Lyme Disease Spreading Northwards into Canada and Northeastern US.

by lmatthews on March 28, 2012

lyme disease spreads northwards

Lyme disease cases likely to rise as tick populations soar.

Many scientists are expecting a surge northwards for Lyme disease this year as the ticks that spread the infection are enjoying optimal conditions. Northeastern states of the US and even a number of places in Canada are gearing up for an increased risk of Lyme disease due to an abundant acorn harvest, mouse population boom, and climate change, all of which conspire to increase tick numbers.

Tick Numbers Increase

Lyme disease is a zoonosis, spread by infected ticks that use animals as a host reservoir. These animals include deer, mice, and even lizards, despite often simply being referred to as deer ticks. The black-legged tick, Ixodes scapularis can choose a number of animal hosts and needs a blood meal for each stage of its life-cycle (larvae, nymph, and adult tick). In North America, nymphal ticks are thought responsible for most human ticks bites and Lyme disease infection. For many years this has helped reduce the risk of Lyme disease by increasing vigilance during Spring and Fall when most ticks are likely to be looking for a meal. Climate change and the confusion of seasons now means that it is increasingly difficult to know when ticks are most active. This is just one reason why Lyme disease is the most commonly reported vector-borne illness in the US, as assessed by the CDC, with cases rising year on year and many still believing that the infection is woefully under-reported.

Increase in Reported Lyme Disease Cases

In recent years, the majority of cases (94%) have been found along the East Coast of the US, mainly in Wisconsin and Minnesota. 2010 saw more than 20,000 cases reported, although some estimate that the actual number may be ten-fold higher. Lyme disease awareness efforts have, so far, been concentrated on those areas seeing most cases but researchers and public health officials are beginning to investigate ways of predicting the likely increase in cases as Lyme disease spreads northwards. In areas where no Lyme disease cases are yet to be reported it is difficult to know whether a lack of knowledge of the infection, or the lack of the infection itself, is responsible as time goes on.

Misdiagnosis of Lyme Disease

Many doctors, and patients, simply dismiss early Lyme disease symptoms as an influenza-like illness, fatigue, or even as a symptom of existing illness such as fibromyalgia, chronic fatigue syndrome, or depression. Many doctors still believe that it cannot be Lyme disease unless the bulls-eye rash, erythema migrans, is apparent. Although precise figures are not known, it is increasingly recognized that this rash does not occur, or is not noticed, in a large number of those with active Lyme disease infection. Misdiagnosis of Lyme disease, though rarely fatal, can lead to permanent disability and complications.

lyme disease pushes northwards acorn and mouse

An abundance of acorns in 2010 led to more mice last year and more ticks this year looking for human hosts.


Acorns, Mice, and Climate Change

Vector-borne disease specialists, such as Rebecca Eisen, a researcher at the CDC, are looking into the effects of temperature and moisture on the ticks that carry Lyme disease bacteria, Borrelia burgdorferi. The climate has a number of effects that can alter geographic distribution of ticks and, therefore, Lyme disease. Oak trees, their acorn production, the mice feeding on acorns, and ticks using the mice as hosts all mean that an abundant acorn harvest like the one in 2010, followed by an increase in the mouse population, like in 2011, most likely means an increase in the number and spread of ticks across North America. Record highs in acorn production in 2010 led to the 2011 boom in the mice population and the ticks taking a meal from the infected mice as larvae or nymphs may then transmit the infection through the rest of its lifecycle. Mice are unaffected by the bacteria and so make no effort to fight it or to remove ticks from each other through grooming; this means that ticks are twice as likely to contract Lyme disease bacteria by biting a mouse than by biting any other animal.

Monitoring Lyme Disease Risk

There is a little cause for hope however, as the 2011 acorn season was a washout, with the number of mice looking set to fall dramatically this year. This may reduce the host reservoir for the zoonosis but it could also mean that more mice come into contact with humans while they search for food and that there are more ticks looking for a host with the favored mice no longer abundant. Humans walking through forested areas, lying in long grass, or even just spending time outdoors in the garden may be increasingly susceptible to tick bites and Lyme disease in 2012, even in areas previously thought inhospitable to the bacteria.


Lyme Disease in Canada on the Rise

In Canada, the warmer spring of 2012 and the relatively mild winter, means that ticks from the south are heading north and across broader areas of land. Lyme disease is an emerging problem in many areas of the northern US and in Canada so increasing awareness of Lyme disease symptoms, preventative measures to take, and the importance of getting early treatment may all become topics of discussion in your local public health authority. An abundant acorn crop, mouse population boom, and the increasing infringement of humans into areas where deer reside all mean that Lyme disease is spreading.

Read on for Maps of Lyme Disease

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