West Nile Virus Questions and Answers

Q: Where did West Nile virus come from?
A: West Nile virus has been commonly found in humans and birds and other animals in Africa, Eastern Europe, West Asia, and the Middle East, but until 1999 had not previously been documented in the Western Hemisphere. It is not known exactly how West Nile virus was introduced into the U.S., but the circulating American viral strain is most closely related genetically to strains found in the Middle East.

Q: How long has West Nile virus been in the US?
A: The first identification of West Nile virus in the U.S. occurred in Queens, New York City during the summer of 1999. By the end of 2005, West Nile virus had spread to 48 states, Canada, and Mexico.

Q: How do people get infected with West Nile Virus (WNV)?
A: The most likely route of human infection with WNV is through the bite of an infected mosquito. Some people have also become infected with the virus following receipt of contaminated blood or blood products, or transplanted organs from an infected donor. Mothers who are recently infected with WNV may also transmit the virus to their unborn child, or to their baby while breastfeeding.

Q: Who is at risk for getting West Nile encephalitis?
A: All residents of areas where virus activity has been identified are at risk of getting West Nile encephalitis.

Q: What is the transmission cycle of West Nile virus?
A: Female 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 WNV to humans and animals while biting to take blood meals. The primary transmission cycle is bird-mosquito-bird, with incidental transmission occurring to people and horses.

Q: What types of animal develop illness from West Nile Virus infection?
A: Birds and horses are most susceptible to disease caused by WNV. Although numerous animals are bitten by infected mosquitoes, illness caused by WNV is uncommon in domestic pets or other wildlife. West Nile virus infections have been proven in a variety of animals, including squirrels, bats, dogs, cats, goats, skunks, domestic rabbits, and even alligators. However, WNV is NOT considered a significant health threat for dogs and cats.

Q: 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?
A: It only takes one bite from an infected mosquito to transmit the disease, however, even in areas where the virus is circulating, less than 1% of mosquitoes are generally infected with the virus. Therefore, the chances you will become severely ill from any one-mosquito bite are extremely small. Persons who have repeated exposures to mosquitoes are at higher risk of acquiring West Nile disease.

Q: What are the symptoms of West Nile virus infection?
A: Most people who are infected with WNV will not have any noticeable illness, or have a milder form of West Nile disease called West Nile Fever. Persons with West Nile Fever typically experience symptoms of fever, headache, nausea, muscle weakness, and body aches lasting 2 to 6 days or longer. Sensitivity when looking at light and a skin rash appearing on the trunk of the body may also be present.
Approximately 20% of persons infected with WNV will develop more severe neurologic disease that may be life-threatening. Adults over the age of 50 years old are at greater risk of having serious disease. Potential symptoms of severe infection (West Nile encephalitis or meningitis) include intense headache, dizziness, severe muscle weakness, neck stiffness, vomiting, disorientation, mental confusion, tremors, muscle paralysis, or convulsions and coma.

Q: What is the incubation period in humans (i.e., time from exposure to onset of disease symptoms) for West Nile encephalitis?
A: Usually 3 to 15 days.

Q: Can you get West Nile virus directly from birds?
A: There is no evidence that a person can get the virus from handling live or dead infected birds. However, persons should avoid barehanded contact when handling any dead animals. Dead birds can be double-bagged and placed in the regular trash for disposal.

Q: Can you get infected with West Nile virus by caring for an infected horse?
A: No. WNV is transmitted by infected mosquitoes. There is no documented evidence of animal-to-person transmission of West Nile virus. However, precautions should be taken to avoid contact with the horse’s saliva because the symptoms of rabies and West Nile encephalitis may be indistinguishable.

Q: Can a mosquito transmit West Nile virus from an infected horse or human?
A: No. A human or a horse that is infected with WNV does not have a high enough concentration of the virus in its blood or tissues to be a source of virus for biting mosquitoes. This is why horses or people that develop West Nile disease do NOT need to be quarantined or otherwise isolated.

Q: Can a horse infected with West Nile Virus infect horses in neighboring stalls?
A: No. WNV is not transmitted between horses. Horses in the same vicinity are being exposed to the same mosquito population, though, so it is common to see more than one infected horse in a herd if they are not protected by vaccination.

Q: Are duck and other wild game hunters at risk for West Nile virus infection?
A: Because of their outdoor exposure, game hunters may be at risk if they hunt in mosquito-infested areas. Using insect and tick repellants will decrease their risk of acquiring a vector-borne disease.

Q: Can I get West Nile Virus from cleaning or eating wild game?
A: Two persons are known to have acquired West Nile disease following knife injuries sustained while harvesting organs from birds infected with WNV. Direct handling of infected birds or animal tissue is insufficient to spread the virus. Hunters are advised to wear gloves when handling and cleaning animals to prevent exposure to other disease agents, such as Salmonella. Game meat should be thoroughly cooked. Normal cooking temperatures will inactivate WNV.

Q: Is there a human vaccine against West Nile encephalitis?
A: No, but two companies are working towards developing a vaccine.

Q: How can I reduce my risk of getting West Nile disease?
A: Practice the four“Ds”!
·  Apply a mosquito repellant containing DEET or another approved active ingredient such as Picaridin or oil of lemon eucalyptus
·  Avoid being outdoors between Dusk and Dawn
·  Drain any standing, stagnant water observed in containers or artificial locations around your home and workplace
·  Dress wearing long sleeves and long pants to shield skin from mosquitoes.

Q: What is "DEET" and how often should I use it to repel mosquitoes?
A: DEET is the shortened acronym for the chemical N,N-diethyl-m-toluamide which is the active ingredient found in most insect repellants that are safe to apply to the skin. Before buying a mosquito repellant, check the label for this chemical name and look at the concentration. DEET-containing repellants are available in concentrations ranging from 4% to 100%. Higher concentrations do not work better, they just last longer. For most outdoor activities, using a 10%-30% product is adequate.

The most effective repellents contain active ingredients of DEET (N,N-diethyl-m-toluamide) or Picaridin (KBR 3020) which repel pests like mosquitoes and ticks. Repellents containing these ingredients have been tested against a variety of biting insects and has been shown to be very effective. Oil of eucalyptus [p-methane 3,8-diol (PMD)], a plant based repellent has been shown to provide similar protection to lower concentrations of DEET. Always follow label directions when applying repellant.

Q: How many cases of West Nile disease occured in my county last year?
A: The Oklahoma State Department of Health has a full summary of the reported cases in horses, mosquitoes, and humans posted on this website under Surveillance Data and Maps. This information can also be provided to you by contacting the epidemiologist on-call at 405-271-4060.