Local immunity and Ostertagia circumcincta: changes in the gastric lymph of immune sheep after a challenge infection

Immunity to Ostertagia circumcincta was demonstrated in 5 previously infected sheep which were killed 10 days after challenge with 50 000 larvae. This immunity was expressed as a reduction in the number as well as the degree of development of the surviving parasites compared with those found in 6 control sheep. Gastric lymph was sampled from the immune group from 2 days before till 10 days after challenge and a secondary local immune response was detected. The main features of this response were a large increase in cell output in the lymph, especially in lymphoblasts and IgA-containing cells, which reached a peak on day 4 or 5, followed by a ten-fold increase in IgA immunoglobulin and IgA anti-worm antibody which reached a peak 7 or 8 days after challenge. The timing of these events suggested that the cellular, but not the IgA, response could have been involved in a putative mechanism which caused arrested development, although both components could have been implicated in mechanisms which may have caused expulsion of developing larvae.

Local immunity and Ostertagia circumcincta: changes in the gastric lymph of sheep after a primary infection

Some aspects of the kinetics of the primary local immune response to O. circumcincta were studied by monitoring the flow and composition of gastric lymph from 4 sheep for 3 weeks after infection with 50 000 larvae. A significant increase in the frequency of lymphoblasts in the lymph showed that all the sheep were responding immunologically to the parasites from day 8 onwards. However, considerable individual variation in degree and timing was evident in other aspects of the immune response; 2 animals responded with large increases in lymphocyte output which reached a peak on day 5 or day 10, whereas the main response in the other 2 sheep appeared to be inflammatory in nature, with large increases in lymph flow and eosinophil output which occurred during the third week of infection. No significant changes in the content of IgA or IgA anti-worm antibody were detected in the lymph, but pepsinogen concentrations were significantly raised from day 12 onwards.

[Uses of immunology in veterinary helminthology]

The uses of immunology in veterinary helminthology are reviewed. The potentialities of sero-epidemiology in bovine nematode infections are stressed. Examination of sera using the ELISA technique offers good opportunities to study the epidemiology of infections, particularly in older cattle.

Studies on the local immune response of the lactating ewe infected with Ostertagia circumcincta

Changes in the flow and composition of gastric lymph were monitored in groups of lactating and non-lactating ewes which were repeatedly infected with Ostertagia circumcincta. As judged by faecal egg counts and worm burdens the lactating group was more susceptible than the non-lactating controls to the challenge infection. Increased amounts of pepsinogen as well as larger numbers of eosinophils and neutrophils entering the gastric lymph indicated considerable abomasal damage and inflammation in the lactating ewes. However, measurement of the flow of lymphocytes as well as the amount of IgA and IgA antibody in the lymph did not indicate that these aspects of the local immune response were impaired during lactation; in fact the output of IgA-containing lymphocytes as well as IgA itself was usually raised in the lactating sheep. Lymph flow was increased and lymph globulin concentrations proportionally decreased in lactating ewes, irrespectively of whether they were infected with worms. It is suggested that these changes were caused by the increase in voluntary food intake which occurs during lactation.

Quantitative recovery of isolated mucosal mast cells and globule leucocytes from parasitised sheep

A method of the quantitative recovery of mast cells and globule leucocytes from the gastric mucosa of parasitised sheep is described. The optimal yields of viable cells from small samples of tissue digested with collagenase and hyaluronidase were measured. Mast cell/globule leucocyte yields were significantly increased in sheep orally challenged with 3000 to 5000 Ostertagia circumcincta per day. In these groups as many as 23 per cent of the cells were mast cells/globule leucocytes. Enrichment of these cells was achieved by Percoll density gradient centrifugation and fractions containing 34 to 84 per cent mast cells/globule leucocytes were isolated.

Ostertagia ostertagi infection and reinfection in cattle of different ages

Twelve cattle, three per group, were each inoculated orally with 100,000 Ostertagia ostertagi infective larvae when they were 2 months, 4.5 months, 12 months, and 24 months-old, respectively. Signs of clinical parasitism did not develop through 30 days when the infections were terminated with an anthelmintic. The cattle were each reinoculated with 500,000 O ostertagi larvae 6 days later. Groups I to III then developed anorexia and diarrhea after 3 weeks. One calf, inoculated at 2 months of age, died 27 days after reinoculation; two calves became emaciated. Group IV calves did not develop clinical signs of parasitic disease. All cattle were necropsied 42 days after reinoculation. Pathologic lesions, characteristic of type I ostertagiasis, were found in cattle of all groups; lesions were most severe in group I and least severe in group IV calves. Groups II to IV averaged 56,397 to 65,817 worms, whereas group I averaged only 29,916 worms. Group I calves expelled the worms during a period of profuse diarrhea. Cattle from 2 to 24 months old were readily infected and reinfected experimentally with O ostertagi, but the oldest cattle were most resistant to the pathogenic effects of the parasites.

