Mosquitoes: a piece of the puzzle for environmental changes affecting human health

Biodiversity, a wide and robust variety of plants and animals in a given area, is usually an excellent indicator of the good health of an ecosystem.

Biodiversity loss itself can result in unhealthy ecosystems. This is a very serious problem worldwide, and it might surprise you to learn that this phenomenon has an impact on even a tiny insect like a mosquito. Environmental changes can significantly alter the population of specific disease-bearing mosquito species and increase human-exposure risks.

Research Scientist Dr. Antoinette Ludwig and her team from the National Microbiology Laboratory (NML) study vector-borne diseases and are conducting environmental surveillance proactively to collect valuable and reliable data on mosquitoes to see what they have to reveal about human health risks, especially at critical times of the year such as summer.

Changes in mosquito biodiversity: a phenomenon undergoing profound transformation

Scientists are observing changes in mosquito biodiversity in Canada that are due to environmental and land-use changes, such as climate change and agricultural and urban expansion. This affects the complex ecology of mosquitoes. The emergence of more favourable environments for a particular species can promote its development, to the detriment of other less well-adapted species.

Even global trade can unintentionally cause exposure of ‘new’ mosquito species in regions where they were not previously know to be found, sometimes affecting the balance of local biodiversity.

Government of Canada scientists and researchers are observing these factors and believe that changes in mosquito biodiversity may even be accelerating.

Mosquitoes that carry diseases in Canada

Mosquitoes can carry and transmit viruses that pose a threat to humans, birds and mammals. Specific species of mosquitoes carry different viruses such as West Nile virus, Eastern equine encephalitis virus or California serogroup viruses (Snowshoe hare virus or Jamestown Canyon virus).

For humans, these viruses do not typically cause severe symptoms. However, in a small percentage of cases, symptoms may be more serious and even lead to death. This is especially true for the most vulnerable populations: people over 70 years old, children, those with reduced immunity (such as cancer patients) or people with a chronic disease (like diabetes or hypertension).

Monitoring to better understand and better anticipate changes

Since 2017, Dr. Ludwig and her team have been studying mosquito biodiversity in Eastern Ontario and Western Quebec. They are studying how the population of each species of mosquito changes according to weather and environmental conditions.

They are collecting mosquitoes from more than 80 sites, every two weeks, in a variety of landscapes, throughout the mosquito season (typically mid-May to mid-September).

The team identifies the collected mosquitoes by species. They then send the mosquitoes to the NML in Winnipeg to check for the presence of viruses.

A concerning situation

Scientists have discovered that, while viral activity (when mosquitoes are carrying viruses) is low to moderate in the region, it is persistent. This confirms the threat of exposure to mosquito-borne diseases for people and the need for continued research.

According to Dr. Ludwig, certain species of mosquitoes that can carry diseases to humans and other animals seem very well adapted to environments transformed by humans. These include:

  • urban environments, in particular residential areas with few trees, swimming pools that are less well maintained, containers that can serve as a breeding habitat for mosquitoes (flowers pots, any jars, or buckets); anywhere stagnant standing water can persist during breeding time periods
  • agricultural environments that offer lots of these potential breeding sites for mosquitoes like abandoned buckets, tires, and drainage network, etc.

"These observations made it evident that a man-made environment can become a very comfortable place for mosquitoes to proliferate."

- Dr. Antoinette Ludwig

The need for collaboration to get the complete picture of the risk for people

A mammalian or bird host is required for the full cycle of virus transmission to humans as mosquitoes only transmit the virus to humans after biting a host animal that was carrying the virus.

It is essential to fully understand the evolution of the biodiversity of other species involved in the transmission cycle, such as birds (American robin, crows, sparrows, etc.), or wild mammals (rabbits, white-tailed deer, etc.).

To achieve this complex task, researchers join forces – this is what Dr. Ludwig has been doing since 2017 inside the Environmental Change One Health Observatory (ECO2), an interdepartmental initiative led by Agriculture and Agri-Food Canada, the Public Health Agency of Canada and Environment and Climate Change Canada, to study, in part, the combined effects of climate and land use change on disease risks to humans, wildlife, livestock and domestic animals.

This interdisciplinary collaboration endeavors to provide a better understanding of impacts of environmental changes (also including changes made by humans) on associated disease risks in working and living environments in Canada.

You can find more information about West Nile virus, a mosquito-borne disease here.