Immune responses of sheep to microdissected parts of Haemonchus contortus.

Adult specimens of Haemonchus contortus were microdissected into four body fragments: oesophagus, cuticle of oesophagus, gut and cuticle with adjacent muscle layer. The antigenicity of these different body fragments was analysed in comparison to total (whole) worm extracts with immunoblotting and ELISA using sera of H. contortus-infected sheep. In particular, oesophagus-derived antigens appeared to be specifically recognized and may prove valuable in diagnostic assays.

Is there a relationship between haemoglobin genotype and the innate resistance to experimental Haemonchus contortus infection in Merino lambs?

Responses to a single or repeated infection with 7000 infective larvae of Haemonchus contortus were studied in an experiment using a total of 106 3-month-old lambs with AA, AB or BB haemoglobin (Hb) genotypes. Results were assessed by faecal egg counts, adult worm counts, haematocrit values, haemoglobin concentrations, total serum protein and serum antibody IgG1 and IgA ELISA titres. None of these parameters showed a strong relationship to the Hb type. The prevalence of low responder (greater than 500 worms) and of high responder (less than 50 worms) animals in groups AA, AB and BB Hb types was 3.8 and 34.6, 20.6 and 35.2, 28.1 and 43.7%, respectively, suggesting that the responsiveness to nematode infection is under the control of gene(s) not closely linked with those determining the Hb genotype. Worm counts of a primary infection are more subject to variation than those of a secondary infection. There is a strong relationship between adult worm counts and faecal egg counts taken close to the time of slaughter. In living animals low and high responder discrimination can be based on individual faecal egg counts around 50 days after a secondary infection. Haematocrit values proved to be of little value in the low and high responder selection. In this regard neither Hb concentration nor total serum protein values are of practical significance. In 3-month-old lambs primary infection induced partial immunity which could prevent the establishment of a part of the secondary infection, irrespective of the presence or absence of the primary worm population. The development of immunity was not associated with an increase of serum IgG1 and IgA antibody levels. Specific antibody production was not influenced by Hb types. Mean antibody levels of low responder lambs showed no difference from those of high responders. Thus, serum IgG1 and IgA levels are of no predictive value in identifying lambs which are genetically resistant to Haemonchus infection.

Activity of luxabendazole against liver flukes, gastrointestinal roundworms, and lungworms in naturally infected sheep.

The anthelmintic potential of luxabendazole was investigated in sheep harboring mixed naturally acquired helminth infections. Results were assessed by comparing worm counts of the treated groups (seven animals each) on days 7-8 posttreatment with those of the nontreated control group, except for protostrongylid lungworms, for which the changes in pre- and posttreatment group mean larval counts/g feces were assessed for intensity effect. A single oral treatment at doses of 10.0 or 12.5 mg/kg body wt removed 97.6% of the adult Fasciola hepatica and 63.2%-83.8% of the Dicrocoelium dendriticum. Luxabendazole at 7.5, 10.0, and 12.5 mg/kg proved 100% effective in removing adult worms of the genera Haemonchus, Ostertagia, Trichostrongylus, Cooperia and Nematodirus as well as tissue-associated larval stages of gastrointestinal nematodes of the abomasal mucosa. The drug showed an intensity effect of 79.7%-87.6% against Strongyloides papillosus. Luxabendazole removed all Dictyocaulus filaria and reduced the fecal excretion of larvae of protostrongylid species (Protostrongylus rufescens, Neostrongylus linearis, Cystocaulus ocreatus, Muellerius capillaris) by 97.8%-99.6%. The efficacy of luxabendazole compared favorably with that of Diplin Kombi (oxyclozanide and levamisole), which was used as a reference drug.

The reversibility of intestinal immune expulsion effects on adult Nippostrongylus brasiliensis.

An attempt has been made to study the extent and nature of the damage occurring in adult Nippostrongylus brasiliensis undergoing immune expulsion from the rat. It was found that worms are not killed nor irreparably damaged when being rejected. On transfer into naive second recipient rats the rate of re-establishment of worms previously incubated in immune rat recipients for 4-17 hr was high (68-69%) and comparable to that shown by worms from normal recipient rats (48-56%). Similarly, worms taken on days 10, 11, and 12 of a primary infection, already passed to the distal half of the small intestine due to immune expulsion effects, on transfer into naive recipient rats re-established themselves well (rates varying from 62 to 80%) compared to those harvested from their normal habitat in the proximal half of the small intestine (rates varying from 44 to 87%). Worm damage is associated with decreased motility and impaired locomotion capacity. The phenomenon of mucosal trapping occurs during expulsion, but merely to the extent of some 30% of the worm population. It is suggested that in principle, worms subjected to immune expulsion are in a state of acute, transient metabolic crisis. The present results support the enteroallergic indirect mechanism for worm rejection.