Search

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.

The objective of this study was to show the existence of genetic variability in resistance of Creole goats to natural infection with intestinal nematodes. Four successive cohorts of male and female kids were reared from weaning during 9 months in intensive pangola pastures (stocking rate 1.4 t/ha, regrowth of 21 days, 300 kg N/ ha/year of fertilization). All cohorts considered, 203 offsprings from 13 bucks and 149 goats were used in the experiment. Animals were treated with an oral dose of ivermectin every seven weeks, from 3 to 11 months of age. They were sampled for fecal egg counts (FEC) and packed cell volume (PCV), 6 weeks after drenching, when 6 and 10 months old. Haemonchus contortus and Trichostrongylus colubriformis were the predominant species. Data of one cohort when 6 months of age and another one when 10 months old were not included in calculations because a self-cure occurred during a rainy season. Estimated means of FEC after square-root transformation were 1054 and 711 respectively for 6-month-old and 10-month-old kids. Phenotypic correlations between FEC and PCV were -0.46 (p < 0.001) and -0.29 (p < 0.01) when 6 and 10 months old, respectively. FEC repeatabilities estimated as variance ratio were 0.47 and 0.06 for within-age measures (data recorded at one week interval) and between age measures (6 vs. 10 months) respectively. No sire effect was significant for PCV. Sire effect on FEC was more significant when 6 months old (p < 0.03) than when 10 months old (p < 0.15). Further studies are now being carried out to confirm this genetic determinism of resistance to natural infection with strongyles in Creole goats.

In merino sheep bred for either increased or decreased resistance to Haemonchus contortus, faecal worm egg counts (FEC) were lower in the resistant line (6,831 vs 17,645 epg, P < 0.01), and circulating eosinophils (EOS) were higher, but not significantly so (3.40 x 10(4) ml(-1) vs 1.40 x 10(4) ml(-1), P = 0.1 1). Another flock was artificially infected with Trichostrongylus colubriformis and significant genetic variation was found in both FEC (heritability 0.40 +/- 0.11) and EOS (0.19 +/- 0.08). In a third flock comprising tropical sheep breeds, a natural challenge with T. colubriformis resulted in significant sire effects on FEC (heritability 0.20 +/- 0.10) but not EOS (heritability inestimable). We conclude that EOS offers no advantage over FEC as it selection criterion for resistance.

In two experiments, groups of calves were exposed to different levels and patterns of infection with Ostertagia spp. and Cooperia spp. The experimental design simulated the stereotypic pattern of herbage infestation, including both as normal and a delayed midsummer increase, under conditions of set-stocking. After this simulated 'first grazing season', calves were followed during the subsequent winter housing. At the end of that housing period some calves were challenged with 100,000 L3 Cooperia spp. and 40,000 L3 Ostertagia spp. and slaughtered 23 days later. All previously infected calves were protected against the establishment of the challenge infection with Cooperia spp., but not against Ostertagia spp. For the latter a significant negative correlation was found between worm count and previous level of exposure to infection. During the simulated first grazing season, changes in the ratio of Cooperia to Ostertagia eggs in the faecal egg output and the genus-specific egg count were influenced by both the level of exposure and the timing of the midsummer increase. It is concluded that acquired immunity against both parasite genera develops depending on the level of exposure to infection during a first grazing season, and that delaying the midsummer increase results in a delay of the acquisition of an effective immunity as measured by faecal egg counts and the ratio of Cooperia to Ostertagia egg output.

