West Nile Virus in People, Horses, Other Animals & Birds
Information Compiled by Avon
Animal Hospital (Updated 4/11/2005)
What is West Nile Virus?
West Nile Virus ‘WNV’ is a type of virus that causes encephalitis, or inflammation of the brain. The virus has been found in Africa, western Asia, the Middle East, the Mediterranean region of Europe and recently in North America, including the United States and Canada. Mosquitoes become infected with the virus after feeding on infected wild birds and then transmit the virus through bites to people, horses, birds and other animals.
What is the prevalence of West Nile Virus in North America?
In 2002, the U.S. Center for Disease Control reported 3852 human cases (232 fatalities). The median age of human cases was 55 years, ranging from 1 month to 99 years (54% males). The total number of equine cases caused by WNV in 2002 confirmed at the USDA's National Veterinary Services Laboratories or reported by state officials was 14,717. Nebraska reported the highest number of equine cases (1,100).
In 2003, the U.S. Center for Disease Control reported 9862 human cases including 264 deaths. The majority of human cases were seen in Colorado, followed by cases in Nebraska and South Dakota. Of the 9862 reported cases, 68% were reported as West Nile fever (milder disease), 30% were reported as West Nile meningitis or encephalitis (neuroinvasive disease) and 2% were clinically unspecified. The total number of equine cases in the US during 2003 as reported by APHIS was 4636, with the majority in Pennsylvania (527), followed by Colorado (426) and New Mexico (420). Interestingly, the state of Nebraska which is among the highest in human cases reported only 38 equine cases.
What is the prevalence of West Nile Virus in Canada?
In September of 2001, WNV was reported in a bird for the first time in Canada, in the province of Ontario. In 2002 Health Canada reported 555 dead birds confirmed positive with WNV. Ontario had the largest number at 281. There were also 81 cases of human infection (76 confirmed in Ontario) and 336 cases of equine infection (236 confirmed in Manitoba).
In 2003 there was 1633 confirmed WNV positive dead birds in Canada. The majority of these birds have been in Quebec (846), Ontario (242), Alberta (232), Saskatchewan (157), Manitoba (133), New Brunswick (6) and Nova Scotia (17). Over 12,223 birds were submitted for testing during 2003.
In 2003, 445 horses in Canada have died from or been confirmed positive for WNV. The majority of these horses have been in Alberta (180), with cases in Saskatchewan (162), Manitoba (53), Ontario (41), Quebec (8), and Nova Scotia(1).
There have been 1220 "probable" (<10%) plus "confirmed" cases of human WNV infection in Canada, including 10 deaths. The majority of confirmed and probable cases have been seen in Saskatchewan (792), followed by cases in Alberta (272), Manitoba (141), Ontario (89), British Columbia (20), Quebec (17), Nova Scotia (2), New Brunswick (1) and in the Yukon (1).
What is the prevalence of West Nile Virus in Nova Scotia?
Nova Scotia saw its first confirmed positive case in a dead bird in September, 2002. By the end of 2002 the number of confirmed positive dead birds totaled 3 and as of December 31st, 2003 the total number of confirmed positive dead birds rose to 17 including cases in the Annapolis Valley. The first two confirmed human cases of WNV in N.S. were also reported during 2003. At least one of these cases may have been related to travel to a WNV prevalent area. In 2003 we also saw the first confirmed case of WNV in a N.S. horse. Nova Scotia is the furthest east that WNV has been detected in North America, at approximately the 65th meridian. As of September 5th, 2004, the virus has not been found (this year) in any birds, mosquito pools, horses or humans in Nova Scotia. Peak season for the virus is August and September. Authorities continue to be on the look out. If you see a dead bird in Nova Scotia, there is information below on precautions to take, who to call and exactly what to do.
What are the signs of West Nile Virus in people?
Most people infected with the virus are asymptomatic and have none of the symptoms associated with WNV. In some cases however, the infection can cause headaches, rash, swollen lymph nodes, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, paralysis and even death.
