Morgan Webb999968815November 26th, 2015Clare Wiseman

The Positive Correlation Between Climate Change and an Increase in Lyme Disease

Introduction

Lyme disease is a tick-borne disease (Monaghan, Moore, Sampson, Beard & Ogden, 2015) that

causes symptoms including a very distinct rash that looks like a bull’s eye, fever, headaches,

body aches and tiredness. In more severe cases, it can lead to arthritis, heart problems, and

neurological symptoms (US Department of Health and Human Services, 2008). There are

numerous kinds of ticks that carry the pathogen Borrelia burgdorferi, which has been attributed

as a cause of Lyme disease (Feria-Arroyo et al, 2014). One of the most common vectors of Lyme

disease is Ixodes scapularis (US Department of Health and Human Services, 2008), which will

be one of the primary focuses of the research in this paper. Another point of focus for this paper

is another another host, Peromyscus leucopus. The objective of this paper is to assess research

regarding a positive correlation between Lyme disease influx (due to an increased population of

the I. scapularis tick as well as a general northern ascent of the population) and climate change.

Lyme disease is very seasonal, ticks thrive in warm weather and this tends to be when their

populations increase. Whereas, they tend to die off during the winter period because they cannot

withstand the cold (Monaghan, et al, 2015). Thus, areas (particularly Northern locations) that

were once protected by the cold climate will experience an increase in Lyme disease or quite

possibly its first case of outbreaks.

Methods

There were multiple methods used to find research on the link between climate change and a rise

in Lyme disease. The first method used was going to the University of Toronto Library website

and searching “Lyme Disease” and “Climate Change” in the database. Search parameters were

then used to narrow the search and make it more specific. The parameters included looking at

articles but more specifically, scholarly journals only, that had the full text online and were

journal articles. From there, the scope of the search was narrowed even further by applying more

restrictions, English only, any subject from 1995 onward. Four articles were used from this

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method: Climate change and the potential for range expansion of the Lyme disease vector Ixodes

scapularis in Canada, Risk maps for range expansion of the Lyme disease vector, Ixodes

scapularis, in Canada now and with climate change, Poleward Expansion of the White-Footed

Mouse (Peromyscus leucopus) under Climate Change: Implications for the Spread of Lyme

Disease and Climate change influences on the annual onset of Lyme disease in the United States.

Another database, Google Scholar, was used to find articles. The search parameters were made

specific “Lyme Disease” and “Climate Change” were looked for in the title of the article. Using

this method, two articles were retrieved: Climate change and habitat fragmentation drive the

occurrence of Borrelia burgdorferi, the agent of Lyme disease, at the northeastern limit of its

distribution and Implications of climate change on the distribution of the tick vector Ixodes

scapularis and risk for Lyme disease in the Texas-Mexico transboundary region.

Results

There are multiple things throughout the journal articles that are commonly known about Lyme

disease and climate change. First, the tick, generally, I. scapularis, is a popular vector for the B.

burgdorferi bacterium which is the leading cause of Lyme disease (Feria-Arroyo et al,

2014). Secondly, I. scapularis ticks go through four main stages in their life cycle: eggs, larva,

nymph and adult. For the latter three stages of the cycle, they need different hosts for survival.

The average lifecycle of a tick is about two years (Fish, 1995) which is crucial because I.

scapularis’ lifecycle tends to end during the winter season. By outcome, studies have shown that

climate change will increase the temperature of the Earth and will consequently have an affect on

the geographical patterns and lifecycles of the I. scapularis species. As, “the temperature is the

most important determinant of environmental suitability for tick population establishment”

(Leighton, Koffi, Pelcat, Lindsay & Ogden, 2012 p. 457) and I. scapularis thrives in heat, it is

evident that the B. burgdorferi pathogen will spread northward (Figure 1). Thus, the

environmental element - climate change, is a risk factor for an increase in B. borgdorferi because

it will create an environment that is better suited for the production and growth of ticks.

