Other Mosquito-Borne Illnesses

The mosquito vector species can transmit viral diseases causing brain inflammation, known as encephalitis. In addition to West Nile Virus, there are several other mosquito-borne illnesses to be aware of for your health.

St. Louis Encephalitis

St. Louis Encephalitis (SLEV), once the most common mosquito borne encephalitis in the United States, is particularly dangerous in the elderly and young. During 1975, the U.S. experienced a major outbreak of St. Louis Encephalitis. In the past, SLEV has been found in all of the United States west of the Mississippi River, as well as, the Ohio River Valley and Florida. Birds are considered the main reservoir of SLEV and species of Culex pipiens and Culex quinquefasciatus are the chief urban vectors. Culex tarsalis is the chief vector in rural areas in Western States. No mosquitoes found in Illinois tested positive for SLEV this year.

Click her for the CDC St. Louis Encephalitis website.

Other Arboviral Encephalitis

In addition to St. Louis Encephalitis and West Nile Virus, viruses such as Eastern Equine Encephalitis and Western Encephalitis can cause serious human disease. These diseases are found primarily on the eastern and western coasts of the United States. Normally these viruses are transmitted harmlessly from bird to bird, however sometimes they are transmitted to horses and humans. Eastern Equine Encephalitis is found along the Atlantic and Gulf coasts and inland in the Mississippi River Valley, including Illinois in limited areas. Culiseta melanura is the vector in the bird-to-bird cycle.

Aedes sollicitans, Aedes vexans, and Mansonia perurbans are vectors in the disease-transmission cycle. Western Encephalitis can be found in all of the states west of the Mississippi River and in Wisconsin and Illinois. The Culex tarsalis mosquito is the most important vector of this disease. La Crosse Encephalitis is found primarily in the Great Lakes region although there has been an increase in the incidence of cases in the Mid-Atlantic States.


Malaria, a disease caused when protozoan parasites of the genus
Plasmodium infect the red-blood cells of humans, continues to devastate many countries both financially and physically throughout the world.

The malaria parasites are transmitted from human to human via the bite of the Anopheles mosquito. Although there are approximately fifteen Anopheles species in the United States, only two are important in malaria transmission. These are Anopheles quadrimaculatus and Anopheles freeborni.

Click here for the CDC Malaria website.


Dengue, also known as break-bone fever, is a serious mosquito-borne virus that has spread throughout the world in a dramatic fashion. Dengue and Dengue Hemorrhagic Fever (first recognized in the 1950’s) are currently endemic in more than 100 countries.

The sudden and explosive expansion of Dengue can be partly attributed to the geographic expansion of the disease’s mosquito vector: the Aedes aegypti Endemic areas include the southeastern U.S., Central and South America, sub-Saharan Africa, India, Australia and Southeast Asia.

In the United States, Aedes sp. mosquitoes such as Aedes albopictus and Aedes aegypti are vectors of the disease. Neither Aedes albopictus nor Aedes aegypti were found in a NSMAD mosquito trap this summer. There were two major outbreaks of Dengue fever in the US and its territories in 2010.

Southern Florida experienced 53 human cases across three counties while Puerto Rico had 9,987. These incidents were considered locally acquired. Additionally, there were 436 imported human incidences across 32 states nationally.

Florida, Hawaii and Puerto Rico reported locally acquired human cases of Dengue in 2011 with 30 states and territories reporting 178 cases of imported human cases.There were three cases of imported Dengue in Illinois this year.

Click here for the CDC Dengue website.

Dog & Cat Heartworm

Dog and cat heartworm is another mosquito-transmitted disease. The causative agent, Dirofilaria immitis, is a nematode whose microfilariae (the immature but infective stage of the worm) are picked up and transmitted to dogs and cats by mosquitoes. The transmission cycle first begins when a hungry female mosquito feeds on an infected dog or cat and picks up the infective microfilariae. When the mosquito takes another blood meal, she transmits the microfilariae via her proboscis from the infected dog or cat to the skin of another dog or cat. Once on the surface of the animal’s skin, the worm penetrates the animal’s dermis and enters its bloodstream. Then, once in the animal’s body, the worms begin to grow and mature. Mature worms, which can sometimes grow to lengths of 8-13 inches, can infect an animal’s heart and cause life threatening pathology.

A veterinarian can prescribe medications for your pet to prevent infection.

Click here for the American Heartworm Society’s website.