Common Diseases Carried by Mosquitoes

As well as being a pest, mosquitoes can carry numerous diseases that can make people and animals sick. Not all mosquitoes carry diseases. The following are the most common diseases found nationwide.

West Nile Virus

West Nile virus (WNV) has been in the United States since 1999, and as been seen in Texas since 2002. West Nile virus is spread to human through a single mosquito bite. WNV is a blood-borne disease, there has not been any cases of a person contracting the virus through everyday contact with an infected individual. Although, there are records of people contracting the disease through organ transplants and blood transfusions.

There are three different gradations of WNV:
  • West Nile Virus
  • West Nile Fever
  • West Nile Nuroinvasive Disease
Most of the public who contract WNV (about 80%) will never show any symptoms, this gradation of the virus is referred to as West Nile virus.

About 20% of the population that contracts the virus will contract West Nile fever. Symptoms of this include fever, headache, nausea, and possible rash. These symptoms are very similar to flu-like symptoms, and many people who contract West Nile fever think they have the flu.

The more severe cases of West Nile (WN) are the neuroinvasive diseases. These can include encephalitis, meningitis, and mengioencephalitis. This gradation of the virus can lead to stroke-like symptoms, coma, paralysis and even death. About 1% of the population that contracts WN will get these more sever symptoms. To read more on West Nile Virus please visit the Texas Department of State Health Services website.


There are three forms of viral encephalitis transmitted by mosquitoes West Nile, St. Louis, and Western Equine. All are carried by wild birds, most of which show no symptoms. Infected birds are then bitten by local mosquitoes that can pass the virus on the human through future bites. Symptoms of encephalitis range from mild flu-like illness to severe brain inflammation that can cause death. West Nile virus and Western Equin encephalitis can affect horses and other animal as well as humans. For more information please Texas Department of State Health Services website.


Malaria is much less likely to occur in Cameron County, due to the necessity for human reservoirs of the disease. Anoplheles mosquitoes, the vectors of malaria, are found in some areas of Texas, and there have been isolated instances where human reservoirs from other countries temporarily provided a source of malaria infection to local residents. For FAQs visit the Texas Department of State Health Services website.


Dengue (déng gee, déeg gáy) is a mosquito-borne infection which in recent years has become a major international public health concern. Dengue is found in tropical and sub-tropical regions around the world, predominately in urban and Peri-urban areas.

Dengue hemorrhagic fever (DHF), a potentially lethal complication, was first recognized during the 1950s, and today is a leading cause of childhood mortalities in several Asian countries. There are four distinct, but closely related, viruses which cause dengue. Recovery from infection by one provides life long immunity against that sero-type but confers only partial and transient protection against subsequent infection by the other three. Indeed, there is good evidence that sequential infection increases the risk of more serious disease resulting in DHF. For more information please visit the Texas Department of State Health Services website and view an article about Dengue (PDF).