1. Corinna LaMorte
Special topics: Ecology of Global Climate Change
Dr. Ruhl
4/18/15
The impact of global climate change on bacterial disease
The rise in global climate change has begun to make a lasting impression on the world in
a variety of ways. Many species are facing extinction, while others thrive from the alterations in
the ecosystem. In this case, global climate change acts as the big picture for what is going on, but
a rise in temperature cannot be put as the sole cause. The rise in climate change is due to land-
use changes and adaptation or lack of adaptation affects the ability for the distribution of species
(Medlock and Leach, 2015). In fact, what cannot be seen with the naked eye is having the
greatest impact globally. Bacterial diseases are thriving from global climate change, and are
therefore affecting a wide range of species. Since 1975, the World Health Organization reports
that over 30 diseases have emerged. This includes diseases having vast impacts on human health,
as well a variety of organisms, such as AIDS, Ebola, Lyme disease, Legionnaire’s disease, toxic
Escherichia coli, a new hantavirus, and a rash of rapidly evolving antibiotic-resistant organisms
(Epstein, 2001). The resurgence of old diseases is also a major concern. Diseases such as malaria
and cholera are making their presence known in a devastating way, once again. Overall, climate
is a key determinant of health and the quality of health for humans and other organisms is being
threatened. As said by Epstein, 2001, climate constrains the range of infectious diseases, while
weather affects the timing and intensity of outbreaks. The future for the health and well being of
all who inhabit the earth is unclear, but what is clear is this. As long as global climate change
poses as an issue, diseases of all dimensions will increase in prevalence and severity. Ultimately,

2. we are being lead to a grim fate of new parasites, severe bacterial diseases, as well as viruses that
could wipe out entire populations.
Each environmental change, whether occurring as a natural phenomenon or through
human intervention, changes the ecological balance and context within which disease hosts or
vectors and parasites breed, develop, and transmit disease. Global climate change causes quite
the snowball effect when it comes to the relationship amongst parasites, transmission, and their
hosts. First, climate change produces ecological disturbances, which then causes geographical
and phenological shifts, and alterations in the dynamics of parasite transmission, which leads to
an increase in the potential for host switching (Brooks and Hoberg, 2007). There are many
responsible parties when it comes to an infection. All infections involve an agent or pathogen,
host(s) and the environment. Pathogens are then carried by vectors or rely immediately on hosts
to complete their life cycle. Climate can ultimately influence these pathogens, vectors, host
defenses and habitat (Epstein, 2001). What needs to be determined is how severe are these
changes parasites face and how will they effect organisms and humans? Some possible responses
include an increase in the amount of parasites and the emergence of these parasites in unusual
places. Locations have been altered due to the change in climate, which has caused drastic
modification in parasite development and survival. Parasites must either alter their normal
habitats to meet the needs of the ever-changing world or face extinction (Brooks and Hoberg,
2007).
Observations in micro and macroparasites have been made for several years now,
especially in marine, terrestrial and aquatic environments. Just in these environments alone,
biotic expansion by hosts and parasites with potential for host and geographic colonization,
shifting patterns of geographic range, changing phenology for habitat use, and even local

3. extinction, has begun to occur (Brooks and Hoberg, 2007). Global climate change leads to biotic
expansion, which allows for hosts to become susceptible with a wide range of parasites, possibly
parasites they normally do not come into contact with. Parasite-host relationships such as
tapeworms (Taenia spp.) in humans, hookworms (Oesophagostomum) and pinworms
(Enterobius) in hominoids, and nematodes (Trichinella) in carnivores are all results of the recent
relationships due to climate change (Brooks and Hoberg, 2007). Not only do these parasite-host
relationships represent the movement of organisms to new locations, but it is also used as an
indication to determine which species are most successful, and will be in the future, at surviving
large-scale environmental changes and mass extinctions. Ultimately, it can be said that the
species that are most successful at surviving global climate changes will be the primary sources
of emerging infectious diseases. Other factors such as recent human activities associated with the
evolution of agriculture, domesticated livestock and urbanization have also served to broaden the
arena and disseminated the risk for emerging infectious diseases on a global scale.
As members of society, it is known that parasites can be attained from a variety of
locations and can affect anyone they come into contact with. Organisms must also be cautious
about parasites, as they can become hosts, carriers, extremely ill, or a combination of all three.
One ecosystem in particular that has one of the most diverse environments is our aquatic
systems. Global climate change has caused an increase in the water temperatures, altering stream
flow patterns, and an increase in storms (Rahel and Olden, 2008). Humans have also had a major
influence in the aquatic systems by intentionally stocking lakes for game, building canals, and
sending out large ships for commercial shipping purposes. The combination of global climate
change and human touch has led to profound effects on the distribution and phenology of species
and the productivity of aquatic ecosystems. Mohseni et al., 2003 predicts that the number of

