Abstract
The present studies were performed to investigate whether the removal of the previously infected site of caeca would influence the subsequent maintenance of immunity to Eimeria tenella in chickens. The chickens used in the studies were White Leghorn males of 2 to 2.5 weeks of age fed an all-mash ration containing no antibiotics or coccidiostats. The results are summarized as follows.
1. Chickens were initially infected by asingle injection of sporozoite suspensions into the lumina of the left caeca isolated from the intestinal tracts, by means of ligation. Approximately two weeks later, the opposite right caeca of these chickens were challenged per os with sporulated oocysts, and thereafter the number of daily discharged oocysts was counted for seven days after the infection.
Chickens in which the ligated left caeca were previously infected with sporozoites showed remarkable resistance to the challenge with oocysts, in comparison with the controls not previously infected withthem. This confirmed the previous works (BURNS and CHALLEY, 1959; HORTON-SMITH et al., 1961) that the resistance to Eimeria tenella in chickens was not limited at the site of the initial infection.
2. Chickens were previously immunized by a single injection of sporozoite suspensions into the lumina of the ligated left caeca. The left caeca of these chickens were surgically removed approximately two weeks after the sporozoite infection. Thesubsequent maintenance of immunity inchickens was determined by daily measurements of discharged oocysts after the oral infection of oocysts.
From the measurements of discharged oocysts, it was found that there is little difference in the resistance to the challenge infection between the chickens with a single caecum and the controls. This suggests that the presence of the actually exposed site to the parasites is not essential for the subsequent maintenance of immunity to Eimeria tenella.
