Climate Change and the Expansion of Animal and Zoonotic Diseases - What is the Agency's Contribution?

Ironically, the countries that have contributed least to global warming – mainly the developing countries – are the most vulnerable to its impact especially from diseases that higher temperatures can bring.

Globalization and climate change have had an unprecedented worldwide impact on emerging and re-emerging animal diseases and zoonoses. Climate change is disrupting natural ecosystems by providing more suitable environments for infectious diseases allowing disease-causing bacteria, viruses, and fungi to move into new areas where they may harm wild life and domestic species, as well as humans. Diseases that were previously limited only to tropical areas are now spreading to other previously cooler areas e.g. malaria. Pathogens that were restricted by seasonal weather patterns can invade new areas and find new susceptible species as the climate warms and/or the winters get milder. There is evidence that the increasing occurrence of tropical infectious diseases in the mid latitudes is linked to global warming. Insect-borne diseases are now present in temperate areas where the vector insects were non existent in the past e.g. trypanosomosis, anaplasmosis. Humans are also at an increased risk from insect-born diseases such as malaria, dengue, and yellow fever.

Vector borne diseases are particularly affected by weather patterns and long-term climatic factors strongly influence the incidence of outbreaks. Most of these diseases are caused by insects and their population dynamics is dependent on the prevailing weather conditions, specifically temperature and humidity. Climate change influences local weather conditions and therefore has a significant impact on the presence of insects and their geographical distribution.

Warmer temperatures are already enabling insects and microorganisms to invade and reproduce in areas where once they could not due to severely low temperatures and seasonal chills. A small rise in temperatures can produce a 10-fold increase in a mosquito population causing an increase of malaria cases hence, malaria is now occurring in several Eastern European countries as well as in the highland areas of countries like Kenya where historically cooler climatic conditions had prevented the breeding of populations of disease-carrying mosquitoes. Freshwater snails, intermediate hosts for Fasciolosis, a disease that affects millions of herbivorous animals and can also affect humans can now be observed in areas above 4200 meters in the highlands of Peru and Bolivia as milder temperatures and altered environment conditions are more favourable to their survival.

It is now evident that diseases carried by insects and ticks are likely to be affected by environmental changes because these creatures are themselves very sensitive to vegetation type, temperature, humidity etc. However, the degree of expansion of diseases is much more difficult to predict, because disease transmission involves many other factors, and not all will be affected to the same extent by environmental change. Therefore, by using historical disease records, present-day ground-based surveillance, remotely sensed (satellite) and other data, mathematical models are being developed that will describe the past, explain the present, and predict the future of vector-borne infectious diseases.