What is West Nile virus (WNV)?
West Nile 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 the United States. Mosquitoes become infected with the virus after feeding on infected wild birds and then transmit the virus through bites to people, animals and other birds.
Can West Nile virus cause disease in horses?
In 1999, 25 New York horses with neurological signs were identified as cases of WNV infection. These horses presented with signs of ataxia, difficulty walking, knuckling over, head tilt, muscle tremors, and the inability to rise. Of these 25 horses, nine (36%) died or were euthanised. WNV was identified in the tissue samples and specific WNV antibody was found. The 16 surviving horses all recovered and also developed WNV antibody titers.
In 2000, the National Veterinary Services Laboratories confirmed 60 horses with WNV infection from the states of Connecticut (7), Delaware (4), Massachusetts (1), New Jersey (27), New York (19), Pennsylvania (1) and Rhode Island (1). Thirty-seven horses survived the infection and 23 (38%) died or were euthanised. In Connecticut, 4 horses recovered and 3 horses were euthanised (43%).
In 2001 over 400 clinical cases of WNV infection in horses from 19 states were reported. Eleven Connecticut horses had clinical signs of disease, seven recovered and four died or were euthanised (36%). National updates and details on equine cases of WNV infection can be found at USDA's Animal and Plant Health Inspection Service.
How do the 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.
Can I get infected with West Nile virus by caring for an infected horse?
Infected mosquitoes transmit WNV to people through blood feeding. There is no documented evidence of person-to-person, or animal-to-person transmission of WNV.
Can a horse infected with West Nile virus infect horses in neighboring stalls?
No. There is no documented evidence that WNV is transmitted from horse-to-horse. Horses with suspected WNV if possible should be protected from additional mosquito bites.
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?
No. EEE, WEE, and VEE are alphaviruses. West Nile is a flavivirus. There is no cross-protection.
Is there a West Nile Virus vaccine for horses?
Yes. On August 1, 2001, the Animal and Plant Health Inspection Service (APHIS) issued a conditional U. S. Veterinary Biological Product License to Fort Dodge Animal Health for the manufacture and distribution of a killed virus, West Nile Virus vaccine. Conditionally licensed products are required to be pure and safe, and have a reasonable expectation of efficacy. APHIS will continue to evaluate potency and efficacy data throughout the conditional licensure period. The conditional license will expire in one year. The vaccine is for intramuscular use in horses. Two doses are required, given 3 to 6 weeks apart.
Should a horse infected with West Nile virus be destroyed? What is the treatment for a horse infected with West Nile virus?
No. There is no reason to destroy a horse just because it has been infected with WNV. Sero surveys suggest that most horses recover from the infection. Horses are humanely euthanised only when they have severe clinical disease with no hope of recovery. 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. The veterinarian will also contact the State Veterinarian and receive help in diagnosis and submitting samples to the appropriate state and federal laboratories.
Dogs and Cats
Can West Nile virus cause disease in dogs or cats?
Although there is a published report of WNV isolated from a dog in southern Africa (Botswana) in 1982, the majority of dogs exposed to WNV exhibited no clinical signs. WNV was isolated from a sick stray kitten found in a storm sewer in New Jersey in 1999. There have been no documented cases of WNV infections in dogs or cats in Connecticut.
How do dogs or cats become infected with West Nile virus?
The same way people become infected by infected mosquitoes bites. The virus is maintained in the mosquito’s salivary glands. During blood feeding, the virus is injected into the animal. The virus then multiplies and may cause clinical signs in a susceptible animal. Most infections are inapparent or mild. If your pet shows signs of fever, depression, incoordination, muscle weakness or spasms, seizures or paralysis, see your veterinarian. Your veterinarian will assess your pet’s condition and give appropriate treatment.
Can sick dogs or cats be carriers and transmit West Nile virus to people and other dogs or cats?
No, this is very unlikely. Infected mosquitoes transmit WNV to people through blood feeding. There is no documented evidence of person-to-person, animal-to-animal, or animal-to-person transmission of WNV. However, people who directly handle sick animals should take precautions such as wearing gloves to protect themselves from contact with saliva from sick animals that may actually have rabies rather than WNV infection.
Should a dog or cat infected with West Nile virus be destroyed? What is the treatment for an animal infected with West Nile virus?
No. There is no reason to destroy an animal just because it has been infected with West Nile virus. Full recovery from the infection occurs in most cases. Treatment would be supportive and customized to the presenting clinical signs. A veterinarian should be seen to evaluate any sick animal’s condition, to provide treatment and to forward samples for laboratory testing.
Does WNV infect other animals?
