Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2009
Publication Date: 7/1/2009
Citation: Mead, D.G., Lovett, K.R., Murphy, M.D., Pauszek, S.J., Smoliga, G.R., Gray, E.W., Noblet, R., Overmyer, J., Rodriguez, L.L. 2009. Experimental Transmission of Vesicular Stomatitis New Jersey Virus From Black Flies (Simulium vittatum) To Cattle: Clinical Outcome Is Determined By Site of Insect Feeding. Journal of Medical Entomology. 46(4):866-872.
Interpretive Summary: Vesicular stomatitis (VS) is a disease characterized by the development of vesicular lesions on the mouth, tongue, nostrils, and hooves of cattle, swine, and horses. In cattle and swine VS is easily confused with foot-and-mouth disease, a devastating disease of livestock. The causal agent, vesicular stomatitis virus (VSV) is insect transmitted and the serotype New Jersey (VSNJV) is the main cause of vesicular disease throughout the Americas. VS occurs sporadically in the western United States with the most recent outbreak occurring in 2004-2006 in nine western states and resulting in over 700 premises and more than 19,000 animals under quarantine. Despite significant economic losses, knowledge surrounding VSNJV transmission remains unclear. Only recently experimental insect transmission of VSNJV to domestic swine was documented. The basic mechanisms of infection and transmission leading to vesicular lesions in cattle remain unclear. In the present study we demonstrated for the first time experimental insect transmission in cattle that resulted in clinical disease. Using experimentally infected black flies (Simulium vittatum) we determined that feeding flies at different sites on the animals determined the outcome of infection. The development of clinical lesions was only observed when infected flies were allowed to blood feed at sites in the animals where VS lesions usually occur: mouth and coronary bands of the hooves. The development of a reliable experimental insect transmission model in cattle will be useful for understanding transmission and pathogenesis of VS.
Technical Abstract: Vesicular stomatitis New Jersey virus (VSNJV) is an insect-transmitted Rhabdovirus causing vesicular disease in domestic livestock including cattle, horses and pigs. The natural transmission of VSV during epidemics remains poorly understood. Transmission of VSNJV from experimentally infected black flies (Simulium vittatum) to mice and swine has previously been demonstrated. This study reports the transmission of VSNJV to cattle by bite from infected black flies. Infection resulted in local viral replication and vesicular lesions only when infected flies were allowed to feed at those sites where VS lesions are characteristically observed (mouth, nostrils, and foot coronary band). Interestingly, when flies were allowed to feed on flank or neck skin, only limited viral replication occurred and lesions were not observed. Clinical disease induced by infected S. vittatum feeding on the coronary band or the muzzle was similar to that observed after natural field infections and resulted in high neutralizing antibody titers (>1:256). In contrast, infected insect bites on the neck did not result in clinical infection and only low levels of neutralizing antibodies were observed (range 1:8 - 1:32). Viremia was not observed in any animals and infectious virus was not recovered from tissues upon necropsy between 8 and 27 days post-infection. However, viral RNA was detected in lymph nodes draining the lesion sites at 8-9 days post-infection. This study demonstrated that clinical outcome after VSNJV infection in cattle by black fly bite is determined by bite site. This experimental insect transmission model in cattle will be useful for pathogenesis studies.