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The Buzz on Mosquito-Borne Viruses

Updated August 20, 2018

Courtesy of CDC/James Gathany

Whether you are spending your summer adventuring outside at home or vacationing out of town, it’s best to prepare for the outdoor environment and protect against mosquito bites. Mosquitoes act as a great vector to carry and spread a variety of diseases that can affect humans. It is important to be aware of not only the types of illness mosquitoes can cause, but the geographic locations where risk may be higher.

Below are brief summaries on some of the more common mosquito-borne diseases. 

  • West Nile virus: Cases of West Nile virus have been reported in all areas of the continental United States. Most infected people have no symptoms. About one in five people who are infected will develop a fever along with other symptoms. Rarely, those infected can develop a serious, sometimes fatal neurologic illness. No vaccine or treatment currently exists for this virus. West Nile virus primarily cycles between mosquitoes and birds; infected mosquitoes can then transmit the virus to humans. Humans are considered “dead-end” hosts, meaning we cannot pass the virus to other biting mosquitoes.
  • Zika virus: Zika has been found in countries around the world. In 2018 so far, no local transmission has been reported in the United States. Thirty-four cases have been reported in travelers returning from affected areas. In U.S. territories, more than 70 reported cases have been presumed to be caused by local transmission. Zika can also be spread through sex with an infected person and from a pregnant mother to her unborn baby. Zika is usually a mild illness that requires no specific treatment, but it can cause serious birth defects—such as microcephaly in infants—or other neuro­logical conditions in both children and adults. There is no vaccine or treatment for Zika.
  • Chikungunya: This disease can demonstrate similar signs and symptoms to dengue and Zika. Most of the disease has been identified in Africa, Asia and the Indian subcontinent. Here in the U.S., cases have been considered travel-associated; local transmission has been identified in Puerto Rico. Most people infected with the chikungunya virus will develop some symptoms, most commonly fever and joint pain. Symptoms can be severe, but rarely lead to death. There is no vaccine or medicine to treat chikungunya.
  • Malaria: Unlike the other diseases previously noted, malaria is caused by a parasite that can infect mosquitoes and subsequently humans. Symptoms of malaria are flu-like, including fever and chills. If untreated, patients can develop complications and die. Most malaria cases and deaths occur in Africa, but dozens of other tropical and subtropical areas are also at risk. According to the Centers for Disease Control and Prevention, 445,000 people died of malaria in 2016. About 1,700 cases of malaria are diagnosed in the U.S. each year, almost all travel-related. While treatment exists, no effective malaria vaccine is currently on the market.
  • Dengue: The dengue virus is believed to be a leading cause of illness and death in tropical and subtropical locations worldwide. Although dengue rarely occurs in the continental United States, it is prevalent in Puerto Rico and other popular tourist destinations, as well as more than 100 countries. Research estimates as many as 400 million people are infected with dengue each year. Possible symptoms of dengue fever are a high fever, severe headache, eye pain and more. There is no vaccine available against dengue, and there are no specific medications to treat this type of infection.

So how do we protect against these types of infections? The best way to prevent mosquito-borne illnesses is to prevent mosquito bites. Here are some steps you can take to reduce your risk of mosquito bites:

  • Use insect repellent.
    • Apply EPA-registered insect repellent on exposed skin and clothing before going outside.
    • Products with chemicals such as DEET or picaridin offer longer-lasting protection and are considered safe for pregnant women.
  • Wear long-sleeved shirts and long pants.
    • You can also treat items with permethrin or buy permethrin-treated clothing.
  • Help to control mosquitoes both inside and outside your home.
    • Use screens on windows and doors.
    • Use air conditioning when available.
    • Use a mosquito bed net.
    • Check your house and surrounding areas for items that hold water. Mosquitoes lay eggs near water; by dumping out items with freestanding water you reduce their ability to breed.

If you think you or a loved one may have a mosquito-borne disease or have symptoms of one of the illnesses after returning from an affected area, it’s important to see a doctor right away.

Looking for more information on any of these vector-borne diseases? Take a look at these additional resources:

CEPAR’s Zika virus travel guidance

Johns Hopkins Medicine Zika virus site

Johns Hopkins Medicine Health Library

World Health Organization

Centers for Disease Control and Prevention