Studies on resistance of sheep to infestation with Haemonchus contortus and Trichostrongylus spp., and on the immunological reactions of sheep exposed to infestation. V. The nature of the 'self-cure' phenomenon.

Abstract

An experimental investigation of the nature and the mechanism of the "self-cure" phenomenon in helminthiasis of sheep has been carried out. As a result of the "self-cure" reaction there was no release of heterologous antibodies into the blood stream of the animal. The administration of an antihistamine drug usually prevented the fall in egg count which is characteristic of the "self-cure" reaction, but did not interfere with the subsequent rise in titre of the specific or homologous antibody in the serum. On 7 of 13 occasions when sheep showed the "self-cure" reaction, the blood histamine level rose to about 0.05 µg per ml. during a period of about 24 hours between the second and fourth day after the administration of larvae. On none of 13 occasions when sheep failed to manifest "self-cure" was there any rise in blood histamine. The difference in behaviour of the two groups was significant statistically. The rise in blood histamine was demonstrated when sheep infested with either H. contortus or Trichostrongylus spp. were given H. contortus larvae and manifested the "self-cure" reaction. It was shown to occur also when "self-cure" occurred in sheep infested with Trichostrongylus spp. following the administration of Trichostrongylus spp. larvae. Increase in blood histamine was not demonstrated when Trichostrongylus spp. larvae were given to seven sheen infested with H. contortus and when "self-cure" did not take place. The increase in blood histamine as not associated with any consistent alteration in the concentration of eosinophils. There was no evidence that the increase in blood histamine was the direct cause of "self-cure". Sheep which manifested "self-cure" showed a strong local reaction to the intradermal inoculation of H. contortus antigen. Continued infestation with mature H. contortus or with mature Trichostrongylus spp. did not sensitize the sheep and sheep which failed to manifest "self-cure" did not exhibit an intradermal reaction. An oedematous change was evident in the mucous membrane of the Abomasum or small intestine, depending upon the site of attachment of the adults, on the day on which a rise in blood histamine occurred after the administration of larvae. The intake of H. contortus larvae produced this change only in the abomasum of a sheep which had been infested with H. contortus and only in the small intestine of a sheep which had been infested with Trichostrongylus spp.

Studies on the Role of Histamine and 5-Hydroxytryptamine in Immunity against the Nematode <i>Trichostrongylus colubriformis</i>

“…There is some evidence that nematodes may be expelled by immunologically non-specific treatments [Briggs, 1963;Panter, 1969], and Stewart [1950Stewart [ , 1953 has shown that 'self cure' reactions in sheep rein fected with the abomasal nematode Haemonchus contortus may lead to the expulsion of other nematode species occupying the abomasum or small intestine. These observations suggest that for worm expulsion, some immunologically non-specific effector mechanism, acting on the parasite and/or the parasitized tissues, occurs.…”

A comparison of the spring-rise phenomenon in the faecal nematode-egg counts of housed sheep with that of sheep grazing infective pasture

“…14 an experimental infec.tio~, were suddenly terminated ~te'r about:ten week's and thereafter !limbs 'diat .had undergone the 'self -cure mechanism were resfstant to challenge doses of infective larvae. The self-cure mechanism lias been extensively 'investlgated by Stewart (-1953Stewart (- , 1955) 'in Australia who found it to occur when a challenge dose of larvae is given to a suitably sensitized and infected sheep-.-· This resUlts in a marked local response in the mucosa of the abomasum, accompanied by·a significant rise in blood histamine and a marked antibody response. Soulsby (1962) believes that, in the case of the spriIig-rise phenomenon, high pasture burdens of infective larvae would be expected to 'occur as a result o~ the marked egg output duriIig the spring-'Fise and these would be sufficient to initiate' tIie response.…”

Immunity: Host Response

“…Anaphylactic shock induced by a nonhelminth antigen accelerated the elimination of Haemonchus contortus adult worms from sheep (Stewart 1953) and prevented the establishment of Nematospiroides dubius in mice (Panter 1969), but it did not eliminate established N. brasiliensis from rats (Ogilvie 1967, Barth et al, 1966. It has been suggested that they may be involved in the sudden elimination of parasites found in some helminth diseases (also known by the nonimmunological term "self-cure").…”