Climate Change and VectorBorne Diseases in the United States

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Climate Change and Vector-Borne Diseases in the
United States

• Ned Hayes, MD
• Division of Vector-Borne Infectious Diseases
• Fort Collins, Colorado

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Disclaimer

• The opinions expressed in this talk are those of
  Ned Hayes,
• and if they are not the official opinions of
  CDC, then they clearly should be -)

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Take-home message Climate is one determinant
of vector-borne disease incidence.

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Hypothesis global warming will increase the
incidence of vector-borne infectious diseases in
the United States

• RATIONALE
• Bugs like warmth
• Vector-borne diseases dont occur much in winter,
  or in the Arctic or Antarctic, or on high
  mountains.
• Dengue, yellow fever, and malaria are three BIG
  vector-borne diseases that occur mostly in the
  tropics
• Therefore if global warming heats up the United
  States, then yellow fever, dengue, and malaria
  epidemics will sweep the country.

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Associated Premise

• Temperature has been limiting the entry of
  vector-borne disease into the United States
• ?

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History of Vector-Borne Diseases in the United
States

• Yellow Fever epidemics New York, 1668 Boston,
  1691 Philadelphia 1699New York, 1870 New
  Orleans, 1905
• Dengue epidemics Philadelphia, 1780Texas, 1922
  500,000 cases
• Malaria 1880s widespread in most states east of
  the Rockies, north to Massachusetts1946 CDC
  mission eradicate malaria from the United States

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Texas
Mexico
1999
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Household Survey

• 622 household surveys
• 313 in Nuevo Laredo
• 309 in Laredo
• 516 blood samples
• 288 from Nuevo Laredo residents
• 228 from Laredo residents

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Seroprevalence of Antibody Against Dengue Virus
in Nuevo Laredo and Laredo, 1999

• Antibody Mexico() U.S.()
• IgM 16.0 1.3
• 95 CI (0.90-22.2)
  (0-2.8)
• IgG 47.8 22.5
• 95 CI (41.0-54.5)
  (17.0-28.0)

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Mosquito Larvae Results

• Mexico U.S.
• House Index 25 37
• Breteau Index 38 91

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Housing Characteristics

• Mexico () U.S.()
• Central AC 1.9 35.8
• Room AC 23.4 51.5
• Evaporative cooler 28.5 17.3
• Screens 54.2 77.7
• Intact screens 35.6 59.9
• occupants 4.52.5 3.82
• Plt0.01

Air conditioning IgM seropositive O.R. 0.39
(0.18 -0.83)
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Dengue on the U.S./Mexico Border

• Climate could not explain the lower incidence of
  dengue on the United States side of the border.
• Differences in lifestyle (air conditioning, human
  behavior) appeared to protect against dengue
  infection on the United States side of the
  border.

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WNV Neuroinvasive Disease Incidence, by County,
US, 1999
N59
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WNV Neuroinvasive Disease Incidence, by County,
US, 2000
N19
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WNV Neuroinvasive Disease Incidence, by County,
US, 2001
N64
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WNV Neuroinvasive Disease Incidence, by County,
US, 2002
N2,946
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WNV Neuroinvasive Disease Incidence, by County,
US, 2003
N2,866
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WNV Neuroinvasive Disease Incidence, by County,
US, 2004
N1,148
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WNV Neuroinvasive Disease Incidence, by County,
US, 2005
N1,309
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WNV Neuroinvasive Disease Incidence, by County,
US, 2006
N1,491
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West Nile Neuroinvasive disease (WNND) cases by
week of onset, US, 1999-2005
reported as of 10/3/2005
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Reisen, et al. J. Med. Entomol. 200643 309-317
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West Nile Virus Basic Transmission Cycle
Enzootic (Maintenance/Amplification)
Amplifying hosts
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Counties Reporting Culex pipiens or C. pipiens
complex to ArboNet 2001-2006
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Counties Reporting Culex tarsalis to ArboNet
2001-2006
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Cumulative Incidence of West Nile Neuroinvasive
Disease 2002-2006
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West Nile Virus in America

• Temperature certainly influences intensity of WNV
  transmission
• WNV was introduced into a naïve ecosystem in
  America. The dynamics of spread are determined
  by multiple ecological factors. Climate is one
  component and its effects on WNV transmission are
  complex.