The total and IgG1 antibody responses to the intestinal nematode parasites Haemonchus contortus and Trichostrongylus colubriformis were measured in the serum of 160 lambs, 4 months of age. These antibodies had developed as the result of natural exposure to the parasites on pasture. Three sires were examined and strong sire effects on half-sib progeny were found. Plotting of ELISA antibody results in two dimensions revealed clustering of responses within sire groups. Bimodal antibody distributions were also observed within sire groups and the whole population for T. colubriformis. A bimodal distribution of antibodies to H. contortus was found for one sire group but not for the whole population. The injection of blowfly larvae (Lucilia cuprina) extract into 42/160 lambs at a later age (12 months) was followed by increased antibodies to L. cuprina and an apparent increase in antibodies to T. colubriformis. A bimodal distribution for antibodies to L. cuprina was found in one sire group and in the whole population. These bimodal distributions of antibodies to L. cuprina did not coincide with the distribution of antibodies to T. colubriformis or H. contortus, measured on the same serum samples. It was concluded that high and low responder sire groups could be differentiated in lamb populations for all three parasites. These effects persisted during lamb maturation and appeared to be genetic effects. Finally, cross-reacting antibodies between L. cuprina and T. colubriformis appear to be stimulated by injection of L. cuprina antigens.

The generation of bone marrow and blood haemopoietic progenitor colony-forming cells (CFCs) in sheep given primary or challenge infections with the nematode parasite Telodorsagia circumcincta is described. Ten days after a primary infection, the frequency of early multipotential-CFCs, eosinophil-CFCs, macrophage-CFCs and mast cell or basophil-CFCs was greater than in controls. These frequencies then declined to pre-infection levels by day 21. Blood CFCs (mainly macrophage-CFCs and eosinophil-CFCs) also increased after infection, indicating a migration of CFCs, presumably to the site of infection. Ten days after challenge infection there was less marked myelopoiesis than in the primary infection on day 10, though both eosinophil-CFCs and mast cell or basophil-CFCs were significantly above control values. Blood CFC output (mainly macrophage-CFCs and eosinophil-CFCs) reached a peak 2-6 days after challenge, evidence of rapid recruitment to the site of infection. Telodorsagia circumcincta infection is therefore associated with an increase in myelopoiesis, particularly for the cell types characteristic of the local inflammatory response to abomasal nematodes. There was no correlation between any of the haemopoietic cell responses measured and worm burdens in individual animals after either primary or challenge infection.

A preliminary trial on the extent of cross-antigenicity among the sheep strongylids Haemonchus contortus, Trichostrongylus colubriformis, Teladorsagia circumcincta and Nematodirus battus in 2.5- to 4-month-old lambs has been carried out using ELISA and Western blotting (WB). Cross antigenicity was tested using soluble extracts from adult and third stage larvae (L3) of H. contortus as antigenic source probed with sera from lambs with monospecific heterologous infections. There was cross-antigenicity between L3 of H. contortus and Trichostrongylus colubriformis in ELISA and WB. Immunodetection results with adult H. contortus antigen showed a closer relationship to Teladorsagia circumcincta. Certain heterologous sera reacted with H. contortus antigens more strongly than the homologous one, but sera from the H. contortus-infected animals had reactivity around the 25 kDa region from adult antigens which could have potential diagnostic use.

This paper reviews the previous mathematical and conceptual models for the parasitic phase of a range of trichostrongylid nematode parasites of cattle and sheep. It reassesses the results of single and trickle infection experiments and suggests as a working hypothesis that the common trichostrongylids are essentially identical with respect to the processes that determine their survivorship in the host. Parasite abundance in the parasitic phase is explained in terms of immune exclusion, which acts on recently ingested third stage larvae, and mortality of established (fifth stage) parasites. The functional forms used to describe immune exclusion and the mortality of fifth stage worms are defined, respectively, as a declining sigmoid and an asymptotic curve.

The present studies were designed to investigate whether experimental, mixed trichostrongyle infections of stabled calves prior to their first grazing season could confer sufficient immunity to significantly reduce egg excretion after turnout, and thereby prevent loss-producing infections later on. The study comprised four groups, each of seven calves. During spring, two of the groups received two different dose levels of infective larvae twice weekly, and one group received larger larval doses at monthly intervals. One group served as non-experimentally exposed controls. In May all groups grazed separately on similarly contaminated plots. All experimental groups had reduced egg counts, and herbage infectivity of their plots was significantly lower than that of the controls. These findings were reflected in serum pepsinogen levels and in specific serum antibody responses. Additionally, clinical disease was only observed in the control group animals.

