Mosquito-Borne Diseases

Mosquitoes cause more human suffering than any other organism -- over one million people worldwide die from mosquito-borne diseases every year. (Courtesy: American Mosquito Control Association)
Please click on the topics below for a detailed description:

What Is West Nile Virus?

West Nile Virus is a disease that is transmitted by an infected mosquito to humans, birds, horses, and other animals. Mosquitoes acquire the disease from infected birds while taking a blood meal and later pass it to other animals or humans.

The disease was first isolated in Uganda in 1937 and was detected in New York in 1999. In 2002, the most extensive outbreak of WNV occurred.

What Are the Symptoms of WNV?

The majority of people who are bitten by an infected mosquito show no symptoms (about 80%).

Up to 20 percent of the people who become infected have symptoms including:

  • Fever
  • Headache
  • body aches
  • nausea or vomiting
  • swollen lymph glands
  • skin rash on the chest, stomach and back

Symptoms can last as short as a few days, though even healthy people have become sick for several weeks. The onset of symptoms usually occurs from 3-14 days after being bitten.

About 1% of those infected with WNV will develop severe illness. The severe symptoms can include high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and can result in permanent neurological damage or death.

Is WNV contagious?

WNV is usually spread by the bite of a mosquito. You cannot become infected through touching or kissing a person with the virus. In a very small number of cases, WNV has been spread through blood transfusions, organ transplants, breastfeeding, and during pregnancy.

What should I do/treatment?

There is no specific treatment for WNV infection. In cases with mild symptoms, people experience symptoms such as fever and aches that pass on their own, although even healthy people have become sick for several weeks. Most people do not necessarily need medical care for mild symptoms. In more severe cases (severe headaches, fever, or confusion), people usually need to go to the hospital where they can receive supportive treatment including: intravenous fluids, breathing assistance and nursing care. Severe WNV illness usually requires hospitalization.

Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.

What Is the Risk of Getting Sick from WNV?

People over 50 are at higher risk of severe illness. People over the age of 50 are more likely to develop serious symptoms of WNV if they do get sick and should take special care to avoid mosquito bites.

Risk through medical procedures is very low. Donated blood is checked for WNV before being used. The risk of getting WNV through blood transfusions and organ transplants is very low, and should not prevent people who need surgery from having it. If you have concerns, talk to your doctor before surgery.

Pregnancy and nursing do not increase the risk of becoming infected with WNV.

What Can I Do to Prevent WNV?

When you are outdoors, use insect repellents containing an EPA-registered active ingredient. Two that work effectively are DEET (N, N-diethyl-meta-toluamide) and Picaridin. Follow the directions on the package.

Many mosquitoes are most active at dusk and dawn. Be sure to use insect repellent and wear long sleeves and pants at these times or consider staying indoors during these hours.

Make sure you have good screens on your windows and doors to keep mosquitoes out.

Eliminate potential mosquito breeding sites by emptying standing water from flower pots, buckets and barrels. Change the water in pet dishes and replace the water in bird baths weekly. Drill drainage holes in tire swings so water drains out. Also, keep children"s wading pools empty and on their sides when they aren"t being used.

St. Louis Encephalitis

  • Transmitted to humans from infected mosquitoes
  • Usually asymptomatic (no symptoms)
  • Symptoms include:
    • fever
    • headache
    • nausea
    • vomiting
    • fatigue
  • Severe neuroinvasive symptoms occurs more commonly in older adults.
  • No specific treatment, care based on symptoms
  • To reduce risk:
    • Wear insect repellant
    • Wear protective clothing
    • indoors at dawn and dusk
    • Eliminate standing water around the home

Eastern Equine Encephalitis

  • Transmitted to humans from infected mosquitoes
  • Rare illness in humans (only a few cases reported a year)
  • Usually asymptomatic
  • Severe cases include a sudden onset of:
    • Headache
    • High fever
    • Chills
    • Vomiting
  • May progress to disorientation, seizures, and death
  • Approximately 33% mortality and significant brain damage in most survivors
  • No specific treatment, care is based on symptoms

La Crosse Encephalitis

  • Transmitted by infected mosquitoes
  • Usually asymptomatic
  • Initial symptoms include:
    • Fever
    • Headache
    • Nausea/vomiting
    • Fatigue
  • Severe symptoms include:
    • Seizures
    • Coma
    • Paralysis
  • Severe disease most often affects children under 16
  • Long-term disability or death can occur

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