Pathogenicity of Eimeria brunetti in Bacteria-Free and Conventional Chickens

Abstract

In pathogenicity studies comparing bacteria-free and conventional chicks parasitized with Eimeria brunetti, mortality was 15/62 in bacteria-free birds as compared to 7/61 in chicks with conventional flora. Visual lesion scoring using a scale of 0 to 4, produced means of 2.6 in bacteria-free birds as compared to 2.4 in the conventional controls. There was no appreciable difference in weight gains, feed conversion or microscopic lesions between the two groups. Cecal lengths were shorter in bacteriafree chickens than in conventional controls. This difference was probably due to a previously unreported effect of the gnotobiotic environment. Gnotobiotic uninfected cecal lengths were similar to those of gnotobiotic infected birds. The prepatent period was 135 hr in both infected groups. Moderate coagulative necrosis of the lower small intestine, rectum and ceca was observed in bacteria-free birds as well as those with normal flora. This study establishes the fact that the presence of secondary microbial invaders is not essential for E. brunetti either to establish itself, or to induce pathological change. Intestinal parasites differ widely in their relationships to the microbiological flora present in the host digestive tract. At one extreme, Histononas meleagridis requires the presence of specific microorganisms for the production of the pathology typical of the disease, as established by Franker and Doll (1964) and Bradley and Reid (1966). On the other hand the tapeworm, Raillietina cesticillus, presents an entirely different picture in which the parasite appears to be unaffected by the presence or absence of bacterial microflora (Reid and Botero, 1967). Study of such interrelationships is of special interest to diagnosticians who have frequently speculated on the role of secondary bacterial invaders in influencing pathogenicity. Clark et al. (1962) conducted gnotobiotic studies with E. tenella and observed that there was very little difference in the pathogenicity of the coccidium between gnotobiotic and conventional chicks. There was, however, a delay of 12 to 15 hr in the appearance of the second generation merozoites in the feces of gnotobiotic chicks. In a more recent study, Visco and Burns (1966, pers. commun.) reported no mortality in 41 gnotobiotic chicks infected with Eimeria tenella as compared to Received for publication 20 August 1968. * University of Georgia College of Agriculture Experiment Stations Journal Series Paper 340, College Station, Athens, Georgia 30601. t Department of Parasitology, Veterinary College, University of Agricultural Sciences, Hebbal, Bangalore, India. t Department of Poultry Science, Auburn University, Auburn, Alabama 36830. 77% mortality in the infected conventional controls. They concluded that a close relationship exists between the host flora and E. tenella in the production of the cecal coccidiosis syndrome. Thus the effects of the bacterial flora on pathogenicity of this species remains unresolved. In the present study Eimeria brunetti was compared for pathogenicity in bacteria-free and conventional chickens. The necrosis originally described by Levine (1942) for infection of E. brunetti has been attributed by some to secondary invaders. MATERIALS AND METHODS Pathogenicity studies comparing the effects of Eimeria brunetti infection in bacteria-free chicks to those in birds with conventional microbiological flora were conducted in 1 preliminary (#1) and 3 (#2, 3, and 4) controlled trials. Sixty-two bacteria-free White Leghorn chicks were hatched and reared in 8 plastic film isolators. They were inoculated orally at 7 days of age with moderately heavy dosages of surface sterilized oocysts of E. brunetti. The quantity of inoculum (estimated at 110,000, 120,000, and 150,000 per bird in the 2nd, 3rd, and 4th trials, respectively) was determined by previous assay on conventional birds of the same age and breed. Selection of the number of oocysts in the inoculum followed a comparison of the effects of a graded series of oocyst numbers on mortality and morbidity using young susceptible birds. Sixty-one chicks of the same breed and age with conventional bacterial flora reared under the same conditions in 8 other isolators were similarly parasitized. The methods of Bradley et al. (1967) were adopted for rearing bacteria-free chicks. The coccidial oocysts were surface sterilized with 0.5% peracetic acid as described by Doll et al. (1963). In the preliminary trial (#1), 6 bacteria-free chicks reared in one isolator were inoculated with