Mosquito Borne Viruses

The most common mosquito-borne diseases found in eastern Virginia include West Nile Virus (WNV), St. Louis Encephalitis (SLE), Eastern Equine encephalitis (EEE), and Dog Heartworm (Dirofilaria immitis).

It is also not uncommon for Virginia to report a few imported cases of a mosquito-borne disease each year. Diseases may include malaria, dengue, chikungunya, or Zika. These cases usually occur in people who have traveled to tropical or sub-tropical areas of the world and come back to the United States.

VDH:  "Bugs & Human Health
CDC:  Protecting Workers from Mosquito Bites can Prevent Diseases

References are available upon request. Please contact the Mosquito Control Superintendent at 757-890-3790 for more information.

West Nile Virus

The most common mosquito-borne diseases found in eastern Virginia. West Nile Virus (WNV) is spread by the bite of an infected mosquito, most symptoms are mild, but there have been cases of encephalitis (inflammation of the brain), meningitis (inflammation of the lining of the brain and spinal cord), or polio-like paralysis.

West Nile Virus Testing

Mosquito Control Division tests mosquitoes that are vectors for West Nile from the end of May/June until the end of October/end of the mosquito season.

Eastern Equine Encephalitis

Eastern Equine Encephalitis (EEE) is a mosquito-borne viral disease and, because of the rate of death among infected persons, is regarded as one of the most serious mosquito-borne diseases in the United States. Luckily for York County residents, there are low numbers of the mosquito species that carries it in the County.

Horse Owners are Encouraged to Vaccinate Horses

The Department of Agriculture encourages horse owners to vaccinate against mosquito-borne diseases, such as West Nile Virus and Eastern Equine Encephalitis.

Read the Full Article to Learn More

Dog Heartworm

Dog Heartworm (Dirofilaria immitis) can be a life-threatening disease for canines.  The disease is caused by a roundworm. Dogs and sometimes other animals such as cats, foxes and raccoons are infected with the worm through the bite of a mosquito carrying the larvae of the worm. The disease in dogs and cats cannot be eliminated but it can be controlled or prevented with pills and/or injections.

St. Louis Encephalitis

St. Louis Encephalitis (SLE) is closely related to West Nile Virus and is transmitted by the same mosquito species.  The virus grows both in the infected mosquito and the infected bird, but does not make either one sick. You cannot get the virus from other people, birds or insects other than mosquitoes. St. Louis encephalitis is more prominent in the Western area of Virginia.

Diseases Likely Carried by Travelers Returning Home

Chikungunya Virus

Chikungunya virus is a pathogen transmitted by mosquitoes, and has established itself in the Caribbean.  The mosquito species that transmit this disease are the Asian Tiger Mosquito (Aedes albopictus) and the Yellow Fever Mosquito (Aedes aegypti). Both species lay their eggs in containers such as cans, discarded tires and other items that hold water close to human habitation, but Ae. aegypti is more geographically confined to the southeastern United States. 

Dengue Fever

Although it has a low mortality, dengue fever has very uncomfortable symptoms and has become more serious, both in frequency and mortality.


Malaria is an ancient disease with more than one million deaths and 300 to 500 million cases are still reported annually in the world.  Minor outbreaks of locally-acquired malaria occur sporadically in the United States, but have been quickly controlled by aggressive mosquito control measures. Anopheles quadrimaculatus is the mosquito in the Hampton Roads Area responsible for the spread of malaria.


Zika is an arbovirus that is spread directly from mosquitoes to humans and vice versa, unlike other arboviruses that are permanently established and spread through bridge vectors, such as birds. The main vector would be Ae. aegypti which have not been found in York County.