Experimental induction of malignant catarrhal fever in pigs with ovine herpesvirus 2 by intranasal nebulization

Malignant catarrhal fever (MCF), a frequently fatal herpesviral disease primarily of ruminant species, has been sporadically reported in pigs. All cases of naturally occurring porcine MCF reported to date have been linked to ovine herpesvirus 2 (OvHV-2), a gammaherpesvirus in the genus Macavirus carried by sheep. Experimental induction of MCF by aerosolization of the virus in nasal secretions collected from infected sheep has been successful in bison, cattle and rabbits. The goals of this study were to determine the susceptibility of pigs to MCF following experimental intranasal inoculation of OvHV-2, and to characterize the disease. Twelve pigs in four groups were nebulized with 10(5), 10(6), 10(7), or 10(8) DNA copies of OvHV-2 from sheep nasal secretions. Three control pigs were nebulized with nasal secretions from uninfected sheep. Three additional pigs were inoculated intravenously with 10(7) DNA copies of OvHV-2 to evaluate this route of infection with cell-free virus. Seven of twelve intranasally challenged pigs became infected with OvHV-2. Five of these seven, all in higher dose groups, developed MCF. Lesions resembled those reported in natural cases of porcine MCF. The most striking and consistent histological lesions were in trachea, lung, kidney and brain. These comprised mucopurulent tracheitis, interstitial pneumonia, necrotizing arteritis-periarteritis, and nonpurulent meningoencephalitis. No infection was established in the intravenously challenged or control groups. The study showed that MCF can be experimentally induced in pigs by aerosol challenge using sheep nasal secretions containing OvHV-2. Domestic pigs are a natural clinically susceptible host for sheep-associated MCF. They represent a useful, cost-effective model for MCF research.