Fourteen male cross-bred Alpine x Saanen kids were infected with Teladorsagia circumcincta and four were used as controls. Three different levels of susceptibility to infection were apparent: resistant to infection and resilient to its adverse effects; intermediate (poorly resistant and poorly resilient); susceptible and relatively resilient. In the susceptible kids the establishment rate of infective larvae was twice as large and the nematode egg output five times greater during Weeks 4-8 after infection than in resistant kids. Susceptible kids harboured larger females with higher numbers of eggs in utero; the proportion of Teladorsagia trifurcata was higher in susceptible than in resistant kids. The blood constituents were significantly modified in infected compared with control animals: a lower number of leucocytes (particularly lymphocytes and basophils) and a higher complement activity were recorded in the latter. Compared with resistant kids, susceptible kids had higher counts of leucocytes, basophils and lower lymphocyte levels, less depleted complement pathway activity, higher pepsinogen values and lower levels of albumin and glucose.

Antibodies against Ostertagia spp., Cooperia spp. and Dictyocaulus viviparus were assessed in serum and individual milk samples of cows and in bulk milk samples from the refrigerating tank. Titres in milk samples were related to serum titers, but also influenced by milk yield, lactation stage and age of the cow. Correlation coefficients between serum and individual milk samples were highly significant, and varied from 0.42 to 0.56. Correlations between herd means of serum titres and herd means of individual milk titres varied from 0.41 to 0.61, and those between herd means of serum titres and means of bulk milk samples from 0.43 to 0.67. Finally, the correlations between herd means of individual milk samples and means of bulk milk samples varied from 0.52 to 0.82. This variation was dependent upon worm species and whether or not correction for milk yield was applied. The discrimination of herds was evaluated by the between/within herd ratio of variances. F-values for all types of samples were highly significant, and at least as high for milk samples as for serum samples. If, as has been shown for serum samples, a positive relationship exists between the milk yield response to anthelmintic treatment and the mean herd titre of milk samples or bulk milk samples, assessment of these titres could offer a rational basis for treatment of dairy cows.

Cooperia oncophora total adult extracts were examined by Western blotting with sera from C. oncophora- and O. ostertagi-infected calves to determine species-specific antigens. It was shown that two antigens with apparent molecular weights of 14.2 and 14.9 kDa were only recognized by calves which received a Cooperia infection and not by Ostertagia mono-infected calves or parasite-naive animals. The partial purification of these two antigens was achieved by gel filtration and ion-exchange chromatography. An enzyme-linked immunosorbent assay (ELISA) was developed based on the fractions containing these two antigens and no cross-reactivity could be noticed with serum from Ostertagia mono-infected calves. In contrast, the ELISA with total worm extracts showed strong cross-reactivity with heterologous serum. It was concluded that the 14.2 and 14.9 kDa Cooperia adult antigens have diagnostic potential, at least to differentiate C. oncophora and O. ostertagi.

An experiment was conducted in calves to investigate the efficacy of a morantel sustained release trilaminate bolus (MSRT) to control gastrointestinal parasitism and to assess the development of immunity during the use of MSRT. Two groups (M and U) of four calves each were infected three times a week with a mixed Ostertagia ostertagi and Cooperia oncophora infection for 12 weeks. Calves of Group M received an MSRT at the start of the experiment. Twenty weeks after the start of the experiment, all animals, including a previously uninfected control group (C), received a challenge with 100,000 Ostertagia and 100,000 Cooperia. After a further 4 weeks all calves were necropsied for worm counts. During the trial calves were weighed and faecal egg counts, larval differentiation and pepsinogen concentrations were determined. The results demonstrated the high level of efficacy of the MSRT in reducing the faecal egg output and preventing parasitic gastroenteritis under conditions of a continuous high rate of infection. Efficacy of treatment was higher for Cooperia than for Ostertagia. Post-mortem worm counts suggested a partially impaired immunity build-up in Group M, at least for Cooperia.

