Age-Related Susceptibility of Turkeys to Enteric Viruses.

Several different enteric viruses have been identified as the causes of gastrointestinal infections in poultry. Enteric virus infections are well characterized in poults, but limited studies have been conducted in older birds. The susceptibility of 2-, 7-, 12-, 30-, and 52-wk-old turkeys to turkey coronavirus (TCoV) and turkey astrovirus (TAstV) was evaluated, as well as the effect of combined infection of TAstV and TCoV in 2-wk-old poults and turkey hens. From cloacal swabs and intestines, TCoV was consistently detected by reverse transcriptase-PCR throughout the experimental period (1-21 days postinoculation [DPI]) from all age groups. In contrast, the last detection point of TAstV gradually decreased to 21, 16, and 12 DPI in birds inoculated at 2, 7, and 12 wk of age, respectively, and viral RNA was rarely detected from cloacal swabs or intestinal contents in turkey hens within 3 DPI. Infection with TAstV alone did not affect body weight in poults or egg production in hens. The combined infection of TAstV and TCoV did not induce more severe clinical signs and pathology than the TCoV infection alone. However, a severe prolonged decrease in egg production (about 50%) was observed in turkey hens in the combined infection group compared with a transient egg production drop in the TCoV-infected hens alone. The underlying mechanism regarding the age-related TAstV susceptibility and the pathogenesis of the TAstV and TCoV coinfection in layer hens needs to be further elucidated.