Vaccination against Haemonchus contortus: performance of native parasite gut membrane glycoproteins in Merino lambs grazing contaminated pasture.

In a replicated trial, parasitological and antibody responses of grazing weaner Merino sheep were assessed following vaccination with gut membrane proteins prepared from adult worms of the gastrointestinal nematode, Haemonchus contortus. Each vaccinated animal received 100 microg native H11 and 100 microg native H-gal-GP combined together in 5mg Quil A administered intramuscularly on days 0, 34, 80 and 127. Control animals received 5mg Quil A alone on the same days. Vaccinated and unvaccinated control animals grazed pastures contaminated with the parasite from day 34 of the trial, and levels of parasitism were monitored by worm-egg counts (WECs) in faeces and packed cell volumes (PCVs) in blood. The level of larval contamination on pasture was estimated from the worm counts of tracer sheep introduced monthly to the paddocks. WECs and anaemia were significantly reduced in vaccinated animals, and, in contrast to vaccinates, all control sheep required salvage treatment with anthelmintic. By the last 2 months of the trial, pastures grazed by vaccinated animals had significantly lower contamination with H. contortus larvae. Vaccinated animals had high levels of vaccine antigen-specific IgG1 and IgG2 antibodies in plasma, whereas those responses in the control sheep were very low. IgG1 titres in the vaccinated group, but not IgG2 titres, were inversely correlated with worm-egg counts. The levels of systemic IgA and IgE remained low but increased in both groups towards the end of the experiment most probably from exposure to the natural infection from pasture. The results showed that H11 and H-gal-GP behaved like "hidden" antigens producing high levels of protection that were probably mediated through mechanisms involving antibodies, and in particular, IgG1. It was concluded that if similar protective effects could be obtained with recombinant versions of the proteins present in either H11 or H-gal-GP, then the prospects for a commercial Haemonchus vaccine were real.

Efficacy of benzimidazole anthelmintics in goats and sheep in the Philippines using a larval development assay.

The negative effects of nematodes in small ruminants can be reduced by use of dewormers but their effectiveness is increasingly limited by the emergence of anthelmintic resistance. The efficacy of benzimidazole (BZ) anthelmintics in the Philippines was estimated by an in vitro larval development assay using worm eggs recovered from faeces collected from goats and sheep. Two hundred and eighteen farms were selected to represent areas of the country with high goat and sheep populations and the full range of farm sizes, from smallholders with just a few animals to commercial and institutional farms with several hundred. Initial surveys of worm control advisers indicated that BZs have been in continuous widespread use for up to 20 years with little use of other chemical groups. A larval development assay (LDA: DrenchRite) was modified for use with BZs alone to allow up to five samples to be analysed on a single microtitre plate. The assay was validated by comparison with the faecal egg count reduction test (FECRT). The dominant nematode genera were Haemonchus and Trichostrongylus with small numbers of Oesophagostomum. The range of BZ efficacy estimated from the LDA results was 0-100% and the distribution of efficacy levels was continuous, with mean efficacy of 82 and 64% for goats and sheep, respectively. There were significant associations between efficacy and parameters measured to characterize the sampled farms: size of animal management group, FEC of sample, recent importation of stock and no access to common grazing were all correlated with decreased efficacy. Likewise, low efficacy was associated with reported frequency and number of years that BZ drenches had been used. The LDA was found to be highly suited to estimate efficacy in nematode populations from small farms where performance of a FECRT for even one chemical would be impractical. Using a larval development assay, we have demonstrated a wide efficacy range for BZs against nematodes from all sizes of goat and sheep farms in the tropics.

Expression of cell surface adhesion molecules by peripheral blood eosinophils during Trichostrongylus colubriformis infection in sheep.

The effect of infection of sheep with the gastrointestinal nematode parasite Trichostrongylus colubriformis on expression of adhesion molecules CD11a, CD11b, CD11c, CD18, CD44, CD49d and CD62L by peripheral blood eosinophils was examined by flow cytometry. Initially, to establish the sensitivity of adhesion molecules to inflammatory signals, eosinophil-rich exudates were elicited in non-lactating mammary glands of immune sheep by infusion of 50 microg of soluble antigen extract from T. colubriformis third stage larvae. Eosinophils comprised 40.8% of mammary leucocytes and 4.5% of peripheral blood leucocytes. In comparison with blood, the percentage of eosinophils expressing CD18 increased and the percentage expressing CD62L decreased in exudates and the mean fluorescent intensity, an indicator of receptor number per cell, for CD11a and CD49d also decreased on exudate eosinophils. Peripheral blood eosinophils were examined over 8 weeks during trickle infection of immune sheep with infective or irradiated third stage larvae of T. colubriformis. During the last 3 weeks of infection, CD11a staining decreased in infected sheep and CD44 staining decreased in sheep receiving either infective or irradiated larvae. Other surface markers did not change. The results indicate that systemic changes in expression of adhesion molecules by eosinophils occur during T. colubriformis infection in sheep.