Calves were infected repeatedly during a period of 6 weeks with Ostertagia ostertagi and Cooperia oncophora, at an age of 3, 6 or 9 months. The inoculations were performed during three periods, February-March, May-June and August-September, to account for possible seasonal effects or effects of larval batches. Observations were done on faecal egg output, antibody titres and weight gains. Calves were slaughtered for post mortem examinations 9 weeks after the start of infections. The influence of age on worm populations and egg output was significant for C. oncophora but not for O. ostertagi. The effect of season or larval batch on worm populations was significant for O. ostertagi but not for C. oncophora. The correlations between worm numbers and several other parameters found for Cooperia were strongly indicative of a process of worm expulsion taking place at the stage of infection (9 weeks after the start of infections) when post mortem examinations were done. Such correlations were absent for Ostertagia. It is concluded that within the range of ages examined here (the range to which first season grazing calves belong), there is no influence of age on Ostertagia populations but a clear effect of age on Cooperia. This difference strongly influences the total faecal egg output of grazing calves and its interpretation.

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. The sequence of three separate cDNA clones predicts the polypeptide to be about 15 kDa, with four N-linked carbohydrate chains and an internal disulphide bond. The clones also indicate the existence of sequence variability in this antigen. Limited sequence homology to a porcine intestinal peptide suggests an influence on host gut physiology.

Infection of rats with 2000 infective juveniles of Nippostrongylus brasiliensis and of lambs with 60 000 infective juveniles of Nematodirus battus results in a well-marked immunity to these nematodes in their respective host. There is a fall in the adenylate energy charge value of these nematodes during the course of these infections, reaching values of 0.37 in males and 0.27 in females of N. brasiliensis, and 0.31 in males and 0.23 in females of N. battus towards the end of the infections. In hosts given relatively small numbers of infective juveniles, the values for the nematodes removed from the hosts late in the infection remain at a relatively high level. These results indicate that the immune response of the host may affect the energy status of these nematodes, and this could help to explain their subsequent expulsion from the immune host.

Monoclonal antibodies to ovine lymphocyte surface antigens were used in an immunohistochemical study of the intestine of sheep. In the epithelium CD8+ cells predominated whereas the majority of lamina propria T lymphocytes were CD4+. Infection of sheep with the parasitic nematode Trichostrongylus colubriformis including sufficiently large numbers of parasites to induce protective immunity did not alter the number of CD4+ or CD8+ lymphocytes in the intestinal mucosa. In contrast, exposure of naive sheep to a single large infection of T. colubriformis resulted in a substantial decrease in number of CD8+ cells and moderate decreases in number of CD4+ cells in the duodenal but not the jejunal mucosa. MHC class II antigens were not detected either in or on epithelial cells of the sheep small intestine.

As the infection progresses in lambs, the developing germ cells of male Nematodirus battus become filled with lysosome-like bodies, electron-dense granules and membrane-bound vesicles, and the organization and division of the gametic nucleus appears to be altered. The epithelial cells of the reproductive tract are also damaged and the secretory-type globules produced by the cells of the vas deferens are denatured. These changes are compared with ultrastructural changes observed in other species of nematode affected by the immune response of their hosts.

Primary immune expulsion of Trichuris muris was markedly delayed by concurrent infection with Nematospiroides dubius. Maximum delay of expulsion was dependent on size and timing of N. dubius infection relative to T. muris infection. In NIH mice infection with 400 N. dubius larvae immediately before or after T. muris infection was found to be most effective in suppressing expulsion. Infection on day 8 of T. muris infection, when mice are sensitized to T. muris, also impaired expulsion. From this evidence it is suggested that the larvae of N. dubius are immunosuppressive and that the efferent role of the immune response to T. muris is inhibited. The results are discussed in terms of non-specific immunosuppression and their relevance to the tropical disease situation is emphasized.

