Equine WNV Spread across Central Europe Investigated

West Nile is a viral disease transmitted to horses by infected mosquitoes.

Photo: Thinkstock

In recent years, West Nile virus (WNV) has slowly spread toward central Europe, with cases confirmed in Hungarian horses since 2003. For the moment, however, a group of Czech researchers report that the disease rate appears to be remaining steady.

“West Nile fever is occurring and spreading (in humans, birds, etc.) now in some Mediterranean regions (such as Italy and Greece), Balkan states (such as Serbia), and Central European countries (Hungary),” said study author Zdenek Hubalek, PhD, of the Institute of Vertebrate Biology in the Academy of Sciences in Brno, in the Czech Republic. “In some of these countries it affects horses.”

West Nile is a viral disease transmitted to horses by infected mosquitoes. Clinical signs include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (drowsiness); propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.

Results from surveillance studies investigating antibodies in horses’ blood showed that the virus is not yet threatening northern Europe, said Hubalek. However, veterinarians have confirmed the virus in horses as far north as Slovakia, he said.

Slightly more than 8% of the unvaccinated horses tested in Slovakia were positive for WNV antibodies, Hubalek said. That figure increased to 15% when only considering the horses living in districts along the Hungarian border. In the Czech Republic, however, located just west of Slovakia, the tested horse population had a 0% WNV antibody presence, he said.

Hubalek believes migratory birds traveling from Africa are the likely source of the virus in central Europe. The international transport of horses from endemic areas, such as the United States, is unlikely to cause disease spread. “The mechanism via imported horses is improbable,” said Hubalek. “Horses infected with WNV are namely considered deadend hosts, in other words, noninfectious for other horses or humans.”

WNV was first isolated in Uganda's West Nile district in 1937. In 1963 it was isolated in Europe in the Rhone Delta region of France, a mosquito-infested area known for its semi-feral Camargue herds. While the virus was found in humans, birds, mosquitoes, and some livestock in several European countries between 1960 and 1990, few countries—mainly France, Portugal, and Italy—reported virus presence in horses, Hubalek said. Outbreaks have been rare, isolated, and usually short-lived.

The virus and its associated disease appear to be “re-emerging” in Europe, however. Weather conditions such as flooding and unusually high temperatures could contribute to the virus' spread, he said.

"It is therefore recommended to be vigilant and monitor the nonvaccinated horse population for antibodies and for clinical cases in various European countries," Hubalek advised. "Vaccination of horses will be helpful in those countries that are already affected by WNV or where its occurrence might be expected or predicted. In other countries, vaccination is unnecessary."

The study, "West Nile Virus equine serosurvey in the Czech and Slovak republics," was published in Vector Borne and Zoonotic Diseases

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More