Observations on the gross pathology of Eimeria praecox infections in chickens.

Authors: Allen, Patricia; Jenkins, Mark; Wilkins, Gary

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2010
Publication Date: 6/1/2010
Citation: Allen, P., Jenkins, M.C., Wilkins, G.C. 2010. Observations on the gross pathology of Eimeria praecox infections in chickens. Avian Diseases. 54:834-840.

Interpretive Summary: Eimeria praecox is one of seven coccidia species that parasitize chickens, and is found in poultry houses world wide. It has been considered to be a relatively benign parasite, since infective doses of about 10 4 per chicken rarely cause morbidity, mortality or reduced weight gain. However, higher experimental infective doses can negatively impact weight gain, suggesting that this parasite could contribute substantially to production losses. Heretofore, no distinct pathological lesions have been described for E. praecox infections making it difficult to characterize and quantitate effects of infections as may become necessary in studies of interactions of this Eimeria species with some of the more pathogenic ones in production situations. In this manuscript, we have described new aspects of gross pathology and changes in blood chemistry that can be linked to development of E. praecox in the chick host. Inflammation in the duodenum and an increase in plasma NO2-+NO3- was found to be coincident with rapid asexual reproduction of the parasite during the first three days of infection. This was followed by a decrease in plasma carotenoids, a small degree of intestinal hyperplasia, production of a large amount of mucoid exudate, and excretion of oocysts. It is apparent that the acute host response to infection with E. praecox is somewhat different from, and occurs earlier than in experimental infections with other, more pathogenic Eimeria sp. These factors need to be considered when investigating pathologies of co-infections, and efficacies of live vaccines.

Technical Abstract: Challenge infections with 1 x 13, 5 x 10 4 ,1 x 10 5 ,or 5 x 10 5 sporulated oocysts of Eimeria praecox caused moderate but significant weight gain reduction at all doses. Substantial reduction in plasma carotenoids, and moderate but significant increased in plasma NO2-+NO3- only at the two higher doses when measured at day 6 post challenge (PC). Daily monitoring of chickens challenged with 50K oocysts revealed an apparent inflammatory response in the duodenum and jejunum beginning at day 1 PC, associated with significantly increased plasma levels of NO2-+NO3- which peaked at Day 4 PC. A moderate, uniform small intestinal hyperplasia and significant depression of plasma carotenoids were seen on Days 4 through 6 PC. Plasma NO2-+NO3- decreased to control levels by Day 6 PC. All infections were accompanied by production of a mucoid exudate in the duodenum and jejunum which became thick and opaque by 4 days PC and tended to obscure mildly inflamed areas. These observations indicate that the acute host response to primary infection with E. praecox is somewhat different from, and occurs earlier than in experimental infections with other Eimeria sp such as E. acervulina, E. maxima or E. tenella. These factors need to be considered when potential pathologies of co-infections of E. praecox with other coccidia, or effects of live vaccines are investigated.