9 December 2009 | EN
Mosquitoes that spread insect-borne diseases digest blood quicker and feed more often in warmer weather
Developing countries must invest in their own research to tackle insect-borne disease and climate change, writes George Kasali.
Climate change is likely to increase the already huge toll of illness and death from insect-borne disease in the developing world.
More than three billion people are already estimated to be at risk from the combined impacts of bilharzia, dengue fever, filariasis, leishmaniasis and river blindness.
Malaria alone causes about one to two million deaths a year. And the overall personal, social and economic burden is even higher due to the impact, year in and year out, of an estimated 300 million cases.
To the list must be added Chagas disease, Lyme borreliosis, plague, Rift Valley fever, sleeping sickness, tick-borne encephalitis, tularaemia, West Nile virus and yellow fever.
Many of these are major causes of hospitalisation in poor countries and are also subject to complex and often unknown impacts from climate change.
In the absence of concerted help from the industrial world — the main contributor to climate change risk — it is clear that developing countries must learn to tackle insect-borne diseases themselves. That means investing much more in local research and development (R&D).
The risk factors
Insect-borne diseases are spread by blood-sucking insects such as mosquitoes, ticks, fleas and flies. Controlling these diseases requires understanding the environmental, social and economic risk factors associated with their transmission and infectiveness.
Some agricultural practices, for example, can increase risk by providing breeding sites for mosquitoes or other disease-carrying vectors. Paddy rice production, irrigation and dam building have all been shown to increase the risk of disease transmission, as have deforestation and other forms of landuse change.
Unplanned urbanisation also favours vectors. The harsh realities of rural life are driving people into urban centres, creating slums with inadequate housing, poor water quality and sanitation, and no garbage or stormwater management. Discarded plastics, tins and tyres provide ideal breeding sites for mosquitoes when rainwater collects in them.
And high levels of malnutrition arising from food insecurity and poor diet weakens immunity, rendering entire communities susceptible to disease.
But by far the biggest risk factor is the lack of R&D capability in developing countries. Instead of surveillance, prevention strategies and health research, inadequate health facilities and low purchasing power are forcing people into self-medication and inappropriate drug use.
One tragic outcome has been the development of widespread drug resistance by malaria parasites, making the disease deadlier and costlier to treat.
Climate change shock
Now comes the shock of learning that developed countries have saddled poor countries with the additional risk from climate change, which is conservatively estimated to be causing around 200,000 extra deaths each year from malnutrition, diarrhoeal disease, malaria and floods, almost all in developing countries.
For insect-borne disease, part of the threat from climate change lies in the effect of temperature on vectors in the range 14–40 degrees Celsius: outside this range the survival of vectors and parasites begins to wane.
Malaria mosquitoes digest blood quicker and feed more often in warmer weather, speeding up transmission — and malaria epidemics have occurred with an increase of just two degrees Celsius above the mean monthly maximum temperature.
Vector multiplication is also affected by rainfall and humidity. It is not uncommon to experience increases in malaria cases of between 200 and 400 per cent during periods of flooding.
Although the Intergovernmental Panel on Climate Change indicates that climate change could alter the incidence and geographical distribution of vector-borne diseases, the impacts are complex and have yet to be fully understood.
Local R&D imperative
The top priority in the fight against vector-borne diseases, therefore, is the development of R&D capacity in developing countries. Research is urgently needed to generate scientific knowledge for developing technological solutions to health problems in general and vector-borne diseases in particular.
For economic reasons too, it is wrong for the governments of developing counties to relinquish their own R&D responsibilities in favour of research driven by donor organisations. R&D is also the cornerstone of socioeconomic development and the main driver of economic competitiveness.
Neglect of R&D explains why developing countries — despite possessing more natural resources than industrial nations — continue to wallow in poverty and disease.
George Kasali is a microbiologist at Copperbelt University, Zambia, and a member of the research network, Energy and Environmental Concerns for Zambia.
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