Why Is It Important to Monitor Ontario’s Mosquitoes?

You may find mosquitos a nuisance in the spring and summer months, but did you know that monitoring them is a vital public health task that helps us prevent mosquito-borne diseases like West Nile virus (WNV) and eastern equine encephalitis virus (EEEV)? Read on to learn more about mosquito surveillance in Ontario.

What is mosquito surveillance?

In Ontario, mosquito surveillance consists of collecting mosquitoes and testing them for WNV and EEEV.

From June through October, over 300 traps collect mosquitoes one night per week across Ontario. Mosquitoes that get caught by these traps are identified to species and counted. This way, we can collect data on the numbers of each species during each season at each trap location. Public health officials use these data to assess the risk of WNV or EEEV infection in the human population.

Since 2002, over 11 million mosquitoes have been collected in Ontario, with 5 million of these identified to species. The most commonly identified mosquitos are:

• Aedes vexans (30% of all mosquitoes identified)
• Coquillettidia perturbans (25%)
• Culex pipiens/restuans (14%)
• Ochlerotatus trivittatus (7%)
• Ochlerotatus stimulans (6%)

Why is mosquito surveillance important?

Besides assessing the risk of mosquito-borne diseases, mosquito surveillance is integral to understanding how mosquito populations change over time. Climate change (rising temperatures in summer and milder winters), increased urbanization, and increased international travel and trade contribute to the increased chance of detecting new mosquito species in Ontario.

As the world has recently seen with the global spread of chikungunya and Zika viruses, mosquito-borne viruses can emerge rapidly, creating a need for a rapid response. Ontario’s mosquito surveillance program is one of the most robust in North America, and allows public health officials to prepare a rapid response to emerging pathogens from invading mosquitoes.

Occasionally, mosquito surveillance detects new mosquitoes in Ontario. While most will never establish here due to absence of appropriate habitat and climate,  if they are given the appropriate habitat and climate, new mosquito species may become established. One particular new species is Aedes japonicus (normally from Southeast Asia), was first detected in Ontario in 2001 and rapidly spread throughout southern Ontario by 2005.

In fall 2016, public health officials discovered Aedes aegypti for the first time in Canada, in the city of Windsor, along with the first evidence of a reproducing population of Aedes albopictus. These species of mosquitoes are aggressive human biters and potential vectors of dengue, chikungunya, yellow fever and Zika viruses in warmer regions of the world. While we do not expect that these Aedes mosquitoes will survive the Ontario winter, it is important to continue surveillance for these species to ensure that neither of these two species establish in southern Ontario.

We know that mosquitoes can be nuisance biters and can carry pathogens, but what are the benefits to having mosquitoes in the environment?