Williamson County and Cities Health District
Frequently Asked Questions
Q: How do people get West Nile virus?
1. Infected Mosquitoes
Humans primarily get West Nile virus through mosquito bites. WNV is spread to humans by the bite of an infected mosquito. A mosquito gets infected by biting a bird that is infected with the virus. An uninfected mosquito cannot bite an infected human and become infected. Mosquitoes also do not transmit the virus between people.
2. Transfusions, Transplants, Mother-to-Child
Rarely, the virus has been spread by blood transfusion, organ transplant, breastfeeding, and from mother to child during pregnancy. Donated blood is check for WNV before being used.
West Nile virus is NOT spread by casual contact such as touching, kissing, or caring for someone who is infected. (3)
Q: What are the symptoms of West Nile virus infection?
A: Symptoms generally occur 2-14 days following the bite of an infected mosquito.
Most people – 80%- of the people who are infected with West Nile have no symptoms or may experience mild illness, then recover fully. Often, these people only know they have West Nile because the virus is detected when they have blood work done for an unrelated reason, such as blood donation or routine lab work.
Up to 20% of people who are infected with West Nile contract West Nile Fever, a flu-like illness that causes symptoms such as fever, headache, body aches, nausea, and, less frequently, skin rash on chest, stomach and back, or sometimes swollen lymph glands or eye pain. Often times this gets diagnosed as general flu-like virus and the patient is not tested for West Nile unless there is known West Nile circulating in the area.
Fewer than 1% of individuals infected with West Nile can develop West Nile neuroinvasive disease, a serious form of the virus that affects the nervous system. Symptoms include encephalitis, severe headache, high fever, stiff neck, disorientation, muscle weakness, numbness, tremors, vision loss, coma, or paralysis. These symptoms last several weeks, and can cause death or permanent brain damage. The elderly are most at risk for this form of West Nile, but anyone who contracts West Nile has a chance of developing this most severe form. There is no treatment for West Nile virus, however doctors can treat the symptoms. Many people that have experience West Nile neuroinvasive disease report long-term effects from the infection. (3)
Q: Do we have West Nile Virus in Williamson County?
A: Yes. West Nile virus is in Williamson County and is transmitted through the bite of the southern house mosquito, Culex quinquefasciatus. WCCHD currently operates a West Nile surveillance program in collaboration with the Texas Department of State Health Services. Maps of current West Nile activity in Williamson County can be found here.
Q: Is there a treatment or a vaccine for West Nile virus infection?
A: There is no specific treatment, medication, cure, or vaccine. Most people who get this illness recover from it on their own. In more severe cases, people may need to go to the hospital where they can receive supportive care to treat their symptoms. There is a West Nile vaccine for horses that can be administered by your veterinarian. (3)
Q: Where did West Nile come from?
A: Outbreaks of WNV disease have occurred in Africa, Egypt, Israel, Asia, Romania, Russia, and France. Before 1999, however, WNV had never before been found in the Americas. The most likely explanation for its appearance here is that the virus was introduced by an infected bird that was imported or by infected mosquitoes that were introduced through shipping ports. (1)
Q: Besides mosquitoes, can you get West Nile Virus from other insects or ticks?
A: Infected mosquitoes are the primary source of WNV. While some tick species have been implemented in West Nile transmission in Africa and Asia, the natural occurrence is very rare and there has been no reported cases from North America. (1, 5)
Q: How long does it take to get sick if bitten by an infected mosquito?
A: The incubation period is 2-6 days, but can range from 2-14 days. This period can be longer in people with certain medical conditions that affect the immune system. (4)
Q: Can dogs, cats and other pets get the West Nile virus?
A: Yes. Horses are very susceptible to West Nile virus but can be vaccinated. Cats and dogs rarely, if ever, get sick. Most infections have been identified in birds, but West Nile virus has been shown to infect dogs, cats, horses, and domestic rabbits, as well as bats, chipmunks, skunks, and squirrels. (2) Birds can become very ill from the virus, so it is recommended that pet birds be kept indoors, especially during dawn and dusk.
Q: I have backyard chickens… can they get or transmit WNV?
