Experimental Vesicular Stomatitis in Swine: Effects of Route of Inoculation and Steroid Treatment

Abstract

Abstract. An enzootic focus of vesicular stomatitis virus New Jersey serotype (VSV-NJ) exists on Ossabaw Island, Georgia. Many questions regarding the epizootiology of this virus at this focus still exist, but evidence suggests that the vector for this virus is a phlebotomine sand fly (Lutzomyia shannoni), with feral swine serving as a potential source of virus for the sand fly and for other swine via contact transmission. We conducted 2 experimental trials in domestic swine using VSV-NJ isolated from a sand fly from Ossabaw Island to determine if route of inoculation or immunosuppression via steroid administration affected the development of disease, viremia, viral shedding, or the neutralizing antibody response. In a third trial, we studied the potential for contact transmission among swine using this isolate. Virus isolations were made from nasal cavity or palatine tonsil of the soft palate, and VSV-NJ neutralizing antibodies developed when pigs were inoculated intradermally in the apex of the snout, ear, or coronary band, intravenously, intranasally, or via scarification of the apex of the snout or coronary band. Vesicles developed only in pigs inoculated in the apex of the snout or coronary band, and these vesicles were at the site of inoculation. Steroid treatment did not potentiate the development of secondary vesicles and did not prolong the period of virus shedding from VSV-NJ-infected swine. Contact transmission, as determined by shedding of virus from the tonsil of the soft palate and the development of VSV-NJ neutralizing antibodies, occurred in pigs in contact with animals inoculated in the apex of the snout but not in contact animals exposed to pigs inoculated intradermally in the coronary band or intranasally. These trials show that contact transmission can occur and VSV-NJ can be shed without the development of clinical disease (i.e., vesicle formation). Viremia was never detected in any of the experimental pigs, suggesting that swine may not be a good amplifying host for VSV-NJ.Vesicular stomatitis is a disease of cattle, horses, and swine caused by related viruses in the genus Vesiculovirus of the family Rhabdoviridae. An enzootic focus of vesicular stomatitis virus (VSV) New Jersey serotype (NJ) exists on Ossabaw Island, Georgia, and evidence suggests that the vector for this virus is a phlebotomine sand fly (Lutzomyia shannoni). This hypothesis is supported by field isolation of VSV-N J from sand flies 5 and through demonstration of viral replication, bite transmission, and transovarial transmission in experimentally infected sand flies.4 Numerous questions, however, remain concerning the epidemiology of this virus, especially with regard to the pathogenesis of VSV-NJ in potential amplifying vertebrate hosts. On Ossabaw Island, vesicular lesions have only been detected in feral swine, and VW-NJ has been consistently isolated from vesicles and from tonsil and nasal swabs collected from this species. The significance of these infections in feral swine as related to

Vesicular stomatitis New Jersey virus (VSNJV) infects keratinocytes and is restricted to lesion sites and local lymph nodes in the bovine, a natural host

“…This result confirms previous reports in swine, horses and cattle [10,11,14]. It could be argued that the samples tested had low titers or that infectious virus was not detectable due to virus inhibitory factors such as interferon, in the blood.…”

“…Previous studies in swine, showed that only intradermal inoculation of the snout or coronary band resulted in lesion formation [11]. Similar results were obtained by inoculation with black flies, with skin lesions observed only when flies were allowed to feed on the skin of the snout but not when they fed on the skin of the abdomen in swine [14].…”

“…Only in two out of seven coronary band-inoculated cattle, was virus found in the pharyngeal fluid, tonsils or lymph nodes draining the oropharynx. This is an interesting finding since tonsils seem to be an important site for viral replication in swine but had not previously been reported in cattle [2,11,14,23]. We could not determine the source of virus in these two cattle, but it is possible that their mouth came in close contact with their inoculated feet during the experiment.…”

“…Vesicular lesions are observed only when the virus is intradermally inoculated at specific sites where lesions are observed during natural infections (snout, lip, feet) and instead subclinical infection occurs when virus is inoculated intradermally at other sites (i.e. ear, abdomen) or by the intranasal or intravenous routes [11,15]. Recently, it was further shown that vesicular lesions only developed when experimentally infected black flies (Simulium vittatum) were allowed to feed on the snout but not when flies fed on the abdomen of swine [14].…”

Rearrangement of the Genes of Vesicular Stomatitis Virus Eliminates Clinical Disease in the Natural Host: New Strategy for Vaccine Development

“…The fifth group was inoculated with culture medium alone and maintained as mock-infected controls. Each group was kept in a separate isolation room under BL-3 conditions and monitored daily for the formation of vesicular lesions characteristic of VSV infection and for rectal temperature (11).…”