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 • 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 reservoirs vector
Factors influencing distribution of Lyme disease • Tick distribution and abundance • Tick phenology • Tick genetics • Distribution of hosts
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 hosts nymphs 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