Mosquito Facts & Diseases

Mosquito Facts

  • All mosquitoes must have water to complete their life cycle.
  • Mosquitoes do not develop in grass or shrubbery, although, flying adults frequently rest in these areas during daylight hours.
  • Only the female mosquito bites to obtain a blood meal. The male mosquito feeds only on plant juices.
  • The female mosquito may live as long as three weeks during the summer or many months over the winter in order to lay her eggs the following spring.

Mosquito Life Cycle

Life cycle of mosquito


Mosquitoes are members of the fly group (Order Diptera) and go through four distinct stages of development. All mosquitoes start their life as an egg. Some species of mosquitoes lay their eggs directly on the surface of the water and others lay their eggs in the moist soil around flood water sites. Eggs will hatch in water and larvae emerge. All larvae must go through four stages of growth, called instars, in the water, often known as wigglers. the next stage is the resting, non-feeding stage called pupa. In this stage, the mosquito becomes an adult.

Mosquito pupae always live in water. Female adult mosquitoes will mate and then leave to find a suitable host to suck blood.

She uses the blood to help develop her eggs and then she lays the eggs to start the cycle all over.

Mosquito "Bites" and Public Health

Mosquitoes can spread disease only when they bite their victim. Although it is commonly called a "bite," the process is actually a piercing-sucking action. Only the female mosquito bites, and takes a blood meal. The blood protein is needed to complete the mosquito's egg production cycle. During the feeding process, the female pierces her victims skin with her proboscis, (a long straw like structure with a sharp end) injects her saliva (which contains anti-coagulants) and then sucks the victim's bloods in through her proboscis. If the victim's blood contains disease-causing organisms, they too get sucked into the mosquitoes stomach. These organisms are then maintained within the mosquito and eventually may be injected into the next victim's bloodstream. In this way the mosquito can spread disease from animal to animal, animal to man, or even from person to person.

In the United States there are now about seven primary mosquito-borne viruses that are capable of crossing the blood-brain barrier in humans and other animals, causing an acute infection of the central nervous system. These include Western Equine EncephalitisSt. Louis Encephalitis, and West Nile Virus which have been known to occur in Texas.

Mosquitoes are responsible for more human deaths than any other living creature. Worldwide, nearly 4 million people die each year from various mosquito-borne diseases.

Learn more about mosquitoes found in America and worldwide(PDF, 2MB)

Mosquito-Borne Diseases

Mosquitoes are responsible for more human deaths than any other living creature. Worldwide, nearly 4 million people die each year from various mosquito-borne diseases. Learn more about mosquitoes found in America and worldwide(PDF, 2MB)

West Nile Virus

What is West Nile Virus?

According to the Centers for Disease Control and Prevention, West Nile virus (WNV) is the leading cause of viral encephalitis in the United States. Originally discovered in Africa in 1937, WNV was first detected in the United States in 1999 in New York City. Since then it has caused seasonal epidemics of West Nile virus; fever and severe disease. West Nile virus is transmitted to humans and animals through the bite of an infected mosquito. Mosquitoes become infected with WNV when they feed on infected birds.

Where did West Nile virus come from?

West Nile virus has been commonly found in humans, birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East, but until 1999 had not been documented in the Western Hemisphere. It is not known where the U.S. virus originated, but it is most closely related to strains found in the Middle East.

How long has West Nile virus been in the U.S.?

It is not known exactly how long the virus has been in the U.S., but Centers for Disease Control scientists believe it has probably been in the eastern U.S. since the early summer of 1999 or possibly longer.

How do people get infected with West Nile virus?

Humans get West Nile virus (WNV) through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. The virus eventually gets into the mosquito’s salivary glands. During subsequent blood meals, the virus may be injected into humans and animals, where it can multiply and possibly cause illness. Other methods of transmission which have been reported, though they are a very small proportion of cases include WNV transmission through: transplanted organs, blood transfusions, or transplacental, from mother-to-child.

If I live in an area where birds or mosquitoes with West Nile virus have been reported and a mosquito bites me, am I likely to get sick?

No. Even in areas where mosquitoes do carry the virus, very few mosquitoes are infected. If the mosquito is infected, less than 1% of people who get bitten and become infected will get severely ill. Approximately 1 in 150 people get severely sick.

Can you get West Nile encephalitis from another person?

No. West Nile encephalitis is NOT transmitted from person-to-person. For example, you cannot get West Nile virus from touching or kissing a person who has the disease, or from a health care worker who has treated someone with the disease.

Besides mosquitoes, can you get West Nile virus directly from other insects or ticks?

Infected mosquitoes are the primary source for West Nile virus. Although ticks infected with West Nile virus have been found in Asia and Africa, their role in the transmission and maintenance of the virus is uncertain. There is no information to suggest that ticks played any role in the cases identified in the United States.

Can you get West Nile virus directly from birds?

There is no evidence that a person can get the virus from handling live or dead infected birds. However, persons should avoid bare-handed contact when handling any dead animals and use gloves or double plastic bags to place the carcass in a garbage can.

Can I get infected with West Nile virus by caring for an infected horse?

West Nile virus is transmitted by the bite of an infected mosquito. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus.

If a person has had West Nile virus, can they still donate blood?

With West Nile virus infection, the virus is usually short lived and people clear it very quickly. Blood centers take appropriate precautions to be sure that donors who have been diagnosed with West Nile virus have fully recovered before donating.

Is there a vaccine against West Nile encephalitis?