A temporal relationship was established between the onset of expulsion of the parasitic nematode Trichostrongylus colubriformis from the intestine of both vaccinated and adoptively immunized guinea pigs with a sudden increase in small intestinal mucosal histamine to two or three times pre-infection levels. However, in guinea pigs whose capacity to expel T. colubriformis was inhibited by treatment with anti-lymphocyte serum, mucosal histamine remained at pre-infection levels. The results support previous findings which suggest an important role for histamine in the effector mechanism of the immune response of guinea pigs against T. colubriformis.

The effect of repeated intradermal injections of small quantities of adult worm extract on the resistance of calves to Cooperia spp. was investigated. A group of five calves injected intradermally was less resistant than a similar group inoculated twice with infective larvae, but more resistant than a group of five calves kept as worm-free controls. The resistance was reflected by worm numbers, worm lengths, inhibition percentage of L4 larvae, number of eggs per female worm, egg production and by antibody titres.

Groups of previously infected and worm-free sheep were serially killed up to 10 days after challenge with 50 000 Ostertagia circumcincta larvae. Two similar groups of sheep were killed 10 days after challenge with 1000 larvae. The previously infected sheep were resistant to the smaller challenge dose in that fewer, stunted worms were recovered from them than from controls. However, this resistance was not as marked as that observed in the previously infected sheep which received the large challenge, because proportionally fewer worms were recovered after the 50000 dose and the great majority of these were arrested at the early fourth stage. The gastric lymph ducts of 6 previously infected sheep were cannulated successfully and a marked local immune response was detected in 3 sheep which were challenged with 50 000 larvae. No response was detected in 3 cannulated sheep challenged with 1000 larvae. In the lymph of the 50 000 dose group, a temporary increase in pepsinogen activity suggested that a hypersensitivity reaction related to the presence of large numbers of mucosal mast cells began between 24 and 48 h after challenge. This was followed by marked increases in the cellular and IgA content of lymph, which reached peaks on days 3 and 6, respectively. It is suggested that the response detected in the gastric lymph reflected aspects of a local immune reaction in the abomasal mucosa and that this reaction accounted for the enhanced degree of resistance to the larger challenge dose.

Sows repeatedly infected with large single doses of third stage infective Hyostrongylus rubidus larvae show an anamnestic circulating agglutinin response to the parasite as detected by the passive haemagglutination reaction. At farrowing the circulating antibody level dropped, whereas the colostral agglutinating antibody level increased for a period of a few hours. The predominant class of immunoglobulin which had agglutinating activity against H. rubidus was IgG. Offspring which had suckled the infected mothers had a demonstrable agglutinin titre 4 days after birth, whereas offspring which suckled non-infected mothers had no demonstable agglutinins. On infection of the offspring, those which suckled infected mothers showed a more rapid and pronounced increase and duration of circulating agglutinins than those which had suckled noninfected mothers. The parasitic burden, as determined by the duration of egg laying and total egg output, was considerably lower for the group reared on the infected mothers. These experiments show that passively transferred agglutinating antibodies, mainly of the IgG class, were associated with protection.

Rats subjected to a 7-day abbreviated enteral infection with Trichinella spiralis subsequently reject more than 90% of a challenge infection within 24 h. This process is known as rapid expulsion. In these experiments parabiotic rats were used to examine the factors that establish rapid expulsion in the intestine. Induction with low to moderate doses of worms required exposure to two separate stimuli. These initiated different responses; one was readily transferred between parabiotic rats, whereas the second response was sessile and restricted to the intestine. These two responses interacted synergistically to produce strong rapid expulsion. Stage-specific exposure of parabiotic rats to preadult or adult trichinae (or the unrelated parasite Heligmosomoides polygyrus) showed that only preadult worms induced the transferable factor. Exposure to adult worms or to H. polygyrus induced a strictly local intestinal effect that was nonspecific. It is suggested that preadult worms initiated an immune response specific for preadults. This was transferable between parabionts but was unable to produce rapid expulsion unless the intestine had been non-specifically stimulated. Intestinal stimulation is accomplished by exposure to adult worms in natural infections or artificial regimes. These results suggest novel techniques for the development of enteral antihelminth vaccines.

