Integrated control of malaria and other vector diseases is crucial

Jun 15 2008

Combating malaria and other so-called vector diseases with chemical controls is increasingly ineffective, besides being hazardous for humans and the environment. These chemical controls must therefore be eliminated. In order to combat the diseases that insects and ticks transmit, all possible strategies must be united.

Only then can we successfully combat these stubborn and escalating disease threats. Prof. Willem Takken made this proposal during his inaugural address as Professor of Medical and Veterinary Entomology at Wageningen University (the Netherlands).

Even now, says Prof. Takken, the many human and animal diseases transmitted by insects and ticks (the so-called vector diseases) claim countless lives in the world, not only in developing countries but also increasingly in the West. Government agencies and public bodies should make combating these diseases a top priority.

Due to the intensification of international commerce and tourism, more tropical and sub-tropical diseases find their way to Europe. In addition, changes in climate mean that these diseases can more often thrive in moderate climate zones. Examples include Bluetongue virus, which recently appeared in the Netherlands, and the increase in Lyme disease, but also West Nile virus, dengue and chikungunya.

Every year, 4 billion people are exposed to malaria worldwide and 500 to 600 million of them become infected. Initially, in the 1940s and 1950s, the disease was combated very successfully with DDT. However, it gradually became apparent that the insects were becoming resistant to DDT and that this pesticide had very detrimental effects on human health and the environment. This led to DDT being banned in many countries, which in turn meant that the control of the disease virtually stopped between 1969 and 1999.

Prof. Takken is alarmed that some countries have again started using DDT. It has been shown that chemical control measures only work for a limited time and are not sustainable. Therefore an entirely different strategy must be developed which will provide a lasting solution to the malaria problem. He draws attention to the biological crop protection agents used for controlling pests and diseases in greenhouse horticulture. Currently, 95% of all vegetables from greenhouse horticulture in Western Europe are grown without insecticides. Prof. Takken wondered why this approach was not being used with vector diseases. Therefore he set the goal of controlling malaria without the use of chemical pesticides.

According to Prof. Takken, there must be more coherence in combating vector diseases. Important steps have been taken in recent decades towards a new approach for controlling malaria. The staff of Wageningen University have contributed to many of these steps, such as a cloth impregnated with a fungus that affects mosquitoes, or more recently, the development of scent traps to lure malaria mosquitoes away from houses and huts and then catch them.

But there are also other strategies, not only spectacular ones such as the biological control of larvae or the genetic modification of mosquitoes so that they can no longer transmit malaria, but also effective everyday methods, such as improving houses so that they keep mosquitoes outside, or better management of surface water where mosquitoes lay their eggs.

Takken argues for what he calls the integrated vector management concept, which takes account of all factors that play a role in the spread of malaria. The risks - which are already obvious - require immediate measures; there is no time to wait for new vaccines or new, acceptable chemical control measures.

Takken cites three scientific and technological developments which could be very important: the major developments in the area of molecular biology, the great progress that has been made with chemical ecology and the new developments in Geographic Information Systems and Remote Sensing. Takken proposes developing a strategy to deal specifically with the insects and ticks that are responsible for many diseases in humans and animals.

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