Horses
What are the signs of West Nile Virus in horses?
In 1999, 25 New York horses with neurological signs were identified as the first equine cases of WNV infection. These horses presented with signs of ataxia (wobbliness), difficulty walking, knuckling over, head tilt, muscle tremors, and the inability to rise. Of these 25 horses, nine died or were euthanized. The 16 surviving horses all recovered.
How do horses become infected with West Nile Virus?
The same way people become infected, by the bite of infected mosquitoes. Many horses will develop mild or inapparent infections, but in more susceptible horses, the virus will leave the blood and enter into the brain and spinal cord where its causes inflammation and interferes with normal central nervous system function leading to severe clinical disease or death of the horse. WNV is not transmitted from horse-to-horse, sick horses will not infect healthy ones in neighboring stalls.
What is the treatment for a horse infected with West Nile Virus?
Treatment would be supportive and customized to the presenting clinical signs. A veterinarian should be called to evaluate any horse with a neurological condition, so that a correct diagnosis is achieved quickly, since the clinical signs of WNV are very similar to rabies. Horses with suspected WNV should be protected from additional mosquito bites.
Should a horse infected with West Nile Virus be destroyed?
There is no reason to destroy a horse just because it has been infected with WNV. Serosurveys suggest that most horses recover from the infection. Horses are humanely euthanized only when they have severe clinical disease and no hope of recovery.
Can I vaccinate my horse against West Nile Virus?
Yes. In August 2001, the USDA and Fort Dodge Animal Health announced the approval of a conditional license for an inactivated vaccine against WNV for use in horses. The license was termed "conditional" because the vaccine had been tested for safety (including use in pregnant mares), but studies for efficacy had not been completed. This vaccine has been in use in the U.S. since 2000. Two vaccines have now been completely approved and are available all over North America. Reports from thousands of veterinarians that have been using these vaccines have been very positive. Many insurance companies such as Henry Equestrian Plan require proof of proper vaccination against West Nile Virus. The Fort Dodge vaccine initially requires two boosters 4-6 weeks apart. A once annual vaccination before mosquito season will then be needed to maintain immunity. Some areas with longer mosquito seasons are vaccinating horses as frequently as every 3 to 6 months. Horses vaccinated against Eastern, Western and Venezuelan equine encephalitis are not protected against WNV. As with most vaccines it is very important for pregnant mares to receive a WNV booster one month before foaling, so that foals will acquire enough antibodies in the colostrum to protect them until they are old enough to respond to vaccination. Further recommendations can be reviewed by clicking on the following link:
WNV Vaccination Guidelines Developed by the American Association of Equine Practitioners
Please make appointments to have your horse(s) vaccinated before mosquito season hits. Currently, a vaccine is only available for horses. A human vaccine is being tested but is at least 1 year from release.
Are WNV vaccines safe for use in pregnant mares?
The following is an excerpt from APHIS veterinary service US government webpage. The page can also be linked to below. "Some recent stories have suggested that the Fort Dodge Animal Health West Nile Virus Vaccine approved by the U.S. Department of Agriculture (USDA) may cause pregnant mares to abort or give birth to deformed foals. The misleading information in those articles has sparked many anxious phone calls from horse owners, veterinarians, and others involved with horses. Unfortunately, as a result, USDA is concerned that horse owners may not use an effective preventive measure against West Nile virus available to them, that of vaccinating their horses. Horse owners should be assured that the vaccine is safe, and it should be used as protection against West Nile virus. Millions of doses of the vaccine have been used since USDA's Center for Veterinary Biologics approved its use in 2001."
"The Center for Veterinary Biologics, within USDA's Animal and Plant Health
Inspection Service, maintains a toll-free telephone hotline (800-752-6255) and a
mailbox on its Web site (www.aphis.usda.gov/vs/cvb) and actively encourages
veterinarians and other vaccine consumers to report problems with vaccines. To
date, there have been a very small number of reports regarding a possible
association between the use of West Nile virus vaccine and abortions, birth
defects, or other reproductive anomalies or failures. It does not appear that
there is a relationship between West Nile virus vaccine use and these
reproductive problems or any other major problems. The Center and the vaccine
manufacturer will continue to collect, monitor, and track the performance of
this vaccine."
