Close up of a mosquito

As summer begins, news programs are rife with stories about the Zika and West Nile viruses. Infectious disease specialists warn about the potential for disease in people. But what about your pets — are they at risk, too?

West Nile Virus in People and Horses

Once limited to Africa, Europe, India, the Middle East, Asia and Australia, West Nile virus (WNV) crossed the ocean to North America in 1999 and has since advanced across the United States and Canada. Most commonly spread by infected mosquitoes, the virus usually infects people and horses.

Infected people and horses may have a fever or show no signs at all. With severe infections, they may display signs associated with encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord), such as disorientation, seizures or paralysis.

Typically, people and horses infected with WNV have very low levels of the virus circulating in their blood, so the virus usually isn’t transmitted to mosquitoes during feeding. That means an otherwise uninfected mosquito generally can’t spread the virus from one horse to another, from a horse to a human or vice versa. To spread the virus, a mosquito must first feed on birds, or in some cases rodents, which typically carry higher levels of circulating virus.

The Impact on Dogs and Cats

Little information is available regarding the susceptibility of dogs and cats to WNV infection. It appears that dogs and cats may be exposed to the virus through a mosquito bite or through ingestion of infected small mammals or wild birds. However, the virus does not appear to cause overt disease in our small companion animals.

In a study of dogs experimentally infected with the West Nile virus, none of the dogs showed clinical signs of disease. The dogs did have measurable amounts of virus in their blood, but the quantity was so low, it was unlikely to result in transmission of the virus to feeding mosquitoes.

Cats experimentally infected with WNV showed mild, nonspecific signs of disease, including lethargy, decreased appetite and fever. Compared with dogs in the study, cats had a higher virus concentration in their blood, which may be enough to infect mosquitoes but not as effectively as infected birds could.

These studies indicate that although dogs and cats can become infected by the WNV, they may not show obvious signs, and neither species is likely to be a source of infection for people.

The Zika Virus in People

Like WNV, Zika virus is spread to people through the bite of an infected mosquito, but in this case, it’s primarily the Aedes species of mosquito. In people, the most common signs of infection include painful joints, fever, rash and eye inflammation. Signs are typically mild and may last for several days to a week. However, if a woman becomes infected while pregnant, the virus can cause a serious birth defect that impacts fetal brain development.

The Outlook for Pets

According to the Centers for Disease Control and Prevention (CDC), animals in the United States are not at risk of developing disease from the Zika virus. At this time, there’s no evidence that animals spread the Zika virus, and infected people do not appear to spread the virus to animals.

Currently, monkeys and apes apparently have the ability to become infected with the virus, but the signs tend to be mild and transient (i.e., lasting only a short time). A very limited study from the late 1970s showed that cows, horses, goats, water buffaloes, ducks and bats could become infected as well, but they did not develop disease or pose a risk for viral transmission to humans. Even so, additional research is needed to better understand how Zika virus affects animals.

Consult Your Veterinarian

Still concerned about the risk of these viruses to your pet? Then speak with your family veterinarian. Numerous veterinary products are available that can kill and/or repel mosquitoes, and your veterinarian can recommend one that’s right for your pet. In addition, you can help reduce your pet’s exposure to mosquitoes by making sure all window and door screens are intact and removing standing water from your yard.

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