WEST NILE VIRUS
WEST NILE VIRUS (WNV)The West Nile virus is transmitted by the bite of mosquitoes that are infected with the virus. Mosquitoes become infected when they feed on infected birds. After an incubation period of 10 days to 2 weeks, infected mosquitoes can then transmit West Nile virus to humans and animals while biting to take blood. Following transmission by an infected mosquito, the virus multiplies in a person’s blood stream and crosses the blood-brain barrier to reach the brain. The virus interferes with normal central nervous system functioning and causes inflammation of the brain tissue (encephalitis). West Nile virus is NOT transmitted from person to person. For example, you cannot get the virus from touching or kissing a person who has the disease or from a health care worker who has treated someone with the disease. Similarly, there are also no known cases of animal to person transmission of the virusThe person infected with the virus will typically experience symptoms of the disease within 3 to 15 days after being bitten by an infected mosquito. Most infections are mild and symptoms include fever, headache and body aches, often with skin rash and swollen lymph glands. More severe infection may be marked by headache, high fever, stiffness, stupor, disorientation, tremors, convulsions, muscle weakness, paralysis, coma and rarely, death. Fatality rates among people range from 3% to 15% and are highest among the elderly.Currently there is no vaccine or specific treatment for West Nile virus. In more severe cases treatment requires intensive supportive therapy, such as hospitalization, intravenous fluids, respiratory support, the prevention of secondary infections (pneumonia, urinary tract, etc.) and good nursing care. It is too early to speculate about the permanent establishment of West Nile virus in the United States. The testing of dead birds is part of the state’s interagency surveillance system for WNV and other mosquito-borne viruses. If you observe an unusual change in the number of dead wild crows, ravens, jays, sparrows and other birds, you are encouraged to report birds that have been dead less than 48 hours to the Department of Health Services at 877-747-2243 or 877-WNV-BIRD. Health Services will send someone out to pick up the dead bird to be tested and inform you if it tests positive for WNV.There is no evidence that a person can get the virus from handling live or dead infected birds. However, avoid barehanded contact with all dead animals, including dead birds. It is a good idea to use gloves or double plastic bags to handle and dispose of the carcass. Background Information Prevention (FAQ) Symptoms of West Nile Virus (FAQ) West Nile Virus and Horses (FAQ)West Nile Virus and Dogs and Cats (FAQ) West Nile Virus and Birds (FAQ) Additional On-line Information on West Nile VirusBackground InformationThe West Nile encephalitis virus (inflammation of the brain) is believed to have originated in Africa and is also found in West Asia and the Middle East. It is not known how long the West Nile virus has been in this country, but scientists at the Centers for Disease Control and Prevention believe that it has probably been in the United States since the early summer of 1999, and possibly earlier. According to the Centers for Disease Control and Prevention, there have been 3 reported human disease cases for the West Nile Virus (WNV) in California during 2003. Of the total 9122 cases reported in the United States for 2003, 6251 cases (69%) were reported as West Nile Fever (milder disease), 2707 (30%) were reported as West Nile meningitis or encephalitis (severe disease) and 164 (2%) were clinically unspecified. There are no reliable estimates available for the number of cases of the disease that occur worldwide.* Information obtained from Los Angeles County West Vector Control and Centers for Disease Control and Prevention.PreventionQ. What can I do to reduce my risk of becoming infected with West Nile virus? A. Here are preventive measures that you and your family can take:Protect yourself from mosquito bites:Apply insect repellent sparingly to exposed skin. The more DEET a repellent contains the longer time it can protect you from mosquito bites. A higher percentage of DEET in a repellent does not mean that your protection is better—just that it will last longer. DEET concentrations higher than 50% do not increase the length of protection. Choose a repellent that provides protection for the amount of time that you will be outdoors.
  • Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children.
  • 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.
  • Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing. Do not apply repellents containing permethrin directly to exposed skin. If you spray your clothing, there is no need to spray repellent containing DEET on the skin under your clothing.
  • When possible, wear long-sleeved shirts and long pants whenever you are outdoors.
  • Place mosquito netting over infant carriers when you are outdoors with infants.
  • Consider staying indoors at dawn, dusk, and in the early evening, which are peak mosquito biting times.
  • Install or repair window and door screens so that mosquitoes cannot get indoors.
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.
  • At least once or twice a week, empty water from flowerpots, 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.
Q. What can be done to prevent outbreaks of West Nile virus?
A. Prevention and control of West Nile virus and other arboviral diseases is most effectively accomplished through integrated vector management programs. These programs should include surveillance for West Nile virus activity in mosquito vectors, birds, horses, other animals, and humans, and implementation of appropriate mosquito control measures to reduce mosquito populations when necessary. Additionally, when virus activity is detected in an area, residents should be alerted and advised to increase measures to reduce contact with mosquitoes. Details about effective prevention and control of West Nile virus can be found in Centers for Disease Control and Prevention’s Guidelines for Surveillance, Prevention and Control at http://www.cdc.gov/ncidod/dvbid/westnile/surv&control.htm.Q. Is there a vaccine against West Nile encephalitis?
