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 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. 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 using mean, maxima and minima of temperature, precipitation, and saturation vapor pressure. Rogers & Randolph (2000. Science 289: ) 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 dynamics Effects of temperature Effect of temperature on mosquito survival: Reeves et al J. Med. Entomol. 31:323. Mosquito longevity declines as ambient temperature increases

Dohm et al J. Med. Entomol. 39:221. Effect of temperature on extrinsic incubation period of WNV in Culex pipiens Viral replication in mosquito is faster as ambient temperature 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 adultslarvaenymphsadults POPULATION 1 POPULATION 2 nymphs adults larvae SPRING SUMMER FALL WINTER SPRING SUMMER FALL hosts YEAR 1YEAR 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 change locally, and yearly patterns will vary with changes in weather patterns - Human activities will strongly influence disease transmission in response to climate change