Isolation and pathogenicity of Australian strains of Eimeria praecox and Eimeria mitis.

Abstract

To determine the presence of E praecox and E mitis in Australia, to isolate representative strains of these species from chickens and determine their pathogenicity. Morphological, physiological and cross protection studies were undertaken to confirm the identity of Australian isolates of E praecox and E mitis. Oocysts were isolated from a backyard flock at Jimboomba, southeastern Queensland and numbers of E praecox and E mitis enriched by passage in chickens immune to five other species of poultry Eimeria. Oocysts of mean conformation and size of the two species were purified by single oocyst passage. Two isolates that closely matched recorded parameters for E praecox and E mitis were selected and designated JP and JM respectively. The cross protection between the isolates and E acervulina was determined by infection and challenge experiments. The virulence of the two isolates was determined by comparing weight gains of groups of birds inoculated with JP isolate or JM isolate with untreated groups. Isolates JP and JM most closely matched recorded parameters of E praecox and E mitis respectively. Groups of chickens, previously infected with JP and JM isolates, showed no significant protection against infection with E acervulina. In a separate trial, groups of susceptible chickens inoculated with 10(5) oocysts of JP and JM isolates showed significantly reduced weight gains compared with untreated controls. Isolates JP and JM are E praecox and E mitis respectively, confirming the presence of these species in Australia. These isolates were found capable of causing significant reductions in weight gains in susceptible chickens.