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West Nile Virus - Overview

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1. What is West Nile Virus?

West Nile Virus is a virus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus which is also found in the United States. The virus can infect:

• Birds
• Horses
• Humans
• Mosquitoes
• Some Other Mammals

2. What are the differences between West Nile neuroinvasive disease (WNND) and West Nile fever (WNF)?

The most severe type of disease due to a person being infected with the West Nile virus is called "neuroinvasive disease" because it affects a person’s nervous system. It is characterized by:

• Disorientation
• Headache
• High Fever
• Neck Stiffness
• Stupor and Other Serious Symptoms

Symptoms can last weeks to months, and can even result in death. West Nile neuroinvasive disease (WNND) only infects approximately 1% of people who have been bitten by a West Nile fever (WNF) - carrying mosquito. West Nile fever is another type of illness that can occur in people who become infected with the virus. It is characterized by:

• Aches
• Fever
• Headache
• Tiredness and Sometimes Rash

Although the illness can be as short as a few days, even healthy people have been sick for several weeks. WNF infects approximately 20% of people who have been bitten by a WNF - carrying mosquito.

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

It is not known how long it has been in the U.S, but the Centers for Disease Control and Prevention (CDC) scientists believe the virus has probably been in the eastern U.S. since the early summer of 1999, possibly longer. It is now established as a seasonal epidemic in North America.

4. How long has West Nile Virus been in Denton County?

Denton County reported its first case of West Nile Virus in 2002.

5. How long is the West Nile Virus season in the U.S.?

Typically, the season lasts from the summer months and into the fall.

6. What is the basic transmission cycle of West Nile Virus?

Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit West Nile Virus to humans and animals while biting to take blood. The virus is located in the mosquito’s salivary glands. During blood feeding, the virus may be injected into the animal or human, where it may multiply, possibly causing illness.

7. What is the incubation period in humans (i.e., time between bite from infected mosquito to appearance of symptoms) for West Nile disease?

Usually 3 to 14 days.

8. How long do symptoms last?

Symptoms of West Nile fever will generally last a few days, although even some healthy people report having the illness last for several weeks. The symptoms of severe disease (West Nile neuroinvasive disease) may last several weeks or months, although neurological effects may be permanent.

9. I think I have West Nile Virus, do I need to report it to the Health Department?

If you believe you have West Nile Virus, see your health care provider. He/she will do a clinical exam and will run blood tests or spinal fluid tap if necessary. If a case is suspected by your health care provider, he/she is required to report that information to the Health Department. The Health Department will then investigate every case, and will contact you if necessary. There are 78 diseases that health care providers are required to report to their county health department, and West Nile Virus is one of them.

10. I've been bitten by a mosquito. Should I be tested for West Nile Virus?

No. Illnesses related to mosquito bites are still uncommon, and only 20% of people bitten by a mosquito infected with West Nile Virus will develop symptoms. However, you should see a doctor immediately if you develop symptoms such as:

• Confusion
• High fever
• If your eyes become sensitive to light
• Muscle weakness
• Severe headaches
• Stiff neck

Patients with mild symptoms should recover completely, and do not require any specific medication or laboratory testing.

11. My doctor told me that I have West Nile Virus. How do I report it to the Health Department?

No. Your health care provider is required to report that information to the Health Department. The Health Department will then investigate every case, and will contact you if necessary. There are 78 diseases that health care providers are required to report to their county health department, and the West Nile virus is one of them.

12. Can a human get the virus twice?

We don’t think so. It is assumed that a person would develop a natural immunity to future infection by the virus and that this immunity would be lifelong. However, this immunity may wane in later years.

13. Is there a human vaccine?

No, but the Centers for Disease Control and Prevention (CDC) is working with several partners towards developing a vaccine.

14. What kind of laboratory tests are done to identify the West Nile Virus in humans?

Various tests can be done. The type of test also depends on the kind of samples available (blood serum, cerebrospinal fluid, brain tissue, etc.). Samples may be tested to find antibodies to the West Nile virus, or there may be an attempt to isolate virus particles from the sample. Tests that can be done include:

• Hemagglutination-Inhibition
• IgM-Capture
• PCR
• Plaque-Reduction Neutralization
• Virus Isolation

15. How many human cases have there been in the United States? How many deaths?

In 1999, 62 cases of severe disease, including 7 deaths, occurred in the New York area. In 2000, 21 cases were reported, including 2 deaths in the New York City area. In 2001, there were 66 human cases of severe disease and 9 deaths. In 2012, there were 2,734 cases of severe disease and 243 deaths.

No reliable estimates are available for the number of cases worldwide of West Nile encephalitis, the disease caused by the West Nile Virus. For the latest up-to-date information, visit the Centers for Disease Control and Prevention website on West Nile Virus.

16. How many human cases have there been in Texas? How many deaths?

The first human death in Texas occurred on August 16th, 2002. In 2012, Texas reported 86 human deaths from the West Nile virus. For the latest up-to-date information on human cases in Texas, see the DSHS West Nile Virus home page on the Texas Health and Human Services website.

17. What is the risk of someone becoming infected with West Nile?

The risk is very low. Even in areas where the virus is circulating, very few mosquitoes are infected with the virus. Even if the mosquito is infected, less than 1% of people who get bitten and become infected will get severely ill. The chances you will become severely ill from any one mosquito bite are extremely small.

18. In addition to being infected by the West Nile Virus, what else can cause bird "die-offs"?

Causes for Die-Offs in Birds

• Chemical Spills
• Drought
• Pesticides
• Severe Weather and Other Diseases

To report a die-off of birds, contact the Texas Parks and Wildlife Department’s Kills and Spills Team (KAST) at 512-389-4848 or visit the Texas Parks and Wildlife Department’s Kills and Spills Team website.

Reminder

The Texas Department of State Health Services (DSHS) does not test birds for West Nile virus. Please do not contact DSHS if you find a dead bird. If you wish to dispose of a bird carcass, wear gloves and dispose of it in the garbage. As a reminder, whenever you handle an animal, you should wash your hands.

19. Can dogs, cats and other pets get the West Nile Virus?

Yes. But they rarely, if ever, get sick. No cases of West Nile disease have been confirmed in dogs and cats. The virus can infect many species of animals, but few actually get the disease. Most infections have been identified in birds, but the West Nile virus has been shown to infect:

• Bats
• Cats
• Chipmunks
• Dogs
• Domestic Rabbits
• Horses
• Skunks
• Squirrels

20. Is there a vaccine for dogs and cats?

No.