Mosquito-Borne Diseases

Stylized mosquito. TexasMosquitoes.org: They'll ruin your day. They'll ruin your life.

en español

Chikungunya

Chikungunya is a disease caused by the chikungunya virus, which usually occurs in tropical and subtropical areas. Most cases in the United States are in travelers and immigrants returning from countries where local transmission is common. The virus is spread by mosquitoes that are most active during daylight hours but can also be active at night. The same mosquitoes that transmit chikungunya can also transmit the Zika and dengue viruses. Chikungunya is not spread from person to person, and pets and livestock do not get sick from chikungunya infection. There is no vaccine to prevent or specific medicine to treat chikungunya virus.

Most people who become infected with chikungunya will develop symptoms. Symptoms usually begin 3–7 days after getting a mosquito bite from an infected mosquito. Most patients will feel better within a week. In some people, joint pain may persist for months. Death is rare.

People at risk for more severe cases of chikungunya include newborns infected around the time of birth, older adults (≥65 years), and people with medical conditions such as high blood pressure, diabetes, or heart disease.

Chikungunya Symptoms:

  • Headache
  • Fever
  • Muscle pain
  • Joint pain and swelling
  • Rash

Chikungunya in Texas
Chikungunya information on the CDC website

Dengue

Dengue is a disease caused by any one of four closely-related dengue viruses. Most cases in the United States are in travelers and immigrants returning from tropical and subtropical countries where local transmission is common. Because there is more than one kind of dengue virus, people can get dengue more than once. People who get dengue a second time can become much sicker than they were the first time they had dengue. Dengue hemorrhagic fever and dengue shock syndrome are more severe forms of dengue infection. The four dengue viruses are transmitted by mosquitoes that are most active during the day, but can also be active at night. These are the same mosquitoes that can transmit the Zika and chikungunya viruses. Dengue is not spread from person to person, and pets and livestock do not get sick from dengue infection.

Symptoms usually begin 4–10 days after being bitten by an infected mosquito. Most patients will feel better within a week or two. Severe dengue has potentially deadly complications. There is no vaccine to prevent or specific medicine to treat dengue. People who think they have dengue should use pain relievers with acetaminophen and avoid those containing ibuprofen or aspirin.

Dengue Symptoms:

High fever and at least two of the following:

  • Severe headache
  • Severe eye pain (behind eyes)
  • Joint pain
  • Muscle and/or bone pain
  • Rash
  • Mild bleeding manifestation (e.g., nose or gum bleed, small red spots on the skin called petechiae, or easy bruising)
  • Low white blood cell count

Generally, younger children and those with their first dengue infection have a milder illness than older children and adults.

Watch for warning signs as temperature declines 3–7 days after symptoms began. Go IMMEDIATELY to an emergency room or closest healthcare provider if any of the following warning signs appear:

  • Severe abdominal pain or persistent vomiting
  • Red spots or patches on the skin
  • Bleeding from nose or gums
  • Vomiting blood
  • Black, tarry stools (feces, excrement)
  • Drowsiness or irritability
  • Pale, cold, or clammy skin
  • Difficulty breathing

Dengue in Texas
Dengue information on the CDC website

▲ Top

Eastern Equine Encephalitis (EEE)

Eastern equine encephalitis (EEE) is a viral illness that is transmitted through the bite of an infected mosquito. The virus is closely related to Western equine encephalitis and Venezuelan equine encephalitis viruses. Horses, other equines, and some birds can develop a severe illness which can be fatal. EEE is very rare in humans, and it is not passed from person to person. There is no specific treatment for EEE; care is based on treating symptoms. There is no vaccine to prevent EEE in humans, but there is a vaccine for horses.

The incubation period for EEE is from 4–10 days and can result in one of two types of illness: systemic or encephalitic. The type of illness depends on the age of the infected person and other factors. Some people who become infected will not develop any symptoms.

EEE Symptoms:

  • Fever
  • Chills
  • Joint and muscle pain

Illness may progress to:

  • Headache
  • Vomiting
  • Diarrhea
  • Disorientation
  • Convulsions
  • Coma

EEE is one of the most severe mosquito-transmitted diseases in the United States, with approximately a 33% mortality rate and significant brain damage in most survivors.

Eastern Equine Encephalitis (EEE) in Texas
EEE information on the CDC website

▲ Top

Malaria

Malaria is a serious and sometimes fatal mosquito-borne disease. It is caused by a parasite spread by infected mosquitoes. About 1,700 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 local malaria transmission is common. Locally-transmitted cases of malaria in the United States are rare and have not occurred recently in Texas. Pets and livestock do not get sick from malaria infection.

Treatment of malaria depends on many factors. In some instances, the illness can be treated with antimalarial drugs. Additional factors such as age, weight, the country in which the person became infected with malaria, and pregnancy status may limit the available options for malaria treatment.

Malaria Symptoms:

  • High fever
  • Shaking chills
  • Muscle aches
  • Tiredness

Malaria in Texas
Malaria information on the CDC website

▲ Top

St. Louis Encephalitis (SLE)

St. Louis encephalitis (SLE) is a viral illness spread from the bite of an infected mosquito. Mosquitoes are infected by feeding on infected birds. The SLE virus grows both in the infected mosquito and the infected bird, but does not make either one sick. Only infected mosquitoes can transmit the SLE virus to humans. SLE is not transmissible from person to person, and pets and livestock do not get sick from SLE infection. The virus is spread by mosquitoes that are most active at night, from dusk to dawn.

