|Malaria Epidemics, Detection and Control Forecasting and Prevention (WHO - RBM - WHO - OMS, 1998, 90 p.)|
|III. EPIDEMIOLOGICAL SURVEILLANCE, FORECASTING AND PREVENTION OF EPIDEMICS|
|9. Epidemiological Information Systems|
In principle, malaria epidemics should be foreseeable, at least from the time of occurrence of the causative disturbances. The occurrence of an epidemic may therefore be considered as:
a) a failure to understand the local epidemiology of the disease, and particularly the interrelation of ecological and socioeconomic processes;
b) a failure to appreciate the consequences of certain economic development or health policies;
c) a failure to translate existing knowledge into appropriate monitoring and preventive activities.
Every epidemic provides an opportunity to refine epidemiological knowledge, detect changes in the geographical limits of the areas considered at risk and, in areas with a risk-monitoring system, find its weaknesses. The follow-up of epidemic control should therefore include the mobilization not only of the resources of the health services, but also those of other sectors and research institutions for the support of epidemiological studies to improve the capacity to forecast and prevent epidemics and the organization of epidemic preparedness.
The recognition of an area as subject to a particular category of epidemic risk gives some indication as to the set of risk factors which should be monitored. However, the further analysis of the local variability of malaria experience and the monitored indicators may show important variations in epidemic risk which should serve to refine the accuracy of the forecasting system. Those events which are not in line with expectations, and in particular unforeseen epidemics, should receive the most intense study. Such studies should be seen not only as means of improving the accuracy of the system and of adapting it to changing circumstances, but also as opportunities for extending intersectoral collaboration to obtain timely information on relevant variables and to improve the speed and relevance of preventive activities.
Graph 13 Nile river levels at Khartoum (normal channel: 1970-1990) compared with levels in epidemic years (1988, 1993 & 1994)
Graph 14 Monthly rainfall at Khartoum (normal channel: 1970-1990) compared with kown epidemic years (1988, 1993 & 1994)
Graph 15 Blue Nile levels at Wad Medani: normal channel (1970-1990) compared with levels on epidemic years (1975,1993 & 1994)
Historical research plays a major role, not only in helping to provide the most solid link with the studies and tested hypotheses of the past, but also in providing, for some specific areas, historical data which may help to identify associations of past epidemics with certain ecological or social variables, thus suggesting possible etiological relations, and therefore playing a role in the search for useful indicators of epidemic risk.
The study of actual epidemics may also show the importance of certain vectors, hitherto considered as secondary, in the genesis of some epidemics, as compared with the main vectors in the area concerned, e.g., A. annularis in parts of Bangladesh, rather than A. philippinensis (Rosenberg & Maheswary, 1982; Maheswary et al., 1993), or A. albitarsis in some epidemics in Colombia, rather than A. darlingi.