4. stream stations with suitable thermal habitat for warm water fishes will increase by 31% across
the United States. This alarming statistics leads to the idea that if there are more warm water
habitats, the potential living space for many species of fish will increase, and therefore there will
be an increase in invasive species.
When humans travel to different parts of the world that they are not native to, parasites
travel with them, the same can be said for these invasive species of fish. As predicted by Sharma
et al., 2007, it was estimated that the distribution of smallmouth bass (Micropterus dolomieu)
and highly invasive common carp (Cyprinus carpio) in Canada would advance northward to
encompass much of the country by the year 2010. With climate warming, 19 warm water fish
species from the Mississippi or Atlantic Coastal basins may invade the lower Laurentian Great
Lakes (Ontario, Erie, and Michigan) and that 8 warm water fish species currently present in the
lower Great Lakes could invade the upper Great Lakes (Huron and Superior) (Mandrak, 1989).
As expected, these 27 fish species would bring with them parasites that normally do not exist in
the Great Lakes. To be specific, 83 species of parasites would be introduced, which would open
the door for epizootic outbreaks of pathogens in immunologically naïve native fishes
(Marcogliese, 2001). At this rate, many of the native species of fish would not be able to survive
with the newly acquired parasites, or in the case they were able to adapt, they would now be
carriers of various invasive species of parasites. The health implications are relatively unknown,
but think about the effect this will now have on the human population. Perhaps the fish in the
Great Lakes account for a wide range of species caught and distributed in the area. Human
interaction with these newly infected species of fish could account for transmission of disease, or
even lose of product as many fish may die off. As the globe continues on an upward spiral of
increased climate change, there is no doubt that severe implications will occur. The prevalence of

5. parasites will broaden to areas previously unknown and will ultimately lead to severe
implications for both humans and organisms.
Most zoonotic parasites display three distinct life cycles: sylvatic, zoonotic, and
anthroponotic. In simpler terms, a parasite first affects only wild animals, then it can be
transmitted from animals to people, and lastly it can be transmitted from humans to animals.
Some of the most common zoonotic diseases include leishmaniasis, cryptosporidiosis, giardiasis,
trypanosomiasis, schistosomiasis, filariasis, onchocerciasis, and loiasis (Patz et al., 2000).
Morbidity and mortality rates have increased dramatically in humans due to a variety of reasons.
Some include deforestation and changes in land use, human settlement, commercial
development, road construction, water control systems, and of course, climate change. Replacing
forests with crops, ranches, and raising small animals on the once forestland can create
supportive habitats for parasites and their host vectors (Patz et al., 2000). The newly deforested
land can also be used for normal human settlement, such as housing developments, which also
allows for opportunities for exchange and transmission of parasites to uninfected humans.
The aggregate effect of temperature, precipitation, humidity, solar radiation and wind
contribute to determining the nature of vector populations. One parasite in particular that is
currently making moves to infecting humans is giardiasis, which is caused by Giardia lamblia,
which harbors in a variety of animals and crops. This zoonotic disease infects a wide range of
animals that humans do not necessarily interact with directly, but constant interaction is made
with their environments. In Colorado, beavers (Castor canadensis) and muskrats (Ondatra
zibethicus) are hosts for Giardia. These two animals shed the parasite cysts in their feces
throughout the year. In late spring and early fall, they contaminate surface waters downstream
from their dams with Giardia sp. Cysts that settle rapidly in the slow moving waters (Patz et al.,