The host is used as a “blood bag” or a means of nutrition for the ticks (Fish, 1995; US

Department of Health and Human Services, 2008). There are many different hosts for the ticks,

including deer (Fish, 1995), migratory birds (Leighton et al, 2012), humans (Simon et al, 2014;

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Leighton et al, 2012) and other small

mammals. One animal that seemed to be

particularly significant as a host for B.

burgdorferi is P.leucopus, more

commonly referred to as the white-

footed mouse (Roy-Dufresne, Logan,

Simon, Chmura & Millien, 2013; Simon

et al, 2014). Furthermore, a pattern has

formed, the location of ticks and the B.

burgdorferi pathogen have been

correlated with the location of the host

species (US Department of Health and

Human Services, 2008). In multiple

models of experimentation, it was found

that the temperature effects both the rates

of production and expansion as well as

the general area where ticks can migrate

(Leighton et al, 2012; Ogden et al, 2006;

Simon et al, 2014). Leighton et al

determined that I. scapularis would

move Northward at an alarming rate of

“46km per year” (Leighton et al, 2012,

pg. 460). Whereas, Ogden et al looked at

present populations of I. scapularis in Ontario and through experimentation made predictions

that their population would increase by “30-100% by the year 2020” (Ogden et al, 2008, pg.67).

Similarly, Simon et al determined that P. leucopus would move northward by “250 – 500 km by

the year 2050” (Simon et al, 2014 pg. 756), essentially carrying the B. burgdorferi vector along

with it. Throughout various forms of scientific exploration, the general consensus from the

research is that with climate change and the increase of global temperatures, I. scapularis

populations will transition towards the north and create more risk for human health with the

spread of B. burgdorferi.

Figure 1 -Risk maps for the occurrence of the Lyme disease vector Ixodes scapularis in Canada. Retrieved from: Risk maps for range expansion of the Lyme disease vector, Ixodes scapularis, in Canada now and with climate change (Ogden et al, 2008, pg. 6).

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The one exception to this transitional trend northward and increase in population was the Texas-

Mexico transboundary study. The study determined that the tick populations that were already

present within this region (Figure 2) would remain fairly stable until 2050 and would not

increase or move further to the North (Feria-Arroyo et al, 2014). By analyzing three hypothetical

outcomes for the future,

the consensus was that the

ticks may move

Northward in Texas but

would tend to stay in

relatively the the same

place everywhere else on

the map. Thus, the

potential areas that may

have been ideal for I.

scapularis expansion were

deemed to be “stable”

environments (Feria-Arroyo et al, 2014).

According to the research, the implications for the increase of Lyme disease will have negative

global affects. This being said, it will have a more severe affect on the regions in the North that

have not had Lyme disease ever before (Roy-Dufresne et al, 2013). With an increase in

temperatures, the findings of the data promote that there will be a positive correlation with an

increase of tick populations, in addition to a Northern ascent of tick populations into lands that

were once protected by their cold climate.

Discussion

The overall findings of the research asserted that there was a positive correlation between climate

change and increase in the B. burgdorferi bacterium that causes Lyme disease. There were a lot

of similarities between the studies that were analyzed. One major similarity between the journal

articles was the people who partook in the studies. For example, Nicholas H. Ogden was a major

contributor, he contributed to 50% of the articles assessed for this paper. Other major

Figure 2 - The geographic location of I. scapularis located in US States and Mexico. Retrieved from Implications of climate change on the distribution of the tick vector Ixodes scapularis and risk for Lyme disease in the Texas-Mexico transboundary region (Feria-Arroyo et al, 2014, pg. 6).

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contributors include: Patrick A. Leighton, L. Robbin Lindsay, Julie A. Simon, Emile Roy-

Dufresne, in addition to many others. There were only three articles that were reviewed that did

not have any association with other articles. The three articles are: Climate change influences on

the annual onset of Lyme disease in the United States by Monaghan et al., as well as,

Environmental Risk and Prevention of Lyme Disease by Durland Fish and lastly, the article

Implications of climate change on the distribution of the tick vector Ixodes scapularis and risk

for Lyme disease in the Texas-Mexico transboundary region composed by Feria-Arroyo et al.

