Resistance of chicks against reinfection with Leucocytozoon caulleryi.
Chickens were inoculated with five to 40 sporozoites of Leucocytozoon caulleryi at 1 to 9 days of age. Mortality, parasitemia, appearance of serum-soluble antigen, and antibodies were examined. Chickens that survived primary infection were reinoculated with 3 x 10(3) to 1 x 10(4) sporozoites and examined for resistance against reinfection by the same criteria used in primary infection. After primary infection, up to 80% of chickens died of leucocytozoonosis. Surviving chickens showed parasitemia from 13 days to 23 or 24 days after inoculation. Serum-soluble antigen and antibodies were detected in most chickens, except for some chickens that were infected at 1 to 3 days of age. After secondary infection, only a few chickens that received primary infection at 1 to 7 days of age showed a small number of parasites in their peripheral blood. Most of the other chickens were resistant to reinfection. Resistance to reinfection was recognized in some chickens that had not showed antibody production before secondary infection.