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As the black-legged tick population continues to grow in southern Ontario, reports of both Lyme disease and lesser-known anaplasmosis are increasing.

Both illnesses are being closely monitored by public health officials in Ontario, while other tick-borne illnesses, including babesiosis, a bacterial infection, and Powassan virus, a rare disease that causes encephalitis and severe illness, are also cause for concern.

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Anaplasmosis, if left untreated, can cause severe respiratory illness and be life-threatening, especially for those with compromised immune systems.

All three conditions were added to the province’s Health Protection and Promotion Act last July, and noted as diseases of public health significance. Here’s what to know.

What is anaplasmosis?

Anaplasmosis is caused by the bacteria Anaplasma phagocytophilum. Symptoms can include fever, severe headache, muscle aches, fatigue, nausea, cough and confusion.

Spread by black-legged ticks, it infects white blood cells in both animals and humans. Like Lyme disease, it is treated with antibiotics.

Where do black-legged ticks live?

Black-legged ticks, also known as deer ticks, are often found in wooded and forested areas, especially areas with thick underbrush. They are also commonly found in tall grasses, including along trails and in fields, and areas with accumulated dead leaves.

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How common is anaplasmosis?

While the first case of anaplasmosis in Ontario was detected in 2018, there were 40 cases in 2023.

Eastern Ontario, in particular, is a hot spot for tick-borne illnesses. More generally, risk is highest in areas with established vector populations — the ticks that are capable of carrying and transmitting pathogens. This includes southwestern and northwestern Ontario, southern Quebec, southern Manitoba and Nova Scotia and New Brunswick.

Infection can occur at any time of year, but is more common in the warmer months, from April to September.

Symptoms generally appear a week or two weeks after the bite.

How does one become infected?

Ticks need about 12 to 24 hours to spread the bacteria that causes anaplasmosis, compared to at least 24 hours for Lyme disease.

While Lyme disease is marked by a circular rash, there is generally no rash with anaplasmosis.

How can you prevent tick-borne illness?

Covering up is one of the best preventive measures, including tucking pants into socks, as well as applying insect repellent that contains DEET.

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Wearing light coloured clothing can make it easier to spot ticks and a full body check after coming inside, along with regular checks while outside, can help catch ticks before they have the chance to spread an infection.

If you find a tick, use clean tweezers to grasp the head as close to the skin as possible and pull the tick straight out with slow and steady pressure. Twisting or squeezing the tick can increase the chance of catching a tick-borne infection as the tick will expel its stomach contents.

It is recommended to report tick bites and submit ticks to public health authorities so they can track populations and the spread of disease.

Online tools and mobile apps like eTick.ca can also be used to help identify the tick.

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