Confirmed cases of Lyme disease in Ontario more than doubled this year as blacklegged ticks officially make Greater Toronto home, new public health data obtained by the Star show.
The National Microbiology Lab confirmed this week that for the second season in a row, a blacklegged tick infected with Borrelia burgdorferi — the bacterium that can cause potentially disabling disease in humans and pets alike — was found in Rouge Valley, which spans Durham, York and Toronto.
“Once the ticks are established in the location… they don’t ever leave,” said Curtis Russell, an expert in vector-borne diseases at Public Health Ontario. “Now we just have to make sure to see where they’re expanding to.”
Public health data released to the Star show 304 confirmed cases and 54 probable cases of Lyme disease have been reported in Ontario between January and November this year. In 2014, 149 cases were confirmed and 71 were probable.
Typical symptoms of infection can include fever, headache, muscle and joint pains, fatigue and skin rash. Untreated, the disease can last for years and cause neurological and musculoskeletal damage. In some cases, it can lead to heart infection and death.
“Over the last few years, Lyme disease in Canada has evolved from an unusual and focal issue, to an emergent and expanding problem,” Health Canada warned in a recent report.
What’s especially concerning is the spread of ticks from relatively isolated forests to more densely populated areas.
Prior to the mid-1990s, Lyme-diseased ticks were found in only one area in all of Canada — Long Point Provincial Park on Lake Erie.
This year, 16 new risk zones were identified in Ontario alone, including Rouge Valley.
The latest Toronto-specific data on human illness has not yet been compiled, but last year, Toronto Public Health reported 34 confirmed and four probable cases — the highest number in Ontario. That doesn’t mean, however, that all these people were exposed to the bacterium in Toronto.
Ticks often travel on the bodies of migratory birds or white-tailed deer. Since the mid-1990s, parks along the northern shores of Lakes Erie and Ontario have gradually become hotbeds for blacklegged ticks.
When travelling birds stop at these parks, the ticks fall off and look for new hosts. Ticks move very slowly. When they want to feed, they will climb to the tip of a grass blade and wait for an animal to latch onto.
A tick can feed on the blood of a single host for days, even a week. If that tick is infected with Lyme, it will take 24 hours to transmit the bacteria from its gut to its salivary glands and into its host, which is why public health agencies urge people who visit leafy, tall-grassy areas to frequently check themselves and their pets for ticks.
At least 900 dogs across Ontario tested positive for Lyme disease this year — a sharp increase from just 91 cases in 2012, according to Idexx, which publishes data on pet disease. The cases are based on an annual, routine test administered to dogs at veterinary clinics. There are several labs that offer this testing, but only Idexx shares its results publicly.
Public Health Ontario reviews animal data, Russell said, but it’s just one piece of the puzzle.
While the numbers seem high, dogs respond much differently to Lyme disease than humans.
Dr. Andrew Peregrine, a clinical parasitologist at University of Guelph, estimates that only five per cent of infected dogs will develop clinical signs, which can include intermittent limping, swollen joints and lethargy, or more serious kidney problems. And while humans will typically show signs of infection within a week or two, two to five months may pass before a dog shows symptoms.
Dr. Scott Stevenson sees between five and a dozen dogs each year that show clinical signs of Lyme disease at his Thousand Islands veterinary clinic. In those cases, he recommends a full month of antibiotic treatment.
Mostly, though, he prescribes prevention strategies for pets and humans such as daily tick checks whenever the temperature is above freezing.
“There isn’t risk 365 days in Ontario, but there is risk in all 12 months of the year because there are days in January where it’s above 4 degrees Celsius and the ticks are out.”
There are no control measures for blacklegged ticks.
“The impact on the environment would be awful if you tried to get rid of them,” Peregrine says. “We really need to start learning to live with them.”
At Queen’s Park on Thursday, NDP MPP Michael Mantha (Algoma-Manitoulin) criticized the health minister for failing to follow through on his commitment last year to create an action plan on Lyme disease.
“If the stakeholders are not consulted, we will get absolutely no changes made to Lyme education, testing and treatment, and patients will continue to suffer,” he said.
Tiny creatures that want your blood
Humans and dogs heading into wooded areas across Ontario should know that blacklegged ticks can transmit Lyme disease at only two stages in their two-year life cycle.
Eggs: An adult female tick that has fed on blood can produce thousands of eggs after mating in the spring. A female infected with Lyme disease cannot pass the bacterium to her eggs.
Larva: Pinhead-sized larvae typically carry no risk of disease until they feed on a small mammal, often a mouse or bird, which can be infected with the bacterium Borellia burgdorferi that causes Lyme disease.
Nymph: By this stage, the tick may already carry the bacterium if it fed on an infected mammal in the larva stage. The size of a poppy seed, nymphs are prevalent in spring. They’re opportunistic and will feed on whatever walks by — small mammals, birds, dogs and people. The blood meal can last three to seven days, after which the fully engorged tick will drop to the ground and moult into its final life stage.
Adults: At their largest size in the life cycle, they’re roughly 3 mm unfed. Engorged, they can balloon to 10 mm, making them easier to see and pick off before they can transmit the bacterium to a person or dog. If an adult tick cannot find a host to feed on before winter, they will become relatively inactive under the snow and resume their search for a host when the temperature rises above zero.