HIV/AIDS and Malaria

AngloGold Health Service engaged Professor Richard Hunt, South African National Institute of Medical Research, an acknowledged expert on the subject, to conduct a malaria vector survey and insecticide susceptibility assay on mosquito populations at the mine. This is in anticipation of an integrated malaria control programme being developed and implemented in the near future. The research was undertaken in late October/early November 2004.

According to Prof. Hunt, "The survey carried out was designed to answer two questions that form the starting point of any malaria vector control programme, namely, which species of the Anopheles mosquito are transmitting malaria in the area, and what is their response to insecticides approved for malaria control."

Species identification and parasite infectivity

Species identification was carried out using DNA analysis protocols that are designed to separate the individual species. Samples of mosquitoes were subjected to biochemical analysis to determine whether they contained the parasites in or near to the salivary glands and therefore were potential transmitters.

Insecticide resistance tests

Five different insecticides were tested: The results indicated a low level of DDT resistance in the Geita funestus population, but both species groups showed full susceptibility to the pyrethroids, carbamates and organophosphates.

The main findings of the research reported by Prof. Hunt was that the three major mosquito vectors are all present at Geita mine, and that the parasite infectivity rate in the three species is in line with historical records for these species in East and southern Africa; that is funestus is the major vector with 6.7% infectivity, gambiae the next best with 3.03% and arabiensis apparently playing no role in malaria transmission at Geita. He notes, however, that these figures will change when sampling is done at different times of the year because the density of the different mosquito populations is dependent on seasonal fluctuations. So, for example, during the drier months, arabiensis will be more predominant and may have a higher infectivity rate than gambiae. This needs to be confirmed by additional mosquito sampling.

Prof. Hunt concludes that a malaria control programme is effective only if the vectors are controlled in addition to accurate diagnosis and treatment of the disease in humans. In addition, he notes that:

• The vector control operations must be targeted at those mosquitoes that are transmitting the parasites, in this case funestus and gambiae. These species are both highly anthropophilic (which means that they prefer feeding on humans) and prefer feeding and resting inside houses. This makes them amenable to control through indoor residual house spraying and through the use of insecticide treated bed nets if the community is willing to participate.
• Insecticide susceptibility tests indicate 100% mortality to the pyrethroid Deltamethrin and so the use of this insecticide is recommended for both house spraying and treated nets. Pyrethroids are recommended by the World Health Organization (WHO) because of their low mammalian toxicity and low impact on the environment. Screening of doors and windows of houses should be encouraged and these can be impregnated or treated with insecticides to make them more efficient.
• Larviciding and environmental management should be practised where appropriate, but these operations need to be carefully planned as they are expensive and not as effective on a broad scale as house spraying or treated bed nets.
• Implementation of the control programme needs to be accompanied by the collection of baseline information on malaria cases as this will be used as an indicator of success of the programme.

Mortality of funestus and gambiae groups exposed to various insecticides used in malaria control