6. 2000). In the Rhode River, Macoma balthica clams also harbor Giardia sp. cysts. These clams
burrow in the mud or sandy-mud substrata, feeding on the surface sediment layer. As the waters
are slow moving, the waterborne Giardia sp. cysts settle to the bottom, contaminating the
sediment. Sediments are constantly being deposited on land, to create new lands, which humans
are settling on. The disturbing truth is that the sediment we are using is more than likely
contaminated with a variety of diseases, such as Giardia. The continued disturbance of natural
ecosystems by destructive changes has modified the distribution and behavior of parasites, their
hosts and vectors. Improvements in monitoring the changes resulting from global climate change
and ecological change is needed immediately. Developing predictive models would serve as a
great tool for developing strategies and mechanisms for minimizing parasitic disease consequent
to expected changes in the environment. Without the use of monitoring and predictive models,
the issue of increased prevalence and severity of parasites, bacterial and viral diseases will soon
be out of control.
Warm temperatures speed up biochemical reactions that expend energy, permitting
increased activity, growth, development, and reproduction. A faster metabolism comes at a high
cost, as it requires higher food consumption rates to maintain a positive energy balance. This can
ultimately lead to a decrease in survivorship as temperature increases, particularly for non-
feeding free-living stages, such as eggs, cysts, and larvae (Lafferty, 2009). However, these
organisms learn to work around the challenging temperature shifts. Adaptation is easily
obtainable; in particular the lineage 1a West Nile Virus strain from New York requires warmer
temperatures for transmission than does the lineage II strain from South Africa (Lafferty, 2009).
Mosquito vectors are sensitive to meteorological conditions. Excessive heat has proven to kill
mosquitoes, but at the same time, an increase in temperature allows for greater reproduction,

7. biting, and the rate at which pathogens mature within the mosquitoes. For example, at 20 degrees
Celsius, malarial protozoa take 26 days to incubate, but at 25 degrees Celsius, the protozoa
mature in half that time, specifically 13 days (Epstein, 2001). This proves that all species have
their temperature limits, however there are multiple variations of organisms that can handle a
wide range of temperatures. Another major part of the climate change-disease relationship, is not
only the ranges they are being observed in, but also the severity of said diseases. Climate affects
the length of the transmission season for a variety of diseases, including malaria. An alarming
fact is, that as the climate increases in temperature and humidity, malaria transmission can
increase from zero to epidemic, hypoendemic, mesoendemic, hyperendemic, and holoendemic
(Hay et al., 2004). An experiment done by Chase and Knight, 2003, investigated the effect of
rainfall on mosquitoes using wetland mesocosms. After a large rainfall, researchers went back to
the mesocosms and counted the number of mosquitoes. The number of mosquitoes that emerged
from previously dried mesocosms was 20 times higher than in consistently inundated
mesocosms, which had developed a high biomass of mosquito predators. This experiment is a
clear indication of the increase in prevalence of vectors, due to the implications of global climate
change. Between the years 1951 and 2000, around 3.3% of the earth’s surface changed from one
climate category to another. In the Arctic, conditions have improved for some disease vectors.
For example, the lungworm of muskoxen can now develop in their intermediate host slugs in just
one year, instead of their usual time of two years. This pattern suggests that this infectious
disease in the Arctic may increase in severity (Kutz et al., 2005).
Through extensive research, it can be said with confidence that there have been dramatic
changes in many vector-borne diseases throughout the world. Malaria has re-emerged in Greece,
and West Nile virus has emerged throughout parts of Eastern Europe (Medlock and Leach,

8. 2015). Diseases that hit closer to home, such as tick-borne diseases like Lyme disease, continue
to increase at alarming rates and change in their geographical distribution. The principal vector
of Lyme borreliosis, also known as Lyme disease, causes more than 1,000 confirmed human
cases each year, with many more unreported. The most common tick species that carries the
vector is Ixodes ricinus, or more commonly known as the deer or sheep tick. The change in the
distribution of Ixodes ricinus is due to several factors, including climate change and alterations in
land-use. In parts of Scandinavia, where this species of tick is not normally found, an increase in
the distribution has been noted. EU climate models suggest that the range of Ixodes ricinus in
Europe might double. In the Alps alone, this species of tick has increased in altitudinal spread by
400m in the past three decades (Medlock and Leach, 2015).
In general, changes in weather, particularly extreme weather, will affect tick activity and
abundance. Ixodes ricinus is acutely responsive to humidity and temperature. Hot, dry summers
are unsuitable for this tick species and force it into summer dormancy. By contrast, mild, wet
winters might prolong winter tick activity, and increase tick densities (Medlock and Leach,
2015). As people spend more time outdoors, they are increasing their possible exposure to ticks
and Lyme disease. The severity of Lyme disease has also increased dramatically over the past
few decades. Many patients dealing with the disease have dealt with much higher fevers, severe
muscle pains, and increased lethargy (Steere et al., 1983). The severity of diseases such as Lyme
disease is a consequence of global climate change. The shifts in climate have led to distribution
shifts, an increase in abundance, and unfortunately new strains of diseases have emerged, with
severe complications for the infected.
Global climate change is a major topic of concern for all who habit this earth. It is natural
as human beings to only show genuine concern when climate change is having a true effect on

