ABSTRACT
This chapter focuses on the intestinal infections, such as coccidiosis, cryptosporidiosis, and salmonellosis, since they represent economically important poultry diseases. Elucidation of the events leading to protection following protozoal infection and identification of protective immunity is the focus of several current clinical and veterinary immunology studies. In most instances, infection of bursectomized chickens, showed no effect on the development of protective immunity following secondary inoculation, although bursectomized chickens were more susceptible following primary infection. Two aspects of immunity to Eimeria will be considered: innate resistance, which refers to a nonspecific immune response following primary infection; and acquired immunity, which refers to an antigen-specific immune response that occurs following secondary infection. Innate immunity is responsible for elimination of parasites during the early phase of primary infection, whereas acquired immunity to Eimeria is usually considered in the context of respect to its effect on secondary and subsequent infections.
