When it comes to tracking blacklegged ticks and preventing Lyme disease and other tick-borne illnesses, public health professionals across Canada rely on a combination of active and passive tick surveillance. Both methods of surveillance play important roles in understanding where ticks are located and whether they’re carrying pathogens that pose a threat to people, pets and/or wild animal populations.
Passive surveillance is probably the better known of the two surveillance methods largely because it relies on tick submissions from the public in addition to professionals. If you've ever submitted a photo to eTick.ca, taken a tick to your local health unit or had a medical doctor or veterinarian submit one on your behalf, you've contributed to passive surveillance datasets.
Accepting ticks this way helps public health units to cover a much wider geographic area than they would otherwise be able to using active surveillance alone. Submitted ticks can point to potential problem areas based on where people or animals are encountering ticks. If a whole bunch of people are running into them at a single location, that alerts public health investigators that ticks may have become established there and active surveillance is needed.
Active surveillance is more of a hands-on approach than passive surveillance. It is also more expensive and labour intensive. When passive surveillance has pointed to a potential problem location, investigators head there and attempt to collect ticks, which they then have checked for diseases like Lyme.
This process is designed to determine where blacklegged ticks are living and whether they present increased risk to people and their pets. Typically the edge of forests, sides of trails or naturalized sites with tall grasses are targeted for dragging. I could go into a long explanation of when and how to conduct dragging, but the two videos below do an excellent job of doing that.
Courtesy of North Central IPM Center Iowa State University.
Courtesy of Public Health Ontario.
The benefit of active surveillance is that it provides hard data that officials can then use to map out the locations where ticks have become established and alert residents and healthcare providers to the risk.
Photo courtesy of Jim Occi / U.S. Centers for Disease Control
