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[en] The effect of ionizing radiations on helminth parasites has been under investigation now for about half a century, but only in the last 15 years has extensive and intensive work been conducted. The results have shown that in numerous host-parasite systems, ionizing radiation has attenuated or partially inactivated the parasite and that infection of host animals with irradiated larvae has stimulated immunity without accompanying disease. The immunity of vaccinated animals has subsequently been challenged by infection with normal larvae and, while unvaccinated control animals have suffered severely from the resultant disease and have often died, vaccinated animals survived the challenge of immunity usually without significant signs of disease. Comparison of the worm burdens from challenge infections in vaccinated and in control animals have further confirmed the protective effect of prior vaccination with irradiated larvae. In addition to economically important helminth diseases, various host-parasite relationships in laboratory animals have been investigated and the immunogenic efficacy of X-irradiated vaccines has been further demonstrated. There are at present two irradiated vaccines in commercial use in veterinary practice and their value has been unequivocally proven. It is probable that within the next few years at least one additional irradiated vaccine will be in use in veterinary practice. Some of die concepts and principles involved in the preparation, use and possible method of action of irradiated vaccines, with particular reference to a vaccine for hookworm disease of dogs, are described. (author)
[en] The lymphocytotoxic effect of sera in mice relatively slowly (C3H/W) or strongly (BDF1) responding to T. spiralis infection was found to be higher in the latter than in the former. The effect was also induced by irradiation. The suppressive action of ionizing radiation on the immunological system of the host, expressed by enhanced intensity of invasion has been confirmed. 6 refs. (author)
[en] In order to confirm whether acquired immunity or resistance can be developed by the repeated hookworm infections, the 150 mature actively moving filariform ancylostoma duodenale larvae obtained from the severe hookworm anemia patients were orally given to 8 healthy volunteers in three divided doses, 50 in each, at 5 day interval. Also the hematological changes as well as several ferrokinetics using 59Fe were done and were compared with 10 controls. The clinical symptoms and signs were checked every day for the first 3 weeks and then twice weekly until the end of the experiment. The appearance of the ova in the stool was examined by the formalin ether method and the ova was counted by the Stoll's method. The following laboratory tests were done:1) Red blood cell count, venous blood hematocrit (micromethod), hemoglobin count (cyanomethemoglobin method) were checked every 5 to 7 day interval. 2) Plasma iron concentration (Barkan's modified method) was determined every 2 to 3 week interval. 3) Radioisotope studies:a) Ferrokinetics: Huff et al and Bothwell's method were applied. Erythropoietic Index (% of normal)= [Subject's turnover/100 ml whole bloodX100] over [Average normal turnover/100 ml whole blood] b) Quantitative measurement of the gastrointestinal absorption of iron:Radioiron (59Fe) balance method was applied. c) Determination of the plasma erythropoietin activity: Fried's method was applied. Following were the results: 1) The serum iron level was lower. The red cell volume was decreased, but with relative increase of plasma volume. 2) The plasma iron disappearance time was accelerated and the plasma iron turnover rate was decreased. The red cell iron turnover rate was markedly increased, while all of the red cell iron concentration, circulating red cell iron, plasma iron pool were decreased. The daily iron pool turnover and red cell renewal rate were increased. 3) The erythropoietic index, erythropoietin activity and intestinal absorption of iron (59Fe) were markedly increased. 4) The infectivity was 9.8±1.31% which was lower than that observed in the single infection. 5) From these observations, it is concluded that the hookworm anemia is essentially iron deficiency in its origin and some immunity acquisition is possible with repeated infections.
[en] The pathogenicity of varying levels of single and repeated infections with Dictyocaulus filaria in local Ethiopian Highland lambs and Hampshire X Ethiopian Highland cross-bred lambs is described. Mortality, increased respiration rates, impaired weight gain or loss of weight were observed in infected animals, often in association with low parasite burdens. The disease was more severe in lambs receiving higher infective doses and the local Ethiopian Highland lambs were more susceptible to D.filaria infection than the Hampshire cross-bred lambs. In a field vaccination trial, it was shown that administration of two doses of irradiated D. filaria larvae conferred a high degree of protection against challenge with normal larvae and resulted in increased weight gains compared with non-vaccinated animals. However, the greatest weight gains were recorded in sheep given a combination of vaccination and treatment with a broad-spectrum anthelmintic, indicating that both strategies are required for efficient parasite control in the Ethiopian highlands. (author). 15 refs, 5 figs, 6 tabs