Zika Virus—Talking Points for Veterinarians

Warmer weather and the start of mosquito season in the United States are fueling concerns about Zika, a mosquito-borne flavivirus that has made headlines worldwide after it was linked to thousands of cases of microcephaly among babies born in Brazil and other countries with tropical climates.

Veterinarians play a key role in educating the public about infectious diseases, and can expect questions from clients about Zika virus. Here are some talking points about Zika virus in animals and humans.

Zika in Animals

The Centers for Disease Control and Prevention (CDC) state that there have been no reports of Zika virus causing illness in pets. There are also no known cases of Zika virus being transmitted from pets or livestock to humans. Zika virus is known to potentially infect nonhuman primates — in fact the World Health Organization (WHO) notes that the virus was first identified in a monkey in the Zika forest of Uganda in 1947.

The CDC reports that infection in nonhuman primates is either asymptomatic or causes a mild, self-limiting fever; therefore, the prevalence of Zika virus in nonhuman primates is unknown. Zika infection has not been linked to microcephaly or other birth defects in animals.

Scientists do not know which other species of animals can potentially acquire Zika virus. One study, conducted in Indonesia in the 1970s, found that the virus could infect horses, cows, water buffalo, ducks, bats, and goats; however, there was no evidence that these animals developed clinical illness or transmitted Zika infection to humans.

Zika in Humans

Since the early 1950s, human outbreaks of Zika virus infection have been reported in tropical Africa, southeast Asia, and the Pacific islands. Zika virus is transmitted by infected mosquitos of the Aedes genus -- primarily Aedes aegypti, which also transmits yellow fever, dengue, and chikungunya viruses. An extensive analysis conducted by researchers at the University of Oxford in the United Kingdom found that Aedes aegypti is only common in Florida, Hawaii, and the Gulf Coast [in the United States]. Other Aedes mosquitos can range as far north as Iowa and New Hampshire, but are not as likely to transmit Zika virus because they do not preferentially feed on humans. Zika virus can also be spread through sexual contact. Infection with the Zika virus is thought to yield long-term immunity after symptoms resolve.

Up to 80% of human Zika virus infections are asymptomatic. However, when symptoms do occur they are typically mild and self-limiting, consisting of rash, fever, joint and muscle pain, and conjunctivitis. Nonetheless, Zika infection can cause serious complications. Zika virus is able to cross the placenta and attack fetal nerve cells. Infection during pregnancy can cause microcephaly and other severe fetal brain defects and malformations. In adults and children, Zika infection has also been reportedly linked to a severe neurological disease known as Guillain-Barré syndrome.

Since 2015, Zika virus infection has been linked to thousands of cases of microcephaly in Brazil, Columbia, French Polynesia, Cabo Verde, Martinique, and Panama. As of May 2016, there have been no reports of Zika virus being transmitted locally in the US states. All reported cases have been among US travelers returning from tropical countries where Zika is known to be circulating. However, Zika virus has been transmitted locally in the tropical US territories of Puerto Rico, American Samoa, and the US Virgin Islands.

Treatment and Control

Currently, there is neither a vaccine against nor a treatment for Zika virus infection. WHO advises resting, drinking plenty of water, taking over-the-counter medications to control fever, and contacting a medical provider if symptoms worsen.

According to the CDC, the best way to prevent Zika virus infection is to wear long sleeves and long pants treated with permethrin, use EPA-registered insect repellants containing DEET, IR 3535, picaridin, oil of lemon eucalyptus, or para-menthane-diol, and stay in places with physical barriers against mosquitos, including mesh screens on windows and doors. Because mosquitos can breed in very small amounts of standing water, it is also important to empty and cover or discard open containers, such as barrels, flower pots, and tires.

Dr. Amy Karon earned her doctorate in veterinary medicine and master’s degrees in public health and journalism from the University of Wisconsin-Madison. She was an infectious disease epidemiologist and “disease detective” (EIS officer) with the Centers for Disease Control and Prevention before becoming a full-time medical writer. She lives in the San Francisco Bay area, where she volunteers for the local Humane Society.