Global warming may push tropical diseases to new regions.
Published today, the effects of changing weather patterns on a number of diseases currently seen as tropical diseases are examined in a special issue of the journal Philosophical Transactions of the Royal Society B (which covers life sciences; the society's "series A" journal deals with physical sciences).
"Climate change represents a potentially serious threat to future human health," says Dr. Paul Parham, an organizer of the special issue and among its numerous authors.
It "seems unquestionable" that climate change will affect many, if not all, vector-borne diseases, Dr. Parham says. The papers presented raise questions not only about the extent of the effects of climate change, but also ask what impact other factors, such as public health response, will have on the risk of infections.
Vector-borne diseases such as malaria, Chagas disease and dengue, transmitted by mosquitoes and other carriers, presently have particularly huge effects in developing countries, and cause over a billion people to become infected and 1 million people to die every year, say the scientists.
"Although malaria causes the greatest global disease burden of all the vector-borne diseases," say the researchers, "other diseases such as dengue, West Nile disease and chikungunya are emerging and resurgent in some regions, increasing in prevalence and distribution."
Understanding climate effects, understanding the responses
It is as important to understand factors such as the decisions of public health authorities as it is to know what the effects of climate change will be on the diseases themselves, says Dr. Parham:
"This new collection of papers is clear and consistent in its message that different vector-borne diseases, transmitted by different vectors, will respond in different ways to changing weather and climate patterns.
Assessing risk and planning public health interventions is of vital importance for tackling these diseases in our changing climate."
The authors of the papers offer the following among their predictions, results and commentaries on the way climate change influences population health affected by vector-borne diseases:
- "About 2.4 billion individuals in a land area of nearly 20.0 million square km will potentially become exposed to the Asian tiger mosquito," a vector of encephalitis, dengue and yellow fever (Yiannis Proestos, et al.)
- The World Health Organization promotes a "practical focus on strengthening current disease control efforts" in addition to the efforts to predict and model the effects of climate change. Managing short-term climate risks "will in turn increase resilience to long-term climate change" (Diarmid Campbell-Lendrum, et al.)
- Emerging infectious diseases are "accidents waiting to happen" and "today, exploding human population, alterations in biodiversity and climate change have produced a real-time emerging infectious diseases crisis" (Eric Hoberg and Daniel Brooks)
- The risk assessment framework used by the UK's weather scientists at the Met Office "may guide assessments of vector-borne disease risks to humans" (Paul Parham, et al.)
- The effect of climate change on the burden of malaria "may be less important than effective interventions" against it - and a 'one size fits all' approach is "unlikely to be best" (Paul Parham and Dyfrig Hughes)
- There is an "emerging consensus" that climate warming "will continue to cause expansion of tick-borne disease in North America and Eurasia" (Richard Ostfeld and Jesse Brunner)
- Simulations predict that both a nematode worm parasite and its blackfly vector "are likely to become more abundant under future climate-change scenarios" - meaning serious consequences for what is currently the "neglected" tropical disease of river blindness, or onchocerciasis (Robert Cheke, et al.)
- 2050 climate projections are likely to have a positive health impact in Venezuela and Argentina in terms of a decline in new annual cases of Chagas disease, or American trypanosomiasis (Paula Medone, et al.)
- Cold-adapted mosquitoes could evolve "very rapidly" in response to higher temperatures (Nina Fefferman, et al.)
- Climate change may have varying effects on blacklegged tick-borne diseases - it may "maintain or increase" the transmission of the bacteria causing Lyme disease, but "inhibit" the transmission of certain viruses (Taal Levi, et al.)
- Recent climatic changes, particularly the temperature increase and fluctuations in rainfall patterns, "have contributed to the spread and maintenance of West Nile virus in various locations in southern Europe, western Asia, the eastern Mediterranean, the Canadian Prairies, part of the US and Australia" (Shlomit Paz).
Interbreeding of mosquito species has led to a "super mosquito" emerging in Mali, according to University of California Davis researchers in the news last month. See: Hybrid malaria mosquito is resistant to bed-net insecticide.
Also in January came news from other California researchers finding that our odor is not reliable enough to lead mosquitoes to bite us - what we breathe out is instead what guides the parasites. See: Exhaled carbon dioxide alerts malaria mosquito to human presence.