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by Dr. Elankumaran Subbiah, Research Associate
VA-MD Regional College of Veterinary Medicine
Q: What is West Nile virus?
A: West Nile virus (WNV) is a mosquito-borne flavivirus 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 Unites States. The virus can infect humans, birds, mosquitoes, horses, and some other mammals.
Q: What are the different types of illness WNV can cause?
A: West Nile encephalitis, West Nile meningitis, or West Nile meningoencephalitis are the severe types of disease caused by WNV in humans. Encephalitis refers to inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, and meningoencephalitis refers to inflammation of the brain and the membrane surrounding it. West Nile fever is another type of illness caused by WNV, characterized by fever, headache, tiredness, aches, and sometimes rashes.
Q: How do humans get West Nile virus?
A: Through the bite of an infected mosquito. In Asia and Africa ticks have also been shown to transmit the disease.
Q: If we normally don't have the virus, how do mosquitoes get it?
A: The virus is kept alive in wild animals, mainly birds. There is a cycle of bird to mosquito transmission that occurs naturally. People and other animals are infected when they are bitten by mosquitoes that have fed earlier on infected birds.
Q: Is the disease seasonal in its occurrence?
A: In the temperate zone of the world (between latitudes 23.5° and 66.5°, north and south), West Nile encephalitis cases occur primarily in the late summer or early fall. In the southern climates where temperatures are milder, West Nile virus can be transmitted year round.
Q: What are the symptoms of West Nile virus infection?
A: Most people who are infected with the West Nile virus will not have any type of illness. It is estimated that about 20% of the people who become infected will develop West Nile fever: the symptoms include fever, headache, tiredness, and body aches and, occasionally, a skin rash on the trunk of the body and swollen lymph glands.
The symptoms of severe infection (West Nile encephalitis or meningitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It is estimated that approximately 1 in 150 people infected with the West Nile virus will develop a more severe form of disease.
Q: What is the incubation period in humans (time from infection to onset of disease symptoms) for West Nile encephalitis?
A: Usually 3 to 14 days.
Q: How does West Nile virus spread?
A: Infected mosquitoes. Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers that become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals.
Transfusions, transplants, and mother-to-child. In a very small number of cases, WNV also has been spread through blood transfusions and organ transplants and from mother to baby during pregnancy and breastfeeding.
Not through touching. WNV is not spread through casual contact such as touching or kissing a person with the virus.
Q: If a person contracts West Nile virus, does that person develop a natural immunity to future infection by the virus?
A: It is assumed that immunity will be lifelong; however, it may wane in later years.
Q: How is WNV infection treated?
A: There is no specific treatment for WNV infection. In milder cases, people experience symptoms such as fever and aches that pass on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment, including intravenous fluids, help with breathing, and nursing care.
Q: What other animals can get the disease?
A: The virus has been found in sheep, cattle, horses, lemurs, camels, dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, and some monkeys and rodents. Only horses, sheep, some monkeys, and some birds actually get sick from natural infection. Pets have not been shown to get sick from this disease.
Q: What animal species have been found positive of WNV=positive in the Unites States?
A:
The National Wildlife Health Center website lists detailed information on various species of animals found positive for WNV in the United States.
Q: Can people get West Nile virus from other people or animals?
A: West Nile virus is not transmitted from person to person. There is no evidence that people can get it from handling live or infected birds, but people should avoid barehanded contact with dead birds and animals. Use gloves and place carcasses in double plastic bags before discarding carcasses in a garbage can.
Q: Can you get infected with West Nile virus by caring for an infected horse?
A: West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of WNV. Follow normal veterinary infection control precautions when caring for a horse suspected to have this or any viral infection.
Q: Can you get WNV from eating game birds or animals that have been infected?
A: There is no evidence that WNV can be transmitted to humans through consuming infected birds or animals. Always follow procedures for fully cooking the meat of birds or mammals, in keeping with overall public health practice and because of the risk of known food-borne pathogens,
Q: What should I do if I find a dead bird?