A: Poultry can neither directly infect other birds, animals, or humans, nor act as a reservoir for the virus.
Although chickens and turkeys can become infected with the virus
when bitten by infected mosquitoes, these birds do not develop the clinical disease. Their immune
system quickly responds to infection by producing antibodies that clear the virus from their body.
Also, because the virus can be transmitted only through the bite of an infected mosquito, infected
poultry present no significant public health risk.
Q: If my chickens were exposed to infected mosquitoes, are the eggs safe to eat?
A: Yes! Poultry can neither directly infect other birds, animals, or humans, nor act as a reservoir for the virus.
If your poultry is exposed to the virus, it cannot be passed from adult bird to egg.
Q: What is the risk of someone becoming infected with West Nile?
A: The risk is very low. Even in areas where the virus is circulating, only around 1% mosquitoes are infected with the virus. 80% of West Nile virus infections are asymptomatic, meaning a person never gets sick. 20% of people may experience West Nile fever, which presents as flu-like symptoms. Less than 1% of people who get bitten and become infected will get West Nile neuroinvasive disease, however the immunocompromised and those >50 years old are more likely to experience West Nile neuroinvasive disease.
Q: I’ve heard of " suspect cases," " positive cases," " confirmed cases," and " probable cases." What does it all mean?
A: Infections with West Nile virus may, or may not, produce illness. A few people who get ill may seek medical care. Those with severe enough disease that has the appearance of West Nile and similar viruses may have blood or spinal fluid sampled for testing. (2)
Testing of samples has two main components:
- Samples may be tested for antibodies to West Nile and other viruses. A positive result indicates that the patient may have been exposed to the virus, but does not prove that the virus is still in the patient.
- Samples may also be tested to find the actual virus. This type of test is more difficult, takes much longer, and may not be successful. A negative test does not prove that the virus did not cause the illness.
Q: Can a human get West Nile virus twice?
A: Medical professionals don’t believe so. Like many other viruses, medical tests indicate that once a person has been infected with West Nile, he/she develops a natural immunity to future infection by the virus for life. However, this immunity may decrease over time or with further health conditions that compromise the immune system. Because West Nile has not been active in the United States for many years, future tests may tell us more about the long-term health implications of West Nile. (3)
Q: What's the best insect repellant to use?
A: Using the right insect repellent and other preventive actions can discourage ticks, mosquitoes, and other biting insects from landing on you. Repellents are available to protect you from insects and give you the length of protection you need, based on your planned activity. Visit the EPA's website for more information and to search for the best repellant for your situation.
Q: What can I do around my home to mamage mosquitoes?
A: Visit the Managing Mosquitoes Around Your Home page for information and tips.
Definitions of terms:
Suspect: A patient with symptoms similar to West Nile might be considered a suspect by their physician. Since they would also be suspect for a multitude of others diseases with similar signs, they are not counted or reported by Texas.
Positive case: Many laboratories can test for West Nile and may find positive results. These results are often cross-reactions with other conditions and may not represent a true West Nile positive. Only those results that meet the case definitions for “Confirmed” or “Probable” will be reported as “cases.”
Confirmed: A febrile illness associated with neurologic manifestations ranging from headache to aseptic meningitis or encephalitis, plus at least one of the following:
- Isolation of WN virus from or demonstration of WN antigen or genomic sequences in tissue, blood, cerebrospinal fluid, or other body fluid;
- Demonstration of IgM antibody to WN virus in cerebrospinal fluid by IgM-capture enzyme-linked immunoassay (EIA);
- A > 4-fold serial change in plaque-reduction neutralizing test (PRNT) antibody titer to WN virus in paired, appropriately timed serum or cerebrospinal fluid samples;
- Demonstration of both WN virus-specific IgM (by EIA) and IgG (screened by EIA or HI and confirmed by PRNT) antibody in a single serum specimen.
Probable case: Symptoms identical to that for a confirmed case plus one or more of the following:
- Demonstration of serum IgM antibody against WN virus (by EIA);
- Demonstration of an elevated titer of WN virus-specific IgG antibody in convalescent-phase serum (screened by EIA or hemagglutination inhibition (HI) and confirmed by PRNT).