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Ticks and Lyme Disease Memo

April 18, 2018

Lyme disease is a bacterial infection caused by the spirochete Borrelia burgdorferi. The black-legged tick is the vehicle for transmitting the bacteria that can cause Lyme disease. Visit our Insect Bites and Diseases section of our website for more information on ticks and prevention of Lyme disease.

I appreciate your support in reporting cases of Lyme borreliosis to the Health Unit. The notification form plus information on clinical presentation, lab tests for, treatment of Lyme disease, and a fact sheet can be found within our Lyme Disease section of our Reportable Disease Toolkit.

Important Updates

Count of confirmed and probable Lyme diagnosis by calendar week

Increase in reported cases of Lyme Disease. 2017 saw a four fold increase in the number of reported individuals diagnosed with Lyme Disease – from 52 in 2016 to 219 in 2017. Most cases were diagnosed between the beginning of June and the end of August. During this time the tick is in the nymphal stage (April to August) and can be hard to detect so it stays on longer causing a greater risk of infection (incubation period 3 to 30 days).

Increase in distribution of reported cases of Lyme Disease Map

Increase in distribution of reported cases of Lyme Disease. The distribution of reported cases of Lyme disease now extends through most of Lanark, Leeds and Grenville. The blue dots on the map below shows the residence of the reported individuals diagnosed with Lyme disease. A 10 km buffer zone shown in yellow extends the possible area where the individual might have been bitten by an infected tick.

Total Tick-Related ED Visits for LGL by Month Graph

Increased summer duration of tick bites. 2017 was a very wet year in Leeds, Grenville and Lanark (405 mm rain from May to July vs. 196 mm in 2016) which may have accounted for increased tick nymph survival resulting in increased human exposure to the tick vector. This is likely reflected in the longer period within which individuals presented to the Emergency Department for tick related concerns in 2017 than 2016 (2016 April to end of July, 2017 April to end of August). The increase in visits in October each year reflects the time the female adult needs a blood meal to lay her eggs.

Please share with your Health Care Provider colleagues.