No, but several companies are working towards developing a vaccine.

Where can I get more information on mosquito repellents?

For a variety of information regarding repellent, visit the Center for Disease Control's Insect Repellent Use & Safety Web page. You can also find information on insect repellents containing DEET at

What are the symptoms of West Nile encephalitis?

Most infections are mild, and symptoms include fever, headache, and body aches, occasionally with skin rash and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and, rarely, death.

What is the incubation period in humans (i.e., time from infection to onset of disease symptoms) for West Nile encephalitis?

Usually 3 to 15 days.

I think I have symptoms of West Nile virus. What should I do?

Contact your health care provider if you have concerns about your health. If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headaches, you should see your doctor immediately.

Can West Nile virus cause illness in dogs or cats?

A relatively small number of WNV infected dogs (<40) and only 1 WNV infected cat have been reported to CDC. Experimentally infected dogs showed no symptoms after infection with WNV. Some infected cats exhibited mild, nonspecific symptoms during the first week after infection–for the most part only showing a slight fever and slight lethargy. It is unlikely that most pet owners would notice any unusual symptoms or behavior in cats or dogs that become infected with WNV.

Can a horse infected with West Nile virus infect horses in neighboring stalls?

No. There is no documented evidence that West Nile virus is transmitted between horses. However, horses with suspected West Nile virus should be isolated from mosquito bites, if at all possible.

Where can I get more information on horses and West Nile virus?

Visit the California Department of Food and Agriculture (CDFA)'s Equine West Nile Virus Web page or the U.C. Davis Center for Equine Health website.

Are duck and other wild game hunters at risk for West Nile virus infection?

Because of their outdoor exposure, game hunters may be at risk if they become bitten by mosquitoes in areas with West Nile virus activity. The extent to which West Nile virus may be present in wild game is unknown. Surveillance studies are currently underway in collaboration with the U.S. Geological Survey (USGS), National Wildlife Health Center (in Madison, Wisconsin) and with state and local wildlife biologists and naturalists to answer this question.

What should wild game hunters do to protect against West Nile virus infection?

Hunters should follow the usual precautions when handling wild animals. If they anticipate being exposed to mosquitoes, they should apply insect repellents to clothing and skin, according to label instructions, to prevent mosquito bites. Hunters should wear gloves when handling and cleaning animals to prevent blood exposure to bare hands and meat should be cooked thoroughly.

More Information on West Nile Virus:

Centers for Disease Control and Prevention (CDC): West Nile Virus Information

Dallas County Health and Human Services: West Nile Virus Information

Zika Virus

The Zika Virus is a newly emergent mosquito-borne virus, which is most commonly transmitted to humans from the bite of an infected mosquito and from infected humans to mosquitoes.

The U.S. Centers for Disease Control (CDC) has recently warned travelers – specifically pregnant women – regarding traveling to countries that are currently affected by the spread of the virus.

More Information on Zika Virus:

Centers for Disease Control and Prevention (CDC): Zika Virus Information

CDC: Travel Advisories

Dallas County Health and Human Services: Zika Virus Information

Chikungunya Virus

Chikungunya (pronunciation: \chik-en-gun-ye) is:

  • a virus that is spread through mosquito bites—the same Aedes mosquitoes that spread dengue.
  • a risk to anyone traveling to a region of the world where chikungunya is found.

Signs and symptoms of disease:

  • Symptoms usually begin 3-7 days after being bitten by an infected mosquito.
  • The most common symptoms are fever and severe joint pain, often in the hands and feet. Other symptoms may include headache, muscle pain, joint swelling, or rash.
  • Most patients will feel better within a week. Some people develop longer-term joint pain that can last weeks to months. Death is rare but can occur.
  • People at increased risk for severe disease include newborns exposed during delivery, older adults
    (≥65 years), and people with medical conditions such as high blood pressure, diabetes, or heart disease.

Global Risk

The virus has been found in parts of Africa, Southern Europe, Southeast Asia, and islands in the Indian and Pacific Oceans.

In 2013, chikungunya was found for the first time in the Americas. Since, it has spread to the Caribbean, South and Central America and in North America.

Traveling? For country-specific information and recommendations, visit

Sick? Could it be Chikungunya?

  • See your doctor if you think you or a family member might have chikungunya.
  • Your doctor may order blood tests to look for signs of chikungunya or other similar diseases, like dengue.

Chikungunya is preventable, but not treatable

  • There is no vaccine to prevent or medicine to treat chikungunya.
  • The mosquitoes that spread chikungunya bite aggressively during the day. The best way to avoid infection is to prevent mosquito bites.
    • Use air conditioning or window/door screens.
    • Use mosquito repellents on exposed skin. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide long lasting protection.
    • Wear long-sleeved shirts and long pants or permethrin-treated clothing.
    • Empty standing water from outdoor containers.
  • People at increased risk for severe disease should consider not traveling to areas with ongoing chikungunya outbreaks.
  • If you are sick with chikungunya, avoiding mosquito bites will help prevent further spread of the virus.

More Information on Chik-V Virus:

Centers for Disease Control and Prevention (CDC): Chikungunya Virus Information

CDC Fact Sheet: Chikungunya - What You Need to Know(PDF, 771KB)

Grand Prairie Environmental Quality: Chikungunya Info PowerPoint(PDF, 629KB)

According to the Centers for Disease Control (CDC), the number of reported cases of disease from mosquito, tick, and flea bites has more than tripled between 2004 and 2016.