The Effect of Climate Change on Human Health

Spring 2012, Lecture 13

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Overview of Effects

• Climate change is expected to have a major influence on certain types of disease

• Changes in both temperature and humidity will play an important role

• Some of the effects are already being seen• Some increased health risk will be due to extreme

weather events, like the 2010 heat wave in Russia, but many problems will involve continual climate modification

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Increased Risk and Benefit

• Some climate changes may produce health benefits, but most will increase risk

• The following slides outline a few examples

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Increased Heat

• Risk - More deaths and increased disease risk due to very hot days

• Benefit – Fewer winter deaths and disease events

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Heat-wave Effects

• According to the IPCC Fourth Assessment (2007), by 2100:o Chicago is projected to experience 25% more

frequent heat waveso Los Angeles is expected to experience a four to

eight-fold increase in heat-wave days• Those with heart problems, asthma, the

elderly, the very young and the homeless can be especially vulnerable to extreme heat

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Increased Heat Stress

• Schematic representation of how an increase in average annual temperature would affect annual total of temperature-related deaths, by shifting distribution of daily temperatures to the right

• Additional heat-related deaths in summer would outweigh the extra winter deaths averted (as may happen in some northern European countries)

• Average daily temperature range in temperate countries would be about 5–30ºC.

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Food Poisoning

• Risk increases due to higher temperatures• Salmonellosis is especially likely to be a

problem

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Aero-allergen Production

• Risk – Increased allergic disorders, including hay fever and asthma due to longer pollen seasons

• Benefit – Reduced exposure to aero-allergrens in some places due to lower productions or shorter seasons of pollen circulationoHigher temperatures and changed humidity may

make the growing seasons shorten for some plants

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Effects of Extreme Temperatures

• A European study of hospital admission data for a dozen major cities found that for every 1ºC rise in temperature, hospital admissions for respiratory and asthma-related illness increase up to 4.5% among the elderly

• The Russian heat wave of 2010 doubled the death rate in Moscow to 700 people per day during the heat wave

• During the summer 1995 heat wave in Chicago, it is estimated there were 700 excess deaths due to heat

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Water-borne Infection

• Risk - Cholera risk will increase in coastal or estuarine regions, due to a warming of water temperatures

• Benefit – risk will diminish in areas where heavy rainfalls decrease

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Vector-borne Infections

• Risk – Both mosquito and tick borne infections are likely to increase

• Benefit – In areas of diminished rainfall, mosquitoes, ticks, and snails may become less prevalent, and regions of very high temperatures may also decrease these vectors

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Vector-borne Disease and Climate Associations

• Vector-borne diseases have been shown to be associated with changing climate conditions, especially El Nino-Southern Oscillation (ENSO ) eventsoMalaria – South Africa, Columbia, VenezuelaoDengue fever – Asia-Pacifico Ross river virus – AustraliaoWest Nile – Numerous places, including the U.S.

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Vector-borne Disease

• In epidemiology, a vector is an insect or any living carrier that transmits an infectious agent

• A vector serves two functions:o It is required for part of the parasite's developmental cycleo It also transmits the parasite directly to subsequent hosts

• Most commonly known vectors consist of arthropods, domestic animals, or mammals that assist in transmitting parasitic organisms to humans or other mammals

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Common Vectors

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• Mosquitoes serve as vectors for Malaria, Dengue fever, Yellow fever, and Chikungunya • Ticks can serve as vectors for

Lyme disease, Rickettsia, and Babesiosis

Climate Effects on Disease Vectors

• High temperatures affect both vector and pathogen

• Rainfall effects are more complexoHeavy rainfall and flooding may trigger outbreaks

of diarrhea in areas where crowding and poverty are present

oVery high rainfall can reduce mosquito populations by flushing larvae from their habitat in pooled water

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Increased Malaria Risk

• The IPCC has noted that the global population at risk from vector-borne malaria will increase by between 220 million and 400 million in the next century

• While most of the increase is predicted to occur in Africa, some increased risk is projected in Britain, Australia, India and Portugal

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The Effect of Increased Heat

• Hotter, more humid weather shortens mosquito breeding cycles

• The incubation of dengue virus is speeded up by increased temperatures

• Milder winters also allow the survival of many disease related organismsoMosquitos, tics and miceo Lyme disease, Rocky Mountain spotted fever, equine

encephalitis, anaplasmosis, and bebesiosis

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Pesticides and Health

• In the decades of the 1950’s and 60’s, DDT was widely used to curtail mosquito breeding grounds

• In her 1962 book Silent Spring, the late Rachel Carson pointed out the tremendous environmental havoc being wrought by DDT and related compounds

• Current opinion is that curtailing DDT may have contributed to the current problem, but today’s problems go well beyond the use of pesticide

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Public Health Opinion

• John Balbus, senior adviser for Public Health at the National Institute for Environmental Health Sciences siad in an article in the December, 2010 Discover magazine:o “Climate change will cause a worsening of the common

health problems we already see. There will be incremental changes in the next 5 or 10 years, but that might not compare to what we’re going to see in a matter of decades. In trying not to be alarmist, scientists have systematically underestimated the threat.”

