Eastern Equine Encephalitis Virus: High Seroprevalence in Horses from Southern Quebec, Canada, 2012

Abstract

Eastern equine encephalitis virus (EEEV) is a highly pathogenic arbovirus that infects humans, horses, and other animals. There has been a significant increase in EEEV activity in southeastern Canada since 2008. Few data are available regarding nonlethal EEEV infections in mammals, and consequently the distribution and pathogenicity spectrum of EEEV infections in these hosts is poorly understood. This cross-sectional study focuses on the evaluation of viral activity in southern Quebec's horses by seroprevalence estimation. A total of 196 horses, 18 months and older, which had never been vaccinated against EEEV and have never traveled outside Canada, were sampled from 92 barns distributed throughout three administrative regions of southern Quebec. Blood samples were taken from each horse and titrated for EEEV antibodies by plaque reduction neutralization test (PRNT). Equine population vaccination coverage was estimated by surveying horse owners and equine practitioners. PRNT results revealed an EEEV seroprevalence up to 8.7%, with 95% confidence limits ranging from 4.4% to 13.0%. Vaccination coverage was estimated to be at least 79%. Our study reveals for the first time in Canada a measure of EEEV seroprevalence in horses. High seroprevalence in unvaccinated animals challenges the perception that EEEV is a highly lethal pathogen in horses. Monitoring high-risk vector-borne infections such as EEEV in animal populations can be an important element of a public health surveillance strategy, population risk assessment and early detection of epidemics.

Emerging arboviruses in Quebec, Canada: assessing public health risk by serology in humans, horses and pet dogs

“…However, the seroprevalence of antibodies to WNV in humans in this study was relatively comparable with the results from a serosurvey conducted in southern Ontario after the 2002 WNV outbreak in humans (3•1% [38]) and helps support the notion that humans are rarely bitten by WNV-infected mosquitoes in eastern Canada. Moreover, as discussed in Rocheleau et al [4], there are specific limitations to the use of serology in horses pertaining to the fact that clear information on vaccination status must be obtained in each horse for adequately interpreting WNV and EEEV serological results. However, to our knowledge, current vaccination protocols have no impact on serological status for CSGV since no vaccines are currently available for these mosquito-borne bunyaviruses.…”

“…Blood samples from horses >18 months of age were collected in 2012 as described previously [4]. All horses resided within Montérégie, Lanaudière or Laurentides regions ( Fig.…”

“…All horses resided within Montérégie, Lanaudière or Laurentides regions ( Fig. 1) and none of the animals had been vaccinated against EEEV or WNV [4]. Sampling design was a convenience cluster sampling with barns as the primary sampling unit.…”

Characterizing areas of potential human exposure to eastern equine encephalitis virus using serological and clinical data from horses

“…The serosurvey dataset included 190 horses sampled in 2012 from 92 barns located within the study area. These horses had never been vaccinated against EEEV at the time of sampling, and 15 were seropositive to EEEV [7]. In addition to EEEV serological results, this dataset included information on horse characteristics (age, sex, breed), animal management (use of mosquito repellent, time spent outside daily, use of horse protective fly sheets or blankets), and characteristics of the barn in which they were housed (type of housing, use of window and door screens).…”

“…In 2012, an equine EEEV serosurvey conducted in the same region revealed that more than 6% of horses had been infected with EEEV, which suggests that ecological niches (i.e. appropriate habitat, vectors and virus) exist to sustain EEEV transmission including potential spillover to human populations [7]. The characteristics of these ecological niches have, however, never been precisely identified.…”