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

hurricanes

sea level

Predicted effects on precipitation differ in different parts ofNorth 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.

Some models predict similar frequency of hurricanes in the future, but with greater average strength.

Sea level is rising and is predicted to continue to rise.

Arthropod vectors

• 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.

Predicted change in distribution of malaria based on models usingmean, maxima and minima of temperature, precipitation, and saturation vapor pressure.

Rogers & Randolph (2000. Science 289:1763-1766) predict <1% change in total # cases.

Malaria

West Nile Virus

enzootic vectors: Culex pipiens, Cx. restuans

reservoirs: robins, house sparrows, crows

bridge vectors: Culex pipiens, Cx. salinarius, Aedes albopictus

pathogen: WNV (flavivirus)

Arbovirus transmission dynamicsEffects of temperature

Effect of temperature on mosquito survival:

Reeves et al. 1994. J. Med. Entomol. 31:323.

Mosquito longevity declines as ambient temperature increases

Dohm et al. 2002. J. Med. Entomol. 39:221.

Effect of temperature on extrinsic incubation periodof WNV in Culex pipiens

Viral replication in mosquito is faster as ambienttemperature increases

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

vector

reservoirspathogen

Factors influencing distribution of Lyme disease

• 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

Life cycle of Ixodes scapularis

adults larvae nymphs adultsPOPULATION 1

POPULATION 2 nymphs adults larvae

SPRING SUMMER FALL WINTER SPRING SUMMER FALL

hosts hosts

YEAR 1 YEAR 2

Tick phenology

Northeastern U.S.

Southeastern U.S.

Hosts of larval Ixodes scapularis[effects of climate change on distributions of hosts?]

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 changelocally, and yearly patterns will vary with changes in weather patterns

- Human activities will strongly influence disease transmissionin response to climate change