Effects of climate change on transmission of
vector-borne diseases
Howard S. Ginsberg, Ph.D.
USGS Patuxent Wildlife Research Center
University of Rhode Island
“Hockey stick” graph shows dramatically increasing
Global temperatures during the past half century
precipitation
Predicted effects on precipitation differ in different parts of
North America. Some areas are predicted to see more precipitation,
some less, and some are predicted to show greater variability with
more intense periods of rainfal and of drought.
hurricanes
Some models predict similar frequency of hurricanes in the future,
but with greater average strength.
sea level
Sea level is rising and is predicted to continue to rise.
Arthropod vectors
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Lice - epidemic typhus
Kissing bugs – Chagas disease
Fleas – plague
Sand flies – Leishmaniasis
Black flies – River blindness
Mosquitoes – malaria, dengue, yellow fever, Japanese
encephalitis, West Nile encephalitis, filariasis
• Tsetse flies – African sleeping sickness
• Chiggers – scrub typhus
• Ticks – Lyme disease, Tick-borne encephalitis, Rocky
Mountain Spotted Fever
Malaria
Predicted change in distribution of malaria based on predicted changes in
temperature and precipitation.
Martens et al. (1999. Global Environmental Change 9:S89-S107)
predict that malaria will spread from the tropics into more northern
and more southern latitudes.
Malaria
Predicted change in distribution of malaria based on models using
mean, maxima and minima of temperature, precipitation, and
saturation vapor pressure.
Rogers & Randolph (2000. Science 289:1763-1766) predict <1%
change in total # cases.
West Nile Virus
pathogen: WNV (flavivirus)
enzootic vectors: Culex pipiens, Cx. restuans
bridge vectors: Culex pipiens, Cx. salinarius, Aedes albopictus
reservoirs: robins, house sparrows, crows
Arbovirus transmission dynamics
Effects of temperature
Effect of temperature on mosquito survival:
Mosquito longevity declines as ambient
temperature increases
Reeves et al. 1994. J. Med. Entomol. 31:323.
Effect of temperature on extrinsic incubation period
of WNV in Culex pipiens
Viral replication in mosquito is faster as ambient
temperature increases
Dohm et al. 2002. J. Med. Entomol. 39:221.
Effects of precipitation and environmental moisture
on arboviral transmission
- Humidity and adult mosquito longevity
- Precipitation, groundwater levels and mosquito abundance
(larval habitat) and larval survival (e.g., EEE)
- Wetspots and concentration of mosquitoes and hosts
(e.g., SLE, WNV?)
- Precipitation and human activity
Lyme disease
pathogen
vector
reservoirs
Factors influencing distribution
of Lyme disease
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Tick distribution and abundance
Tick phenology
Tick genetics
Distribution of hosts
Tick distribution
Lyme disease distribution in the U.S.
Centers for Disease Control and Prevention
Tick phenology
Life cycle of Ixodes scapularis
adults
larvae
nymphs
adults
POPULATION 1
hosts
nymphs
hosts
adults
larvae
POPULATION 2
SPRING SUMMER FALL WINTER SPRING SUMMER FALL
YEAR 1
YEAR 2
Hosts of larval Ixodes scapularis
[effects of climate change on distributions of hosts?]
Northeastern U.S.
Southeastern U.S.
Effects of global climate change on transmission
of vector-borne diseases
- Some diseases will spread to areas where they are
currently absent
- Some diseases will disappear from areas where
they currently exist
- Intensity of transmission of some pathogens will change
locally, and yearly patterns will vary with
changes in weather patterns
- Human activities will strongly influence disease transmission
in response to climate change