Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/15/2004
Publication Date: 3/1/2005
Citation: Li, H., O'Toole, D., Kim, O., Oaks, J.L., Crawford, T.B. 2005. Malignant catarrhal fever-like disease in sheep after intranasal inoculation with ovine herpesvirus-2. Journal of Veterinary Diagnostic Investigation. 17:171-175. Interpretive Summary: Sheep are the carriers for ovine herpesvirus 2 (OvHV-2), the causative agent for sheep-associated malignant catarrhal fever (MCF). Virtually all sheep are subclinically infected with the virus under natural flock conditions and serve as the source for viral transmission. Spontaneous cases of MCF-like disease in sheep have been suspected but never confirmed. In this study, MCF-like disease was induced experimentally in three sheep following aerosol transmission. Three MCF virus-negative sheep were aerosolized with 2 ml each of nasal secretions containing a high dose of the virus from a sheep experiencing an intensive viral shedding event. All three sheep became infected within a week and developed clinical signs with severe nasal discharge and fever around 14 days after aerosolization. One of three clinically affected sheep was euthanized for pathological examination at 18 days and the remaining two sheep recovered from the clinical disease at about 25 days. The clinical syndrome and pathological changes were distinctive, uniform, and had features similar to those of acute MCF in cattle and bison. The study revealed that clinical signs and lesions resembling MCF can develop when uninfected sheep are exposed to a high dose of the virus.
Technical Abstract: A malignant catarrhal fever (MCF)-like disease was induced experimentally in three sheep following aerosol transmission with ovine herpesvirus 2 (OvHV-2). Each of three OvHV-2 negative sheep was nebulized with 2 ml of nasal secretions containing approximately 3.7 x 10(9) OvHV-2 DNA copies from a sheep experiencing an intensive viral shedding episode. OvHV-2 DNA became detectable by PCR in the peripheral blood leukocytes of all three sheep within 3 days and animals seroconverted between 6 and 8 days post aerosolization (PA). The sheep developed clinical signs with severe nasal discharge and fever around 14 days PA. One of three clinically affected sheep was euthanized at 18 days PA. The major lesions at necropsy were multifocal linear erosions and ulcers in mucosa of the cheeks, tongue, pharynx, and proximal esophagus, and mild disseminated pneumonia. Microscopically, there was extensive moderate superficial histiocytic-lymphocytic rhinitis, with epithelial hyperplasia, disorganization, and degeneration. Moderate multifocal histiocytic bronchointerstitial pneumonia was associated with loss of terminal bronchiolar epithelium. Vasculitis was present only in the lung. The study revealed that clinical signs and lesions resembling MCF can develop when uninfected sheep are exposed to a high dose of the virus.