The article by Monaghan et al. was the most recent study (2015) about climate change and Lyme

disease. It was interesting to note that none of the contributors to previous articles were directly

associated with this one. Previous authors work, such as Nicholas Ogden and Julie Simon were

referenced in Monaghan et al’s paper. This being said, there was no surprise when the findings of

Climate change influences on the annual onset of Lyme disease in the United States supported

the research of the previous works conducted.

Durland Fish’s work, Environmental Risk and Prevention of Lyme Disease was not as much as a

study as it was a reference for Lyme disease for this paper. There was a lot of general

information in the entry about how Lyme disease is spread however the overall focus of the

article was about the prevention of the disease. Fish placed a strong emphasis on the use of

insecticides including: “carbaryl, diazinon, chlorpyrifos, and cyfluthrin”, that he attested to

having “comparable success rates” (Fish, 1995, pg. 5). Carbaryl is one of the chemicals that is

greatly associated with the gas leak disaster that occurred in Bhopal, India in 1984 (Dikshith,

Kumar, Raizada, Srivastava, & Ray, 1990). To this day, Bhopal has not fully recovered from the

spill. Another one of the chemicals that Fish proposes as a method of prevention is chlorpyrifos.

Following Fish’s work in 1995, Chlorpyrifos has since been deemed as the “second most

commonly detected pesticide in food and water” (John & Shaike, 2015, pg. 269). Thus, looking

at the chemicals that Fish has proposed using and their negative health effects, it calls into

question the validity of his work.

The article, Implications of climate change on the distribution of the tick vector Ixodes

scapularis and risk for Lyme disease in the Texas-Mexico transboundary region is similar to

Monaghan et al’s paper because none of the main contributors authored any of the other studies

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assessed in this paper. However, it too referenced the work of Nicholas Ogden. The research

conducted in this paper differentiates itself from the rest of the studies assessed in this paper

because it is the only study that stated that tick populations would be stable.

When searching for articles there were multiple limitations. It was imperative that they were in

English because foreign languages would be difficult to interpret. The articles had to be scholarly

as a means of validating the credibility of the source, if they were not scholarly it was difficult to

assess whether or not the material was accurate. This was a limitation because it meant that

sources like Wikipedia, which tend to be easy to understand, could not be used because it is a

source that anyone in the public realm can create and edit. It meant that some of the texts found

via Google Scholar and the University of Toronto database were difficult to read because they

were very scientific. Linked to the kinds of texts found, another limitation was the databases

used to find materials. Only two databases were used: Google Scholar and the University of

Toronto Library database. If more databases were used it is possible that there would have been

more articles to review. It was important that the articles were from 1995 onwards to show that

the research was recent. Any sources that were earlier than 1995 might not have held as much

credibility because of advances made in science and technology. This posed as a limitation

because it meant that any research prior to 1995 was left out. The words “Lyme Disease” and

“Climate Change” were preferably in the title of the article, however articles with both words in

them were used as well. Since “Lyme Disease” and “Climate Change” were the words searched

for within articles, it meant that it was also limiting the results. Perhaps to get more results,

words like “Ixodes scapularis”, “Borrelia burgdorferi”, “Peromyscus leucopus”, “Global

Warming” and “Ticks” could have been used to broaden the results. Another limitation on the

research was that all of the journal articles found were online with the full text available. Another

method that could have been utilized would to have gone to a library and get tangible research

materials.

A huge limitation about the journal articles that were reviewed was that a lot of them were

focused on different geographical regions. The general trend was that the I. scapularis species

would migrate North due to climate change and temperature increases however the results in

regards to how much the species, and thus how far Lyme disease would spread, varied from

study to study. A few of the studies were focused on Canada and a couple of the other studies

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focused on the United States. Only one study focused on somewhere elsewhere: Mexico in

addition to other parts of the United States. Thus, it was difficult to compare and contrast the

results. Similarly, the same problem occurred with numerous hosts that carried the B. burgdorferi

bacterium. There are many distinct hosts associated with the pathogen. Thereby, it was difficult

to compare results when these host species live in various geographical locations and react and

behave independently within cold temperatures. It is challenging to compare the results of the

studies analyzed because they differentiate in regards to the host they focus on. Relatedly, there

are different types of vectors that spread Lyme disease, most of the research focused on I.

scapularis however there are other types of tick species that carry the disease such as Ixodes

pacificus (US Department of Health and Human Services, 2008) that were not accounted for.

