Current methods used for the control of malaria invariably rely on prevention through minimizing exposure to mosquitoes, and drug treatment of clinical disease. The fact that the parasite has to rely on an insect vector for its transmission immediately highlights a weakness that is currently under-exploited. Malaria can be stopped by attacking the vector host effectively, as was proven by the WHO’s (ultimately abandoned) eradication campaign in the early 1950s.
By residual spraying of effective insecticides such as DDT, it is possible to reduce mosquito numbers to levels which do not permit the transfer of the parasite. Large scale public anti-mosquito measures such as the introduction of larvicides to breeding sites, non-selective residual insecticide spraying and effective drainage of potential breeding sites have all achieved the successful reduction of malaria in the past. Before the wide-scale use of DDT in India, for example, there were 75 million malaria cases and 0.8 million deaths from the disease yearly. This fell to 100,000 cases per year during the 1960s when around 18,000 tonnes of DDT were used annually. By the year 2000, when DDT use had been considerably reduced due to the development of resistance in mosquitoes and environmental concerns, there were over 3 million incidences of the disease (Sharma GK, 1987).
Personal anti-mosquito measures such as insecticide treated bed-nets have also been shown to greatly reduce the prevalence of disease in areas where they are used correctly. Admittedly, such anti-mosquito control strategies work best in areas of low transmission, as shown by the effective elimination of the disease from many temperate countries in the latter half of the 20th century. There are powerful arguments, however, for the introduction of free insecticide treated bed-nets to areas of Africa where the disease is endemic in order to attempt to reduce the terrible burden inflicted by the disease on children.
There are, however, many problems associated with effective anti-mosquito measures. The indiscriminate use of large amounts of insecticides may have environmental repercussions, and outcry by powerful environmental lobbyists, had, rightly or wrongly, greatly reduced the (very effective) use of residual DDT spraying until the United Nations Environmental Program sanctioned its use for malaria control (but not for agriculture) in 2000 (Taverne J, 2001). Mosquitoes have evolved resistance to widely used insecticides, both biologically and behaviorally. For example, the rationale behind spraying the inner walls of houses with insecticide was that mosquitoes settle there after taking a blood-meal. Extensive implementation of this technique was shown to select for those mosquitoes that flew straight out of the window after feeding. Other problems include the need to educate local populations effectively about the correct way to implement personal control methods, especially the need to maintain effective bed-nets.
In areas of high transmission, where large numbers of malaria cases are inevitable, there is a reliance on anti-malarial drugs to treat the disease. The drugs used vary depending on the local conditions (prevalence and specificity of drug resistance, economic status, etc). |
