Diagnosis of malignant catarrhal fever by PCR using formalin-fixed, paraffin-embedded tissues.

A previously described polymerase chain reaction (PCR) assay (amplification of a 238-bp fragment of ovine herpesvirus 2 [OHV-2] genomic DNA) for diagnosis of sheep-associated malignant catarrhal fever (MCF) was adapted for use on formalin-fixed, paraffin-embedded tissues. Variables affecting its use were examined. Archived tissues from cattle, white-tailed deer (Odocoileus virginianus), and bison (Bison bison) diagnosed with MCF by clinical signs or histologic lesions were obtained from 2 veterinary diagnostic laboratories. Tissues from healthy animals and from animals diagnosed with other common bovine viral diseases were examined as controls. A total of 86 blocks from 37 suspect MCF cases were examined. Forty-one blocks from healthy animals and animals with unrelated viral diseases were examined as controls. The assay was specific for sheep-associated MCF and did not yield false-positive signals from healthy animals or from cases of infectious bovine rhinotracheitis, bovine virus diarrhea, mucosal disease, or parainfluenza-3 virus infection. A wide variety of tissues were suitable substrates, including spleen, lymph node, intestine, brain, lung, and kidney. Extracted DNA provided a more suitable target than did unextracted tissue lysate. The highest levels of viral DNA were present in lymphoid organs and intestine, but the data indicate that in acute clinical cases, most organs contain sufficient viral DNA to serve as a suitable diagnostic specimen. Fixation of 0.5-cm3 blocks of tissue in 10% neutral buffered formalin was deleterious to the target DNA, and PCR signals progressively diminished after fixation for >45 days. Detection of genomic DNA of OHV-2 by PCR was successful for archived tissues that were 15 years old.