Mosquito-borne disease surveillance: Technical notes: Vector-borne disease surveillance in Canada

Vectors, such as mosquitoes, spread diseases between humans or from animals to humans, usually by biting. Diseases spread by vectors are called vector-borne diseases. Find out how we monitor mosquito-borne diseases in Canada.

  • Last updated: 2024-06-28

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When we think of mosquito-borne diseases, we often think of malaria or yellow fever, which are more common in warm, humid climates. However, there are mosquito-borne diseases in Canada, and the Public Health Agency of Canada (PHAC) works with partners to monitor the risk of these diseases here.

Definitions: Zoonotic diseases, vectors and vector-borne diseases

Zoonotic diseases (also known as zoonoses): Infectious diseases that are spread between animals and humans in various ways such as direct contact, indirect contact or through vectors.

Vectors: Living organisms, most commonly invertebrates such as mosquitoes, ticks and flies, that can carry and spread infectious diseases between animals and humans.

Vector-borne diseases: Infectious diseases caused by pathogens such as parasites, viruses or bacteria, which are spread between animals and humans by infected vectors, usually by biting.

Human surveillance

Case-based surveillance versus lab-based only surveillance

Mosquito-borne diseases that are significant to public health are ‘nationally notifiable’ in Canada. A national case definition is developed for each nationally notifiable disease. In this case-based system, provinces and territories voluntarily report cases that meet national case definitions for these diseases.

West Nile virus (WNV) was first detected in Ontario, Canada in 2002 and has been a nationally notifiable mosquito-borne disease since 2003.

Some mosquito-borne diseases in Canada are not nationally notifiable and do not have a national case definition. We monitor these diseases through other methods, such as lab-based only surveillance. This method relies on lab data for diseases that are usually identified through the testing of sick people. Some mosquito-borne diseases in Canada that are not nationally notifiable include:

West Nile virus surveillance

The WNV surveillance system complies with the regulations of the federal/provincial/territorial Multi-Lateral Information Sharing Agreement. For a summary history of the WNV surveillance system, refer to the Overview of the national West Nile virus surveillance system in Canada: A One Health approach.

Data sources: West Nile virus human data

Other mosquito-borne disease surveillance

Data sources: California serogroup viruses human data (CSGV)

Human samples are submitted to the National Microbiology Laboratory (NML) to test for CSGV or for further subtyping. Counts are a subset of confirmed lab-based only surveillance cases. They may not represent the true number of cases in Canada. The NML provides us with an extract of this data upon request.

Data sources: Eastern equine encephalitis virus human data (EEEV)

Human samples are submitted to the NML to test for EEEV. Counts include confirmed and probable lab-based only surveillance cases. They may not represent the true number of cases in Canada. The NML provides us with an extract of this data upon request.

Non-human surveillance

We use a One Health approach, which recognizes the interdependence of humans, animals, and the environment.

In addition to data on human cases, the mosquito-borne disease surveillance system maintains data from various sources about:

Mosquito surveillance

For more information about mosquito surveillance, please refer to Mosquito surveillance.

Data sources: Mosquitoes

Equine (horse) surveillance

For more information about equine surveillance, please refer to Horse surveillance.

Data sources: Equines

CFIA monitors WNV and EEEV in horses across Canada, and shares data with PHAC every 2 weeks during the mosquito season. These data include location, time of illness onset and testing information.

Dead wild bird surveillance

The Canadian Wildlife Health Cooperative (CWHC) coordinated a massive national surveillance project to monitor WNV in wild birds from 2001 until 2012. Since then, monitoring has continued as part of ongoing surveillance efforts, but there’s no longer a dedicated WNV program. About 300 dead wild birds per year have been tested for WNV since 2009. It’s up to the pathologist to decide whether a submitted dead wild bird should be tested for WNV.

For more information about bird surveillance, please refer to Bird surveillance.

Data sources: Dead wild birds

CWHC maintains a comprehensive cause-of-death database, with data about:

CWHC collects these data for dead wild birds tested in all provinces and territories except Manitoba, and shares it with PHAC every 2 weeks during the mosquito season.

Manitoba doesn’t routinely test dead wild birds, but they do share any positive test data with PHAC throughout the season.

