Studies on the host-parasite relationship between Trichostrongylus colubriformis and susceptible and resistant sheep.

This study examined whether infective larvae (L3) of Trichostrongylus colubriformis could establish throughout the small intestine and were not restricted to the anterior duodenum in susceptible and resistant sheep. The location of worms was similar in susceptible animals given doses of T. colubriformis between 10,000 and 80,00 T.

Effect of Freund's adjuvants on guinea pigs infected with, or vaccinated against, Trichostrongylus colubriformis.

Soluble antigens that protected guinea pigs against experimental challenge with Trichostrongylus colubriformis were found to be less effective if injected as emulsions in Freund's adjuvants. This occurred despite the production of higher antibody titres in guinea pigs given emulsified antigen. Investigations of this phenomenon showed that an intraperitoneal injection of Freund's complete adjuvant (FCA) delayed rejection of primary infections and partially abrogated resistance to challenge infection.

Expulsion of Trichostrongylus colubriformis by high and low responder guinea-pigs.

Guinea-pigs with genetically determined susceptibility to infection with Trichostrongylus colubriformis (or low responders) rejected both primary and secondary infections with this parasite more slowly than resistant animals (high responders). Low responders were not protected with a vaccination procedure which was highly effective in outbred animals. The relatively poor protective immune responses that develop in low responder guinea-pigs are evocative of the responses of the natural host to infection with this parasite and suggest that low responder guinea-pigs have potential for the study of T.

Changes in inflammatory mediators and larval inhibitory activity in intestinal contents and mucus during primary and challenge infections of sheep with Trichostrongylus colubriformis.

Helminthologically naive merino sheep were given either a single infection of 30,000 or a trickle infection of 6000 Trichostrongylus colubriformis infective larvae (TcL3) per week. Faecal egg counts started to fall after 8 weeks in the single infection and after 11 weeks in the trickle infection. Small intestinal contents were collected from indwelling intestinal fistulae over the next 14 weeks.

Rejection of heterologous nematodes by sheep immunized with larval or adult Trichostrongylus colubriformis.

Sheep immunized by truncated larval infections or by the adoptive transfer of adult Trichostrongylus colubriformis were subsequently challenged with single infections of T. colubriformis, Nematodirus spathiger, Haemonchus contortus or Ostertagia circumcincta or combinations of the parasites. Sheep vaccinated with larval infections were > 90% protected by 4 days after challenge (DAC) against T.

Production of vaccines against gastrointestinal nematodes of livestock.

Three international collaborations involving Australian research scientists are currently developing vaccines against Haemonchus, Trichostrongylus and Ostertagia parasites using recombinant DNA technology. The variety of protective antigens identified can be classified as 'conventional' (stimulate naturally acquired immunity) or 'novel'/'convert'/'concealed' (protective once immunity is induced by vaccination). To date, the most gratifying progress has resulted in 60-90% protection against Haemonchus and other blood-sucking parasites (e.

A new simplified assay for larval migration inhibition.

A simple method is described for the in vitro detection of substances that impair the motility of third-stage larvae of gastro-intestinal nematodes. The test is based on the ability of larvae to freely migrate through selected mesh sizes of nylon sieves and the reduced ability of larvae to migrate after preincubation with, and in the presence of, substances that inhibit or reduce larval motility.

A serial study of rejection of Trichostrongylus colubriformis by immune sheep.

Host responses and the rejection of worms were measured at intervals following challenge of immune and susceptible sheep with T. colubriformis infective larvae. Immune sheep rejected most of their larvae within the first day after infection.

Studies of stage-specific immunity against Trichostrongylus colubriformis in sheep: immunization with adult parasites.

Merino sheep immunized by the adoptive transfer of adult T. colubriformis for 8 weeks were significantly protected against a challenge infection of 20,000 larvae. Two additional groups of sheep received a primary infection of 9000 adult worms which were allowed to persist for 14 weeks before one group was drenched.

Studies of stage-specific immunity against Trichostrongylus colubriformis in sheep: immunization by normal and truncated infections.

Sheep immunized with multiple normal infections of 30,000 Trichostrongylus colubriformis larvae (T.c. L3) suppressed the fecundity, establishment and survival of adoptively transferred adult worms, showing that these parasites were susceptible to the effects of host immunity.

The isolation, characterization and cloning of a globin-like, host-protective antigen from the excretory-secretory products of Trichostrongylus colubriformis.

An 18-kDa component from the excretory-secretory (ES) products of adults of Trichostrongylus colubriformis was isolated and characterized, and was shown to induce 60-84% protection of guinea pigs from challenge infection following a single intraperitoneal injection. Amino-terminal sequence analysis of gel-purified protein enabled oligonucleotides to be synthesized and used to screen a lambda gt10 cDNA library made from young adult worm mRNA, and to synthesize full-length clones from cDNA using the polymerase chain reaction (PCR). The full-length clones coded for a 20-kDa precursor protein of 173 amino acids which had a strongly hydrophobic leader sequence of 15 residues.

Effects of Freund's adjuvants on local, draining and circulating lymphocyte populations in sheep.

