Download Environmental Changes and Infectious Disease

Environmental Changes
and Infectious Disease
William R. Barnett
PUBH 605
Introduction


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Changes in the ecosystem are contributing to
the prevalence of infectious disease in some
regions of the world.
These changes are brought on by either
natural occurrence or through human
interference.
Developing nations in Sub-Sahara Africa,
Latin America, South America, and Asia are
primarily affected by these environmental
changes.
Overview of environmental
changes

Climate:
• Temperature
• Rise in average temperatures
• Rainfall
• Increase in precipitation
• Intense weather patterns:
• Heat waves
• Droughts
• Floods
Overview of environmental
changes con’t

Land
• Deforestation
• Loss of trees in tropical rainforests
• Soil degradation:
• Soil erosion
• Overgrazing and cultivation
• Construction
• Human settlements
• Roads
Overview of environmental
changes con’t

Water
• Natural water source diversion:
• Irrigation
• Reservoirs and dams
• Urban water management
• Waste water systems
• Storm water systems
• Water chemistry:
• Desalination and pH
Factors influencing
environmental changes

Global warming:
• Emission of “greenhouse gases” by
automobiles, industrial factories, and other
sources.

Agricultural development:
• Clearing of forests for farming and ranching.
• Efforts to irrigate water-poor lands.
Factors influencing
environmental changes con’t

Human intrusion into environment:
• Construction of reservoirs, dams, and roads
•
•
to accommodate development.
Logging of tropical forests.
Expansion of human population.
Specific infectious diseases

Vector-borne:
• Mosquito
• Malaria
• Yellow fever
• Dengue fever
• Filariasis
• Other vectors
• Leishmaniasis (sand flies)
• Trypanosomiasis (Tsetse fly)
Infectious disease con’t
• Onchocerciasis (Blackfly)
• Loiasis (Chrysops fly)

Parasitic (non vector-borne):
• Schistosomiasis
• Cryptosporidium
• Giardia
Filariasis
Filariasis con’t
Sand fly
Leishmaniasis con’t
Tsetse Fly
Schistosomiasis
Onchocerciasis
Chrysops fly
Loiasis
Cryptosporidiosis
Giardia
Connecting environmental
changes to infectious disease

Environmental changes can adversely
affect human health by providing:
• Breeding areas and habitat for vectors and
animal intermediates.
• Adaptation of vectors to new habitats.
• Additional animal species to the region,
which provide reservoirs for
microorganisms.
• Increased interaction between pathogen and
host.
Impact of environmental
changes on infectious disease

Temperature and rainfall:
•
•
•
Small increases in existing low temperatures have
been shown to exert increased transmission of
malaria.
Malaria incidence is on the rise in higher altitude
areas, such as highlands, due to temperature
changes.
Heavy rainfall has lead to contamination of water
supplies by Cryptosopridium, which is resistant to
chlorine treatment during these periods.
Source: Patz, et. al. (2000)
Deforestation
Impact of environmental changes on
infectious disease con’t

Deforestation:
• One of the major human activities associated with
•
the resurgence of malaria, yellow fever and other
mosquito-borne viruses.
Provides the opportunity for the “sylvatic” cycle of
yellow fever in monkeys and mosquitoes to be
transferred to humans in the “urban” transmission
cycle through deforestation activities.
Source: Norris (2004)
Impact of environmental changes on
infectious disease con’t



Removal of the forest canopy has created pools
for the expansion of mosquito breeding habitats.
New mosquito species, such as An. Gambiae,
have become associated with malaria
transmission around deforested areas.
The removal of intact forest has resulted in the
emergence of newly recognized pathogens.
Source: Norris
Impact of environmental changes on
infectious disease con’t
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Replacement of deforested areas with cocoa,
coffee, oil palms, or mango trees provide a
habitat for tsetse flies.
Although deforestation has reduced the
prevalence of the Chrysops fly, the vector has
adapted itself to rubber tree plantations.
Farmland grown over deforested regions has
increased fox populations, which are excellent
reservoirs for leishmaniasis.
Source: Patz, et. al.
Agriculture
Impact of environmental changes on
infectious disease con’t

Agricultural development:
• Sedimentation and runoff in water sources
•
can block stream flow, decrease water depth
and provide shallow water with no flow, which
is an ideal mosquito habitat.
Rice paddies over immense areas are
habitats for development of immature
mosquitoes.
Source: Norris
Impact of environmental changes on
infectious disease con’t
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The prevalence of schistosomiasis parallels
the degree of irrigation intensity.
Rice cultivation is associated with increased
prevalence of filariasis
Raw sewage used to irrigate farmland has
been contaminated with giardia.
Domestic animals, such as pigs and cows
create shallow habitats for mosquitoes.
Source: Patz, et. al.
Impact of environmental changes on
infectious disease con’t
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
Increase in maize production has resulted in a
supply of pollen to mosquito larvae.
Pesticides aimed at removing parasites have
contributed to the growth of less dominant
species of tsetse flies that carry
trypanosomiasis.
Source: Sutherst (2001)
Aswan Dam (Egypt)
Impact of environmental changes on
infectious disease con’t
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Construction:
• Dams, reservoirs, and canals have
•
•
contributed to an increase in cases of
schistosomiasis.
Road construction leads to soil erosion and
creation of ponds when the water rises
creating mosquito breeding areas.
Human activity in previously inaccessible
areas provides more interaction between
vectors and hosts.
Impact of environmental changes on
infectious disease con’t
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Urbanization:
• Storm water handling systems provide breeding
•
•
sites for mosquitoes when surface waters are
scarce.
Dengue virus exposure is greater for people
living close to wells or service manholes.
Discard materials, such as tires, cans, and
barrels can provide a breeding habitat for
mosquitoes.
Source: Norris (2004).
Impact of environmental changes on
infectious disease con’t
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Other impacts:
•
•
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Reduction of water salinity and conversion from acidic
to alkaline conditions increase the growth of
freshwater snails, which contribute to the cycle of
schistsomiasis.
Movement by humans, who do not have protective
immunity and are unaware of preventive measure
against vectors, in remote areas.
Animal and vector adaptability to changing
environments and competition among species.
Source: Part, et. al.
Conclusion
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Without a doubt, the changes in the world’s
ecosystems contribute to the cycle of infectious
disease.
In particular, human activities, such as
deforestation, increased development
agricultural lands, and movement of humans
into previously inaccessible areas.
Changes in climate, such as greater rainfall,
are another driver for increased cases of
infectious disease.
Conclusion con’t
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
These activities and natural occurrences
provide habitats for vectors and
reservoirs, but also allow humans and
animals more contact with infectious
disease.
Still, most of these issues are driven by
population growth, economic conditions,
and the availability of food throughout
the world.
References
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Norris, D. E. (2004). Mosquito-borne Diseases as a
Consequence of Land Use Change. EcoHealth,
1, 19-24.
Patz, J.A., et. al. (2000). Effects on Environmental
Change on Emerging Parasitic Disease.
International Journal for Parasitiology, 30, 13951405.
Sutherst, R. W. (2001). The Vulnerability of Animal
and Human Health to Parasites Under Global
Change. International Journal for Parasitology,
31, 933-948.