West Nile Virus detected in Churchill County
July 25, 2017
The record snow pack in the Sierras has posed a number of threats for Churchill County this spring and summer.
Brilliant collaboration and cooperation between a number of agencies has gotten our County through potential flood mitigation efforts. Nonetheless, with the water poses another concern…mosquitoes!
Residents in Churchill County experienced our typical early spring mosquito populations in March 2017. Since then, we have seen water being "spread" to all sections of the County to lessen the amount of water in Lahontan Reservoir. This water is beginning to recede in these locations. This leads to a scenario of warmer and potentially more stagnant water bodies in water-saturated areas, which are then prime conditions for mosquito breeding areas.
Churchill County Mosquito, Vector and Noxious Weed Abatement District has been assessing and treating these areas for juvenile mosquitoes (larvae) for the last four months. This effort will continue into October. With the mosquitoes unfortunately comes the risk of mosquito-borne illnesses.
The increased health risk during a significant water year is due to animals and livestock being exposed to increased numbers of mosquitoes, which may be infected with a number of viruses. The viruses most likely to be carried by mosquitoes in our local area are West Nile Virus, Western Equine encephalitis and St. Louis encephalitis. Our staff traps adult mosquitoes on a weekly basis. This testing is done with carbon dioxide traps being used to collect adult mosquitoes.
These adult mosquitoes are separated by species into samples of 50 mosquitoes (or less) and are referred to as "mosquito-pools" which are then tested by the Department of Agriculture State Animal Disease Lab for the mosquito-borne illnesses listed above.
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This week, our District was notified that ten "pools" were confirmed as positive for West Nile virus. These mosquito pools were collected from five different areas in Churchill County. These areas have since been adulticided with truck mounted fogging units. This fogging effort has to be done after dusk when there is peak mosquito activity and especially that of flight activity of Culex tarsalis, which is the species that is the most competent vector of encephalitis and other arboviral diseases.
These areas have been treated and will be retested next week. The District has trapped live mosquitoes in over sixty locations since June and will continue to do so throughout the summer.
These confirmations mean that the virus is active in the valley. Although last year was more of a drought year, we had positive mosquito pools at about the same point in the summer. "Active virus" in the valley means that mosquitoes have become infected with West Nile virus after they have fed on infected birds. The virus amplifies in the bird's system. These birds are called "reservoir hosts".
The virus may kill the bird or the bird may continue to perpetuate the virus without showing any noticeable symptoms. An infected mosquito can then transmit or pass the disease on to humans, horses or other mammals. The "human, horse or other mammal" is considered a terminal, dead-end "host". Unlike birds, they are unable to develop high levels of virus in their blood stream and cannot pass the virus on to other biting mosquitoes.
Extensive water may increase the bird populations around the valley which, in turn, may increase the number of infected mosquitoes during an unusually wet season. The wet season assists in part to provide habitat for birds and mosquitoes to co-exist in the same location and for the female mosquitoes to have optimal conditions to lay her eggs. The eggs have ample time in the water to go through their evolutionary cycle to become the next generation of adult mosquitoes to feed on the infected birds again.
The District continues to treat larvae (juvenile mosquitoes) in the water in order to prevent their emergence into adult mosquitoes. District Staff will continue to adulticide (fog) adult mosquito populations throughout the valley.
If residents within Churchill County have any specific questions regarding mosquito control or mosquito-borne illnesses, please call the office (775-423-2828) and leave a message with your name, address and phone number as we will log all calls as "service requests."
With these service requests, our technicians assess the areas noted by the callers and treat any larvae they find or plan on when to fog the adult mosquito populations, working within weather parameters and pesticide label restrictions. Other questions, can be submitted to District staff via email at firstname.lastname@example.org.