skip to content

West Nile Virus

August 27, 2009

Eastern Equine Encephalitis and West Nile virus

Message from Vermont State Veterinarian Dr. Kristin Haas and Vermont Assistant State Public Health Veterinarian Erica Berl

Dear Vermont Veterinarian:

 

The mosquitoes are biting, which means arbovirus season has begun. The Vermont Department of Health and the Vermont Agency of Agriculture are continuing surveillance for West Nile virus (WNV) in mosquitoes, humans and birds, and for Eastern Equine Encephalitis virus (EEEV) in mosquitoes and humans. Domestic animals, especially horses, can also be infected with these viruses. Detecting these viruses in animals is helpful for assessing the risk to the public and other animals. We encourage you to test animals that have clinically compatible illness and to report positive results to the State Veterinarian.

 

We are particularly interested in EEEV because it can cause devastating disease in humans and animals. Although EEEV has never been detected in Vermont, it has been found in nearby areas, and the main mosquito vector, Culiseta melanura, is present in our state. In recent years, EEE has been diagnosed in horses in New Hampshire, Maine, Clinton County, New York and Quebec. EEEV has also been detected in emus and alpacas. So far this year, an alpaca in New Hampshire and a horse in central Maine have died of EEE.

 

WNV has been detected in our state in almost every year since 2000. Eleven equine cases have been reported to us over that time, although activity has been low the past three years.

 

WNV should be considered in horses that develop neurologic symptoms without an alternative explanation. EEEV can cause severe neurologic symptoms or sudden death in horses, donkeys, llamas and alpacas. Emus are also susceptible to EEEV infection, but they usually present with a severe hemorrhagic gastroenteritis or sudden death.

 

The Vermont Department of Health and Agency of Agriculture can facilitate testing in some cases by sending brain tissue samples for arbovirus testing to Wadsworth Laboratory, which is part of the New York State Department of Health. Samples from horses, donkeys, alpacas and llamas that die or are euthanized with neurologic signs should first be tested for rabies. Those samples that are negative can then be forwarded to Wadsworth for arbovirus testing.

  

Please remember that both WNV and EEE in animals are reportable diseases in Vermont. To report animals diseases please call the State Veterinarian’s office at 802-828-2421. If you have any questions about arbovirus testing or arboviruses in general, please call the State Veterinarian’s office or the Health Department’s Infectious Disease Epidemiology program at 802-863-7240.

 

For more information on arboviruses and mosquito control, please go to our websites: http://healthvermont.gov/prevent/wnv/wnv.aspx - or - http://www.vermontagriculture.com/ARMES/plantindustry/entomology/mosquito/index.html

 

Thank you for your help.

 

Steps You Can Take To Avoid West Nile Virus

  • Wear long sleeved shirts and long pants whenever possible outdoors.
  • Limit the amount of time you spend outdoors at dawn and dusk since that is when mosquitoes are most active.
  • Use insect repellant that contains up to 30 percent DEET for adults and up to 10 percent DEET for children and apply sparingly. Be sure to follow the product directions. DEET can be harmful if used in large amounts or used incorrectly. Never use DEET on infants.
  • Regularly empty any outdoor containers that hold standing water including wading pools, trash cans, tires and empty flower pots. Turn them over or cover them when they are not being used.
  • Clean leaves and other debris out of clogged gutters.
  • Repair holes in screens and make sure they fit tightly to the window or door frame.

More information about West Nile virus, national and Vermont statistics, and others ways to protect yourself can be found on the Vermont Department of Health website: www.HealthyVermonters.com .

West Nile Virus and Horses

West Nile affects horses much more often than any other domestic animals. Many horses infected with West Nile do not develop any illness, but of horses that become ill about one-third die or need to be euthanized. Other livestock and poultry do not commonly show any illness if infected with West Nile.

Q. How do horses become infected with West Nile virus?
A. The same way humans become infected—by the bite of infectious mosquitoes. The mosquitoes become infected after feeding on an infected bird. Mosquitoes cannot get West Nile virus from an infected horse.

Q. Has West Nile virus caused severe illness or death in horses?
A. Following transmission by an infected mosquito, West Nile virus, may cause a mild transient self resolving fever or it may infect the brain causing inflammation or “encephalitis”. The vast majority of horses that are bitten by infected mosquitoes do not become ill, but those that develop severe encephalitis often die.

Q. Can I get infected with West Nile virus by caring for an infected horse?
A. West Nile virus is transmitted by infectious mosquitoes. The infected horse is not contagious to humans or to other horses. Normal infection control precautions should be followed when caring for a sick horse.

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.

Q. My horse is vaccinated against Eastern Equine encephalitis, Western Equine encephalitis and Venezuelan Equine encephalitis. Will these vaccines protect my horse against West Nile virus infection?
A. No. These three viruses 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 conditionally licensed West Nile virus vaccine for horses is available. Contact your large animal veterinarian for more information.

