Disease Prevention and Control / Communicable Diseases / Malaria
Malaria Epidemics: Forecasting, Prevention, Early Detection and Control:
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Full-Text Report (52 pp, PDF) PAHO Malaria Page |
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Executive SummaryIdentification of epidemic-prone areas and populations at risk | Malaria epidemics are serious public-health emergencies. Typically, they occur with little or no warning in areas where the health system is unprepared to deal with the emerging problem. In most situations, however, epidemic conditions develop over several weeks, theoretically allowing time for preventive action. Even when an epidemic occurs, it may still take several weeks before it reaches its peak, so that some effective control may still be possible if implemented immediately. A rapid response is possible solely if national authorities in epidemic-prone countries adopt an "epidemic preparedness plan of action" based on a strategic approach to epidemic prevention and control. An epidemic preparedness plan of action should aim to
Identification of epidemic-prone areas and populations at risk There is a lack of reliable, validated maps with clearly demarcated epidemic-prone areas and methods for estimating populations at risk. Hard copy and sketch maps based on local expert opinion should be used for setting the boundaries of epidemic areas and plotting the distribution of cases, local population, availability of health services and any significant environmental modifications. Geographical information systems (GIS) are currently also being evaluated as tools for estimating populations at risk and decision-making in malaria epidemic-prone areas. Long-range forecasting (LRF), early warning (MEWS) and early detection (EDS) The LRF-MEWS-EDS continuum has the potential to provide complementary information with increasing accuracy and spatial resolution (continent-country-district-locality) but decreasing leadtimes (10–14 months to 1–2 weeks). However, many programs simply do not have the resources to implement the entire continuum of long-range forecasting, early warning and early detection. The capacity of countries in malaria epidemiology and planning malaria epidemic prevention and control is generally weak. Few are able to collect and analyze relevant data and process them rapidly enough to allow effective prevention or control. The keys to success will be capacity building, realistic planning and community awareness. It is more realistic to begin modestly and give priority to improving surveillance using a restricted number of validated indicators: the complexity of the system can be stepped up as staff capabilities improve, new information and techniques become available from research, and closer teamwork is established with other partners and information sources. Long-range forecasting Long-range forecasting is still a predominantly research-based technique. Current research is focused on how the El Niņo Southern Oscillation (ENSO) affects the risk of malaria epidemics in highland and desert-fringe areas. While more accurate prediction models and systems continue to be developed, rough and ready warning methods can already be used to advantage for prospective monitoring and validation; for example, the Southern Africa Malaria Control Program (SAMC) is translating seasonal climate forecasts into seasonal malaria forecasts. Early warning (MEWS) The full practical potential of MEWS has yet to be realized. Over the past few years, attempts have been made in Africa to transform MEWS from a research project into a practical public health tool. The method is showing promise in southern Africa where some countries now routinely use rainfall, temperature and population vulnerability as early warning indicators of malaria epidemics, and others also regularly evaluate drought and food security status. Early detection The group recommended that a system of weekly reporting should be introduced wherever possible, while recognizing that this is currently beyond the reach of some countries. For some, monthly reporting and a concerted effort to improve the quality of data collection and reporting would be a better starting-point. In countries with poorly developed laboratory diagnostic facilities, it may be more cost-effective to designate selected health centers with laboratory facilities in epidemic-prone areas as sentinel surveillance sites. Data from these centers could then be relayed to the district and provincial authorities on a weekly basis. Malaria sentinel sites now exist in many African countries, such as Angola, Botswana, Kenya, Malawi, Mali, Mozambique, Namibia, Niger, Senegal, and Uganda. Integration of malaria EDS into more general disease surveillance systems should be encouraged. It is likely to be beneficial in terms of both improving data quality and enhancing system efficiency provided that two conditions can be met: provision of appropriate training and feed-back at the peripheral level and surveillance approaches being consistent with malaria control needs. The drugs used to treat uncomplicated malaria in epidemics should be highly efficacious (at or above 95%) and safe and should offer good compliance. To date, artemisinin-based combination therapy, ACT, is the only appropriate treatment for uncomplicated malaria in falciparum epidemics and in mixed falciparum/vivax epidemics. The only exceptions are central America and Hispaniola where P. falciparum remains sensitive to chloroquine and sulfadoxine/pyrimethamine. In vivax-only epidemics chloroquine remains the drug of choice. Anti-relapse therapy with primaquine should be considered only once the epidemic subsides. Intramuscular-injectable artemether is the drug of choice for management of severe disease during epidemics because quinine use is impractical in most epidemic situations. If injectable artemether is not available, artesunate suppositories are recommended for emergency use in outlying areas when severely ill patients are unable to swallow oral medication. Where referral is impossible, treatment with rectal artesunate should be continued until oral drugs can be taken. Once malaria has been established as the cause of the epidemic, mass treatment of fever cases (MFT) with ACT is appropriate as a strategy to reduce mortality. There is no evidence to support mass drug administration (MDA), i.e. indiscriminate distribution of treatment to the entire population at risk. While the first priority in an epidemic is the prompt and effective diagnosis and treatment of malaria, vector control can significantly contribute to reducing the risk of infection and saving lives provided that it is well planned, targeted and timely. Anti-vector measures for epidemic prevention and control can be implemented effectively only if they are buttressed by an infrastructure of well trained personnel, adequate supplies and equipment, preparedness planning, and supervision and evaluation. Epidemic-prone countries without an infrastructure of this kind should develop one. Implementation of vector control is most cost-effective when used for prevention, and for control at the very start of an epidemic, and when high (>85%) coverage levels can be achieved. It can be used preventively for long-term suppression of transmission in the following situations: to hinder the resurgence of malaria in a previously controlled area, to prevent a gradual transmission buildup over years and/or seasonal transmission surge, and to target communities in which an epidemic is expected soon. Indoor residual spraying is especially well adapted to epidemic prevention and response. DDT, where effective, meets the criteria for situations in which resources are limited and a residual action beyond 6 months is required, provided WHOPES specifications are met and the requisite safety precautions for its use and disposal are taken. Synthetic pyrethroids are an effective alternative to DDT: they have a residual action of 2–6 months, are safer to apply than most other insecticides and still enjoy limited resistance. There is limited documented evidence on the impact of insecticide-treated mosquito nets (ITNs) in epidemic prevention and control. Community use of ITNs in most epidemic-prone areas is limited and, given the overriding importance of implementing epidemic control measures, distributing ITNs would be impractical. The effectiveness of ITNs is dependent on behavioral change. This requirement limits their suitability in most epidemic situations where ITNs are seldom used in the long non-transmission periods. In some circumstances, however, it may be quicker to implement ITNs for prevention and control than indoor residual spraying (IRS). This is likely to be the case where
Larval control is unsuitable for epidemic control but may be useful for prevention in exceptional circumstances where breeding sites are few, permanent, identifiable and accessible. There is no evidence to support the use of ULV space spraying (fogging) as a means of epidemic prevention and control.
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