Elevated Methemoglobin in the Pathology of Avian Coccidia (Protozoa, Apicomplexa) and Histomonas (Protozoa, Sarcomastigophora)

Abstract

Inflammation of tissues causes an increase in peroxide formation, which may directly cause the irreversible oxidation of hemoglobin to methemoglobin (Paul and Sbarra, 1968, Biochem. Biophys. Acta 156: 168-178; Cohen and Hochstein, 1961, Science 134: 1756). Such oxidation lowers the oxygen-carrying capacity of blood and may contribute to the pathogenicity of many types of infections. After a preliminary experiment indicated that methemoglobin is indeed elevated in chicken coccidiosis infections, we conducted a series of experiments to characterize the methemoglobinemia during coccidiosis infections and to compare this disease with histomoniasis in the turkey. Four species of coccidia were used, since there is considerable variation among species in virulence, type of lesions caused and location in the intestinal tract. Groups of 20 chicks (2-wk-old, parasite-free, Arbor Acres cockerels) were inoculated with sporulated oocysts of Eimeria tenella, E. maxima, E. brunetti, or E. necatrix which had been isolated from commercial poultry farms. The dose of oocysts was selected from prior titration in susceptible chicks. To provide birds for daily collection of blood samples, 100 chicks were inoculated with E. tenella and 10 were selected at random each day. Heparinized blood samples were taken at the peak of the infection (on days 4-7 postinoculation) (Experiment 1), or throughout the infection (Experiment 2). Other samples collected in heparinized capillary tubes were centrifuged for determination of packed cell volume (PCV). Intestinal lesions were graded at necropsy according to Johnson and Reid (1970, Expl Parasit. 28: 3036). Groups of 20 turkey poults (male, Nicholas) were infected with blackhead disease at 4 wk of age by cloacal inoculation of Histomonas meleagridis cultured in vitro (McDougald and Gal-