Environmental & Extension Services Department - Pest Management Division
Health Issues
Mosquitoes are man’s worst insect enemy. They are able of transmitting a wide range of diseases including malaria, dengue fever, yellow fever, filariasis, and encephalitis. For example, during the construction of the Panama Canal in Central America, thousands of workers died of yellow fever carried by mosquitoes. During World War II, 500,000 military personnel contracted malaria from mosquito bites, more than were lost to actual enemy fire. There were similar cases during the Korean and Vietnam wars.
Throughout Florida’s history, there have been repeated large epidemics of serious mosquito-borne disease. Today, these same diseases are a possible threat to Florida residents because of the available mosquito carriers and our close proximity to the Caribbean. The main mosquito-borne diseases we are concerned about in Charlotte County are St. Louis Encephalitis (SLE), Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV).
- St. Louis Encephalitis
- Eastern Equine Encephalitis
- Malaria
- Dengue
- Yellow Fever
- Heartworm
- West Nile Virus
- Disease Surveillance
- How to Avoid Being Bitten
St. Louis Encephalitis (SLE) is the most common mosquito-borne human pathogen in the U.S. The first human outbreak of SLE occurred in St. Louis, Missouri in 1933. Since then, many SLE epidemics have been documented in North America with the mosquito vector varying by area. In Florida and Charlotte county, the mosquito vector is Culex nigripalpus, a fresh and stagnant water breeder.
SLE virus is maintained in the bird population during the summer. The mosquitoes are primarily feeding on these birds and may pick up the virus. In late summer to early fall, the mosquitoes change hosts from whom they seek blood meals. The focus turns to mammals, especially humans. This is when the disease is able to be passed to people. We cannot pass it on to other people or mosquitoes. We are dead-end hosts, meaning the virus does not replicate in great numbers in our bodies.
Most people who contract the virus survive. Older citizens and infants are at a greater risk of developing severe symptoms. Less than 1% of SLE infections in people are clinically apparent; most go undiagnosed. The symptoms of SLE range from flu-like headaches, fever, and a stiff neck in mild cases to convulsions and coma in severe cases. There is no vaccine.
Eastern Equine Encephalitis (EEE) is not as common as SLE in Charlotte county but the vectors for the disease are found here. EEE is frequently a fatal disease of humans, horses, and exotic bird species (such as pheasants, emus, and ostriches) in areas where the disease is prevalent. Most human cases are isolated and few in number.
EEE virus was first identified in the 1930’s and occurs along the eastern seaboard, the Gulf Coast, and some inland Midwestern locations. The virus is maintained in the bird population and the vectors prefer to feed upon birds. The vectors, which vary widely from area to area, usually do not bite humans or other mammals, but occasionally do. There is a commercially available horse vaccine for EEE, but none exist for man.
Symptoms of EEE begin with a sudden onset of fever, general muscle pains, and a headache of increasing severity. It many progress to more severe symptoms such as seizures and coma. About 1/3 of those with clinical encephalitis caused by EEE will die and those who recover may suffer permanent brain damage. EEE has not been found in Charlotte county.
Human malaria is a disease caused by infection of 4 parasitic protozoan species that have a complex life cycle requiring mosquitoes as one of the hosts. Currently, human malaria kills at least 2 million people annually throughout the world. In Florida, malaria is usually confined to imported cases from residents who have returned form international travels. However, the vectors for malaria are still found in Florida and the possibility for malarial reestablishment exists.
Malaria is now rare in the U.S., but it was once the major scourge of Florida, occurring in all 67 counties. Mosquito control efforts contributed to a large reduction in malaria for Florida during the 1930’s and 1940’s.
In humans, the symptoms of malaria will depend on the malaria species. The initial attack may start with lethargy, headache, anorexia, occasional nausea, and vomiting. The fever that occurs is comprised of a cold stage (shivering and a feeling of intense cold), a hot stage (distressing heat, dryness, burning, intense headache, nausea, and vomiting), and a profuse sweating phase. A typical attack often lasts 8 to 12 hours. There is no vaccine.
Dengue is a viral, mosquito-borne disease that has not been seen in Florida since the 1930’s. It is caused by any of 4 distinct dengue viruses. Humans are the only natural vertebrate host for the dengue viruses. The vectors are mosquitoes commonly found in Florida, the Caribbean, the Pacific Islands, Africa, and Central and South America. They breed in artificial container that occur in urban areas in close association with humans. Because the vectors exist in Florida, the threat of dengue becoming reestablished is very real.
The symptoms of dengue include sudden onset, high fever, severe headache, pain behind the eyes, joint and muscle pain, and rash. Nausea and vomiting, loss of appetite, and altered taste sensation are common. Dengue is also known as “break bone fever” because of the severe pain in the muscles and joints it causes. Dengue may also present as a severe and sometimes fatal hemorrhagic disease, called dengue hemorrhagic fever (DHF). There is no specific treatment for dengue. Dengue cannot be transmitted person to person. There is no vaccine.
