West Nile virus in Ontario, Canada: A twelve-year analysis of human case prevalence, mosquito surveillance, and climate data

Abstract

West Nile Virus (WNV) first arrived in Ontario, Canada in 2001 and has since spread throughout most of the province, causing disease in humans. The provincial government established a province-wide surveillance program to monitor WNV transmission throughout the 36 regional health units. Here we have acquired records of WNV human and mosquito surveillance from 2002 to 2013 to describe seasonal and geographic trends in WNV activity in southern Ontario. Additionally, we obtained climate data from seven municipalities to investigate how temperature and precipitation affect WNV transmission dynamics. We identified a strong quadratic relationship between the number of confirmed human cases and positive Culex mosquito pools recorded at the end of each year (R2 = 0.9783, p < 0.001). Using Spearman rank correlation tests, we identified that the minimum infection rate of Culex pipiens/restuans pools are the strongest predictor of human cases at a 1 week lag period. We also identified positive correlations between minimum infection rates, temperature, vector abundance, and cumulative precipitation. Global Moran’s I index indicates strong positive autocorrelation and clustering of positive Culex pool counts in southern Ontario. Local indicators of spatial association tests revealed a total of 44 high-high and 1 high-low trap locations (n = 680). In the current work we have identified when and where hot spots of WNV activity have occurred in southern Ontario. The municipalities surrounding the western shore of the Lake Ontario and Windsor-Essex County have the largest records of positive mosquitoes and human cases. We identified that positive mosquitoes are a strong indicator of human cases to follow in the coming weeks. An epidemic action threshold of cumulative positive Culex pools was established, allowing Ontario public health officials to predict an epidemic at epidemiological week 34 (rho = 0.90, p < 0.001). These data have the potential to contribute to more efficient larvicide programs and awareness campaigns for the public.

The drivers of West Nile virus human illness: fine scale dynamic effects of weather, mosquito infection, social, and biological conditions

“…Taking the most extreme possibility, when there was only one mosquito in a pool and it tested positive, this would yield a MIR of 1000 in contrast to MIR of 20 when a pool with 50 mosquitoes was tested positive. In Ontario, Canada, the cumulative number of positive mosquito pools up to week 34 was suggested as an action threshold potential to estimate the total annual human cases [16]. In Chicago, we obtained this signal three weeks earlier, which can be crucial to the ability to intervene in the upcoming potential human WNV outbreak.…”

“…We also found increased MIR up to four weeks earlier will increase the probability of an area being positive for a WNV human case. The temporal association between lagged MIR and human WNV cases is relatively well established [10,16,51]. However, it was interesting to find the positive association of MIR when spatiotemporal variabilities of human cases were considered.…”

A 15 Year Evaluation of West Nile Virus in Wisconsin: Effects on Wildlife and Human Health

“…Results from the linear and logistic regression model were interpolated using a kriging analysis (Empirical Bayesian method). Empirical Bayesian kriging was chosen for the prediction analysis as it contains a distribution of semivariograms and is known to be an accurate assessment for Gaussian distributed datasets [38]. Kriging analyses were conducted using the interpolation toolset in the ArcGIS 10.5 geostatistical analyst package.…”

Les changements climatiques pourraient-ils entraîner la propagation de maladies exotiques transmises par les moustiques au Canada?

“…tarsalis, qui sont les principaux vecteurs du virus du Nil occidental au Canada, peuvent survivre tout l'hiver en entrant en diapause, et le seuil de température pour leur développement est en général inférieur à celui Cette oeuvre est mise à la disposition selon les termes de la licence internationale Creative Commons Attribution 4.0 des espèces tropicales/subtropicales (5). Pour ces raisons, les maladies transmises par des moustiques exotiques sont seulement contractées à l'étranger, alors que les maladies transmises par des moustiques endémiques sont contractées à l'étranger et au Canada au cours des mois chauds (6)(7)(8)(9)(10).…”

“…Il existe deux scénarios d'introduction internationale dans lesquels les vecteurs sont soit présents, soit absents au Canada (Tableau 2). 'endémie au fil du temps (comme dans le cas du virus du Nil occidental)(6,(67)(68)(69). La malaria et le virus Chikungunya font partie des maladies qui pourraient émerger selon ce scénario parce que des populations de vecteurs de ces maladies déjà établies ou ayant émergé depuis peu sont présents Canada…”