Malaria cases linked to homesteads in the Mamfene area, Ubombo, 1993
Linking malaria cases to individual homesteads, and plotting them at this "micro-epidemiological" level allows one to track down each case accurately in time and space. In this way small-scale environmental featres, which contribute to an increase in malaria risk, can be identified.
The figure shows malaria cases in Mamfene (one control area in the Ubombo district) plotted over four months. It is clear that most malaria cases are associated with the large swamp, where mosquitoes breed in great numbers. However, cases were also occurring recurrently at Point A which is further away from the swamp than mosquitoes tend to fly. There was an interruption period where no cases were reported for two months. The reason was that the control programme had come in to treat the patients, thus eliminating the parasite reservoir. In June, a new localised outbreak occurred at Point A which suggested that there might be some environmental features which allow mosquitoes to continue breeding in this locality.
Initial digitising was done at a scale of 1:250 000 and no unusual geographical features could be seen that were associated with the focus. Digitising was then carried out at 1:10 000 from aerial photos and the association between the localised malaria cases and a number of perennial and seasonal water bodies was clearly evident. The mosquitoes breeding in these ponds were causing renewed outbreaks as soon as a person with the parasite entered this locality. Such small-scale breeding sites, once identified, can then be targeted for environmental management, which would remove or modify the hazard points, so that they are no longer suitable for vector breeding. In this way GIS and epidemiology can be used to target areas for more focussed, long term, non- chemical methods of control.