WNV infections have been documented in sheep, cattle and pigs in Africa and Eurasia. Most infections were without clinical signs and animals developed antibodies to the virus. However, in laboratory studies sheep infected with WNV exhibited fever, abortion and encephalitis.
What about domestic birds?
Birds usually do not show any clinical signs when infected with WNV. Chickens can be infected with WNV and not become sick. However, natural disease due to the virus has been reported in domestic geese, ducks, pigeons and chickens. No domestic birds have been found in Connecticut carrying the disease. There have been no cases of indoor pet birds becoming infected. It is also important to point out that birds are not currently suspected of transmitting WNV to humans. Regardless, gloves should be worn if handling any dead bird or animal.
How can I protect my animals and birds from WNV?
You can protect your animals and birds from WNV infection by reducing their 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 and are 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.
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.
What measures are being taken to protect domestic animals and birds?
The State of Connecticut has developed and implemented a statewide WNV response plan that includes surveillance, control strategies, and dissemination of information. State and federal agencies are working together to identify the presence of WNV. Reducing mosquito-breeding habitats in each community can greatly lower the potential for West Nile virus to become a significant threat to humans and domestic animals.
Where do I call if I need more information on West Nile virus in domestic animals and birds?
Call the Office of the State Veterinarian, Department of Agriculture at (860) 713-2505.
2002 West Nile Virus Update
Four horses have been diagnosed with clinical WNV infection. The horses ranged in age from 2 to 20 years and were stabled in four different towns (Canaan, Canterbury, Wallingford, Norwalk). Onset dates of clinical signs ranged from September 16 to October 22. Three horses recovered and one was euthanised. All four horses had no history of recent travel. Three horses were not vaccinated against WNV and the fourth horse only had one injection. On August 1,2001, the USDA Animal and Plant Health Inspection Service issued a conditional U.S. Veterinary Biological Product License for the manufacture and distribution of the Fort Dodge Equine WNV vaccine. On August 3, 2001, the Connecticut State Veterinarian approved the distribution and sale of the vaccine within the State and only to licensed veterinarians.
Nationally as of December 15, 2002, state officials in 40 states have reported 14,516 horse cases of WNV infection.
Seventeen people have been diagnosed with illness attributed to WNV infection. None have died from their illness. The patients are residents of Ansonia (1), Bridgeport (2), Greenwich (3), Hartford (3), Meriden (1), North Haven (1), Plainville (1), Stamford (2), Stratford (1), and West Hartford (2). They had onset of illness from the second week of August to the first week of October. The median age of the ten hospitalized patients was 62 years.
Nationally as of December 11, 3829 human cases of WNV infection have been reported from 39 states and the District of Columbia. Of the people infected, 225 have died.
528 wild birds tested positive for WNV from April 30 through October 21, 2002 coming from 103 towns and 8 counties in Connecticut. Ten different species of birds were collected – the most common were crows (501) followed by blue jays (16).
Fifteen Connecticut towns had positive mosquito pools for WNV (Bridgeport, Darien, Easton, East Haven, Greenwich, Hamden, Hartford, Manchester, New Britain, New Haven, Newington, Norwalk, Shelton, Stamford, Stratford). The majority of positive mosquitoes consist of Culex pipiens and Culex restuans, predominantly bird-feeding species. Positive mosquito species trapped in Easton, Culex salinarius, Hartford, Aedes vexans, Newington, Ochlerotatus trivittatus, Shelton, Aedes vexans, Stamford, Culex salinarius, Aedes vexans and in Stratford, Culex salinarius, Ochlerotatus trivittatus also feed on mammals including people. West Nile virus was also isolated from these species during 2001.
State of Connecticut Mosquito Management Program
The State's mosquito monitoring and management program is a collaborative effort involving the Department of Environmental Protection (DEP), the Department of Public Health (DPH), and The Connecticut Agricultural Experiment Station (CAES), Department of Agriculture (DOAg) and the Connecticut Veterinary Diagnostic Laboratory at the University of Connecticut (UCONN). The program is coordinated by the Department of Environmental Protection.
Mosquito Management Program Information:
Department of Environmental Protection
(860) 424-4184 - Latest information on test results, spray locations, protective measures.
(860) 642-7630 - Technical questions regarding mosquitoes, mosquito controls measures.
Connecticut Agricultural Experiment Station
(203) 974-8500 - Mosquito trapping.
Department of Public Health
(860) 509-7994 - WNV infections in people.
(860) 509-7742 - Effects of pesticides on people.
Department of Agriculture
(860) 713-2505 WNV infections in domestic animals, including livestock, poultry and pets.
Call your local health department to report dead birds. You can find the number in the blue pages of your local phone book.