West Nile virus: Data definitions and data notes

Human data definitions
Case classification
Cases are classified as suspect, probable or confirmed, based on the national WNV case definition. For surveillance reporting purposes, probable and confirmed cases are counted.
Disease classification
Cases are classified using the clinical and lab criteria in the WNV national case definition. If a case meets both the lab and the clinical criteria, it’s classified as West Nile neurological syndrome (WNNS), West Nile non-neurological syndrome (WN non-NS), or, if no clinical classification has been provided, West Nile unspecified clinical case. If a case meets the lab criteria but none of the clinical criteria, it’s classified as a West Nile asymptomatic infection. Asymptomatic cases are typically identified through testing of donated blood.
Death
A case of WNV that was reported as deceased. In most cases, WNV was the direct or contributing cause of death. Death is recorded at the local, provincial or territorial level at the time of investigation or public health follow-up. There may be differences in the way death is classified or investigated from one jurisdiction to another.
Episode date
This refers to the earliest of the following dates reported to PHAC:
  • symptom onset date
  • specimen collection date
  • lab tested date, or
  • report date
Travel
Whether the case involved travel that was relevant to acquiring West Nile virus. Travel cases are categorized as ‘infected in Canada’ or ‘infected outside of Canada’ in the dashboard. Categorization of travel and public health follow-up on travel-related cases vary by jurisdiction.
Mosquito data definitions
Number of mosquito pools positive for WNV
The number of mosquito pools positive for WNV by time and place is based on the:
  • date the mosquitoes were collected or tested, and
  • location of the trap
Mosquito pool
A mosquito pool is generally a group of 1 to 50 female mosquitoes of the same species found in a trap.
Positive mosquito pool
A positive mosquito pool is a mosquito pool with at least 1 mosquito testing positive.
Equine data definitions
Number of horses positive for WNV
The number of horses positive for WNV by time and place is based on the:
  • date submitted (for example, the date the lab received the sample), and
  • province of residence
Dead wild bird data definitions
Count of dead wild birds positive for WNV
The count of dead wild birds positive for WNV by time and place is based on the:
  • date the CWHC lab received the sample, and
  • location where the bird was found

Data notes

California serogroup viruses: Data definitions and data notes

Human data definitions
Case classification
In the absence of clinical data, we derive infection counts from lab-based criteria only. For CSGV infections, counts are a subset of confirmed lab-based only surveillance cases.
Episode date
This refers to the earliest date a case was reported to PHAC, which may be the:
  • specimen collection date
  • lab tested date, or
  • report date
Mosquito data definitions
Number of mosquito pools positive for CSGV
The number of mosquito pools positive for CSGV by time and place is based on the:
  • date the mosquitoes were collected or tested, and
  • location of the trap
Mosquito pool
A mosquito pool is generally a group of 1 to 50 female mosquitoes of the same species found in a trap.
Positive mosquito pool
A positive mosquito pool is a mosquito pool with at least 1 mosquito testing positive.

Data notes

Eastern equine encephalitis virus: Data definitions and data notes

Human data definitions
Case classification
In the absence of clinical data, we derive infection counts from lab-based criteria only. For EEEV infections, counts are a subset of confirmed lab-based only surveillance cases.
Episode date
This refers to the earliest date reported to PHAC, which may be the:
  • specimen collection date
  • lab tested date, or
  • report date
Mosquito data definitions
Number of mosquito pools positive for EEEV
The number of mosquito pools positive for EEEV by time and place is based on the:
  • date the mosquitoes were collected or tested, and
  • location of the trap
Mosquito pool
A mosquito pool is generally a group of 1 to 50 female mosquitoes of the same species found in a trap.
Positive mosquito pool
A positive mosquito pool is a mosquito pool with at least 1 mosquito testing positive.
Equine data definitions
Number of horses positive for EEEV
The number of horses positive for EEEV by time and place is based on the:
  • date submitted (i.e., date the lab received the sample) and
  • province of residence

Data notes

Data limitations

Acronyms

PHAC
Public Health Agency of Canada
CFIA
Canadian Food Inspection Agency
CWHC
Canadian Wildlife Health Cooperative
CBS
Canadian Blood Services
HQ
Hema Quebec
WNV
West Nile virus
CSGV
California serogroup viruses
JCV
Jamestown Canyon virus
SSH
Snowshoe hare virus
LCV
La Crosse virus
EEEV
Eastern equine encephalitis virus
WEEV
Western equine encephalitis virus
NML
National Microbiology Laboratory

Acknowledgements and suggested citation

This dashboard would not be possible without the collaboration and dedication of local, provincial and territorial public health data providers. We would also like to acknowledge the Canadian Wildlife Health Cooperative, Canadian Food Inspection Agency, Canadian Blood Services, and Hema-Quebec for their data contributions to this dashboard.

Suggested citation

Vector-borne disease surveillance in Canada. Ottawa, Canada: Public Health Agency of Canada. https://health-infobase.canada.ca/zoonoses/mosquito/

Related links

Government of Canada

Provincial, territorial and international surveillance

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