Interactions between gastrointestinal worms (Ostertagia ostertagi, Cooperia oncophora) and lungworms (Dictyocaulus viviparus) in calves were studied by assessing the effect of primary infections with either group of worms on the development of homologous or heterologous challenge infections. Primary infections with lungworms resulted in some degree of resistance to challenge with gastrointestinal worms, but this resistance was lower than that found after homologous infection. Primary infections with gastrointestinal worms did not confer any resistance to challenge with lungworms. On the contrary, an indication was found of some enhancing effect of previous gastrointestinal worm infection on the establishment of lungworms. The highest degree of resistance against lungworm challenge was found where calves have been primarily infected with lungworms. Lungworm infections produced some elevation of serum pepsinogen levels. Gastrointestinal worms evoked a rise in circulating eosinophils, although this rise was smaller and occurred later than in lungworm-infected calves. Under the conditions of the experiment, the effect of 6000 infective lungworm larvae on weight gain was larger than the effect of 100,000 L3 of Ostertagia ostertagi and 100,000 L3 of Cooperia oncophora.

The influence of genes in the major histocompatibility complex (MHC) of the guinea pig on the susceptibility to infection with the parasitic nematode Trichostrongylus colubriformis was investigated. Back-cross analysis of 2 lines of guinea pigs suggests that genes that map in or near the I region of the guinea pig MHC influence susceptibility to infection by the parasite. However, other genes, possibly not linked to the guinea pig MHC, may also be required for the full expression of susceptibility.

Lymphocytic responses in peripheral blood and visceral lymph to Cooperia oncophora antigen and skin tests were determined in 35 Holstein male calves that were inoculated orally with single or multiple doses of C oncophora infective larvae. Several calves were vaccinated or given immune serum before larvae were inoculated. Antigen-specific in vitro blastogenesis of blood and lymph lymphocytes and delayed-type hypersensitivity reactions were observed in several inoculated, vaccinated, and/or passively immunized calves. Most calves that had delayed skin reactions also had in vitro lymphocyte responses to C oncophora antigen. The lymphocyte and skin responses were inconsistent and variable in time of onset--the earliest lymphocyte response occurring 7 days after calves were inoculated. A cellular immune response was induced by both dermal vaccination and oral inoculation; however, passive immunization by IV administration of immune serum simultaneously with inoculation did not have an apparent effect on the cellular response, as measured by the lymphocyte blastogenesis test or dermal testing. Although cellular immune responses were observed in several calves infected with C oncophora, there was no apparent relationship between the specific responses and number of nematodes establishing infection in calves after either single- or multiple-dose oral inoculations.

The intraduodenal injection of synthetic prostaglandins did not lead to the expulsion of Trichostrongylus colubriformis from the intestine of guinea pigs. Treatment of immune guinea pigs with aspirin and indomethacin failed to inhibit the expulsion of a challenge infection with this nematode. These results suggest that in this infection, unlike Nippostrongylus brasiliensis infection in the rat, prostaglandins do not play an important role in the immune expulsion of the parasite from the intestine.

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. IgA antibodies to this protein were also found in intestinal lymph of a naturally infected sheep. Fluorescent antibody studies indicated that this 94 kDa component was associated with cells in the central body cavity of third-stage larvae, but was absent from fourth-stage larvae or adult worms. Fractionation and protection assays in guinea pigs revealed that while the native and aggregated 94 kDa protein conferred some host protection, it was not the only protective component of the excretory-secretory products of exsheathed third-stage larvae of T. colubriformis.