A: Check with your local or state health department for instructions on reporting and disposing of dead birds. If you need to pick up a dead bird or local authorities tell you to dispose of it: Avoid bare-handed contact with any dead animals, and use gloves or an inverted plastic bag to place the bird carcass in a garbage bag.
Q: Do birds infected with West Nile virus die or become ill?
A: In the 1999 New York area epidemic, there was a large die-off of American crows. Since then, West Nile virus has been identified in more than 100 species of birds found dead in the United States. Most of these birds were identified through reporting of dead birds by the public.
Q: Can West Nile virus (WNV) cause illness in dogs or cats?
A: A relatively small number of WNV-infected dogs (less than 40) and only 1 WNV-infected cat have been reported to CDC during 2003. Experimentally infected dogs showed no symptoms after infection with WNV. Some infected cats exhibited mild, nonspecific symptoms during the first week after infection--for the most part only showing a slight fever and slight lethargy. It is unlikely that most pet owners will notice any unusual symptoms or behavior in cats or dogs that become infected with WNV.
Q: How can my veterinarian treat my cat or dog if they are/may be infected with WNV?
A: There is no specific treatment for WNV infection. Full recovery from the infection is likely. Treatment should be supportive (managing symptoms, if present) and consistent with standard veterinary practices for animals infected with a viral agent.
Q: Does my dog/cat becoming infected pose a risk to the health of my family or other animals?
A: There is no documented evidence of dog- or cat-to-person transmission of West Nile virus. The evidence suggests that dogs do not develop enough virus in their bloodstream to infect more mosquitoes. Cats develop slightly higher levels of virus in their bloodstream, but it is unclear if this would be enough to infect mosquitoes. It is very unlikely that cats further the spread of the virus. If your animal becomes infected with WNV, this suggests that infected mosquitoes are in your area. Take measures to prevent mosquitoes from biting you (use repellent and wear protective clothing). Veterinarians should take normal infection control precautions when caring for any animal (including birds) suspected of having this or any viral infection.
Q: How do cats and dogs become infected with West Nile virus?
A: Dogs and cats become infected when bitten by an infected mosquito. There is also evidence that cats can become infected with the virus after eating experimentally infected mice.
Q: Can I become infected with WNV if a dog with the virus bites me?
A: Preliminary studies have not been able to detect virus in the saliva of infected dogs. This suggests that dog bites pose a low risk, if any, of transmission of WNV from dogs to other animals or people.
Q: Is there a vaccine for cats or dogs?
A: No.
Q: Should a dog or cat infected with West Nile virus be destroyed?
A: No. There is no reason to destroy an animal just because it has been infected with West Nile virus. Full recovery from the infection is likely. Treatment should be supportive and consistent with standard veterinary practices for animals infected with a viral agent.
Q: Can I use insect repellent on my pets?
A: DEET-based repellents, which are recommended for humans, are not approved for veterinary use (largely because animals tend to ingest them by licking.) Talk with your veterinarian for advice about the appropriate product to use on your pet.
Q: Is there a risk of getting infected with West Nile virus (WNV) if I eat turkey or another animal that has been infected with the virus?
A: There is no evidence that people can become infected with WNV from eating infected meat. The small, theoretical risk of infection can be eliminated by proper handling and thorough cooking of meat before eating it.
Q: Has West Nile virus caused severe illness or death in horses?
A: Yes. While data suggest that most horses infected with West Nile virus recover, results of investigations indicate that WNV has caused deaths in horses in the United States.
Q: How do the horses become infected with West Nile virus?
A: The same way humans become infected-- by the bite of infectious mosquitoes. The virus is located in the mosquito's salivary glands. When mosquitoes bite or "feed" on the horse, the virus is injected into its blood system. The virus then multiplies and may cause illness. The mosquitoes become infected when they feed on infected birds or other animals.
