Although Nematodirus battus is a serious threat to the health and survival of young lambs, there are few options to control this parasite. Bayesian Monte Carlo Markov Chain modelling with a zero-inflated Poisson distribution was used to estimate the heritability of egg counts in both June and July for each of five consecutive cohorts of 200 Scottish Blackface lambs. In one of the 10 analyses, the results failed the diagnostic tests. In seven of the analyses, there was no convincing evidence that the variation in egg counts was heritable. In the 2 years of high infection, the heritability was approximately 0.4 in June but the estimates lacked precision and the 95% highest posterior density credible intervals ranged from just above zero to 0.7. Selective breeding for resistance to N. battus will be difficult because genetically resistant or susceptible lambs cannot be consistently identified by phenotypic markers.

Mismatch in the phenology of trophically linked species as a result of climate warming has been shown to have far-reaching effects on animal communities, but implications for disease have so far received limited attention. This paper presents evidence suggestive of phenological asynchrony in a host-parasite system arising from climate change, with impacts on transmission. Diagnostic laboratory data on outbreaks of infection with the pathogenic nematode Nematodirus battus in sheep flocks in the UK were used to validate region-specific models of the effect of spring temperature on parasite transmission. The hatching of parasite eggs to produce infective larvae is driven by temperature, while the availability of susceptible hosts depends on lambing date, which is relatively insensitive to inter-annual variation in spring temperature. In southern areas and in warmer years, earlier emergence of infective larvae in spring was predicted, with decline through mortality before peak availability of susceptible lambs. Data confirmed model predictions, with fewer outbreaks recorded in those years and regions. Overlap between larval peaks and lamb availability was not reduced in northern areas, which experienced no decreases in the number of reported outbreaks. Results suggest that phenological asynchrony arising from climate warming may affect parasite transmission, with non-linear but predictable impacts on disease burden. Improved understanding of complex responses of host-parasite systems to climate change can contribute to effective adaptation of parasite control strategies.

Detailed knowledge of the effects of water on the migration of infective larvae of economically important trichostrongyloid species is urgently needed to feed into prediction models of future epidemiology. The influence of water on the migration of the parasitic nematodes Nematodirus battus, Haemonchus contortus and Teladorsagia circumcincta from sheep dung onto grass was examined in a series of laboratory experiments. Turf plots were seeded with larvae, which were recovered from grass clippings by serial sampling. Free water was necessary for larvae to escape from dung, but not for vertical migration onto grass. When temperature and relative humidity were held constant, the proportion of a population of live larvae present on herbage reached a plateau of around 2 (1–10)% after 24 h, and then changed little over time. Larvae in soil and dung formed a reservoir, such that a similar proportion of the larval population was maintained on grass after clipping. These findings suggest continuing random movement of free larvae. Implications for the epidemiology of trichostrongyloid species are discussed in the context of trade-offs faced by the parasites.

Natural populations of 3rd-stage Nematodirus battus larvae were present on pastures in North Wales throughout the year; highest numbers were present in late spring, with smaller peaks occurring in autumn. Inter-site variation was observed in the timing and magnitude of these peaks. Hatching on experimental plots occurred 2 months to 2 years following deposition of eggs. Intraspecific and inter-site variation occurred in the timing, and inter-site variation occurred in the magnitude, of the mass hatch on upland and lowland experimental plots. Arrested 4th-stage N. battus were recovered from Welsh Mountain lambs. Percentage arrest and number of arrested worms was greatest during winter and early spring. The prevalence and intensity of N. battus infection in 1-, 2- and 3-year-old Welsh Mountain ewes was low. The plasticity exhibited in the parasite's life-history is discussed in relation to potential changes in the epidemiology of nematodiriasis.

