations of the helminth parasites of wood mice, Apodemus sylvaticus

Two populations of Apodemus sylvaticus, one in deciduous woodland and another in coniferous forest in Co. Down, Northern Ireland, were trapped at monthly intervals over 33 months. The dynamics, reproduction and age structure of the mouse populations differed between years with over a 40 fold range of population size. Nine species of helminths were recovered from the alimentary tract and associated organs of the mice. The prevalence and mean worm burden of the cestodes, Catenotaenia lobata, Hymenolepis hibernia and Taenia taeniaeformis varied erratically. The trematodes, Corrigia vitta and to a lesser degree Brachylaima recurva, had seasonal changes in abundance. The nematodes Capillaria murissylvatici and Nematospiroides dubius had strongly seasonal cycles of abundance associated with the onset of host reproduction. Trichuris muris was the rarest helminth. Despite protracted periods of absence this species maintained a seasonal increase in mean worm burden in late winter. The nematode, Syphacia stroma, had a weakly seasonal pattern of dynamics. The bases of these cyclical and non-cyclical dynamics of the helminths of A. sylvaticus are discussed.     

In vivo and in vitro egg production by Nematospiroides dubius during primary and challenge infections in resistant and susceptible strains of mice

Experiments were conducted to examine adult worm burdens, fecal egg output, and in vitro fecundity of Nematospiroides dubius in resistant LAF1 and susceptible CBA mice 12, 15, 18, and 21 days following primary and challenge infections. A strong correlation was obtained on the number of eggs produced by worms cultured in vitro and the egg production as assessed by fecal egg count. Worm counts, fecal egg counts, and in vitro fecundity were similar on all days studied following a primary infection in both mouse strains. However, after challenge infection, LAF1 mice showed lower worm burdens, fecal egg output, and in vitro egg production when compared to CBA mice. Although the egg production of surviving female worms from immune LAF1 mice was decreased, it never fell below a threshold of 100 eggs/day. The reduced fecundity may be a manifestation of a general anti-worm response rather than responses directed specifically at worm reproduction.     

Experimental Oesophagostomum dentatum infection in the pig: Worm populations resulting from single infections with three doses of larvae

This report describes the effect of different dose levels of infection upon worm burdens and development and fecundity of the parasites. Three groups each of 40, 9-week-old, helminth naïve pigs were inoculated once with either 2000 (group A), 20,000 (group B), or 200,000 (group C) infective third stage larvae of Oesophagostomum dentatum. Subgroups of 5 pigs from each major group were killed 3, 6, 11, 14, 18, 25, 34 and 47 days post inoculation (p.i.) and the large intestinal worm burdens were determined. Faecal egg counts were determined at frequent intervals after day 13 p.i. There were no overt clinical signs of gastrointestinal helminthosis during the experiment. Faecal egg counts became positive in groups A and B at around day 19 p.i., whereas most pigs in the high dose group C did not have positive egg counts until day 27–33 p.i. and some pigs remained with zero egg counts until the end of the study. Throughout the experiment the worm populations in group C consisted mainly of immature larval stages, while those in groups A and B were predominantly adult stages after days 14–18. Adult worms from the low dose group A were significantly longer than those from group C. At high population densities, stunted development of worms and reduced fecundity among female worms were found. Furthermore, there was a tendency for the distribution of the worms within the intestine to be altered with increasing population size.     

Concurrent infections of Fasciola, Schistosoma and Amphistomum spp. in cattle from Kafue and Zambezi river basins of Zambia

