Attenuation phenotype of the recombinant AH/AA<i>ca</i> virus in chickens.

aSix-week-old specific-pathogen free chickens were inoculated i.n. with 106 EID50 of virus in a 0.1-ml volume. Swabs were collected from the birds on day 3 and day 5 postinoculation and titrated in eggs. <, virus not detected. data are means±standard deviations. No. sick/deaths/total; numbers of chickens that were sick and died, as well as the total number of chickens during the observation period. Birds that showed disease signs, such as depression and ruffled feathers, but recovered at the end of the observation were counted as sick animals. SC/total, number of chickens that seroconverted out of the total number of chickens at the end of the 2-week observation period. NA, all birds died by the end of the observation period and thus could not be studied for sera conversion. bSix-week-old white Leghorn chickens housed in high-efficiency particulate air-filtered isolators were inoculated i.v. with 0.2 ml of a 1∶10 dilution of bacterium-free allantoic fluid containing virus for intravenous pathogenicity index (IVPI) testing, based on recommendations of the Office International Des Epizooties. cOnly animals that showed disease signs but recovered by the end of the observation period were identified as sick birds.