Most people infected with this virus will have either no symptoms or a mild illness with fever. The onset of symptoms is typically abrupt.

Symptoms usually show up suddenly within 5–15 days after being bitten by an infected mosquito. A small percentage of people, especially infants and elderly persons, may develop encephalitis (inflammation of the brain). There is no specific treatment for SLE; care is based on treating symptoms. There is no vaccine to prevent or specific medicine to treat SLE. Hospitalization may be needed for severe cases.

SLE Symptoms:

  • Fever
  • Headache
  • Nausea
  • Vomiting
  • Tiredness

Illness may progress to:

  • Stiff Neck
  • Confusion
  • Disorientation
  • Dizziness
  • Tremors
  • Coma

St. Louis Encephalitis (SLE) in Texas
SLE information on the CDC website

▲ Top

West Nile

West Nile virus (WNV) is spread to people, horses, birds, and some other animals through the bite of an infected mosquito. The virus is closely related to the St. Louis encephalitis virus. The virus is not passed from person to person. There is no specific treatment for WNV; care is based on treating clinical signs and symptoms. There is no vaccine to prevent WNV in humans, but there is a vaccine for horses. The virus is spread by mosquitoes that are most active at night, from dusk to dawn.

Some infected birds, especially crows and jays, are known to get sick and die from a WNV infection. Reporting and testing of dead birds is one way to check for the presence of WNV in the area. DSHS does not test dead birds for WNV, but some surveillance programs rely on citizens to report dead bird sightings to local authorities. Check with your local city or county government to see if they accept birds for WNV testing.

Most people infected with WNV will not have any signs of illness. For those who do develop symptoms, infection results in one of the two forms of the disease:

  • West Nile fever (WNF), with milder symptoms; or
  • West Nile neuroinvasive disease (WNND), with more severe symptoms.

Twenty percent of people who become infected will develop the milder form of the disease, WNF, whereas only 1 out of 150 will develop the more severe form, WNND. People with weakened immune systems are at an increased risk for developing symptoms, and people older than 50 have the highest risk of severe disease. Mild disease may last a few days, and symptoms of severe disease may last several weeks, although neurological effects may be permanent. Rarely, death can occur.

WNF Symptoms:

  • Fever
  • Headache
  • Body aches
  • Rash on the trunk of the body
  • Swollen lymph glands

WNND Symptoms:

  • Headache
  • High fever
  • Stiff neck
  • Stupor/disorientation
  • Tremors
  • Convulsions
  • Muscle weakness
  • Paralysis
  • Coma

West Nile Virus (WNV) in Texas
WNV Fact Sheet (PDF)
WNV information on the CDC website

▲ Top

Western Equine Encephalitis (WEE)

Western equine encephalitis (WEE) is a viral illness that is transmitted to people and horses through the bite of an infected mosquito. The WEE virus is closely related to the Eastern equine encephalitis and Venezuelan equine encephalitis viruses. Illness caused by the WEE virus is very rare in Texas and the United States. The virus is spread by mosquitoes that are most active at night, from dusk to dawn. There is no vaccine to prevent WEE in humans, but there is a vaccine for horses.

Most people infected with this virus will not become ill. Others may develop a mild illness with fever within 1–2 weeks of being bitten by an infected mosquito. A small percentage of people, especially infants and elderly persons, may develop encephalitis (inflammation of the brain), which may require hospitalization and may be fatal. There is no specific treatment for WEE; care is based on treating symptoms.

WEE Symptoms:

  • Headache
  • High fever
  • Stiff neck
  • Weakness
  • Vomiting

Illness may progress to:

  • Disorientation
  • Irritability
  • Seizures
  • Coma

Western Equine Encephalitis (WEE) in Texas

▲ Top

Zika

The Zika virus spreads to humans primarily through the bite of certain types of mosquitoes. Most cases in the United States are in travelers and immigrants returning from tropical and subtropical countries where local transmission is common. The mosquitoes that transmit Zika virus are most active during the day, but can also be active at night. These are the same mosquitoes that can transmit the dengue and chikungunya viruses.

If infected while pregnant, a mother can pass Zika to her unborn child. Zika infection during pregnancy can cause birth defects like microcephaly, a condition where a baby’s head is much smaller than expected, as well as other brain defects and developmental delays in the child. Zika virus can also be passed from person to person through sexual contact and blood transfusions. Zika infection does not generally cause illness in pets or livestock.

Currently, there is no vaccine or specific treatment for Zika. The best protection is to avoid infection by preventing mosquito breeding and bites and practicing safe sex. Pregnant women, travelers to countries where Zika is common, and those who spend a lot of time outdoors should be especially cautious.

Most people with Zika don’t have any symptoms. However, people who don’t develop symptoms can still pass the virus to others. If a person does have symptoms, they are usually mild and last several days to a week. Men can potentially transmit Zika virus to their sexual partners for up to 3 months after infection.

Zika Symptoms

  • Joint pain
  • Conjunctivitis (red eyes)
  • Fever
  • Rash (often itchy)

Zika in Texas
Zika information on the CDC website

▲ Top

Last updated March 1, 2019