Effect of x-irradiation upon the infective larvae of ancylostoma caninum and the immunogenic effect in dogs of a single infection with 40 kr-irradiated larvae

TLDR: The effects of X-irradiation on the parasite and an attempt to immunize dogs by a single vaccination regime using such irradiated larvae are described.

Abstract: X-irradiation of the infective larvae of Ancylostoma caninum reduces the infectivity of the larvae as measured by subsequent intestinal establishment of adult hookworms. As the dose of radiation is increased the infectivity of the larvae is decreased and the pathogenicity to the host of the resulting burden of hookworms is reduced. Male larvae are more sensitive to the effects of X-irradiation than are female larvae, particularly at the higher levels of irradiation. At radiation doses of 40 kr and greater the female worms in the resulting population are invariably sterile. A single subcutaneous vaccination of dogs aged 3 months with 1,000 40 kr-irradiated larvae confers a highly significant resistance. This vaccination confers highly satisfactory resistance to the pathogenic effects of such a challenge, when measured in terms of hematological, clinical, and coprological changes. In a number of host-helminth systems it has been shown that the previous administration of X-irradiated infective larvae will protect the host against a potentially pathogenic challenge of normal larvae. The present state of these helminth vaccines has been surveyed by Urquhart et al. (1962). The work of Herrick (1928), McCoy (1931), Foster (1935), Otto and Kerr (1939), and Otto (1941) has demonstrated that dogs can be immunized against subsequent severe challenge of Ancylostoma caninum by the administration of normal infective larvae. This resistance to challenge was manifested by reduced worm establishment from the challenge of normal larvae, and in some cases also by a reduction in worm egg output. Cort and Otto (1940) and Otto (1948) have surveyed the literature on the subject of experimental vaccination against ancylostomiasis in dogs. Many of the recorded results describe experiments in which stray or "pound" dogs of unknown age and originating from hookworm enzootic areas were used. Resistance shown to challenge infection in these often uncontrolled experiments, ascribed by the author to Received for publication 27 April 1964. be a result of either age or acquired immunity, appears retrospectively and in the light of current knowledge to have been, in many cases, a combination of both manifestations of resistance. This paper describes the effects of X-irradiation on the parasite and an attempt to immunize dogs by a single vaccination regime using such irradiated larvae. MATERIALS AND METHODS Since this is the first of such reports, the details of technique are described in full. Acquisition and preparation of experimental animals Dogs of mixed breeding were purchased from dealers as newly weaned litters at the age of 6 weeks and were isolated in small groups until approximately 3 months of age. During this period they were vaccinated against canine distemper, contagious canine hepatitis, and leptospiroses canicola and icterohaemorrhagiae (Canilep-Glaxo Laboratories, Ltd., Greenford, England) and were treated twice with piperazine adipate for ascarids (Coopane-Cooper, MacDougall and Robertson, Ltd., Berkhamsted, England). Repeated fecal examination of all dogs after purchase and prior to any anthelminthic medication has demonstrated the absence of strongyle eggs and hence precludes the possibility of prior exposure to hookworm (including Uncinaria stenocephal7).