Gastrointestinal nematode immunization trials in cattle

Three experiments were conducted to immunize calves against Ostertagia ostertagi, Trichostrongylus axei, and T colubriformis. Calves were given intraperitoneal injections with in vitro-grown parasitic larvae of the three species and IV and intraperitoneal injections of exoantigens obtained from culture media used to grow O ostertagi. None of the treatments provided immunity to subsequent oral challenge exposure with normal infective larvae.

The effect of age, acquired resistance, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi

An experiment is described in which the effects of age, previous infection, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi were studied. It was found that an acquired resistance to the establishment of worms developed more rapidly in 20-month-old heifers than in calves, that it was unaffected by pregnancy of the host but that it was largely lost by heifers in early lactation. The rate at which populations were turned over, i.e. the mean life-span of worms through the late 4th and 5th stages was unaffected by the factors studied. Although, in the conditions of the experiment, development of the worms was not arrested in susceptible calves, both age of the host and its previous experience of infection were significant causes of arrest, and in previously infected 20-month-old cattle 86% of the worms of a challenge infection were arrested. Pregnancy did not affect the proportion of worms that was arrested but in lactating heifers only marginally more worms were arrested than in calves. Worms that were not arrested grew more rapidly in calves and in lactating heifers than in empty heifers or those in mid-pregnancy.

Immunoglobulins in bovine ostertagiasis

Lowered albumin levels with normal or slightly elevated γ-globulin levels are well known features of various gastro-intestinal disorders in cattle. Thus, this picture is a prominent finding in clinical ostertagiasis, where hypercatabolism of both albumin (Nielsen 1966) and IgG (Nansen 1970) has been demonstrated. The hypercatabolism is explained by gastric loss, and evidence suggests that this takes place as a non-selective loss of protein through the hyperplastic abomasal wall (Murray 1969). The albumin hypercatabolism is not compensated for by an increased synthesis, and thus leads to hypoalbuminaemia also during part of the non-diarrhoeal phase. The IgG hypercatabolism, on the other hand, is compensated for by increased synthesis, which may lead to elevated serum IgG levels, especially in phases without diarrhoea. There seems to be no comparative data available for IgG-1, IgG-2, IgM, and Ig A levels in ostertagiasis. The purpose of the present study was to analyse the influence of ostertagiasis on the serum levels of immunoglobulins, albumin and total protein in young cattle. The study comprised two groups of randomly selected Red Danish calves, approx. % year old. Half the calves (Group A) grazed the same paddock from May to late September and were exposed to heavy infection from August onwards as evidenced by high herbage larval counts, high faecal egg counts, and elevated serum pepsinogen levels (see Table 1). Most of the calves were clinically affected, and in the last part of August and September some had profuse diarrhoea. The other calves (Group B) were moved in mid July to a paddock not grazed earlier that season. Accordingly, these calves were exposed to only a relatively low pasture infection in the second half of the grazing season. None of them showed clinical signs, and pepsinogen levels were only slightly elevated (Table 1).

Parasitism and calfhood diseases

That animals can and do acquire an effective immunity against helminth parasites has been demonstrated extensively experimentally, and the fact that domestic animals such as cattle, sheep, and horses become adults while maintaining good health in spite of constant exposure to reinfection long has suggested that immunity must be important to such survival. Although our attempts to date to vaccinate calves against helminth parasites have either failed or been unsatisfactory because of the pathosis induced by the experimental vaccines, the results are not surprising or discouraging. In contrast to the long history of immunization research on bacterial and viral diseases, only within a relatively short time have serious efforts been directed at exploiting hostal immunity for prevention and control of helminthic diseases. Unlike the comparatively simple structures of viruses and bacteria, helminths are complex multicellular animals with vast arrays of antigens and complicated physiological and immunological interactions with their hosts. Much more fundamental information on helminth-bovine interactions, on helminth antigens, and on cattle antibody systems must be developed before progress on control of cattle helminths by vaccination can be meaningful.

Preliminary results using metabolites and in vitro grown larvae of Ostertagia circumcincta to immunise lambs against oral challenge

An attempt was made to immunise lambs by the intra-muscular injection of concentrated metabolites obtained from the in vitro culture of Ostertagia circumcincta, by the oral administration of lyophilised metabolites or by the subcutaneous injection of living third, fourth and fifth stage worms grown in vitro. Protection appeared to have been elicited by each treatment as the worm burdens, the lengths of the worms and the faecal worm egg counts in the immunised lambs were less than those of the control lambs.