2012 Annual Report
1a.Objectives (from AD-416):
1. Elucidate the virus-vector-host interactions responsible for virulence and transmission.
1.1. Determine the tissue tropism in natural hosts after insect transmission and the events mediating viral infection, early pathogenesis, and transmission
1.2. Characterize the mechanisms of insect-to-insect transmission while co-feeding in cattle and assess the role of cattle as amplifying hosts for VSV.
1.3. Test the potentiation of VSV infection by S. vittatum salivary factors.
1.4. Testing virulence and transmissibility of VSV strains making incursions into northern Mexico (and/or southwestern US).
2. Ascertain the viral ecology of disease and factors mediating the re-emergence of VSV in the US.
Genetically characterize the viral strains circulating in endemic areas of Mexico and the epidemiological and ecological factors associated with the emergence and maintenance of specific viral genetic lineages in endemic versus non-endemic settings.
1b.Approach (from AD-416):
1. To examine the virus-vector-host interactions responsible for virulence and transmission, studies will be conducted to determine tissue tropism in cattle after viral infection through insect bite, and the events mediating viral infection, early pathogenesis and transmission. The mechanisms of insect-to-insect transmission while co-feeding in cattle will be characterized and the role of cattle of amplifying hosts for VSV will be assessed. Tests will be conducted to determine the level of potentiation of VSV infection by black fly (Simulium Vittatum) salivary gland factors. Studies will be conducted on the virulence and transmissibility of VSV strains making incursions into northern Mexico.
2. Viral strains circulating in endemic areas of Mexico will be genetically characterized, and the epidemiological and ecological factors associated with emergence and maintenance of the specific viral genetic lineages in endemic settings will be analyzed in comparison to non-endemic virus strains.
In FY 2012 we initiated studies aimed at testing if black fly (S. vittatum) salivary factors potentiate Vesicular Stomatitis Virus (VSV) infection. VSV infection results in more severe disease after insect transmission than after needle inoculation. Studies were initiated to establish in-vitro systems to assess the effect of insect salivary factors on cell innate response and viral growth. Primary embryonic bovine kidney (EBK) cells pre-treated or untreated with salivary gland extracts (SGE) from black flies (Simulium vittatum) were infected with VSNJV. However, innate response was undetectable and viral growth was not enhanced by SGE treatment. These results were attributable to the fact that VSV on its own inhibits innate responses in vitro and requires no additional help from the SGE treatment. Alternate approaches are being explored to evaluate the effect of SGE In viral growth in-vitro.
In June 2012 an outbreak of VSNJV started in New Mexico. An ORISE research fellow was recruited to initiate work on the viral ecology and disease re-emergence (objective 2). A large number of viral strains collected between 2005 and 2011 were obtained through Mexico’s Exotic Animal Disease Laboratory (EADL). Strains were genetically characterized and it was determined that a predominant genetic lineage was able to migrate from endemic areas in southern Mexico to northern Mexico, causing severe outbreaks in northern Mexico, very close to the US border in 2009-2010. It is suspected that this viral lineage caused outbreaks in southwestern US in 2009 and 2010, however no viral strains from those outbreaks were available for comparison. In 2012 an outbreak in New Mexico began and the viral strain causing this outbreak was shown to be almost identical to the Mexican genetic lineage predominating in northern Mexico in 2008-2010. This is the first time a direct incursion of a viral strain from endemic regions of Mexico to southern US was predicted at least a year before it occurred.
Characterization of Exotic South American Vesicular Stomatitis Virus (VSV) strains. South American strains of VSV are exotic to the US and pose a threat to US agriculture. Little was known about the genetic makeup of these viruses. ARS researchers at Greenport, New York sequenced the complete genomes of exotic VSV strains and compared with strains occurring in the US. We determined that current molecular diagnostic tests require to be adjusted to detect these pathogens. This work was documented in a recent publication.
Pauszek, S.J., Barrera, J.C., Goldberg, T., Allende, R., Rodriguez, L.L. 2011. Genetic and antigenic relationships of veicular stomatitis viruses from South America. Archives of Virology. 156(11):1961-1968.