West Nile Virus Doesn’t Pose A Huge Threat, But Animal Owners Should Remain Cautious

a white horse in front of a sunset

This summer, mosquitos sampled as part of routine surveillance in Texas have tested positive for West Nile Virus, a disease commonly associated with humans but that can also affect birds, bats, horses, cats, dogs, and rabbits. 

Although the summer months are waning, because mosquitos remain active during warm months, people and pets are not out of the woods for WNV even during the fall. 

Dr. Sarah Hamer, an epidemiologist and associate professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences and director of the Texas A&M Schubot Center for Avian Health, said that mosquito bites are the most common source of WNV transmission, and a mosquito typically contracts and spreads the virus after feeding on an infected bird before spreading it to people and other animals.  

“WNV is the most common mosquito-transmitted disease in the U.S. It historically occurred in Africa and the Middle East and has since spread across Europe and the U.S.,” explained Hamer, who is an expert in many zoonotic diseases, including WNV. “The virus infects many animals in nature, predominantly birds. Many wild birds are natural reservoirs and amplify the virus to a high level in their blood, so that they then infect mosquitoes that feed on them.”

As a zoonotic disease, WNV can affect animals for a long time before it spreads to humans. Most  infected animals are asymptomatic, and modern medicine has yet to find a treatment for the virus or a vaccine for most animals. 

Viral infection such as WNV can lead to encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the spinal cord) in animal companions and pet owners alike. 

In some cases, febrile illness (fever) may be noticeable among the symptoms, and the range of signs that may manifest in animals includes weakness, trembling, head tremors, inability to fly or walk, and inattention. 

“Dogs and cats can become infected but are unlikely to show signs of disease, and infected dogs and cats are unlikely to infect mosquitoes, other animals, or people,” Hamer said. “Fortunately, WNV is not a major concern for companion animal health.” 

For horses, however, WNV does pose a much more virulent and lethal threat. According to the American Association of Equine Practitioners, horses represent 96.9% of all reported non-human mammalian cases of WNV disease.

Equine WNV complications range from debilitating to lethal. According to the AAEP, horses showing clinical signs of WNV infection have an approximate 33% mortality rate, and research indicates that 40% of horses that survive the acute illness caused by WNV still exhibit residual effects, such as gait and behavioral abnormalities, six months post-diagnosis. 

Fortunately, an equine vaccine is available, and Hamer recommends that owners vaccinate their hoofed friends each spring, before the insect season begins.

Additionally, preventing mosquito bites from occurring is crucial in preventing diseases like WNV. 

“Owners can help prevent mosquito bites by following mosquito control efforts around the neighborhood. This includes getting rid of standing water around the home and yard so mosquitoes will not lay their eggs in it,” Hamer advised. 

Even though there is no cure for WNV, the risks to your pets are low. 

“Most infected animals will not show signs of disease, but those that do can be treated with supportive care,” Hamer said. 

As with most mosquito-borne diseases, prevention is key. With the right vaccinations and veterinarians, owners have the power to transform this mosquito season into just another nuisance.

Pet Talk is a service of the College of Veterinary Medicine & Biomedical Sciences, Texas A&M University. Stories can be viewed on the web at vetmed.tamu.edu/news/pet-talk. Suggestions for future topics may be directed to editor@cvm.tamu.edu.


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