The effects of host age on the poultry cestode, Raillietina cesticillus (Molin, 1858) Fuhrmann, 1920

Abstract

The present study has shown that age resistance to R. cesticillus, manifested by worm destrobilization, occurred in male chickens. In females, age resistance developed more rapidly than in males, until the birds were about 84 days old and from this age onwards the manifestations of resistance declined. The roles of immune responses, mucus secretion and host hormone balance in the development of age resistance to R. cesticillus were subsequently investigated. Host resistance to superinfection with R. cesticillus was demonstrated for the first time and this resistance was inhibited by the immunosuppressant dexamethasone. Further evidence for the immunogenicity of the cestode was provided by histological studies and by the demonstration of immunocytes and of ring precipitin and immunofluorescent antibodies. Experimental evidence suggested that these antibodies are not protective and it is probable the protective immune response is cellular. An in vitro culture system, described by Schiller (1970), kept young adult cestodes in an active condition for more than eight days, although growth was poor. Chicken intestinal mucus extracts were shown to be lethal to R.cesticillus in vitro and mucus from old birds appeared to have a greater effect than 'young' mucus. The effects of gonadal steroids on the course of infection of R. cesticillus were investigated by caponising male birds and implanting oestradiol or testosterone pellets. This procedure reproduced to some degree the patterns of infection of R. cesticillus observed in intact, untreated, mature birds. Scolex transplantation and the correlation of worm weights down the intestine with destrobilization strongly implicated intestinal environmental factors as being responsible for the phenomenon of worm destrobilization. The possible mechanisms whereby the immune response, mucus secretions and host hormone balance affect worm viability are discussed.