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

Abstract

Eastern equine encephalitis (EEE) is a rare but severe emerging vector-borne disease affecting human and animal populations in the northeastern United States where it is endemic. Key knowledge gaps remain about the epidemiology of EEE virus (EEEV) in areas where its emergence has more recently been reported. In Eastern Canada, viral activity has been recorded in mosquitoes and horses throughout the 2000s but cases of EEEV in humans have not been reported so far. This study was designed to provide an assessment of possible EEEV human exposure by modelling environmental risk factors for EEEV in horses, identifying high-risk environments and mapping risk in the province of Quebec, Canada. According to logistic models, being located near wooded swamps was a risk factor for seropositivity or disease in horses [odds ratio (OR) 4·15, 95% confidence interval (CI) 1·16-14·8) whereas being located on agricultural lands was identified as protective (OR 0·75, 95% CI 0·62-0·92). A better understanding of the environmental risk of exposure to EEEV in Canada provides veterinary and public health officials with enhanced means to more effectively monitor the emergence of this public health risk and design targeted surveillance and preventive measures.

The Role of Urban-to-Rural Gradients in Mosquito-Borne Disease Risk in Ontario, Canada

“…In addition to the effect of urban landscapes, I found that forested land cover was positively associated with EEEV seroprevalence in Song Sparrows, and negatively associated with WNV seroprevalence. For EEEV virus, this is consistent with the importance of forested wetland areas to the main vectors of EEEV, notably Culiseta melanura (167)(168)(169)(170). In Eastern Ontario, Culex pipiens/restuans mosquitoes are less prevalent in forests (171), which explains my observation that WNV seroprevalence in Song Sparrows was lower in forested land covers.…”

“…For EEEV however, studies investigating a relationship between human landscapes and disease risk are scarce. This is likely a consequence of an established relationship between EEEV prevalence, its primary mosquito vector Culiseta melanura (59), and forested wetland habitats (167)(168)(169)(170). However, mosquitoes involved in EEEV transmission, most notably Culiseta melanura, are still found in urban and agroecosystems (171) that may include patches of forest and wetlands used by these mosquitoes (172,173).…”

Association of Human Eastern Equine Encephalitis With Precipitation Levels in Massachusetts

“…Despite these data, estimating the risk of EEE infection is complex and not easily explained simply by precipitation data, and large-scale epidemiologic investigations of EEE are limited by the low number of cases diagnosed each year. 5,6 Temperature also plays a role in risk of EEE cases, as exemplified by the 2012 data that included 7 human EEE cases. Notably, 2012 was the warmest year in Massachusetts from 1895 through 2012.…”