Health Risks and Climate Change
By: Dr. James P. Goltz
AUGUST 13, 2018 — Climate change will undoubtedly pose risks to human and animal health, as experiences and observations are verifying predictions made through foresight exercises and climate change modelling. The major health risks associated with climate change are likely to be physical (e.g., hyperthermia and/or hypothermia related to extreme
temperatures; traumatic injury from extreme weather events such as flooding, wind and storms; cardio-respiratory problems from allergens and smog) and infectious diseases, especially those borne by arthropod vectors, or resulting from water contamination after intense rainfall or food contamination during hot weather (PHAC, 2017).
Vectors of disease are organisms that transmit disease from one living organism to another. The arthropod vectors of disease of greatest concern to humans in regard to climate change are mosquitoes and ticks. Arthropod vectors and the diseases they can potentially carry are likely to spread poleward as climate warms in temperate areas; tropical and subtropical vector-borne diseases are more likely to be introduced into and become established in areas that are currently temperate; sustained warmer temperatures will increase the likelihood of vectors and vector-borne diseases being spread by increased human migration related to climate change, and surviving throughout the year and becoming more abundant in new areas; and new genetic variants of vector-borne pathogens are likely to emerge and become established as dynamics between animal hosts and vectors change in the new environments (Ogden & Lindsay 2016).
Populations of ticks and mosquitoes (and the diseases they carry) are likely to be affected by climate change, although in somewhat different ways. Mosquitoes are highly mobile and can be dispersed by wind and air, have a short life cycle of several weeks, and can respond quickly to short-term changes in weather and climate; mosquito populations can explode in response to rainfall and warm temperatures, resulting in emerging and re-emerging epidemics of the diseases they can transmit (e.g., West Nile Virus, Eastern Equine Encephalitis). Ticks rely on dispersal via mammalian and avian hosts, have a multiyear life cycle, tend to be generalists with respect to their hosts and suitable woodland habitats, and spend much of their life in habitat refuges; tick populations do not respond rapidly to rainfall and temperature due to long life cycles, so the risk of tick-borne diseases is usually long-term with little variation from year to year (Ogden & Lindsay 2016). Which arthropod vectors and their diseases are of greatest concern to us as climate changes? The Asian Tiger Mosquito (Aedes albopictus) has spread from Asia to all continents except Antarctica, breeds in sheltered containers (e.g., water pooled in water storage tanks, tires, bottles, or aquaponics containers) and is capable of transmitting at least 11 different diseases including dengue, West
Nile virus, chikungunya, Japanese Encephalitis and Eastern Equine Encephalitis. The Yellow Fever Mosquito (Aedes aegypti) spread from Africa to become established worldwide in tropical and subtropical areas, thrives in areas of human cohabitation where it breeds in artificial containers, and is capable of transmitting diseases such as yellow fever, dengue, Zika and chikungunya (NCCID 2017). Small sporadic outbreaks of malaria have been transmitted by local species of anopheline mosquitoes in New York and New Jersey in the 1990s; malaria caused nearly 500,000 deaths globally in 2015 (WHO 2017). The Black-legged Tick (Ixodes scapularis) is capable of transmitting Lyme disease, several other Lyme-like Borrelioses, human granulocytic anaplasmosis and Babesiosis; this tick species is annually dispersed throughout New Brunswick by migrating birds, but the greatest risk for exposure to Black-legged Ticks and the diseases they carry is currently in the vicinity of Saint John, Grand Manan and St. Stephen. The American Dog Tick (Dermacentor variabilis) is capable of transmitting Rocky Mountain spotted fever, ehrlichiosis and tularemia; this tick species is well-established in Nova Scotia and southern Maine and reports from New Brunswick are increasing.
The best tools and strategies to help prevent health problems related to climate change are knowledge, education (including preventing arthropod bites), surveillance, and collective action by individuals, municipalities, provinces and countries around the globe to help reduce the risk of climate change.
References
PHAC .2017. http://www.phac-aspc.gc.ca/hp-ps/eph-esp/fs-fi-a-eng.php
Ogden, N.H. and L.R. Lindsay. 2016. Effects of Climate and Climate Change on Vectors and Vector-Borne Diseases: Ticks
Are Different. Trends in Parasitology 32 (8): 646-656.
NCCID. 2017. https://nccid.ca/publications/review-of-literature-on-effects-of-climate-change-on-mosquito-borne-illnessesin-canada/
WHO. 2017. http://www.who.int/bulletin/archives/78%289%291136.pdf
Information about the author
Dr. James P. Goltz, Fredericton, marph@nbnet.nb.ca