Retrospective diagnosis of bluetongue virus in stored frozen and fixed tissue samples using PCR.

Stored frozen (-70 degrees C) and formalin-fixed tissue samples constitute a valuable resource for retrospective studies of infectious diseases, or for diagnostic investigations. The polymerase chain reaction (PCR) affords an accurate and rapid method for detection of viral nucleic acids. It was applied to stored tissue samples collected from sheep inoculated with two Australian serotypes of bluetongue virus, BTV 1 and 23, and two North American serotypes, BTV 11 and 17. Specific nested PCR products were detected in both frozen and formalin-fixed samples from the Australian sheep after storage for 3.5 years. The tissues from sheep inoculated with the North American serotypes yielded specific nested PCR products after storage at -70 degrees C for 14 years. No specific primary PCR products were detected in any frozen or formalin-fixed samples. The PCR assay offers a potential benefit for epidemiological studies, and for screening of stored semen, embryos and tissue banks.