Allergy and Immunity in Coccidial Infections.

Abstract

Immunity to the several species of coccidia which occur in chickens has been thoroughly demonstrated by Tyzzer 1 and by Henry. 2 A similar host response has been shown to occur in rabbits (Bachman 3 ) and in cats and dogs (Andrews 4 ).

The purpose of this paper is to report the development of a similar immunity in guinea pigs infected with Eimeria caviae, together with the appearance of degenerate forms of the parasite in partially immune animals, observations on the production of hypersensitivity to the protein of the infecting organism, and a cutaneous hypersensitivity to E. caviae in this host.

The reinoculation of 35 previously infected guinea pigs has in all cases shown the presence of some immunity. In most cases the resistance has been sufficient to completely prevent the occurrence of clinical symptoms, which are invariably present in initial infections. While the mortality in guinea pigs upon infection with E. caviae for the first time has been found to be 40%, not one of the guinea pigs infected 2 or more times died from a typical coccidial infection.

A rather constant indication of the effect of previous infection was the altered prepatent period in cases of the second infection. While this period has been found to be exceedingly constant in all of the initial infections, a variation from 2 to 4 days from the normal 111/2-day period in the appearance of oocysts was found in most cases. A more striking indication of the effect produced by the host upon the parasite as a result of the development of partial immunity is the occurrence of degenerate cysts. These occur only in the later stages of initial infections, whereas in instances of the second to the sixth infections thus far tested they occur in the early stages, either alone or associated with normal cysts.