Diseases

Mosquito-Borne Diseases in Florida

St. Louis Encephalitis

This disease is caused by a virus that is associated with wild birds. Since 1959, this disease has become the most common mosquito-borne disease of humans in Florida. Epidemics cause disruption of activities of residents, and causes reduction of tourism. Night time activities such as football games often must be curtailed during outbreaks. Economic loss to the state by this disease is not easy to quantify, but probably has been considerable.

Eastern Encephalitis

This disease also is associated with wild birds and also is caused by a virus. The disease can be fatal to humans, horses, and exotic birds. There are rarely more than one or two human cases of Eastern Encephalitis per year in Florida.

Dengue

Dengue is almost unique amongst mosquito-borne viruses in that it uses only humans as a host. Symptoms can range from mild flu-like illness to severe hemorrhage, shock, and death. There are four distinct dengue viruses; all of them occur in the Caribbean. Dengue has been increasing in the Caribbean and South America since the early 1980s. Dengue epidemics had a major impact on the early development of Florida. Epidemics occurred in the 1930s in Miami and Tampa. The Miami epidemic encompassed more than 15,000 cases.

Yellow Fever

Yellow fever has not been seen in Florida since 1905. The mosquito that transmits the virus to humans is still common in parts of the Florida Keys.

Venezuelan Equine Encephalomyelitis

Venezuelan equine encephalomyelitis is actually a complex of related viruses. One subtype, Everglades virus, is known to be associated with the black salt marsh mosquito, among other species. This virus apparently does not cause disease in horses in Florida, although two Florida residents suffered severe illness due to infection by this virus.

Malaria

Human malaria is caused by infection by one of four parasitic protozoa. These parasites have complicated life cycles that require both mosquitoes and humans for completion. In the past, malaria was a serious problem in Florida. Until the early 1930s, about one-half of Florida's counties had death rates of at least 100 per 100,000 population. Mosquito control efforts in the 1930s contributed to the decrease in malaria mortality in Florida. Infected travelers can bring the parasite with them, as happened in Key West in 1998. Local mosquitoes may then acquire the parasite and transmit it to uninfected people. This happened in the panhandle region of Florida in 1990, and again in Palm Beach County in 1996.

Dog Heartworm

Dog heartworm is transmitted to dogs by the bite of an infected mosquito. Adults live in the dog's heart and release microscopic young worms into the dog's blood. This infection is often fatal to the dog. Cats are also susceptible to infection by dog heartworm, although to a lesser degree than are dogs. Human infections are sometimes discovered, usually during lung X-rays.