Prevalence of Eimeria acervulina, Eimeria necatrix, Eimeria brunetti and Eimeria tenella in Georgia (USA) as demonstrated by immunity challenge techniques.

Eimeria acervulina, E. necatrix, E. brunetti and E. tenella were found to be widely distributed in north-east Georgia. 2. Using immunity challenge techniques 17 flocks from 12 to 72 weeks of age showed significantly lower lesion scores for the first three species compared with susceptible control flocks similarly challenged. Only one flock was found to be susceptible to E. tenella. No mortality occurred in the field flocks after challenge while 20 to 60% mortality occurred in the susceptible controls. 3. Partial immunity occurred more frequently in field flocks aged 28 weeks of age or less (62%) than in older flocks (30%). Lesion scores ranged from 0-1 to 2-2 with the former and 0-1 to 0-6 with the latter group. 4. A modification of the immunity challenge method was developed using lesion scores as the major criterion determining immunity. The method permits testing of four species infecting different parts of the digestive tract in one group of birds.