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Mosquito-Borne Diseases

State health officials are urging Hoosiers again this year to take steps to protect themselves from mosquito-borne diseases, including Eastern Equine encephalitis, St. Louis Encephalitis and West Nile Virus.  In 2009, there were three human cases of mosquito-borne disease in the state. 

  • Eastern equine encephalitis (EEE) is caused by a virus that is usually transmitted between birds and mosquitoes, like West Nile virus (WNV).  The virus is found in mosquitoes and birds that live in freshwater, hardwood swamps.   Humans and horses only get EEE when bitten by infected mosquitoes and cannot spread the virus.  Mosquitoes must feed on infected birds to spread the virus.

    State health officials say although eastern equine encephalitis is rare, 30 percent of people who develop the disease may die, making it one of the deadliest mosquito-borne diseases in the United States.  According to the State Department of Health, approximately half of those who survive EEE illness will have permanent neurological problems.  Most people infected with the virus will not have symptoms.  Health officials say if symptoms occur, they will normally show up 3 to 10 days after people are bitten by an infected mosquito.  Symptoms of EEE include: fever, malaise, headache, nausea, vomiting, abdominal pain, and eye pain when exposed to light, weakness, paralysis, confusion, incoordination, seizures, and loss of consciousness.  There is not a vaccine available to prevent the disease in humans, nor is there a specific treatment.
  • La Crosse encephalitis virus (LACV) is transmitted to humans by the bite of an infected mosquito. Most cases of LACV disease occur in the upper Midwestern and mid-Atlantic and southeastern states (see map).

    Many people infected with LACV have no apparent symptoms. Among people who become ill, initial symptoms include fever, headache, nausea, vomiting, and tiredness. Some of those who become ill develop severe neuroinvasive disease (disease that affects the nervous system). Severe LACV disease often involves encephalitis (an inflammation of the brain) and can include seizures, coma, and paralysis. Severe disease occurs most often in children under the age of 16. In rare cases, long-term disability or death can result from La Crosse encephalitis.

    There is no specific treatment for LACV infection-- care is based on symptoms. If you or a family member have symptoms of severe LACV disease or any symptoms causing you concern, consult a healthcare provider for proper diagnosis.

    The best way to reduce your risk of infection with LACV or other mosquito-borne viruses is to prevent mosquito bites. Use insect repellent, wear long sleeves, long pants and socks or even stay indoors while mosquitoes are most active. The mosquitoes that spread LACV are most active during the daytime.

  • St. Louis encephalitis is a viral disease found throughout much of the United States, including Indiana. Many persons infected with St. Louis encephalitis virus have no apparent illness. People with mild illness often have only a headache and fever. More severe infection is marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions (especially in infants) and spastic (but rarely flaccid) paralysis.
  • The West Nile Virus usually causes West Nile fever, a milder form of the illness, which can include fever, headache, body aches, swollen lymph glands, or a rash. A small number of individuals can develop a more severe form of the disease with encephalitis or meningitis and other neurological syndromes, including flaccid muscle paralysis. Health officials report individuals age 50 and over are at greatest risk for serious illness and even death from West Nile virus.  However, people of all ages can be and have been infected with the virus.
  • Dengue is transmitted to people by the bite of an Aedes mosquito that is infected with a dengue virus.  The mosquito becomes infected with dengue virus when it bites a person who has dengue virus in their blood.  The person can either have symptoms of dengue fever or DHF, or they may have no symptoms.  After about one week, the mosquito can then transmit the virus while biting a healthy person.  Dengue cannot be spread directly from person to person.  Dengue has emerged as a worldwide problem only since the 1950s. Although dengue rarely occurs in the continental United States, it is endemic in Puerto Rico and in many popular tourist destinations in Latin America and Southeast Asia; periodic outbreaks occur in Samoa and Guam.  Learn more about the Dengue virus.

    Learn more about Arborviral Encephalitis