La Crosse Viremias in White-Tailed Deer and Chipmunks Exposed by Injection or Mosquito Bite

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  • Department of Animal Health and Biomedical Sciences, and Department of Entomology, University of Wisconsin, American Biogenetic Sciences, Inc., Institute for Environmental Studies and School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin
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To further understand the role of wild mammals in the maintenance of La Crosse virus (LACV) in nature, we investigated the effects of inoculation method and virus source on the duration and amplitude of LACV viremia in vertebrate hosts. Earlier work suggested that deer are not sufficiently susceptible to LACV to play an important role in its maintenance. We re-evaluated the susceptibility of deer since subsequent studies showed that they constitute 65% of Aedes triseriatus blood meals, and thus would be exposed frequently to the virus. In our study, deer developed higher and longer viremias following exposure to LACV by infected Ae. triseriatus than those previously reported by inoculation with needle and syringe. However, susceptible Ae. triseriatus that fed on these viremic animals did not become infected. Because a large number of uninfected mosquitoes can feed upon a viremic deer in nature, we believe that deer should not be disregarded completely as a possible amplifier in the LACV transmission cycle. We also infected chipmunks to determine if there were significant differences in viremia response from mosquito delivery of virus to the chipmunk host, compared with artificial exposure by injection. Chipmunks exposed to infected mosquitoes had higher and longer viremias than the ones produced by intramuscular injection of an LACV suspension. These findings show the importance of using LACV infected mosquitoes for transmission experiments in mammals.