West Nile Virus (WNV) is a mosquito-borne virus that can infect humans, birds, horses, and other mammals. You can reduce your risk of being infected with WNV by using insect repellent and wearing protective clothing to prevent mosquito bites. Approximately 80% of 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, with milder symptoms; or
- West Nile neuroinvasive disease, with more severe symptoms.
About 20% of people who become infected will develop the milder form of the disease, West Nile fever, whereas less than 1% of infected persons will develop the more severe form, West Nile neuroinvasive disease.
What Are The Symptoms?
West Nile Fever Symptoms:
- Fever (Body Temperature: 99.6 F to 100.3 F)
- Headache
- Body aches
- Rash on the trunk of the body
- Swollen lymph glands
West Nile Neuroinvasive Disease Symptoms:
- Headache
- High fever (Body Temperature: 100.3o F & above)
- Stiff neck
- Stupor/disorientation
- Tremors
- Convulsions
- Muscle weakness
- Paralysis
- Coma
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. More severe cases require intensive hospital care. 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.
How Is West Nile Virus Spread?
- Infected Mosquitoes. Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite.
- Transfusions, Transplants, and Mother-to-Child. In a very small number of cases, WNV also has been spread through blood transfusions, organ transplants, breastfeeding and even during pregnancy from mother to baby.
- Not through touching. WNV is not spread through casual contact such as touching or kissing a person with the virus.
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.
How is West Nile Virus treated?
There is no specific treatment for WNV. Most people who become infected will get better on their own. In more severe cases, intensive supportive therapy is indicated, i.e., hospitalization, intravenous (IV) fluids and nutrition, airway management, ventilator support if needed, prevention of secondary infections and proper nursing care.
How long does it take to get sick if bitten by an infected mosquito?
Most people who are infected with WNV have no symptoms or experience only mild illness. If illness does occur, symptoms generally appear between 3 to 15 days of being bitten by an infected mosquito.
Click here for more information about West Nile Virus.
Click here to view the DSHS fact sheet on West Nile Virus.
Zika is spread mostly by the bite of an infected Aedes species mosquito. These mosquitoes bite during the day and night. 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.
Common symptoms of Zika
- Fever (Body Temperature: 99.6 F to 100.3 F)
- Rash
- Joint Pain
- Conjunctivitis (Red Eyes)
A pregnant woman can pass Zika to her fetus during pregnancy or around the time of birth, which can cause a serious birth defect. Also, a person with Zika can pass it to his or her sex partner(s). 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, 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.
People who have traveled to or live in places with risk of Zika are encouraged to protect themselves by preventing mosquito bites and sexual transmission of Zika.
- Both male and female condoms can reduce the chance of getting Zika from sex
- Use Environmental Protection Agency (EPA)-registered insect repellents
- Wear long-sleeved shirts and long pants
- Sleep under a mosquito bed net if air conditioned or screened rooms are not available or if sleeping outdoors.
Please see the Zika virus information video provided by the CDC:
Click here for general information on the Zika virus.
Chikungunya virus is primarily transmitted to people through the bite of an infected mosquito, mainly Aedes aegypti and Aedes albopictus.
Most common symptoms of Chikungunya
- Fever (Body Temperature: 99.6 F to 100.3 F)
- Joint Pain
Other symptoms may include
- Headache,
- Muscle Pain,
- Joint Swelling, Or Rash
Most people who become infected with chikungunya will develop symptoms, usually after four to 8 days after a mosquito bite. 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 (over 65 years), and people with medical conditions such as high blood pressure, diabetes, or heart disease. There is currently no vaccine to prevent or medicine to treat chikungunya virus infection.
Beginning in 2014, chikungunya virus disease cases were reported among U.S. travelers returning from affected areas in the Americas and local transmission was identified in Florida, Texas, Puerto Rico, and the U.S. Virgin Islands.
In late 2013, the first local transmission of chikungunya virus in the Americas was found in Caribbean countries and territories. As of the beginning of 2023 chikungunya cases in the Americas had reach over 210,000.
Travelers can protect themselves by preventing mosquito bites. When traveling to countries with chikungunya virus, use insect repellent; wear long-sleeved shirts and pants; and stay in places with air conditioning or that use window and door screens.
Click here for more info about Chikungunya Virus.
Dengue viruses are spread to people through the bite of infected mosquitoes. It is caused by one of any four related viruses. For this reason, a person can be infected with dengue virus multiple times in their life. The mosquitoes that infect people with the dengue virus are the same type that spread Zika and chikungunya viruses.
Symptoms usually begin four to 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.
Symptoms of Dengue
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
Vaccine is approved for use in children aged 9–16 years with laboratory-confirmed previous dengue virus infection and living in areas where dengue occurs frequently. The vaccine is not approved for use in U.S. travelers who are visiting but not living in an area where dengue is common.
Most outbreaks in the United States have been relatively small and limited to small areas. But because the types of mosquitoes that spread dengue are common throughout many areas of the United States, local spread of dengue is possible. The most recent dengue outbreaks occurred in Hawaii (2015), Florida (2013, 2020), and Texas (2013).
Click here for more info about Dengue Virus.
Malaria is a serious and sometimes fatal disease caused by a parasite that commonly infects a certain type of mosquito which feeds on humans. Malaria is transmitted among humans by female mosquitoes of the genus Anopheles. Female mosquitoes take blood meals for egg production, and these blood meals are the link between the human and the mosquito hosts in the parasite life cycle.
Symptoms of Malaria
- Fever and Flu-Like Illness
- Shaking Chills
- Headache
- Muscle Aches
- Tiredness
Malaria may cause anemia and jaundice (yellow coloring of the skin and eyes) because of the loss of red blood cells. If not promptly treated, the infection can become severe and may cause kidney failure, seizures, mental confusion, coma, and death.
About 2,000 cases of malaria are diagnosed in the United States each year. Most cases in the United States are seen in travelers and immigrants returning from countries where malaria transmission occurs, many from sub-Saharan Africa and South Asia.
The risk for a traveler contracting malaria differs substantially from region to region and from traveler to traveler, even within a single country, based upon travelers’ behaviors and circumstances.
A travel or tropical medicine specialist can be an excellent source of guidance when making these decisions. Depending on level of risk, it may be appropriate to recommend no specific interventions, mosquito avoidance measures only, or mosquito avoidance measures plus chemoprophylaxis.
CDC has a list of countries where malaria transmission occurs and the malaria drugs that are recommended for prevention in each country.
Click here for more info about Malaria.