An adenovirus, designated T-75 isolant, was isolated from the cloacal swab of a clinically normal turkey, 13 weeks old. The T-75 isolant was identified as an adenovirus on the basis of physicochemical properties, cytopathology, and agar-gel precipitin test. Producing two-way cross-neutralization reactions with CELO virus, the isolant was classified as an avian adenovirus of serotype 1. The T-75 isolant was pathogenic to both chicks and turkey poults, causing hepatitis, respiratory disease, atrophy of the bursa of Fabricius, and/or growth depression of experimentally inoculated birds, varying with the host and route of inoculation.

Cell smears of chicken-embryo-fibroblast (CEF) cultures and bursa of Fabricius from chickens experimentally infected with six different strains of infectious bursal disease virus (IBDV) were examined for the presence of IBDV by the avidin-biotin-peroxidase complex method of immunoperoxidase (IP) staining using a monoclonal antibody specific for IBDV designated BK70. IBDV of different strains and serotypes were readily detected by the IP method in cell smears prepared from infected CEF cultures and from bursas. Bursal cells were positive for IP stain in most of the infected bursas (87.5%), despite their mild IBD lesions. Positive IP staining of bursal smears was well correlated with the recovery of IBDV from the bursas and with IBD lesions in the bursas. IP stain with a monoclonal antibody (BK70) appeared potentially useful for rapid and definitive diagnosis of IBD.

The growth and plaque formation by turkey herpesvirus (HVT) amd Marek's disease herpesvirus (MDHV) were examined in QT35 cells, a continuous fibroblast cell line derived from chemically induced tumors of Japanese quail. HVT grew and formed plaques consistently in QT35 cells when inoculated with cell-culture-propagated virus or peripheral mononuclear leukocytes (PML) from chickens that had been inoculated with HVT. Both oncogenic and nononcogenic strains of MDHV, however, failed to grow and induced neither plaques nor cytopathic effects in QT35 cells, whether inoculated with cell-culture-grown virus or heavily infected PML. When PML from chickens infected with both HVT and MDHV were assayed, only HVT plaques had developed, despite the presence in the inocula of high levels of MDHV with less HVT. The QT35 cell line provides a simple in vitro system for differentiating between HVT and MDHV and for selective isolation and identification of HVT from chickens infected with both HVT and MDHV.

An experimental line of White Leghorns (WSU-VS) and a commerical line inoculated with turkey herpesvirus (HVT) at 1 or 8 weeks old did not differ in the occurrence of infectious cell-free HVT in their feather-tip preparations (FT-HVT). The birds examined at 2 weeks postinoculation (PI) were always positive for FT-HVT regardless of age at virus inoculation, dose of HVT inoculated, or genetic line of chickens, whereas only a few were positive at 4 weeks and none at 6 weeks PI.

Sonic extraction of cell-free Marek's disease herpesvirus (MDHV) and turkey herpesvirus (HVT) from infected cell cultures was improved by incorporating sorbitol in the suspending media. Yields of cell-free virus of virulent MDHV were significantly increased with 10% sorbitol added to SPGA-EDTA buffer. Avirulent strains of MDHV and HVT were respectively readily extracted with SPGA-EDTA and SPGA as the suspending medium, and extraction of their cell-free viruses was moderately improved by adding sorbitol to the suspending medium.