Lymphatic cannulation and serial biopsy were used to examine changes in cell traffic and lymphocyte populations after injection of adjuvant in order to explain the mechanisms of the subversive effect that Freund's adjuvants (FA) have on protective immunity against nematode parasites in sheep. Within 4 days of intradermal injection of complete or incomplete FA into sheep there was a selective depletion of the T19+ TCY gamma delta+ T lymphocyte subpopulation from efferent lymph draining the local lymph node. Transient depletion of CD8+, T19+ and CD5+ cells from jugular blood was evident at day 2.

Purified glutathione S-transferases from parasites as candidate protective antigens.

Glutathione S-transferase (GST) activity was detected in larvae of the Australian sheep blowfly Lucilia cuprina, and in the nematode Haemonchus contortus. A specific inhibitor of the enzyme was shown to affect survival of both species of parasite in vitro. GST from both parasites has been purified and partially characterized.

Correlation between gut hypersensitivity and resistance to Trichostrongylus colubriformis infection of outbred and inbred lines of guinea pigs.

The relationship between gut sensitivity and immunity to challenge infection was examined in outbred and inbred guinea pig lines. Primary infections terminated at 3,6,9 or 13 days and multiple infections of 3 days' duration confirmed the importance of direct gut stimulation and the period of exposure in the induction of immunity and gut hypersensitivity. The studies with the multiple 3-day infections confirmed that the third-stage larvae alone are capable of inducing strong protective immunity and showed that this is accompanied by pronounced gut sensitivity to parasite extracts and secretions.

Molecular characterisation of a protective, 11-kDa excretory-secretory protein from the parasitic stages of Trichostrongylus colubriformis.

An 11-kDa protein occurring as a major component of the non-glycosylated fraction of 4th larval stage (L4) and adult Trichostrongylus colubriformis excretory-secretory (ES) fluid has been found to be highly protective in guinea pigs, an alternate host for T. colubriformis. The protein has been purified, characterised and partly sequenced.

Vaccines against gastrointestinal nematode parasites of ruminants.

A consequence of intensive livestock production is an increase in the incidence and impact of gastrointestinal (GI) parasites. Farmers have sought to redress this shift in the natural host-parasite relationship by chemotherapy. However, with the widespread development of resistance to anthelmintics and the current impetus for sustainable agricultural practices, alternatives such as vaccines are being sought to maintain animal productivity.

The response of immune sheep to challenge with Trichostrongylus colubriformis: enteric plasma loss and secretion of biogenic amines.

Sheep were challenged with a single large dose of larvae after vaccination with irradiated Trichostrongylus colubriformis larvae. Worm counts performed on vaccinated sheep 6 or 7 days after challenge (DAC) showed that they were solidly immune and only retarded L3 larvae were recovered at this time. Enteric plasma loss (EPL) in vaccinated animals increased immediately after challenge to peak 4-6 DAC and then decreased to pre-challenge levels.

Characterization, cloning and host-protective activity of a 30-kilodalton glycoprotein secreted by the parasitic stages of Trichostrongylus colubriformis.

The helminth Trichostrongylus colubriformis is a parasitic nematode infecting the small intestine of sheep. We report the isolation and characterization of a 30-kDa glycoprotein capable of partially protecting guinea-pigs against the parasite. This glycoprotein is secreted by the L4 and adult parasitic stages of the worm.

Gut hypersensitivity reactions in guinea pigs following vaccination or infection with Trichostrongylus colubriformis.

A quantitative approach to measuring gut hypersensitivity responses to parasite antigens is described. Guinea pigs exposed to infection with Trichostrongylus colubriformis, were sensitised to excretory-secretory products and homogenates of third-stage larvae (L3), fourth-stage larvae (L4) and adult worms. The nature of these responses and their modification by pharmacological agents were typical of immediate-type hypersensitivity reactions.

Characterization of the major immunogen in the excretory-secretory products of exsheathed third-stage larvae of Trichostrongylus colubriformis.

The excretory-secretory products of exsheathed third-stage larvae of Trichostrongylus colubriformis conferred some protection to guinea pigs against homologous challenge. A glycoprotein with an apparent molecular mass of approximately 94 kDa was the dominant immunogen in post-exsheathment products. Immunoblots revealed IgG antibodies to this glycoprotein in sera from multiply-infected guinea pigs and some sheep, and in sera of guinea pigs after three truncated infections which had been restricted by anthelmintic treatments to development of the third parasitic stage.

A novel host-protective antigen from Trichostrongylus colubriformis.

The detergent-soluble fraction from Trichostrongylus colubriformis third-stage larvae contained a simple set of antigens, one of which (molecular weight 41,000) induced 43-51% protection in guinea pigs following immunization. Isolation and partial amino acid sequence analysis of this protective antigen showed it was parasite tropomyosin.

Experimental Haemonchus contortus infections in guinea pigs.

Approximately 40% of exsheathed Haemonchus contortus larvae administered to guinea pigs established in the stomach and developed into fourth stage larvae. Most worms were then lost between 5 and 7 days after infection and the guinea pigs were resistant to a second infection. Haemorrhage, oedema and infiltration with inflammatory cells, especially eosinophils, developed in the stomach wall of infected guinea pigs and reactive hyperplastic changes occurred in the gastric lymph node.

Relationship between the resistance of cattle to Haemaphysalis longicornis and to Boophilus microplus.

Cattle that had been exposed to Haemaphysalis longicornis were as susceptible to Boophilus microplus as cattle that had never been exposed to either species of tick. Cattle with acquired resistance to both species ranked consistently for levels of resistance to each when infested separately. Concurrent infestation with H.