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Saturday, March 25, 2017

Phone: 757-890-3790   TDD: 757-890-3621 

Mosquito Borne Viruses


Mosquito Borne Viruses




Mosquito Control
145 Goodwin Neck Road
PO Box 532
Yorktown, VA 23692-0532  

Phone: 757-890-3790
TDD: 757-890-3621
FAX: 757-890-3794
SPRAY HOTLINE: 757-890-3793
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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, or chikungunya, or Zika. These cases usually occur in people who have traveled to tropical or sub-tropical areas of the world.

West Nile (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. It was first identified in the United States in New York in 1999. Mosquitoes become infected by biting a bird that carries the virus. The genus Culex is associated with the spread of west Nile and St. Louis encephalitis. There are over 30 species nation-wide known to be vectors for West Nile and St. Louis encephalitis.

St. Louis encephalitis (SLE) is closely related to West Nile virus and is transmitted by the same mosquito species. Mosquitoes become infected by feeding on birds infected with SLE. 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.  SLE was first reported in humans in Virginia in 1975 and a total of 13 cases have been reported in Virginia to date.

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. EEE occurs in the eastern half of the US and is most commonly detected around swamps in Virginia’s coastal plain. Symptoms range from mild flu-like illness to encephalitis, coma, and death. About 35% of people who develop the disease die. It is estimated that 35 percent of people who survive EEE will have mild to severe neurologic after effects from this disease. Human cases of EEE are somewhat rare.  The most recent human case of EEE was reported in 2003. Horses and certain birds like ostriches and emus can become infected with, and die from, EEE virus infection.

The EEE virus is maintained in a cycle between Culiseta melanura mosquitoes and avian hosts in freshwater hardwood swamps. Cs. melanura is not considered to be an important vector of EEE to humans because it feeds almost exclusively on birds. Transmission to humans requires mosquito species capable of creating a "bridge" between infected birds and uninfected mammals such as some Aedes, Coquillettidia, and Culex species.

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.

Malaria is an ancient disease. In all likelihood originating in Africa, it has been described by the Chinese as far back as 2700BC and the Sumerians from 1700 BC. The malaria parasite (plasmodium) is transmitted by female Anopheles mosquitoes.  More than one million deaths and 300 - 500 million cases are still reported annually in the world.  In the United States malaria affected colonization along the eastern shore and wasn't effectively controlled until the 1940s when mosquito control organization instituted Anopheles control programs. 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.

Dengue is a serious arboviral disease of the Americas, Asia and Africa. Although it has a low mortality, dengue has very uncomfortable symptoms and has become more serious, both in frequency and mortality, in recent years. Aedes aegypti and Aedes albopictus are the vectors of dengue. These mosquitoes prefer to lay their eggs in containers close to human habitations and are not well-controlled by standard spraying techniques. Over the last 16 years dengue has become more common; for example, in south Texas 55 cases were reported in 1999 causing one death. More recently, Hawaii recorded 85 cases of dengue during 2001 and the Florida Keys reported over 20 cases in 2010. In 2010, Puerto Rico experienced its largest outbreak, with 21,000 cases reported. In 2009, Florida reported the first cases of local dengue transmission in 75 years, within Old Town, Key West.

Chikungunya virus is a pathogen transmitted by mosquitoes, and has established itself in the Caribbean (approximately 350,000 suspected cases in the Western Hemisphere since December 2013). It has now resulted in 2 cases of locally-transmitted Chikungunya virus in Florida in July of 2014. As of July 22, 2014, 497 travel-related cases have been found in 35 states, Puerto Rico and the U.S. Virgin Islands. The name “Chikungunya” is attributed to the Kimakonde (a Mozambique dialect) word meaning “that which bends up”, which describes the primary symptom – excruciating joint pain. Although rarely fatal, the symptoms are debilitating and may persist for several weeks.

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. Traditional mosquito methods of truck-mounted and aerial sprays are ineffective in controlling these mosquitoes. Removal of water-bearing containers and sanitation are key preventive strategies.

Zika is an emerging 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 possible vector of Zika in this area is Aedes albopictus, the Asian Tiger mosquito. There are two strains of Zika virus, African and Asian; the strain causing the current outbreaks in South America is the Asian strain. Zika virus may be transmitted by infectious mosquito bites, infection of unborn children by their infected mothers, blood transfusions from asymptomatic, Zika - infected blood donors, and by sexual transmission of Zika virus in infected sperm. The virus produces a range of symptoms including rash, fatigue, fever, conjunctivitis, itching, joint pain, and swelling. The virus is also being correlated with an increase in the birth defect microcephaly and the Guillain-Barre syndrome. Current research is showing that pregnant women that are bit by an infected mosquito within the first trimester are at highest risk. With the exception of the microcephaly and Guillain-Barre syndrome; the Zika virus in itself is not fatal and produces relatively mild symptoms. Also, only about 20% of those afflicted with the virus are symptomatic; the remaining 80% are asymptomatic.

References are available upon request.  Please contact the Mosquito Control Superintendent at 757-890-3791 for more information.