Yellow Fever is caused by one virus species and typically causes profound hemorrhagic symptoms. It is often fatal. Yellow Fever has not been seen in Florida since 1905, but the vectors are still common. Yellow Fever has a jungle transmission cycle involving an obscure forest-dwelling mosquito that can transmit the disease to its offspring or to forest monkey species bitten by these mosquitoes. The urban transmission cycle involves mosquito vectors found in close association with humans and breed in artificial containers usually found around homes.
Yellow fever is typically recognized by hemorrhage symptoms. Milder symptoms include those associated with dengue. More severe disease, frequently fatal, includes jaundice, various hemorrhagic symptoms (e.g. black vomit), and abnormally slow heartbeat. Severe forms may conclude in coma or delirium. There is a vaccine, although not widely available or utilized.
Heartworm is a chronic disease of dogs and sometimes cats caused by a mosquito-borne filarial worm parasite. Large adult worms live in the heart and release large numbers of microscopic, embryonic worms into the bloodstream. These embryonic worms are ingested by blood-feeding mosquitoes and go through part of their life cycle in the mosquito before being transmitted to another host. Untreated, heartworm is commonly fatal to dogs. Your veterinarian can provide preventive medication for your pet.
West Nile Virus (WNV) is a disease that has been recently introduced to the United States. The first outbreak was in the New York City area in 1999. West Nile Virus (WNV) was first detected in Florida in 2002
The disease is closely related to St. Louis Encephalitis. It is can be severe in the elderly, but it is usually mild in healthy adults and children. Humans infected with WNV can experience mild to severe symptoms including fever that comes on quickly and lasts from 5 to 6 days. Other symptoms include severe headache, rash, swollen lymph nodes, gastrointestinal problems, and pain associated with the eyes, muscles, and back. In serious cases, the symptoms of encephalitis can cause death.
St. Louis Encephalitis (SLE), Eastern Equine Encephalitis (EEE), and West Nile Virus (WNV) are the only diseases regularly monitored for in Florida and Charlotte county. This is due to the fact that SLE and EEE are the most prolific mosquito-borne diseases still found in the state. WNV testing is done to monitor for the virus presence throughout the state. For the other mosquito-borne diseases, surveillance is entirely restricted to the monitoring of human cases by public health agencies.
Surveillance in Charlotte county (and a number of counties) for SLE, EEE, and WNV is done by testing sentinel chickens in established sites throughout the county. A small amount of blood is drawn each week during the mosquito season for testing at the Florida Department of Health Tampa Branch Laboratory for the antibodies to these two viruses. The number of vector mosquitoes found in our surveillance traps is also taken into account during periods of viral activity.
The best way to avoid being bitten by mosquitoes is to stay indoors during peak mosquito biting hours, especially at dusk and dawn. If you must be out during the times, take these precautions:
- a) Wear long sleeves and pants that are light in color and loose fitting.
- b) Use a mosquito repellent.
- c) Avoid wearing perfumes, colognes, or scented lotions.
- d) Stay away from shaded, humid areas where there is little wind.
The most effective mosquito repellent is one that contains DEET or N,N-diethyl-meta-toluamide. It is sold in pump sprays, aerosols, lotions, creams, soaps, and sticks. Concentrations of 10%-35% work the best. Use the lowest concentration effective for you. Be sure to thoroughly read the label before use.
DEET can have some side effects. At high concentrations, it can make you feel unpleasantly oily and can melt plastic, watch crystals, and paint finishes. It is safe on nylon, cotton, and wool. However, it can damage rayon, acetate, and spandex. DEET can also irritate the eyes and sensitive skin. Some people are allergic to DEET. To minimize any adverse reactions, do the following:
- a) Apply the repellent sparingly and only to clothing to reduce DEET absorption through the skin.
- b) Avoid using products with concentrations over 50%, particularly on children and infants.
- c) Do not inhale or ingest repellents or get them into the eyes or on wounds or irritated skin.
- d) Avoid applying repellents to portions of children’s hands that are likely to have contact with eyes or mouth.
- e) Wash repellent off of your skin after coming indoors.
- f) If a suspected reaction to insect repellent occurs, wash the treated skin and call your doctor.
There are a few repellents that do not contain DEET for those who are sensitive. They can be applied directly to the skin. These products include those with citronella or eucalyptus and Avon’s Skin-So-Soft®. They are not effective for everyone. These are good choices for children, although they must be reapplied more frequently. All of these are much less effective than DEET.
Mechanical controls for areas include a variety of repellent plants, candles, coils, and area repellents that contain citronella, pyrethrums, or a similar synthetic compound are on the market. These have limited uses and you should read and following label directions carefully. They should not be used indoors, but they may help in screened-in porches and around pools or patios where there is very little air movement. Bug zappers are popular and expensive. They are also ineffective in killing biting insects. They do kill mosquitoes but also kill many beneficial insects that prey on mosquitoes. They also attract more mosquitoes to your yard than if you did not have it. Birds and bats will not control mosquito populations in your yard. Likewise, there is no scientific evidence to support the claims that eating garlic, vitamins, onions, or any other food will make you more repellent to mosquitoes.
For more information
Charlotte County Environmental & Extension Services
25550 Harbor View Road, Unit 2, Port Charlotte, FL 33980
941.764.4360
