Remember West Nile Virus?

Mosquito trapping and testing is underway in many states, including Kentucky, as part of overall public health programs. The relatively mild winter of 2016-2017 favored greater survival of species, such as the house mosquito complex, that overwinter as adults. In some cases, the pathogens mosquitoes may carry may have also survived.

According to 2017 news reports, West Nile Virus (WNV) has been detected in mosquitoes captured this year in Ohio, Indiana, and Tennessee; a human case has been confirmed in Mississippi. While there are no reports from Kentucky to date, it is likely that the virus has survived in some mosquitoes here, too. Consequently, it is a good time to review the disease, its vectors, and protective measures.

Disease Vectors & Symptoms

House mosquitoes move the virus among various bird species. When abundant, they and mosquito species (such as the Asian tiger mosquito) can serve as bridge vectors to move the virus into humans (and horses). Most people (70-80%) who become infected with West Nile virus do not develop any symptoms. Less than 1% develop encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord in some infected humans).  This disease can cause significant mortality in unprotected horses, if not diagnosed quickly.

West Nile Virus Cases

Initially detected in New York, WNV spread quickly and now cases occur annually throughout the continental U.S. According to Centers for Disease Control (CDC) data, the greatest number of diagnosed cases (75) in Kentucky occurred in 2004. Since then, the annual number of diagnosed cases has been between 3 and 8. Exceptions occurred in 2008 (31) and 2012 (23).

According to a CDC report on the 2012 resurgence (5,674 cases nationally), “outbreaks can result from  many factors, including higher-than-normal temperatures that influence mosquito and bird abundance, the replication of the virus in its host mosquitoes, and interactions of birds and mosquitoes in hard-hit areas. Because the factors that lead to West Nile virus disease outbreaks are complex, CDC cannot predict where and when they will occur.” The picture for 2017 will develop over the summer.


The best way to prevent West Nile (or Zika) virus infections is to avoid mosquito bites.

  • Use insect repellents when going outdoors. Use repellents containing DEET, picaridin, IR3535, and para-menthane-diol (PMD) because these repellents provide longer-lasting protection than other products.  Always follow the instructions on the label.
  • Wear long sleeve shirts and pants at dawn and dusk when many mosquitoes are most active.
  • Repair or install screens on windows and doors. Use air conditioning, if available.
  • Help reduce the numbers of mosquitoes present around your home by emptying standing water from items such as gutters, flowerpots, buckets, and kiddie pools. Change birdbaths weekly


By Lee Townsend, Extension Entomologist

Posted in Human Pests
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