9. our well-being. Humans are adaptable creatures, if it is too hot, we go inside, or if it is too cold,
we put an extra layer of clothing on. But what do we do when the rise in temperature causes
fluctuations in the prevalence and severity of various diseases? The fix is not as simple. Mother
nature has been testing the human population for some time now with extreme weather. For
example, in 1998, Hurricane Mitch dropped six feet of rain on Central America in three days.
This caused the wake of malaria, dengue fever, cholera, and leptospirosis, which ultimately led
to the death of many people. In 2000, rain and three cyclones inundated Mozambique for six
weeks, and the incidence of malaria rose fivefold. In 2003, a heat wave in Europe was so drastic
that it killed tens of thousands of people, wilted crops, set forests ablaze, and melted 10 percent
of the Alpine glacial mass (Epstein, 2005). Not only can extreme weather cause direct effects on
the human population, but they can also affect us indirectly. For example, prolonged droughts
fuel fires, which end up releasing respiratory pollutants into the air. Not only can these pollutants
cause respiratory distress, but they can also cause severe infection in those who inhale them
(Epstein, 2001). Moist environments are suitable habitats for insects, which are the perfect
carriers for many bacterial diseases. Insects carried the plague, which was caused by the bacteria
Yersinia pestis.
The grim reality is that smallest events can have the greatest impact on the world. An
increase of about 1 to 2 degrees Celsius globally can cause extreme weather, which leads to the
uprising of diseases the human race have not seen in decades or the onset of new diseases that
medicine cannot yet treat. The issue of global climate change needs to be monitored and
surveyed for patterns, especially in the case of different diseases. The human population is facing
a major threat from microscopic organisms; parasites are emerging in areas they once never
were, there is an increase in the abundance, and the severity of the diseases they transmit is

10. alarming. If there is one thing I have learned through class lectures and research, is that global
climate change can influence the world in a variety of ways. Climate change can lead to the
extinction or emergence of species, it can alter relationships within ecosystems, and it can
threaten the human race through a variety of bacterial diseases.

11. Works Cited
Brooks, D.R., Hoberg, E.P. 2007. How will global climate change affect parasite-host
assemblages? Trends in Parasitology. 23(12): 571-574.
Epstein, P.R. 2001. Climate change and emerging infectious diseases. Microbes and Infection. 3:
747-754.
Epstein, P.R. 2005. Climate change and human health. The New England Journal of Medicine.
353(14): 1433-1436.
Hay, S.I., Guerra, C.A., Tatem, A.J., Noor, A.M., Snow, R.W. 2004. The global distribution and
population at risk of malaria: past, present, and future. Lancet Infectious Diseases. 4:
327-336.
Kutz, S.J., Hoberg, E.P., Polley, L., Jenkins, E.J. 2005. Global warming is changing the
dynamics of Arctic host-parasite systems. Proceedings of the Royal Society B. 272: 2571-
2576.
Lafferty, K.D. 2009. The ecology of climate change and infectious diseases. Ecology. 90(4):
888-900.
Mandrak, N.E. 1989. Potential invasion of the Great Lakes by fish species associated with
climatic warming. Journal of Great Lakes Research. 15: 306-316.
Marcogliese, D.J. 2001. Implications of climate change for parasitism of animals in the aquatic
environment. Canadian Journal of Zoology. 79: 1331-1352.
Mohseni, O., Stefan, H. G., Eaton, J. G. 2003. Global warming and potential changes in fish
habitat in U.S. streams. Climate Change. 59:389–409.
Medlock, J.M., Leach, S.A. 2015. Lancet Infect Dis. 23 Mar, 2015. Web. 18 Apr, 2015.
www.thelancet.com/infection

12. Patz, J.A., Graczyk, T.K., Geller, N., Vittor, A.Y. 2000. Effects of environmental change on
emerging parasitic diseases. International Journal for Parasitology. 30(12-13): 1395-
1405.
Rahel, F.J., Olden, J.D. 2008. Assessing the effects of climate change on aquatic invasive
species. Conservation Biology. 22(3): 521-533.
Sharma, S., Jackson, D.A., Minnus, C.K., Shuter, B.J. 2007. Will northern fish populations be in
hot water because of climate change? Global Change Biology. 13: 2052-2064.
Steere, A.C., Hutchinson, G.J., Rahn, D.W., Sigal, L.H., Craft, J.E., DeSanna, E.T., Malawista,
S.E. 1983. Treatment of the early manifestations of Lyme disease. American College of
Physicians. 99: 22-26.