A. No, but several companies are working towards developing a vaccine.Q. Where can I get information about the use of pesticide sprays that are being used for mosquito control?
A. The federal agency responsible for pesticide evaluation is the Environmental Protection Agency (EPA). Visit the EPA website, http://www.epa.gov/pesticides/factsheets/skeeters.htm for detailed answers to the questions about pesticides used for mosquito control.* Information obtained from Los Angeles County West Vector Control and Centers for Disease Control and Prevention.Symptoms of West Nile Virus 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 20% of the people who become infected will develop West Nile fever: mild symptoms, including fever, headache, and body aches, occasionally with 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 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease.Q. What is the incubation period in humans (i.e., time from infection to onset of disease symptoms) for West Nile encephalitis?
A. Usually 3 to 14 days.Q. How long do symptoms last?
A. Symptoms of mild disease will generally last a few days. Symptoms of severe disease may last several weeks, although neurological effects may be permanent.Q. If I have West Nile Fever, can it turn into West Nile encephalitis?A. When someone is infected with West Nile virus (WNV) they will typically have one of three outcomes: No symptoms (most likely), West Nile Fever (WNF in about 20% of people) or severe West Nile disease, such as meningitis or encephalitis (less than 1% of those who get infected). If you develop a high fever with severe headache, consult your health care provider. WNF is typically a mild disease in people, characterized by symptoms such as fever, body aches, headache and sometimes swollen lymph glands and rash. WNF generally lasts only a few days, though in some cases symptoms have been reported to last longer, even up to several weeks. WNF does not appear to cause any long-term health effects. There is no specific treatment for WNV infection. People with WNF recover on their own, though symptoms can be relieved through various treatments (e.g. medication for headache and body aches, etc.).Some people may develop a brief, WNF-like illness (early symptoms) before they develop more severe disease, though the percentage of patients in whom this occurs is not known. Occasionally, an infected person may develop more severe disease such as "West Nile encephalitis," "West Nile meningitis" or "West Nile meningoencephalitis." Encephalitis refers to an 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. Although there is no treatment for WNV infection itself, the person with severe disease often needs to be hospitalized. Care may involve nursing IV fluids, respiratory support, and prevention of secondary infections.* Information obtained from Los Angeles County West Vector Control and Centers for Disease Control and Prevention.West Nile Virus and HorsesQ. 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 West Nile virus 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 to have 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 mosquito bites, 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 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 (i.e., 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 it 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 would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.Q. Where can I get more information on horses and West Nile virus?
A. Visit the USDA (U.S. Department of Agriculture Web site for Animal Plant Health Inspection Service: http://www.aphis.usda.gov/lpa/issues/wnv/wnv.html* Information obtained from Los Angeles County West Vector Control and Centers for Disease Control and Prevention.West Nile Virus and Dogs and CatsQ. Can West Nile virus cause illness in dogs or cats?
A. Since 1999, there has been one confirmed death of a dog, and of one cat, infected with West Nile virus. It should be understood, however, that the dog was already in poor health, and was immune compromised - and therefore is not representative of dogs in general. 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 would 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 would be supportive 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 viruses 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 would be important in furthering the spread of the virus. *If your animal becomes infected with WNV, this suggests that there are infected mosquitoes in your area. You should 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 to have 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 would 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 when licking.) Talk with your veterinarian for advice about the appropriate product for use on your pet. * Information obtained from Los Angeles County West Vector Control and Centers for Disease Control and Prevention.West Nile Virus and BirdsQ. Do birds infected with West Nile Virus die or become ill?A. American crows in areas with the WNV seem most vulnerable, however the WNV has been identified in more than 70 species of birds found dead in the United States.Q. How can I report a sighting of dead bird(s) in my area?A. If you find a dead bird, please call the West Nile Virus Bird Surveillance Program with the Division of Communicable Disease Control of the California Department of Health Services, telephone: 877-MNV-BIRD.* Information obtained from Los Angeles County West Vector Control and Centers for Disease Control and Prevention.Additional On-line Information on West Nile VirusLos Angeles County West Vector & Vector-Borne Disease Control District http://www.lawestvector.orgCalifornia West Nile Virus Surveillance Information Center http://westnile.ca.govCenters for Disease Control and Prevention http://www.cdc.govLos Angeles County Department of Health Services http://lapublichealth.org/acd/westnile.htmAnimal Plant Health Inspection Service http://www.aphis.usda.gov/lpa/issues/wnv/wnv.html