Vector Borne Diseases

vector borne diseasesVector borne diseases are a significant threat in the United States. Several vector-borne diseases showing up around the nation include: West Nile Virus (WNV), Chikungunya, Dengue, Eastern Equine Encephalitis (EEE), St. Louis Encephalitis (SLE), Lacrosse Virus,  Malaria and Zika Virus.

Zika Virus

Zika virus is spread to people through mosquito bites and a new threat in the USA. According to the CDC, the most common symptoms of Zika virus disease are fever, rash, joint pain, and conjunctivitis. The illness is usually mild with symptoms lasting from several days to a week.

Outbreaks of Zika have occurred in areas of Africa, Southeast Asia, the Pacific Islands, and the Americas. Because the Aedes species mosquitoes that spread Zika virus are found throughout the world, it is likely that outbreaks will spread to new countries. In January 2016, the United States reported its first confirmed Zika virus case.

There is no vaccine to prevent or medicine to treat Zika. Travelers can protect themselves from this disease by taking steps to prevent mosquito bites. When traveling to countries where Zika virus or other viruses spread by mosquitoes have been reported, use insect repellent, wear long sleeves and pants, and stay in places with air conditioning or that use window and door screens.

West Nile Virus

West Nile Virus (WNV) was first detected in the United States in 1999. Most infected individuals do not know they are infected because there are no symptoms for the virus. However, symptoms may develop if the virus progresses into West Nile Fever or severe West Nile Disease. Symptoms may include fever, headache, fatigue and body aches. Occasionally a skin rash or swollen lymph glands will develop. WNV can also lead to serious complications of the liver or nervous system, inflammation of the brain (encephalitis) or paralysis. According to the Centers for Disease Control and Prevention (CDC), more than 43,000 Americans have been infected with WNV, with more than 1,800 cases resulting in death. ADAPCO carries a test for WNV where a pool of mosquitoes is tested in an advanced RAMP system to determine whether or not one or more of the mosquitoes in the pool contains the virus.


Chikungunya is a viral disease that is spread by mosquitoes. It causes fever and severe joint pain. Other symptoms include muscle pain, headache, nausea, fatigue and rash. The disease is transmitted  by the same mosquitoes involved in the dengue transmission (Aedes aegypti and Aedes albopictus); also shares some clinical signs with dengue, and can be misdiagnosed in areas where dengue is common. There is no cure for the disease and treatment is focused on relieving the symptoms. The proximity of mosquito breeding sites to human habitation is a significant risk factor for Chikungunya. The disease occurs in Africa, Asia and the Indian subcontinent. In 2007, disease transmission was reported for the first time in Europe, in a localized outbreak in north-eastern Italy. On December 2013, PAHO/WHO received confirmation of the first cases of autochthonous transmission of Chikungunya in the Americas (Caribbean).

Chikungunya is characterized by an abrupt onset of fever frequently accompanied by joint pain, other symptoms or pain during chronic phase can include fatigue and depression. In addition, it includes muscle pain, headache, nausea, and rash. Most patients recover fully, but in some cases the joint pain may be chronic. Serious complications are not common, but in older people, children and pregnant women the disease can get worse.

The virus is transmitted by the bites of infected Aedes aegypti and Aedes albopictus mosquitos, both present in the Americas. After the bite of an infected mosquito, onset of illness occurs usually between 3 and 7 days but can range from 2 to 12 days.

Chikungunya must be distinguished from dengue. While both diseases patients may have diffuse body pain, having Chikungunya the pain is much more intense and localized in the joints and tendons than dengue. There are no specific drugs to cure the disease. Treatment is directed primarily at relieving the symptoms, including the joint pain. There is no commercial Chikungunya vaccine.


Dengue is an infectious disease caused by the dengue virus (DENV). It belongs to the genus Flavivirus of the Flaviviridae family, which in turn, belongs to the group of Arboviruses (arthropod-borne viruses). There are 4 serotypes called DENV-1, DENV-2, DENV-3 and DENV-4. Infection with one serotype produces lifelong immunity against that serotype reinfection. Successive infection with two different serotypes is a risk factor for developing the severe forms of the disease. All serotypes have been isolated in the Americas. In several countries they circulate simultaneously, creating a serious risk for an epidemic.

The Aedes aegypti and Aedes albopictus mosquitoes are transmitters of dengue. The Aedes aegypti female mosquitos are the main source of dengue transmission. These species bite during the day, with the most active feeding period 2 hours before and after dawn and dusk. The mosquito bites an infected person and ingests blood with the dengue virus, which incubates in the mosquito for a period of 8 to 12 days, after which the mosquito begins to transmit the virus biting others. The newly infected person may have symptoms after 5-7 days of infection. Immediate mechanical transmission can also occur when the mosquito interrupts feeding on an infected person and immediately feeds on a susceptible host. This form of transmission does not require virus incubation.

Eastern Equine Encephalitis

Eastern Equine Encephalitis (EEE or “Triple E”) is a vector borne disease that occurs most often in the eastern United States. It takes four to 10 days after being bitten for individuals to develop symptoms of EEE, beginning with the sudden onset of fever, general muscle pain and headaches of increasing severity. Many individuals will progress to more severe symptoms, such as seizures and coma. Approximately one-third of all people with clinical encephalitis caused by EEE will die from the disease. Of those who recover, many will suffer permanent brain damage that requires institutional care.

St. Louis Encephalitis

St. Louis encephalitis can occur throughout most of the United States. Since 1964, there have been more than 4,000 reported human cases of St. Louis encephalitis, with an average of 102 cases reported each year. An infected mosquito of the Culex species transmits the virus during blood meals. Symptoms of the virus will appear approximately five to 15 days after being bit. Symptoms include headache, high fever, neck stiffness, disorientation, coma, tremors and occasional convulsions or spastic paralysis. For a link to the CDC map of where the virus is in the US, click here.

LaCrosse Encephalitis Virus

LaCrosse encephalitis is a rare viral disease that is spread by infected mosquitoes and usually affects children. Found mostly in the upper Midwestern and mid-Atlantic and southeastern states, LaCrosse encephalitis is a vector borne disease that affects the central nervous system and cause severe complications. Symptoms of the virus include mild illness with fever, headache, nausea and vomiting, and tiredness. More severe cases can produce seizures, coma, paralysis and even brain damage.


Domestically generated malaria has been virtually eradicated in the United States since the 1950s, but the risk of infection has not. Two of the 10 species of Anopheles mosquito responsible for malaria transmission (Anopheles quadrimaculatus in the eastern states and An. freeborni in the west) are still widely prevalent in the continental United States. These vectors can become carriers by biting an infected human. Malaria is a mosquito-borne disease caused by a parasite. People with malaria often experience fever, chills, and flu-like illness. Left untreated, they may develop severe complications and die.

According to the CDC, in 2013 an estimated 198 million cases of malaria occurred worldwide and 500,000 people died, mostly children in the African Region. About 1,500 cases of malaria are diagnosed in the United States each year. The vast majority of cases in the United States are in travelers and immigrants returning from countries where malaria transmission occurs, many from sub-Saharan Africa and South Asia.