Maintenance and transmission of vesicular stomatitis viruses: New data for an old puzzle

Abstract

Insect and rodent samples were collected from suspected VSV-NJ enzootic areas over 2 consecutive field seasons (1996-1997) and from southern Arizona only during 1998. Insect samples were screened for arboviruses, and rodent sera were tested for the presence of VSV-NJ and VSV-IN neutralizing antibodies. Vesicular stomatitis virus New Jersey serotype was isolated from a pool of Culicoides sp. collected in 1997 near Belen, New Mexico. All rodent sera were negative for specific VSV-NJ and VSV-IN antibodies. Genetic analysis of the hypervariable region of the phosphoprotein gene demonstrated that the 1997 Belen VSV-NJ isolate was more closely related to viruses isolated from livestock during the 1982-83 western U.S. epizootic than to other VSV-NJ isolates. This suggests that VSV-NJ may be enzootic in the western U.S. Simulium vittatum was shown to be a competent vector of VSV-NJ. Virus-infected females were allowed to feed on laboratory mice and on deer mice. All laboratory mice seroconverted by day 21 post-exposure. Neutralizing antibody titers increased from an average of 1:4 at baseline to >1:1,024 on day 21. An age-related effect on viral pathogenesis was evident in Peromyscus maniculatus following VSV-NJ exposure by black fly bite. Lethal encephalomyelitis was evident in all 6-week-old mice, but in only one 6-month-old mouse. Peromyscus maniculatus did not meet the standard definition of a reservoir host for VSV-NJ because a viremia, was not detected. Nonetheless, P. maniculatus may play a role in virus maintenance since non-infected black flies became infected while co-feeding with infected black flies on the same non-viremic host. These results represent the first example of a western U.S. insect species becoming infected with VSV-NJ by feeding on a host. Simulium vinatum and S. notatum were shown to be competent laboratory vectors of VSV-IN. Saliva from experimentally infected Simulium vittatum and S. notatum was collected and tested for the presence of infectious virus. Virus was detected in the saliva of both species following oral infection. Independent experiments were conducted to determine if transovarial transmission of VSV-NJ and VSV-IN occurs in black flies. Transovarial transmission was not detected. Transstadial transmission of both virus serotypes was detected.