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Lyme Disease
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Lyme Disease High Incidence Counties, United
States, 1997
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Lyme Disease High Incidence Counties, United
States, 2002
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Historic Estimates of White-tailed Deer in
Connecticut
Est. 2003 winter population 75,774
Avg. deer density 21/mi2
Estimated Deer Population
Data CT Dept. of Environmental Protection. Slide
courtesy of Dr. Kirby Stafford, CAES.
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Monhegan Island, MainePhoto courtesy of Chuck
Lubelczyk, Maine Medical Center Research Institute
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Rand PW, Lubelczyk C, Holman MS, Lacombe EH,
Smith RP Jr. J Med Entomol. 200441779-84
Courtesy of Chuck Lubelczyk, Maine Medical Center
Research Institute
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Rand PW, Lubelczyk C, Holman MS, Lacombe EH,
Digaetano AT, Smith RP Jr. Journal of Vector
Ecology 200429164-176
Isolines of sufficient degree days to allow
Ixodes scapularis larval hatching(Based on mean
temperatures from 1991-2000)
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Rand PW, Lubelczyk C, Holman MS, Lacombe EH,
Digaetano AT, Smith RP Jr. Journal of Vector
Ecology 200429164-176

• despite warmer temperatures in recent years,
  there has been no apparent shift of the
  (sufficient degree day) isolines (from 1971 -
  2000)

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Some Possible Ecological Determinants of Lyme
Disease Incidence

• Residential incursions into forested areas
• Abundance of white-tailed deer
• Abundance of rodent hosts
• Food source for rodents (acorns?)
• Abundance of competitive hosts (skinks)
• Climate humidity, temperature, precipitation?

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What are the effects of severe weather patterns
that might be induced by climate change?

• Increased rainfall can increase vector abundance
• but so can drought.
• Need to consider effects on human housing, water
  storage, preventive behavior.
• Need to consider effects on pathogen hosts and
  reservoirs (birds, lizards, rodents)

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Oleary DR, et al. AJTMH. 20026635-9
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• Dr. Paul Reiter
• The natural history of mosquito-borne diseases
  is complex, and the interplay of climate,
  ecology, vector biology, and many other factors
  defies simplistic analysis.
• Environmental Health Perspectives, Vol. 109,
  2001. pp. 141-161.

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H.L. Mencken

• For every complex problem there is an answer that
  is clear,
• simple,
• and wrong.

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How will climate change affect vector-borne
infectious diseases?
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Some Effects of Changing Temperature on
Vector-Borne Diseases

• Increased temperature decreases extrinsic
  incubation period should increase transmission
• Increased temperature usually decreases vector
  survival should decrease transmission
• Warmer temperatures can shorten vector
  development time increase transmission
• Increased or decreased geographical range of
  vector, hosts, and competitors (? Northward
  movement of both low and high temperature disease
  boundaries?)

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Some Effects of Changing Climate on Vector-Borne
Diseases

• Changes in rainfall and irrigation can alter
  distribution and abundance of vectors and hosts
• Changes in human behavior
• Outside in the evening?
• Hunkered down next to the air conditioner?

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International commerce and travel
Human behavior and prevention strategies
Water storage and irrigation
Poverty
Modified from Sutherst R.W. Clin Micribiol Rev
200417136-73
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Aedes aegypti Distribution in the Americas
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Aedes aegypti Distribution in the Americas
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Aedes aegypti Distribution in the Americas
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Opportunities for Prevention of Vector-Borne
Disease in an Age of Change

• Early detection of pathogen introduction due to
  travel and commerce
• Develop and disseminate vector control strategies
  and vaccines
• Improve water supply and sanitation
• Assure public health services family planning,
  immunization, health education

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Acknowledgments

• Nicole Lindsey
• Alison Hinckley
• Jennifer Lehman

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Climate Change and Vector-Borne DiseasesResearch
Options

• Expanded evaluation of the effects of temperature
  on vector distribution (survival, development)
  and vector-pathogen interactions
• Models to determine the potential northern and
  southern limits of diseases under various
  scenarios of climate change
• Further define the host characteristics and
  behaviors that limit disease incidence
• Surveillance to monitor changes in disease
  incidence with varying climatic conditions