Climate change and ticks

Ticks can be found everywhere [1], however, they need certain environmental conditions to flourish that are warm and moist. [2]. Study about ticks’ dates to the early 1900s. It is now well known that not all bites cause serious disease. Even sometimes you may not notice being bitten. However, pain and a rash will occur if you are allergic [3]. If the tick carries disease, it can be transmitted to the host e.g. human. In this case, you may feel weakness, fever, and neck stiffness [3]. Among diseases that can potentially be passed to humans from ticks, is Lyme disease. Lyme disease is becoming more and more common in North America. If not properly treated after being infected, Lyme disease can result in serious complications. It must be stressed that even being bitten by a tick that carries the bacteria causing Lyme disease, does not necessarily result in you being infected. Unlike other insects e.g. bed bug, flea, and mosquito, ticks do not bite and leave. They remain on the host for up to 2 days. Therefore, it is possible to prevent being infected since a single bite does not necessarily transmit the disease [4]. A proper investigation of the skin can reduce the chance of having ticks hanging out on the host’s skin (human, pet) for a prolonged time. There is a seasonal and a geographical trend of the deer tick – also called black-legged – distribution, which is the tick responsible for the Lyme disease. This means we are not necessarily at risk for Lyme disease all the time and everywhere. On top of that, a young tick is less likely to feed on a human. A deer tick has a three-stage life cycle, as can be seen in the figure below.

Figure 1: the life cycle of deer tick [5]

In the larvae stage, they are less likely to attach to humans. Small rodents and birds are the best hosts for them. The larvae that survives the winter are nymph once the spring arrives. A nymph can potentially transmit the Lyme disease to humans. After sufficiently being fed by the host, the nymph undergoes the second hibernate period of the tick life cycle. In the spring, the grownup nymph that is an adult (that feeds on large mammals such as deer) now is ready to lay eggs [6]. It must be stressed that larvae are not being naturally born with the risk of transmitting the Lyme disease to us (or it is very rare). It depends on the environment. For example, the larvae that are neighboring with certain kinds of mice are more likely to cause Lyme disease if they bite humans [5]. Approximately, only one-third (tested in Ottawa) of deer ticks cause this infection [7]. As mentioned previously, timely treatment can control this epidemic disease. But what is the role of climate change in the Lyme disease?

The role of climate change here is two-fold: climate change can boost the Lyme disease by affecting both the seasonality and the geographical distribution [6]. Deer ticks need a certain number of warm days to survive [8]. Climate change gives the ticks this opportunity. Moreover, in a warmer environment, ticks are more likely to find a perfect host, including humans. Naturally, we have more outdoor activities in warmer months. That is why most infections of Lyme disease occur in July [9]. On the other hand, climate change extends the frost-free season and adds new territories as desirable locations for deer tick activity. This is why Lyme disease is now a serious problem in Ontario while this was not the case a few decades ago. To shed more light on the effect of climate change on Lyme disease, please see the table below.

Table 1: number of probable and confirmed Lyme diseases in Ontario, 2017 [9]

Public Health Unit # of cases %

5-year average

(2012-2016)

Incidence per 100,000
Algoma District 2 0.2 2.5 1.7
Ottawa 180 18.8 47.4 18.1
North Bay Parry Sound District 1 0.1 1.3 0.8
Timiskaming 0 0.0 0.0 0.0

As can be observed, the south of Ontario is a better environment for deer ticks. This trend has increased seriously in recent years, all over Canada including Ontario. The number of Lyme disease cases in 2017 is more than 3 times as much as the 2012-2016 average across Ontario [9]. This increase is more pronounced Canada-wide. In less than 10 years, reported Lyme disease cases increased 15 times [10]. Now we know there are certain connections between Lyme disease and climate change. Bonfield is not among risk areas as it is obvious from Table 1; however, some precautions can minimize the risk even more: keep the grass short and store wood logs in a dry place [11] as ticks are mostly found in grassy and wooded environments [4]. Shower after outdoor activities so that ticks can be found and removed from the skin [11]. Cover the skin and clothes with repellent [4]. Finally, long sleeves and long socks can reduce exposure to deer ticks [4,11].

In the end, remember that even being bitten by a deer tick – that carries disease – does not mean that you are now certainly infected by Lyme disease. However, if you suspect that you are, promptly visit a doctor for proper treatment. The Township of Bonfield, in collaboration with the North Bay Parry Sound District Health Unit, is in the process of raising awareness of the residents about vector-borne diseases and climate change.

References

[1] L. Magnarelli, 2009, Global Importance of Ticks and Associated Infectious Disease Agents, Clinical Microbiology Newsletter V31

[2] G. Nutfall, 1904, Ticks and tick-transmitted diseases, Transactions of the Epidemiological Society of London

[3] https://www.healthline.com/health/tick-bites#symptoms

[4] https://www.mayoclinic.org/diseases-conditions/lyme-disease/symptoms-causes/syc-20374651

[5] www.health2016.globalchange.gov/vectorborne-diseases/content/lyme-disease

[6] I. Dumic and E. Severnini, 2018, “Ticking Bomb”: The Impact of Climate Change on the Incidence of Lyme Disease, Canadian Journal of Infectious Diseases and Medical Microbiology

[7] M. Kulkarni et al., 2018, Ixodes scapularis tick distribution and infection rates in Ottawa, Ontario.

[8] https://www.nrdc.org/experts/juanita-constible/new-reality-climate-change-and-lyme-disease-canada

[9] M.P. Nedler et al., 2018, The continued rise of Lyme disease in Ontario, Canada: 2017. Canada Communicable disease report, climate change and Lyme disease

[10] N.H. Ogden, 2019, What is the real number of Lyme disease cases in Canada? BMC Public Health

[11] https://www.canada.ca/en/public-health/services/diseases/lyme-disease/prevention-lyme-disease.html