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West Nile Virus

• Another vector borne disease is West Nile virus• It first occurred in Uganda in 1937, with later

outbreaks in Israel in the late 1950’s, and Romania in 1996

• It has since spread to the U.S., appearing in New York in 1999

• The vector is Culex pupiens, a common house mosquito

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Conditions for Spreading West Nile

• West Nile becomes a threat after periods of hot, dry weather

• In New York in 1999, there was a period of ten days with temperatures over 100ºF, followed by heavy rains

• The resulting floods created mosquito breeding grounds, and populations increased rapidly

• Birds drinking in stagnant pools of water were infected

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Bronx Zoo

• Birds at the Bronx Zoo became infected, with deaths of several specieso Crowso Flamingoeso Bald Eagles

• More than 30,000 West Niles cases have occurred in the U.S. since 2002, with over 1000 deaths

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Infectious Diseases

• Many infectious agents, vector organisms, non-human reservoir species, and rate of pathogen replication are sensitive to climatic conditions

• Salmonella and cholera bacteria, for example, proliferate more rapidly at higher temperatures, salmonella in animal gut and food, cholera in water

• In regions where low temperature, low rainfall, or absence of vector habitat restrict transmission of vector-borne disease, climatic changes could tip the ecological balance and trigger epidemics

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Dengue Fever in the United States

• Dengue fever was thought to be eradicated in the U.S., but has been making a comeback

• There are two formso Classic dengue fever has been present in northern

Mexico (Matamoros) and is occurring in Brownsville, Texas

oDengue Hemorrhagic Fever was seen in Brownsville, for a resident who contracted the disease in the U.S., in 2005, and has been spreading

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Dengue Hemorrhagic Fever

• The appearance of Dengue Hemorrhagic Fever in the United States was of great concerno There is no vaccine to protect against ito There is no medicine to cure it

• The patient in Brownsville recovered, but those people who have other health problems would probably not be so lucky

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Flooding

• Floods are classified as low-probability, high impact events

• For the decade 1992-2001, there were nearly 100,000 flood related deaths, and 1 to billion people were affected by flooding

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Increased Risk of Floods

• More injuries and deaths due to flooding• Increased risk of infectious disease due to

flooding, and mental health disease brought on by flood-related stress

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Short Term Flood Effects

• Some health consequences arise during or soon after the flooding

• These include injuries, communicable diseases, or exposure to toxic pollutants

• Excessive rainfall facilitates entry of human sewage and animal wastes into waterways and drinking water supplies, increasing the risk of water-borne diseases

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Longer Term Flood Effects

• Other effects of flooding may appear later• These include malnutrition, caused by crop

loss, and mental health disorders resulting from the stress of flood-related problems

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Droughts• Droughts represent the other extreme of weather related

precipitation problems• Globally, disaster effects are greatest for droughts (and

associated famines) because of their regional extent, which are usually much larger than flood-related regions

• Another pollutant of concern is "particulate matter," also known as particle pollution or PM

• Climate change may indirectly affect the concentration of PM pollution in the air by affecting natural or “biogenic” sources of PM such as wildfires and dust from dry soils

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Particulate Matter

• PM is a complex mixture of extremely small particles and liquid droplets

• When inhaled, these particles can reach the deepest regions of the lungs

• Exposure to particle pollution is linked to a variety of significant health problems

• Particle pollution also is the main cause of visibility impairment (haze) in the nation’s cities and national parks

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Poverty and Disease

• Susan Fisher-Hoch, an epidemiologist at the University of Texas School of Public Health said,o “If dengue moves into a population that hasn’t experienced

it and has no natural immunity, we are going to see more severe disease”

o “The way we live hermetically sealed in our houses – with screens on the windows and air-conditioning – protects us enormously. But what about those who don’t live well – the people in trailer parks sitting on their porches surrounded by mosquitoes?”

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Additional Problems

• According to a paper by McMichael et al. (2006) in The Lancet, IPCC modeling indicates a future increase of 5-10% in the number of malnourished people

• Conflicts over food, together with migrant and refugee flows likely to result from these wider-ranging effects would create additional problems

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Anticipated Consequences

• These additional effects include:o Increase in infectious disease casesoMalnutritionoMental health problemso Injury and violent death from conflict

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The Effects of Climate Change

• The video shows a report that resulted from a collaboration between the British medical journal, The Lancet, and University College London

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