Mosquito-Borne Disease in Missouri

West Nile Virus

West Nile Virus (WNV) originated in Africa, first discovered in 1937. Since then, ships and airplanes brought the virus to America where it was first isolated in 1999. The virus thrives in the Americas thanks to urbanization and climate change. Birds and horses host WNV, while Culex mosquitoes are the vector of the virus. When a mosquito bites a horse or bird infected with WNV, it can transmit the virus to a human with its next bite. WNV transmission is higher in urban areas where Culex mosquitoes tend to thrive.

The Centers for Disease Control and Prevention (CDC) reports most people (about 8 out of 10) will not have any WNV symptoms. One in five people infected with WNV may develop a fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Around two percent of people infected with WNV will experience severe symptoms such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord). People with asymptomatic and mild WNV symptoms usually clear the virus and recover completely. However, WNV patients who experience fatigue and weakness may have symptoms for weeks or months.

Right now, there is no vaccine or treatment for WNV.

Zika Virus

The Zika virus is spread from person to person through the bite of an infected Aedes aegypti or Aedes albopictus mosquito. Zika is endemic to 50 countries including the U.S.. In Missouri, several people have reported Zika infections, but no infection was due to a Missouri mosquito bite. The Missouri Department of Health and Senior Services is monitoring mosquitoes in the state to find if any carry Zika virus.

Most people infected with Zika won’t show any symptoms. People can pass the virus to another person through sexual contact. The most common symptoms of Zika are fever, rash, joint pain, and irritated, red eyes. Symptoms usually last for several days to a week, beginning one to two weeks after an infected mosquito bite. Zika virus during pregnancy can cause serious birth defects like microcephaly and other severe fetal brain defects.