"Since West Nile virus' detection in the United States in 1999, the number of
horses affected by the virus steadily continues to grow. In 2002 alone, there
were 14,717 equine West Nile virus cases. To help reduce the number of cases,
the USDA recommends that horse owners not only vaccinate their animals but
implement safeguards to prevent animals' exposure to mosquitoes, which spread
the virus."
Movie Clip: West Nile Virus in Horses
The movie (video only) depicts some of the more characteristic signs of
encephalitis in horses affected by West Nile Virus. You will need the latest
version of Quick Time to view this movie. You can download Quick Time for free
at
The following movie clip may be helpful to equine practitioners in California
and other western states in preparing themselves to deal effectively with a
disease that may soon become a serious clinical problem in their practice areas.
The movie (video only, no audio) depicts some of the more characteristic signs
of encephalitis in horses infected by the West Nile virus. You will need the
latest version of Quick Time to view this movie. You can download Quick Time for
FREE at
http://www.apple.com/quicktime/download
High Bandwidth Movie
(DSL or faster connection
56k Modem Movie - Larger View
Minimum of 20 min download time
Dogs, Cats & Other Animals
Can West Nile Virus cause disease in dogs, cats and other animals?
WNV infections have been documented in other animals including dogs, cats, domestic birds, sheep, cattle and pigs. Infection in these species is however, extremely rare. Most reported infections were without clinical signs and animals developed antibodies to WNV. Domestic geese, ducks, pigeons and chickens have been more commonly reported with natural disease. Illness and death due to the virus has also been documented in wildlife species including thousands of wild birds (mostly crows), a reindeer, a wolf, mountain goats, deer, squirrels, a harbor seal, alligators and other reptiles.
Can I get infected with West Nile Virus by caring for an infected animal or from an infected person?
No. It is the infected mosquito that transmits WNV to people through blood feeding. Other possible but less common modes of transmission include intrauterine transplacental (‘vertical’) transmission (to a fetus from an infected mother), contaminated blood transfusions, organ transplant, and breast feeding. Pregnant woman should take precautions to reduce their risk for WNV. There is no documented evidence of direct person-to-person or animal-to-animal transmission. Animal-to-person transmission is also unlikely, although at least 2 US lab workers became infected with WNV in 2002 when their skin was cut while handling infected animals.
How can I protect myself and my animals from West Nile Virus?
Horses should be vaccinated in areas where WNV has been confirmed
You and your animals can be protected by reducing your exposure to infected mosquitoes:
· Reduce the mosquito population around your home and where animals are housed.
· Minimize the time spent outdoors between dusk and dawn when mosquitoes are most active.
· Apply products that kill or repel mosquitoes. Animal products should be approved and labeled for animal use. Your veterinarian can help you decide on the appropriate product to use on your animal depending on species, age, health status, and degree of exposure. Do not use products that contain DEET on animals.
· Use screens on windows and doors at home and, if possible, where animals are housed.
· If you can't avoid the nasty pests visit the Mosquito Bytes website to learn about their biology and behavior
What can be done to reduce the number of mosquitoes where animals are housed?
Mosquito populations can be reduced significantly by eliminating the amount of standing water.
Dispose of bottles, cans, plastic containers, ceramic pots or similar water-holding containers that have accumulated on your property. Do not overlook containers that have become overgrown by vegetation.
Empty standing water from used or discarded tires that may have accumulated on your property. The used tire has become the most important domestic mosquito producer in this country.
Drill holes in the bottom of recycling containers and animal feeders that are left out of doors. Drainage holes that are located on the sides will allow enough water to collect for mosquitoes to breed.
Clean clogged roof gutters on an annual basis, particularly if the leaves from surrounding trees have a tendency to plug up the drains. Roof gutters are easily overlooked and can produce millions of mosquitoes each season.