Q: How does the virus cause severe illness or death in horses?
A: Following transmission by an infected mosquito, West Nile virus multiplies in the horse's blood system, crosses the blood-brain barrier, and infects the brain. The virus interferes with normal central nervous system functioning and causes inflammation of the brain.
Q: Can I get infected with West Nile virus by caring for an infected horse?
A: West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus. Normal veterinary infection control precautions should be followed when caring for a horse suspected of having this or any viral infection.
Q: Can a horse infected with West Nile virus infect horses in neighboring stalls?
A: No. There is no documented evidence that West Nile virus is transmitted between horses. However, horses with suspected West Nile virus should be isolated from mosquitos, if at all possible.
Q: My horse is vaccinated against eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE). Will these vaccines protect my horse against West Nile virus infection?
A: No. EEE, WEE, and VEE belong to another family of viruses for which there is no cross-protection.
Q: Can I vaccinate my horse against West Nile virus infection?
A: A West Nile virus vaccine for horses from Fort Dodge Animal Health was recently approved, but its effectiveness is unknown.
Q: How long will a horse infected with West Nile virus be infectious?
A: We do not know if an infected horse can be infectious (cause mosquitoes feeding on it to become infected). However, previously published data suggest that the virus is detectable in the blood for only a few days.
Q: What is the treatment for a horse infected with West Nile virus? Should the horse be destroyed?
A: There is no reason to destroy a horse just because it has been infected with West Nile virus. Data suggest that most horses recover from the infection. Treatment should be supportive and consistent with standard veterinary practices for animals infected with a viral agent.
Q: What can be done to reduce the risk of becoming infected with West Nile Virus?
A: When mosquitoes are active:
- Stay indoors at dawn, dusk, and in the early evening, when mosquitoes are most active.
- Wear long-sleeved shirts and long pants whenever you are outdoors.
- Apply insect repellent sparingly to exposed skin. An effective repellent will contain 20% to 30% DEET (N,N-diethyl-meta-toluamide). DEET in high concentrations (greater than 30%) may cause side effects, particularly in children; avoid products containing more than 30% DEET.
- Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children. Do not apply insect repellents to children less than 3 years old.
- Spray clothing with repellents containing permethrin or DEET, as mosquitoes may bite through thin clothing.
- Whenever you use an insecticide or insect repellent, be sure to read and follow the manufacturer's DIRECTIONS FOR USE, as printed on the product.
- Note: Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites.
Although there is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus, avoid handling dead animals or animals known to be infected. If handling is unavoidable, take precautions by using proper protective garments, especially gloves. This is especially important for those interacting with wildlife and equines.
Help reduce the number of mosquitoes in areas outdoors where you work or play by draining sources of standing water. In this way, you reduce the number of places mosquitoes can lay their eggs and breed. Take these precautions:
- At least once or twice a week, empty water from flower pots, pet food and water dishes, birdbaths, swimming pool covers, buckets, barrels, and cans.
- Check for clogged rain gutters and clean them out.
- Remove discarded tires and other items that could collect water.
- Be sure to check for containers or trash in places that may be hard to see, such as under bushes or under your home.
Note: Vitamin B and "ultrasonic" devices are NOT effective in preventing mosquito bites.
Q: Who should be contacted about...?
- Crows or other birds:
Maryland Department of Natural Resources
1-866-866-2769 (CROW)
- Other wildlife:
Center for Veterinary Public Health
410-767-5649
- Pets with signs of infection:
Maryland Department of Natural Resources
Owners should check with their veterinarian
If pet is showing clinical signs veterinarians should contact MDNR, 1-877-620-8DNR (8367)
- Horses with signs of infection:
Maryland Department of Agriculture
Owners should check with their veterinarian. If horse is showing clinical signs, veterinarian should contact MDA, 410-841-5870.
- People with symptoms:
First consult with your personal physician, then contact the Maryland Department of Health and Mental Hygiene, 410-767-6493.
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