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. Supportive care and time are all that most horses need to fully recover.

Q. How can I help protect myself and my family from West Nile Virus?
A. Horse owners should make sure that empty buckets and water troughs are not breeding sites for mosquitoes. Turn over buckets when they are not in use, and clean the water trough regularly. Make sure that faucets are turned off and do not drip.

The best way to protect you from West Nile virus, or any other mosquito-borne illness, is to reduce the number of mosquitoes around your home and neighborhood and to take personal precautions to avoid mosquito bites. These are some of the preventative steps that you can easily take:

  • Eliminate standing water where mosquitoes can breed. Check for items outside the home that collect water, such as cans, bottles, jars, buckets, old tires, drums and other containers.
  • Change water in flower vases, birdbaths, planters and animal watering pans at least twice a week.
  • Repair leaky pipes and outside faucets, and move air conditioner drain hoses frequently.
  • Avoid being bitten by mosquitoes when going outside at night by using insect repellent. Wear lightweight clothing that covers the arms and legs.

Q. Where can I get more information on horses and West Nile virus?
A. USDA’s Animal and Plant Health Inspection Service Web site at www.aphis.usda.gov/oa/wnv/.

Recent media reports have prompted many questions regarding West Nile virus (WNV) infection in species other than birds, horses, and humans. As an "emerging disease" in the United States, WNV has clinical and health effects on various animal species and populations that have yet to be described or fully reported. The following information is offered on the current knowledge of WNV infection in other species.

It is currently believed that any type of bird or mammal may be susceptible to WNV infection, but very few species appear to develop clinical illness due to infection. Since entering North America in 1999, WNV has been reported in thousands of birds, horses, and humans (over 2768 people and 146 deaths, as of Wed 9 Oct 2002). Before this year, WNV infection had been reported in several bat species, chipmunks, gray squirrels, striped skunks, a rabbit, and 3 cats. Laboratory trials had indicated that cats would become viremic and ill, but that dogs were relatively resistant to infection with WNV.

Serosurveys in New York following the 1999 outbreak revealed that 8-11 percent of dogs had antibody titers to WNV, but had not become ill. As WNV has moved across the country this summer, infection and illness have now been reported in a domestic sheep, a mountain goat, a dog, a 7-month-old wolf pup, a llama, and an alpaca. Serologically positive black bears and white-tailed deer have also been detected, but these animals did not develop clinical illness.

Some of the animals that became ill had another underlying health condition and/or a compromised immune system predisposing them to development of clinical disease. For instance, the one 8-year-old dog in Illinois was immune-compromised. From what is currently known, WNV does not appear to pose a significant health risk for species other than birds, horses, and humans. The extremely small number of cases in other species, the active surveillance conducted for the last 4 years, and reports from 42 states that have detected WNV suggest that most of these species are extremely resistant to developing clinical illness from infection. There is also no current evidence that any of these species are capable of serving as a reservoir for the virus.

It is likely more cases in other hosts will be found as WNV enters and becomes established in new areas. As additional information becomes
available, the relative health significance of WNV infection in these populations will become more clearly established.

Suggestions for protecting animals from the deadly West Nile Virus

The USDA is recommending that animal owners take several precautions to protect their animals from the West Nile virus. The following recommendations are based on current knowledge about the virus and the 1999 US outbreak.

Mosquito breeding sites:

Remove all potential sources of stagnant water where mosquitoes might breed.

Precautionary steps include the following:

  • Dispose of any water containers, including discarded tires.
  • Drill holes in the bottom of containers that are left outdoors
  • Clean clogged roof gutters annually.
  • Turn over plastic wading pools or wheelbarrows when not in use, and do not allow water to stagnate in birdbaths.
  • Ventilate ornamental pools or stock them with fish.
  • Clean and chlorinate swimming pools that are not in use.
  • Thoroughly clean livestock troughs monthly.

Insect repellents:
Use of insect repellents may be of some value in decreasing exposure of horses to adult mosquitoes. Repellents alone should not be relied on, however, to prevent mosquito exposure.

Screened housing:
Housing animals in structures with well-maintained insect screening can reduce exposure to adult mosquitoes. Be sure to eliminate mosquitoes from inside the structure first through the use of mosquito adulticides and fans.

Outdoor exposure:
The mosquitoes responsible for the transmission of the West Nile virus to horses and other mammalian species generally feed at dawn, dusk, and during the night. The USDA recommends caution when exposing animals to areas inhabited by mosquitoes during these times.

USDA's actions to protect agriculture:
The USDA-APHIS Veterinary Services has developed a diagnostic test for the West Nile virus and is on the lookout for virus activity along the Atlantic seaboard. The program surveillance investigates horses showing clinical signs of encephalitis, when other common causes such as rabies can be ruled out. APHIS' Wildlife Services program carries out wild bird specimen collection, initially focusing on East Coast states from Connecticut to Florida, for West Nile virus testing.