Insecticides as Strategic Weapons for Malaria Vector Control

Abstract

Malaria is a parasitic disease confined mostly to the tropical areas, caused by parasites of the genus Plasmodium and transmitted by mosquitoes of the genus Anopheles. Annually, nearly a million human deaths, mainly of children ≤5 years of age, are registered among 500 million cases of clinical malaria, whereas 2.37 billion people are estimated to be at risk of infection by P. falciparum, the most virulent among Plasmodia (Guerra et al., 2008). In 2007, the Bill and Melinda Gates Foundation, rapidly endorsed by the World Health Organization (WHO) and the Roll Back Malaria association, claimed for malaria eradication as the primary goal to be prosecuted (Roberts & Enserink, 2007). In order to achieve such an ambitious objective, several strategies are being adopted, involving multidisciplinary areas such as treatment, chemoprevention, vaccine research, health system assessment and of note vector control (Greenwood, 2008; Khadjavi et al., 2010). Indeed insecticides, which have already been essential components of previous malaria control programs, are supposed to play a key role in the new eradication program, where they will be employed either for indoor spraying or treated bednet approaches (Greenwood, 2008; Khadjavi et al., 2010). The present chapter will review the status of insecticides currently used for malaria vector control, along with present evidence on their benefits and risks in relation to the available alternatives. After a brief description of the Plasmodium life cycle, occurring either in mosquito vector (sexual reproduction) or in human host (asexual replication), the insecticides currently allowed by WHO for malaria vector control, including organophosphates (OP) for larval control and organochlorines (OCs), pyrethroids (PYs) and carbamates (Cs) for the control of adult mosquitoes, will be described; formulation, side effects and cost-effectiveness will be discussed. A special attention will be paid to 1,1,1trichloro-2,2-di(4-chlorophenyl)ethane (DDT), which is presently used by approximately fourteen countries, while several others are preparing to reintroduce it. Nevertheless, the concerns about the continued use of DDT and the recent reports of high levels of human exposure associated with indoor spraying amid accumulating evidence on chronic health effects will be taken in account. Furthermore, the big issue of growing resistances to the