Turn over plastic wading pools, buckets, pails and feeders when not in use.
Turn over wheelbarrows and change water in birdbaths and stock tanks at least twice weekly. Both provide breeding habitat for domestic mosquitoes.
Aerate ornamental pools or stock them with fish. Water gardens can become major mosquito producers if they are allowed to stagnate.
Clean and chlorinate swimming pools that are not being used. A swimming pool that is left untended by a family that goes on vacation for a month can produce enough mosquitoes to result in neighborhood-wide complaints. Be aware that mosquitoes may even breed in the water that collects on swimming pool covers or polytarps.
Use landscaping to eliminate standing water that collects on your property. Mosquitoes can develop in any puddle that lasts more than 4 days.
Handling dead birds
In Nova Scotia, dead birds should be reported to the Department of Natural Resources who will retrieve the carcasses and send them to Atlantic Veterinary College for testing. Check the Provincial Government section of the Blue Pages of your telephone directory for your local number or visit the DNR Website. After hours, the toll free number is 1-800-565-1633. They ask that you do not handle dead birds and instead report accurately the location of any carcass. In most cases, they will arrange to pick up the birds. In the event where you have to handle a dead bird, it is unlikley that you will be infected with WNV, however, precautions should be taken not to come in contact with the virus. Do not touch dead birds with bare hands, wear heavy waterproof gloves. Be sure you and your clothing do not contact the bird or its blood, secretions or feces. One alternative is to put your hand inside a leak-proof plastic bag (or two), grasp the bird while pulling it into the bag as you turn it inside out. Care should be taken so that the beak and claws do not puncture the bag. Close the bag tightly. Always make sure the bird is double bagged. After the bird is appropriately contained, wash your hands thoroughly. The bird can then be refrigerated (not frozen) and delivered to a laboratory for testing within 24-36 hours. If a longer interval is anticipated, the bagged dead bird can be frozen and delivered to the Department of Natural Resources. Do not let it thaw.
Department of Natural Resources (Hants-District Office Windsor) 902-798-2016
DNR (After hours) 1-800-565-2224
Wildlife Division (Central Office) 902-679-6091
To learn more about WNV visit
Nova Scotia Department of
Health website
Nova Scotia's Public Health Service (health-related questions) 1-877-9ENVIRO
West Nile Virus
Communication Coordinator;
Canadian Cooperative Wildlife Health Centre; Atlantic Veterinary College,
550 University Avenue, Charlottetown PEI C1A 4P3
Tel: 902- 628-4314 FAX: 902-566-0851 E-mail:ccwhc@upei.ca
Learn More about West Nile Virus
West Nile Virus Vaccination Program
West Nile Virus Vaccination in Mares and Foals
Residual Effects of West Nile Virus in Horses
West Nile Virus
West Nile Virus Continues to Spread
Prevention and Control of WNV in Horses, Livestock & Poultry
West Nile Virus Comprehensive Information from The Horse.com
What is WNV and how does it affect humans and horses?
(C. Roxanne Rutledge, assistant professor, Jonathan F. Day, professor, and Walter J. Tabachnick, professor and director, Florida Medical Entomology Laboratory, Vero Beach, FL; Entomology and Nematology Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville)
Equine Emerging Diseases New Threats for Horse Owners
Mosquitoes In and Around the Home
Update on the Current Status of West Nile Virus in the United States
West Nile Virus Surveillance Information for Canada
Health Canada - West Nile Virus Website
Restrictions on Equidae being Imported into the European Union
**Clarification on the Issue of the West Nile Virus Vaccine: Vaccine Safe for Use**
This article contains information compiled & modified by AAH. Our sources include the Center for Disease Control, USDA's NVSL, Various State and Provincial websites, Cornell University - Center for the Environment, the Nova Scotia Veterinary Medical Association 9/01 newsletter, The Horse.com , and Equine Disease Quarterly 1/02 Vol 10, No 2.
Use the Back Button on your Browser to Return to Previous Page