Serum IgE concentration has been considered a valuable measurement in parasitic infections, yet little has been reported regarding cattle. This study examines the association of IgE levels of nematode-naïve Holstein steer calves and the level of gastrointestinal parasitism acquired by grazing irrigated pasture for 30 days. Total IgE levels were determined by enzyme-linked immunosorbent assay (ELISA) specific for bovine IgE on serum collected both before and after exposure to parasite-infected pastures. Following necropsy, parasite loads were determined by direct count from the contents of the abomasum, small intestine, cecum and large intestine; species of Ostertagia and Cooperia being the most common helminths found. Significant increases of IgE in the serum of calves with light infestations were seen, whereas calves with moderate to heavy infestations showed only mild IgE increases. With increased parasite burden, the frequency of increased IgE levels was reduced. Additionally, there appeared to be a seasonal correlation relating the level of serum IgE detected to the number of worms counted and to the course of parasite development.

During expulsion by guniea-pigs of both first and second infections with the intestinal nematode parasite Trichostrongylus colubriformis, increased numbers of basophils and eosinophils were present in the bone marrow and blood. In addition, increased numbers of basophils, mast cells and eosinophils, many possessing reduced numbers of cytoplasmic granules, accumulated at the sites of infection. Blood eosinophil counts, however, did not show significant changes during the early part of a first infection.

The suppression of immune responsiveness to heterologous antigenic stimulation during concurrent infection with Nematospiroides dubius was reproduced using soluble antigens derived from adult parasites. Immunosuppression appeared to be selective in that the administration of equivalent quantities of an irrelevant heterogeneous antigen had no immunosuppressive effect, and suppression was transferable using spleen cells from parasite antigen-treated donors. The differential immunomodulatory activity of parasite antigens from a variety of nematode species suggested that a correlation might exist between suppressor activity and chronicity of infection. A role for suppressor T cell activity in the infected host was implicated by the restorative effect of 2'deoxyguanosine treatment on the immune response, and non-specific suppressor cell activity was detected in splenocyte populations from infected mice. It is suggested that a parasite-induced defect in antigen processing led to the induction of suppressor cell activity in the infected host and that this may be one mechanism of parasite survival. The relevance of these observations to vaccination against chronic gastrointestinal nematode infections is discussed.

Resistance to challenge infection with Trichostrongylus colubriformis was studied in an outbred strain of guinea-pigs. Resistance was conferred by previous infections of 50 or 100 infective larvae and by intraperitoneal, intramuscular and subcutaneous administration of dialysed transfer factor prepared from guniea-pigs infected with T. colubriformis, by intraperitoneal administration of transfer factor prepared from the blood of sheep infected with T. colubriformis and on one of three occasions using transfer factor prepared from guinea-pigs which had not been infected with T. colubriformis. No significant resistance was transferred by administration of antigen prepared from adult T. colubriformis, or by non-dialysed transfer factor, or by dialysed transfer factor prepared from T. colubriformis-infected guinea-pig tissue which had been stored for several months at - 20 degrees C.

The faecal egg counts and worm burdens of mice selected over 7 generations as refractory (R), random (Rd) or liable (L) to primary infection with Nematospiroides dubius were significantly different, but the antibody titres (generation 8 mice) after 21 days infection were similar, demonstrating that selection had separated populations of mice which differed in their innate immunity. Variations in adaptive immunity were also shown between the three colonies in terms of protection after challenge infections, self-cure reactions, humoral antibody titres and ability of immune serum from R, Rd and L donors to passively protect recipient Quackenbush (Q) strain mice. R mice were more refractory to primary infection and more proficient in acquiring protective levels of adaptive immunity than L colony mice. Correlation of the faecal parasite egg count after primary with that after secondary infection supported the conclusion that the genetic control of liability to primary infection and of the adaptive immune response following challenge infections were at least partially linked.