An in vitro and in vivo evaluation of the virulence of egg drop syndrome virus for the chicken reproductive tract.

The virulence of strains of egg drop syndrome (EDS) 1976 virus for the female reproductive tract of chickens was assessed in vitro using oviduct organ cultures (OOC) prepared from precociously induced oviducts in young chicks by oestrogen treatment. Ciliostasis, haemagglutination and virus titres in infected OOC supernatants, histology and immunoperoxidase test results indicated the pathogenic ability of the four viruses for the precocious oviducts. One of the isolates, EDS TN4, produced higher virus titres in the supernatants of infected OOC and more severe glandular atrophy and necrosis, but caused slightly delayed ciliostasis. When this isolate was used in vivo, virus could not be detected by haemagglutination, but was detected in a few birds using a polymerase chain reaction on the allantoic fluids of infected duck embryos. Ciliostasis of OOC and histological lesions were confined to early stages of infection. This technique could be a pointer to possible variations in virulence of EDS virus isolates, and warrants further investigation. The potential value of OOC from young chickens for EDS diagnosis is emphasized.