WNV has been a seasonal epidemic in Toronto since 2001. Nine of the twelve species of mosquito that carry WNV – known as vectors – live in the Toronto region. Since West Nile virus was first discovered in Southern Ontario, wetlands and storm water management ponds have been suspected of providing breeding grounds for WNV-carrying mosquitoes. The Toronto and Region Conservation Authority (one of the founding partners of CC-RAI) being the largest land owner in the Toronto region started their monitoring activities in response to these concerns.

From 2005-2009, Krishnaraj and her team have carried out the monitoring of selected wetlands and stormwater management ponds that are located on TRCA properties to determine the types of mosquitoes that were breeding, their relative abundance, and the risk of human WNV exposure originating from one of these sites. This work has been conducted as part of TRCA’s broader Regional Watershed Monitoring Program.

What did the TRCA research reveal? Wetlands generally have higher numbers of mosquito larvae than stormwater ponds but fewer WNV vector species. The overall risk of WNV exposure from wetlands and stormwater ponds is relatively low and, large numbers of mosquitoes (larvae) does not necessarily mean a higher risk of contracting WNV.

In all years except for 2006, wetlands had fewer species of WNV carrying mosquitoes than non-vector mosquito species. Storm water management ponds had very high percentages of vector mosquitoes, but the absolute number was generally not high enough to be a risk to the community. On average, there were only one or two high risk sites per year out of all the wetlands and storm water management ponds monitored.

On November 22nd Thilaka Krishnaraj, an entomologist at the Toronto and Region Conservation Authority (TRCA) gave a presentation on the outcomes of West Nile Virus (WNV) larval monitoring and surveillance activities in the Toronto region to a group of researchers and students from the Laboratory of Mathematical Parallel Systems (LAMPS) at the LAMPS Weekly Interdisciplinary Workshop.

Dr. Huaiping Zhu, an associate professor and project leader at LAMPS welcomed the opportunity to share expertise and understanding on the relationship between ecology and epidemiology.

Both TRCA and LAMPS realize the importance of monitoring, modeling and the additional research that is needed in understanding the ways in which ecosystems and consequently, epidemiology may well be impacted by a changing climate.