A very important limitation is the fact that the research and studies in the journal articles is based

on the mere possibility of events occurring. This is a limitation because it deals with the

unknown. Although backed up by scientific rigor, it is difficult to say what exactly might take

place in future events. A lot of the studies analyzed accounted for this by applying different

scenarios to their study. However, who is to say that they got the scenario correct? Additionally,

there is a lot of skepticism surrounding climate change even occurring, there is a minority of

people who do not believe that climate change is a current phenomenon (Whitmarsh, 2011). This

poses as a huge limitation for the research because there will be a set of people who do not

believe the research upon hearing the phrase “Climate Change” associated with it.

The journal articles had different methods that they used for studying and researching the effects

that climate change would have on Lyme disease. As previously mentioned, a lot of the studies

used scientific hypothesis in their studies that cannot necessarily be proven at this point in time

because it is an issue of temporality. Methods varied from scenario maps and climate models

calculated using specific algorithms (Ogden et al, 2006; Ogden et al, 2008), to looking at ticks

from different geographical locations and apply parametric survival regression (Leighton et al,

2012). One study used a climactic model to track the patterns of the white-footed mouse and

applied a species distribution model that included field sampling and performing an ecological-

niche factor analysis (Roy-Dufresne et al, 2013). A similar method was used by Simon et al, 34

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sites were established for field studies across Quebec (Simon et al, 2014). The different methods

of gaining data lead to similar but different results from the other methods.

It is difficult to make suggestions for future research because the subject is linked to temporality

and the unknown. Feasibly, more research can be done focusing on other vectors and types of

hosts that carry Lyme disease. It would also be very interesting to look at the Lyme disease

occurrences outside of North America. For example, is there Lyme Disease in Africa or Europe

and what would the effects of climate change have on these other continents in relation to Lyme

disease?

The effects of climate change are horrific and what is scary is that there are people who do not

believe that it is even occurring. The occurrence of draughts and flooding, the melting of polar

ice caps, violent storms like hurricane Katrina, the destruction of ecosystems, the rise of PH

levels in the oceans and the shortage of the worlds natural resources are all problems that are

arising because of climate change. This study is important because it sheds light on yet another

devastating impact that climate change is endorsing. This study is important because it provides

another reason, of many, to try to slow down and control climate change. Thus, the study has

global implications because if these studies are correct, then there will be negative consequences

worldwide.

On another note, the study is important because by studying Lyme disease and making

calculations about its future occurrence, it is possible to take preventative measures to protect

against Lyme disease as a collective. Climate change has become a very hot topic in recent news

as people are becoming more aware and educated of the phenomenon. There have been a lot of

political negotiations regarding climate change, including the famous Kyoto Protocol. Although

there has not been a worldwide policy regarding climate change, individual countries are making

an effort. For example, some methods of controlling or limiting pollution, specifically

greenhouse gas emissions (which is a contributor to climate change), are policies like cap n’

trade and carbon taxing. Perhaps with more research about the negative outcomes that climate

change is imposing on both and the lives of other species, more policies can be implemented to

help regulate climate change. It is unrealistic to stop greenhouse gas emissions altogether, but

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regulating them is achievable. On a smaller scale, there are things that individuals can do to help

lower GHG emissions such as riding a bike, carpooling, taking shorter showers, and using

energy efficient light bulbs. Perhaps the possibility of an influx of climate change, if not for the

other horrific consequences of climate change, individuals will feel that it is their moral duty to

do what they can to reduce the amount of climate change.

According to the Center for Disease Control and Prevention, approximately 30,000 cases of

Lyme disease are reported to the CDC every year. These reports are only based upon cases in the

United States and do not account for every case of Lyme disease (Centers for Disease Control

and Prevention, 2015). This is the amount of Lyme disease that there is now, however this study

predicts a lot more cases in the not so distant future. Through preliminary action, the

consequence that would be endured from an increase in Lyme disease can be evaded, unlike

other negative outcomes of climate change that we have been too late to change.

Words: 2,989 *excluding citations

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