News on Mosquitoes and Diseases

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ENCEPHALITIS

Encephalitis in various forms such as St. Louis, Western Equine, La Crosse, Eastern Equine, and West Nile, which was recently discovered in the Northeast is endemic to the United States and increasing in incidence. Although extremely rare, Eastern Equine Encephalitis has a 30% - 60% mortality rate once contracted. Severe damage to the central nervous system occurs in those that survive the illness.

Eastern Equine Encephalitis (EEE) is maintained in nature through a cycle between the Culiseta melanura mosquito and birds that live in freshwater swamps. Although Culiseta melanura do not bite humans, some mosquitoes will "cross bite"; i.e., bite an infected bird and then bite a human or animal (horse, emu, and other exotic birds), thereby spreading the disease. These mosquitoes are also known as "bridge vectors". A vector is a species that transmits a disease from one host to another. These bridge vectors may take a meal from a bird and later take another meal from a mammal.

Symptoms usually occur within two to ten days after being bitten by an infected mosquito. These symptoms include high fever, stiff neck, headache, confusion, and lethargy. Encephalitis, swelling of the brain, is the most dangerous symptom. Rhode Island has confirmed five cases of EEE with two deaths in the last thirteen years. The last death was reported in 1993.

For more information on EEE...
University of Rhode Island EEE Facts
University of Rhode Island
State of Connecticut Department of Public Health

For more information on St. Louis Encephalitis...
Centers for Disease Control and Prevention

WEST NILE FEVER

West Nile Virus symptoms include fever, headache, nausea, vomiting, and rash, which are mild symptoms to severe symptoms that include neck stiffness, stupor, disorientation, tremor, coma, vision loss, and paralysis. These severe symptoms could last weeks or could be permanent. The onset of symptoms usually begins three to 14 days after a mosquito bite. Unlike Eastern Equine Encephalitis, 80% of the people who are infected with WNV will show no symptoms at all. 20% will show mild to serious symptoms. People who are mostly likely to show symptoms if bitten by an infected mosquito are infants, the elderly and people with auto-immune difficiencies.

For information on West Nile Fever see...
Centers for Disease Control and Prevention - Questions and Answers About West Nile Virus
Rhode Island Department of Health
Georgia Dept. of Agriculture

DENGUE FEVER

Dengue fever is primarily a disease of the tropics that is transmitted by the Aedes aegypti mosquito. Aedes aegypti is a day-biting mosquito that prefers to feed on humans. It is also transmitted by the Aedes albopictus (also called the "tiger mosquito"). Those infected with dengue can suffer from a spectrum of illnesses ranging from a viral flu to severe and fatal hemorrhagic fever (DHF).

The dengue virus is passed back and forth between mosquitoes and humans and causes an extraordinarily painful ailment that exists in four known strains or serotypes. Dengue is especially dangerous to children, who generally have one infection, but if bitten again can get a more serious infection that can lead to dengue hemorrhagic fever (DHF). DHF causes severe internal bleeding, shock, and circulatory collapse, and is usually fatal to children.

Until recently, dengue was relatively unknown in the Western Hemisphere. In the 1970's, a dengue epidemic swept through Cuba and other parts of the Caribbean. In 1981 a second strain broke out in Cuba, accompanied by hemorrhagic fever. The second epidemic resulted in more than 300,000 hemorrhagic fever cases, and more than 1,000 deaths. Most were children. In the summer of 1998 an epidemic broke out on the island of Barbados.

Dengue is increasingly becoming a plague of global proportions and may soon eclipse malaria as the most significant mosquito-borne viral disease affecting humans.

For more information on Dengue Fever...

WHO Division of Control of Tropical Diseases
CDC Division of Vector-Borne Infectious Diseases

MALARIA

Malaria is caused by a parasite that is transmitted from person to person by the bite of an Anopheles mosquito. Anopheles bite during the nighttime and are present in almost all countries in the tropics and subtropics.

Symptoms of malaria include fever, chills, headache, muscle ache, and malaise. In its early stages it can resemble the onset of the flu. These symptoms can develop 6-8 days after being bitten by an infected mosquito or as late as several months after the traveler has left the area.

Malaria can sometimes be prevented by the use of antimalarial drugs and protection against mosquito bites. Some estimates place 40% of the world's population at risk for malaria. It is estimated that worldwide, malaria claims over one million lives annually. (World Health Organization 1989)

For more information on malaria... at World Health Organization Control for Tropical Diseases.

YELLOW FEVER

Yellow fever is a disease caused by the bite of the Aedes aegypti mosquito. It does not occur in the U.S. but is common in parts of Africa and South America. The symptoms of yellow fever include fever, chills, headache, backache, nausea, and vomiting; jaundice can also occur. More serious cases may affect the blood, liver, and kidneys. The disease can be fatal.

The disease is spread when an infected mosquito bites a person with yellow fever and then transmits it by biting another person.

There is no specific treatment for yellow fever, other than to relieve the symptoms. Once a person has had yellow fever, they are immune to further infection. The best way to prevent the disease is through vaccination and mosquito control.

For more information on yellow fever...
World Health Organization Fact Sheet