West Nile Virus

West Nile Virus is an arbovirus (ARthropod BOrne VIRUS) that naturally cycles within local bird populations.  It is passed along most often through the bite of a female mosquito, which comes looking for blood from the bird for protein to create a batch of eggs.  If there are enough virus particles in the blood of the bird to withstand the mosquito’s digestion process and to spread to her salivary glands, the mosquito then becomes able to pass along the virus to the next bird, horse, or human that she bites.  Interestingly, the host (source of blood) preference of the main vector of WNV in Teton County (Culex tarsalis) has been shown to shift as the season progresses, moving from mostly birds in May & June to a more mammal-based diet in July, August and September. For this reason it is important to stay vigilant and protect oneself against mosquito bites long into the season, even when the peak number of summer mosquitoes has dissipated.


Teton County Weed & Pest personnel set traps throughout the County to collect adult mosquitoes. The samples from these traps are sorted speciated and then tested for West Nile virus in our lab. This year we will again run many tests looking for West Nile Virus within mosquitoes. We perform these tests by separating the mosquitoes by species and then placing them in pools of 50 or fewer mosquitoes. We have been performing these tests for several years beginning in 2002.