A possible role of caesium radiations in the control of propagation of hookworm.

Faeces charcoal mixtures containing eggs of sheep hookworm, Haemonchus contortus were exposed to caesium radiations (23 r to 1656 r) from 1st to 7th day of incubation. Each plate was exposed only once. A dose related inhibition of transformation of eggs to infective larvae was observed. The maximum effect was observed on 2nd day of incubation. The radiation has maximum effect on the 1st stage larvae followed by 2nd stage. The 3rd stage or ineffective larvae are relatively resistant to the effect of radiation.

Influence of dietary protein on the immune responsiveness of sheep to Haemonchus contortus.

Twenty helminth-free lambs were fed diets containing either 169 g crude protein (CP) kg-1 dry matter (DM) or 88 g CP kg-1 DM from the age of seven months. One month later five lambs from each dietary group were vaccinated against Haemonchus contortus by the oral administration of 10,000 irradiated larvae on two occasions, four weeks apart. Four weeks following the administration of the second dose of irradiated larvae both the vaccinated and unvaccinated lambs were exposed to an experimental infection of 10,000 non-irradiated H contortus larvae Faecal egg output and haematological changes were monitored throughout the study. The lambs were slaughtered 28 days after challenge when worm burdens were assessed. Vaccination was equally successful in inducing a strong resistance to the challenge infection regardless of dietary status. It was concluded that dietary protein does not influence the response to vaccination with irradiated H contortus larvae of lambs more than seven months old.

Some factors influencing the immunisation of sheep with irradiated Haemonchus contortus larvae.

Over the last 6 years a number of experiments in which sheep were successfully immunised with 2 doses of 10 000 Haemonchus contortus larvae, irradiated at 60 krad in a gamma-source, have been reported by the authors. In this paper, the failure of such a regimen of immunisation, using the same strain of larvae, is reported together with an investigation of the possible causes. Technical errors were eliminated as a cause, on the grounds that the failure occurred in 2 separate laboratories using different 60Co sources, as was increased radiosensitivity of the continuously passaged strain of H. contortus as measured by the percentage development of irradiated larvae in 6 naive lambs. From experiments utilising 18 lambs and using both irradiated and normal larvae, it was postulated that the strain had lost its original degree of immunogenicity. Subsequently, in 2 experiments involving 27 lambs, it was shown that irradiation at 40 krad was completely successful in restoring immunogenicity and producing a degree of protection against challenge similar to that previously reported with 60 krad. It was concluded that, with the current strain of H. contortus, 60 krad is now too high a level of irradiation of larvae to produce a consistently high degree of protection against challenge.