West Nile is Not

September is upon us. Kids are back in school and pumpkin spice lattes are on the menu already, but in many parts of the country, mosquito season is not yet behind us. Thanks to late season heat and rainfall totals, conditions have been ripe for mosquito breeding, with populations – and disease activity – quickly rising in communities all across the country.

WNV disease incidence reported to the CDC by week of illness onset, 1999-2016. Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention.

According to the latest CDC data published on September 18, 2018, 47 states have reported the presence of West Nile Virus (WNV) in humans, birds or mosquitoes, and there are 1,077 confirmed human cases across the country. Since the last time the CDC reported WNV activity data on September 4, the number of confirmed human cases nearly doubled (up from 559)! Historically, late August into mid-September is when the U.S. sees the greatest number of confirmed WNV cases, and 2018 is proving to be no different. Why? Because ideal late summer breeding conditions lead to a spike in adult mosquito populations, causing more people to get bitten by infected mosquitoes.

Protecting Public Health

Mosquito control programs exist not only to make spending time outdoors more comfortable, but more importantly, to protect people from WNV and other mosquito-borne diseases like Zika, dengue and others. With this objective in mind, the most important thing that mosquito control entities can do right now is continue providing adult mosquito control measures through the remainder of the late summer season, and conduct larval control in those habitats where mosquitoes commonly breed, like storm drains, catch basins, sewage tanks, ditches and other areas that retain stagnant water for days at a time. As an industry, we must always be vigilant in controlling mosquitoes and educating the public about preventing mosquito bites to reduce the risk of virus transmission, especially during this late season.

What is WNV?

WNV is a vector-borne disease transmitted to humans by the bite of an infected Culex mosquito.  Most people, about 4 out of 5, experience no symptoms after contracting WNV, but the other 20% of people typically develop a fever, headaches, joint and muscle pain, vomiting and a rash.  It can take anywhere from a few days to two weeks after a bite for WNV symptoms to appear.  While there is no vaccine or antiviral to treat WNV, and cases may resolve on their own, diagnosis and monitoring by a health care professional is important to detect and manage neuroinvasive disease cases.