West Nile Virus is Most Common in Late Summer

Late summer is often when the presence of mosquito-borne diseases like West Nile Virus (WNV) upticks rapidly, thanks to ideal weather conditions (regular rainfall, humidity levels, and warm air temperatures) for mosquito breeding. Data reported to the Centers of Disease Control (CDC) by state health departments each year highlights the historical trend for a late summer uptick in West Nile Virus cases (see chart):

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.

How is the presence of West Nile Virus identified?

Mosquito surveillance traps, such as the ones in Clarke’s network across Illinois, are used to monitor regional mosquito populations and the presence of disease. Adult mosquitoes collected in surveillance traps are routinely collected and transported back to a laboratory where they are identified by species, counted, and then tested for the presence of West Nile Virus (WNV) using a RAMP or PCR diagnostic test.

What happens if mosquitoes test positive for West Nile Virus?

If mosquito samples test positive for West Nile Virus, that means there’s potential for the virus to transfer to humans through the bite of an infected mosquito.

Adult mosquito control treatments can help reduce the public health threat. If local or regional mosquitoes begin testing positive for WNV, many communities elect to schedule a preventative treatment to protect residents from the disease threat. It may also be appropriate to perform larval control in known breeding areas to prevent future transmission.

What are the symptoms of West Nile Virus?

The CDC is the most credible source of information on West Nile Virus. It reports that most people infected with WNV are asymptomatic. But if physical symptoms do present, they may include a fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. If you have these physical symptoms, the CDC recommends seeking medical treatment.

What can individuals do to protect themselves from West Nile Virus?

The CDC recommends these protective measures to protect against West Nile Virus transmission, and they all focus on avoiding mosquito bites when spending time outdoors.

  1. Avoid outdoor activity at dawn and dusk when mosquito activity is typically highest.
  2. Apply an EPA-registered, CDC-recommended mosquito repellent. Look for products that contain one or more of the following active ingredients: DEET, Picaridin, IR3535, Oil of lemon eucalyptus (OLE), Para-menthane-diol (PMD), or 2-undecanone.
  3. Limit skin exposure by wearing long pants and long sleeves, and apply the repellent over your clothing.
  4. Keep mosquitoes outside. Use air conditioning to manage indoor temperatures, and ensure windows and doors have functioning screens and tight seals.
  5. Eliminate standing water sources. Without a water source, female mosquitoes cannot lay their eggs.

We all appreciate being able to spend time outdoors without the nuisance of mosquito bites. But especially when mosquito-borne diseases are active in our communities, we’re reminded that mosquito control programs play a critical role in protecting public health.