Young lambs (6–8 weeks of age) were infected with 50000 infective stage larvae of the trichostrongyle nematode Nematodirus battus. Initial mean adult worm burdens of 23884±1678 (S.E.M.) at day 14 post-infection (p.i.) were reduced significantly (P < 0·01) to a mean burden of 5383±1397 by day 21 p.i. Blood samples were taken and serum analysed using ELISA and Western blotting techniques for IgG antibodies specific for N. battus. Pre-infection serum from young naive animals showed IgG recognition of adult and larval N. battus whole worm homogenate. Recognition of adult antigens became reduced during the first 14 days after infection, followed by a subsequent increase beginning between days 14 and 18 p.i. and peaking at day 28 p.i. IgM recognition of N. battus antigens showed a single response peak, starting between days 14 and 18 p.i., without the pre-infection elevated titre as observed with IgG. These results show that young lambs can mount a significant serum response to a primary infection with N. battus during rejection of adult worms and that lambs receive from their dams IgG antibodies that are capable of recognizing adult and larval N. battus during the first few weeks of life.

Vasoactive intestinal polypeptide (VIP)-Hke protein was detected by dot blot analysis in the excretions/secretions (E/S) of Nematodirus battus and Ascaridia galli and was confirmed in the E/S of Nippostrongylus brasiliensis. ELISA analysis showed that N. brasiliensis E/S contained the highest proportion of VIP-like protein (28·04 pmoles/mg of total E/S protein) and A. galli E/S contained the lowest (10·89 pmoles/mg of total E/S protein). Peptide histidine isoleucine (PHI)- like protein was detected by dot blot analysis in the E/S products of N. brasiliensis, N. battus and A. galli. ELISA analysis suggested that A. galli E/S contained the highest proportion of PHI (20·77 nmoles/mg of total E/S protein) and N. battus E/S contained the lowest (0·67 nmoles/mg of total E/S protein). The possible significance of VIP-like and PHI-like substances in the E/S of gastrointestinal nematodes is discussed.

Understanding the frequency distribution of parasites and parasite stages among hosts is essential for efficient experimental design and statistical analysis, and is also required for the development of sustainable methods of controlling infection. Nematodirus battus is one of the most important organisms that infect sheep but the distribution of parasites among hosts is unknown. An initial analysis indicated a high frequency of animals without N. battus and with zero egg counts, suggesting the possibility of a zero-inflated distribution. We developed a Bayesian analysis using Markov chain Monte Carlo methods to estimate the parameters of the zero-inflated negative binomial distribution. The analysis of 3000 simulated data sets indicated that this method out-performed the maximum likelihood procedure. Application of this technique to faecal egg counts from lambs in a commercial upland flock indicated that N. battus counts were indeed zero-inflated. Estimating the extent of zero-inflation is important for effective statistical analysis and for the accurate identification of genetically resistant animals.

The excretory–secretory (E–S) products of the parasitic nematodes Trichostrongylus colubriformis and Nematodirus battus were found to modify the in vitro proliferation of the tumorous colic HT29-D4 cell line of epithelial origin. A characteristic feature of these E–S products is the presence of a high level of acetylcholinesterase (AChE) activity, the biological significance of which remains unclear. To determine a possible role of AChE on cell growth, the enzyme was purified from E–S products using edrophonium chloride. Purity was confirmed by polyacrylamide gel electrophoresis, using silver and Karnovsky stains, before assessing its effects on cell proliferation. The purified AChE was incorporated at different concentrations in a culture medium of HT29-D4 cells. A mitogenic effect was shown for low concentrations (0·1–14 units). By contrast, an inhibitory effect was noted at high concentrations (35–1400 units). Furthermore, polyclonal antibodies were prepared and depletion of AChE in E–S products by immunoprecipitation or affinity chromatography resulted in a partial or total disappearance of the stimulatory effect of cell growth. Thus, the results from this in vitro study suggest a modulatory role for AChE secreted by nematode parasites on the proliferation of epithelial cells of the host.

Helminthologically naive 8-week-old lambs were administered 50000 infective-stage larvae of the trichostrongyle nematode Nematodirus battus. Initial mean adult worm burdens were significantly reduced (P < 0·01) at day 21 post-infection (p.i.). Peripheral blood eosinophil counts showed a significant increase (P < 0·001) by day 25 p.i. when compared with uninfected control animals. Sections of small intestine taken at post-mortem from the area of adult worm establishment over the course of infection showed a significant increase in mucosal eosinophil and mast cell numbers during the period of adult worm rejection, when compared with uninfected control animals. These results show that young lambs develop significant increases in the numbers of cells associated with an inflammatory reaction in the intestine during the development of a partially protective immune response to this parasitic nematode.