Mosquito Diseases

Mosquitoes transmit disease causing organisms to humans and animals such as:

West Nile Virus

West Nile virus is a disease spread by mosquitoes. People react differently to the virus ranging from mild to severe reactions.

West Nile virus was first identified in 1937 in Uganda in eastern Africa. It was first discovered in the United States in the summer of 1999 in New York. Since then, the virus has been reported throughout the United States.

The West Nile virus is a type of virus known as a flavivirus. It is believed West Nile virus is spread when a mosquito bites an infected bird and then bites a person. Mosquitoes carry the highest amounts of virus in the early fall, which is why the rate of the disease increases in late August to early September. Although many people are bitten by mosquitoes that carry West Nile virus, most do not know they’ve been exposed. Few people develop severe disease or even notice any symptoms at all.

Signs of West Nile virus infection are similar to those of other viral infections. There may be no specific findings on a physical examination. However, up to half of patients with West Nile virus infection report having a rash.


Encephalitis is an acute infection and inflammation of the brain. Meningitis is the inflammation of the layers covering the brain.

Encephalitis is generally a viral illness. Viruses such as those responsible for causing cold sores, mumps measles and chickenpox, can also cause encephalitis. A certain family of viruses, the Arboviruses are spread by insects like mosquitoes and ticks. Although viruses are the most common source of infection, bacteria, fungi and parasites can also be responsible.

The illness resembles the flu and usually lasts for 2-3 weeks. It can vary from mild to life-threatening, and even cause death. Most people with a mild case can recover fully. Those with a more severe case can recover although they may have damage to their nervous system. This damage can be permanent.

Dengue (DEN-ghee)

Dengue [DEN-ghee] is a flu-like viral disease spread by the bite of infected mosquitoes. Dengue hemorrhagic fever is a severe, often fatal, complication of dengue. Dengue occurs in most tropical areas of the world. Most U.S. cases occur in travelers returning from abroad, but the dengue risk is increasing for persons living along the Texas-Mexico border and in other parts of the southern United States.

There is no specific treatment for dengue. Dengue and dengue hemorrhagic fever are caused by any of the Dengue family of viruses. Infection with one virus does not protect a person against infection with another. Dengue is spread by the bite of an Aedes mosquito. The mosquito transmits the disease by biting an infected person and then biting someone else. Dengue viruses occur in most tropical areas of the world. Dengue is common in Africa, Asia, the Pacific, Australia, and the Americas. It is widespread in the Caribbean basin.

Dengue is most common in cities but can be found in rural areas. It is rarely found in mountainous areas above 4,000 feet. The mosquitoes that transmit dengue live among humans and breed in discarded tires, flower pots, old oil drums, and water storage containers close to human dwellings. Unlike the mosquitoes that cause malaria, dengue mosquitoes bite during the day. Most dengue infections result in relatively mild illness, but some can progress to dengue hemorrhagic fever

Yellow Fever

Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The “yellow” in the name refers to the jaundice that affects some patients. Up to 50% of severely affected persons without treatment will die from yellow fever. There are an estimated 200 000 cases of yellow fever, causing 30 000 deaths, worldwide each year.

The virus is endemic in tropical areas of Africa and Latin America, with a combined population of over 900 million people. The number of yellow fever cases has increased over the past two decades due to declining population immunity to infection, deforestation, urbanization, population movements and climate change. There is no cure for yellow fever. Treatment is symptomatic, aimed at reducing the symptoms for the comfort of the patient. Vaccination is the most important preventive measure against yellow fever. The vaccine is safe, affordable and highly effective, and appears to provide protection for 30–35 years or more. The vaccine provides effective immunity within one week for 95% of persons vaccinated.

Once contracted, the virus incubates in the body for 3 to 6 days, followed by infection that can occur in one or two phases. The first, “acute”, phase usually causes fever, muscle pain with prominent backache, headache, shivers, loss of appetite, and nausea or vomiting. Most patients improve and their symptoms disappear after 3 to 4 days. However, 15% of patients enter a second, more toxic phase within 24 hours of the initial remission.


Malaria is a mosquito-borne disease caused by any one of four different blood parasites, called Plasmodia. The disease is transmitted to people by the Anophelesmosquito. This disease is a leading cause of debilitating illness, with over 200 million cases each year from around the world. Any person residing in or traveling to a country where malaria is prevalent is at risk for contracting the disease.

Malaria is currently a problem in tropical or subtropical areas of Asia, Africa and Central and South America. Susceptibility to malaria is universal except for a portion of Africans that have a natural immunity. Malaria is spread by the bite of an infected Anophelesmosquito. With certain malaria species, dormant forms can be produced which may cause relapses of malaria months to years later. Malaria may also be transmitted by transfusion of blood from infected people or by the use of contaminated needles or syringes.

Symptoms include fever, chills, sweats and headache, and in some instances may progress to jaundice, blood coagulation defects, shock, kidney or liver failure, central nervous system disorders and coma. Cycles of chills, fever and sweating occurring every one, two or three days is a good indicator of malaria in a person recently returning from a tropical area. The time between the infective mosquito bite and the development of malaria symptoms can range from 12 to 30 days depending on the type of Plasmodiainvolved.

Mosquitoes also transmit Heartworm in dogs.