Equine health alert: West Nile Virus on the rise in Canada
11.04.2019 - source: horse-canada.com
2018 showed an alarming rise in the number of reported cases across the country, most notably:
- more than 2x the reported cases nationally, compared to 2017;
- cases reported in almost every Province, with extreme increases in Alberta and Saskatchewan*
*CRA reported cases to December 15, 2018, compared to 2017.
more info here.
West Nile virus (WNV) is an enveloped single‑stranded RNA virus of the Flaviviridae family. It is transmitted by a variety of mosquitoes and has so far been discovered in more than 40 different mosquito species and in several tick species. Birds represent the vertebrate reservoir. Acting as incidental hosts, mammals can also become infected when bitten by an infected mosquito.
Other than humans, usually only horses become ill after natural infection. After an incubation period of three to fifteen days, most horses show a short period of viraemia with low virus titers. Generally, humans and horses are considered as dead‑end hosts owing to the low‑level viraemia. Only around 10 % of infected horses show clinical symptoms. The first symptoms are mostly unspecific and include fever, depression, loss of appetite and colic. When the infection proceeds, neurological disorders often follow, leading to lameness and ataxia or even paresis, which are considered as predominant clinical symptoms. In rare cases, problems of the facial nerves, photosensitivity and blindness, subsultus as well as general sensitivity and personality changes are observed.
In horses with a mild course of the disease, recovery usually takes two to seven days. In severe infections, recovery may take 20 days or several weeks. 20 % of horses with past severe infection show long‑term sequelae such as weight loss, lethargy, ataxia and cerebral nerve problems. In non‑vaccinated horses, the infection is fatal in 24 % to 45 % of clinical cases. Intensive medical care is the only possibility to positively influence the illness. A vaccine with formalin‑inactivated WNV is available for horses.