An entero-like virus associated with the runting syndrome in broiler chickens

A small round unenveloped virus, 31 nm in diameter, and with no obvious surface structure, was identified during the first week of life in the gut contents of broiler chickens which later developed runting. This virus grew in the cytoplasm of the villous epithelial cells of the small intestine, with a predilection for the mid small intestine. Broilers orally infected at 1 day old with a crude inoculum containing the small round virus and reovirus passed abnormal faeces, gained weight and feathered more slowly than controls, which were either uninoculated or inoculated with faeces from SPF chicks. The small round virus was passaged four times through broilers using gut contents collected from experimentally infected birds between 2 and 3 days after inoculation. Clinical signs as described above were obtained at each passage. The small round virus could not be grown serially in cell cultures. However, immunofluorescence showed that viral antigen was synthesised in the cytoplasm of infected chicken embryo liver and chick kidney cell cultures. The small round virus was resistant to pH3. It is suggested that the small round virus is an enterovirus but no evidence for an antigenic relationship with avian encephalomyelitis virus was obtained.