This study investigated interactions among Fasciola gigantica, Schistosoma spp. and Amphistomum spp. concurrent natural infections in Zambian cattle, based on egg and worm counts. In the abattoir 315 cattle were screened for worms of F. gigantica in the liver, Schistosoma spp. in mesenteric veins and/or Amphistomum spp. in the rumen. One hundred and thirty-three (42.2%) of the abattoir-examined cattle harboured one, two or all three trematodes. Of 133 cattle, 50 were randomly selected for worm and egg counts. The mean numbers (+/- SD) of Amphistomum, Schistosoma and Fasciola were 622.08 (+/- 97.87), 33.68 (+/- 7.44) and 19.46 (+/- 4.58), respectively. A total of 32% harboured all the three trematodes, 66% had F. gigantica and Amphistomum spp. infections, 52% had Schistosoma spp. and Amphistomum spp. infections while 32% had F. gigantica and Schistosoma infections. A positive correlation (P = 0.014) was found between F. gigantica and Amphistomum worm burdens. There were no correlations between Amphistomum and Schistosoma worm burdens and between F. gigantica and Schistosoma worm burdens. It may be concluded that there is no significant cross-protection among these trematodes in cattle in endemic areas.     

Helminth infracommunities of Rana vaillanti brocchi (Anura: Ranidae) in Los Tuxtlas, Veracruz, Mexico

A total of 76 adult individuals of Rana vaillanti were collected in Laguna Escondida, Los Tuxtlas, Veracruz, Mexico, and their helminth infracommunity structure was determined. Among the 21 helminth taxa collected (10 digeneans, 8 nematodes, and 3 acanthocephalans), the digenean Langeronia macrocirra reached the highest prevalence (64.4%), mean abundance (6.6), and mean intensity (10.4), as well as the highest total number of individuals (499). Only 2 frogs were uninfected, the remainder harbored between 1 and 7 helminth species and 1-102 individuals; mean species richness and abundance were 3.49 +/- 0.22 and 16.1 +/- 16.3, respectively. Langeronia macrocirra dominated in 50.6% of the infracommunities, with relatively low Berger-Parker index values (0.56); for this reason, the evenness was high (0.70 +/- 0.31), and consequently, diversity values are the highest recorded to date in species of Rana. However, patterns of helminth infracommunity richness and diversity were similar to those previously observed in amphibians. This structure is attributed to the feeding habits (between 66.7 and 81% of helminth species parasitizing R. vaillanti enter using the food web dynamics) and low vagility (the remainder species infect by host penetration).     

The consequences of short-term grazing of bioactive forages on established adult and incoming larvae populations of Teladorsagia circumcincta in lambs

The objective of this study was to investigate the consequences of short-term grazing on bioactive forages on (i) the viability and fecundity of established adult Teladorsagia circumcincta population and (ii) the establishment and development of incoming T. circumcincta infective larvae. Forty-eight, parasite naive, 3-month old, grazing lambs were artificially infected with 8000 infective larvae of T. circumcincta on day 1 of the experiment. On day 21 p.i., lambs were allocated to one of three bioactive forage grazing treatments; chicory (Cichorium intybus), sulla (Hedysarum coronarium), lotus (Lotus pedunculatus), and the control grass/clover (Lolium perenne/Trifolium repens) forage. On day 28 of the experiment a second dose of 8000 T. circumcincta infective larvae was administered to the lambs to investigate the effects of forages on the ability of infective larvae to establish within the host. All animals were slaughtered for worm recovery on day 35, while liveweight gain, feacal egg counts (FEC) and total worm egg output were monitored regularly throughout the experiment. Although FEC or total egg output were similar among the groups, adult worm burdens at slaughter were significantly affected (P<0.05) by forage treatment during the 2 week grazing period. Lambs grazing chicory had the lowest adult worm burdens and significantly lower numbers of male worms compared to those grazing on grass/clover (P<0.01), while the lambs grazing on sulla or lotus had similar adult populations to grass/clover fed animals. The results from the worm recoveries of the second dose (immature worm burdens) were affected by physiologically and/or immunologically mediated mechanisms, which reduced larval establishment in all treatments. Nevertheless, immature worm burdens at slaughter were similar between chicory, sulla and grass/clover group, while the immature worm recoveries from the lotus group were significantly higher (P<0.05) compared to those from lambs grazing grass/clover. Overall, the results of the present study support the view that chicory can be a promising candidate species in pasture management practices to control T. circumcincta burdens.