Québec Eastern Equine Encephalitis Outbreak of 2008 Reviewed

Following is a report by the animal health surveillance network (RAIZO) of the Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec.

Only two cases of Eastern equine encephalitis (EEE) had been reported in Québec in the past 35 years until the fall of 2008, when the province experienced an outbreak of the disease. The first case was reported by Sonia Chénier, doctor of veterinary medicine and animal pathologist with the Laboratoire d'épidémiologie animale du Québec (the state animal epidemiology laboratory), which is associated with the Ministère de l'Agriculture, des Pêcheries et de l'Alimentation (MAPAQ).

The situation was analyzed by MAPAQ's animal health surveillance network (RAIZO), which rapidly relayed the information to veterinary practitioners, Québec horse industry stakeholders, and public health authorities. The 2008 report that is currently being drafted will provide a clearer idea of the threat posed by EEE for equine and human health in North America.

RAIZO, whose activities are overseen by MAPAQ, is mandated to protect Québec's herds and public health. It consists of a number of sentinel networks that correspond to the various animal industry sectors. The equine network works mainly on collecting, analyzing, and distributing the information required in order to protect equine and public health. Thanks to the veterinary practitioners who make up this equine network, it was possible to quickly detect the EEE outbreak in Québec last fall.

In early September 2008, Dr. Chénier issued an advisory about suspected EEE in two horses from the same stable presenting with neurological and pathological lesions compatible with the disease. On September 25, 2008, laboratory tests confirmed the diagnosis. The information was immediately transmitted by RAIZO. In the weeks that followed, other horses were diagnosed and found to be EEE positive along with a flock of severely affected emus. None of the EEE-positive horses had been vaccinated in the previous 12 months.

Cases were reported in the four Québec regions of Estrie, Centre-du-Québec, Lanaudière, and Montérégie. All but one of the horses died or had to be euthanized as a result of the infection. As of December 31, 2008, the annual count of equine cases of EEE in Québec was 16 confirmed cases and three presumed cases. It has been mandatory in Québec since 2003 to report cases of human EEE . None were reported.

Birds are the reservoir for the EEE virus, and their movement may have contributed to extending the range of the infection to include Québec. Note that cases were recorded in the northeastern United States, notably in New York, Maine, and New Hampshire (see map). Another possible explanation for this unusual outbreak of EEE is the presence of infected mosquitoes borne by hurricane-induced air currents on the East Coast and mosquito reproduction due to the damp 2008 summer in Québec.

In Canada, EEE is a disease that must be reported immediately by the diagnostic laboratories to the Canadian Food Inspection Agency. Until now, in Canada and the northeastern United States, the incidence of the disease has been sporadic at most. It is hard to predict what Eastern equine encephalitis has in store for us in the future. However, given that the disease has mosquito vectors and that the birds that are reservoirs are found in Québec, precautions are called for. The most important recommended courses of action in preventing a fresh outbreak in 2009 are the vaccination of horses and measures to protect horses and humans from mosquito bites.

Contact: Dr. Nathalie Hébert, 418/380-2100, extension 3956; Institut national de santé animale, Ministère de l'Agriculture des Pêcheries et de l'Alimentation du Québec; Québec, Canada

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.