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close this bookMalaria Epidemics, Detection and Control Forecasting and Prevention (WHO - RBM - WHO - OMS, 1998, 90 p.)
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Open this folder and view contentsII. EARLY DETECTION AND CONTROL OF EPIDEMICS
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Table A True Epidemics

Form of presentation

Main determinants


Expected evolution

Primary control measures

· Sudden or explosive épidémic affecting a wide area almost immediately

· Abnormally prolonged and heavy rains
· Extensive floods of large rivers crossing dry plains
· Unusually warm humid and long summer in high-altitude valleys
· Abnormally prolonged dry seasons in well-drained, humid valleys, leading to formation of pools in river beds
· Prolonged periods of warm and relatively humid conditions in oases

· In Asia, the Pacific and the Americas, the process starts with a P. vivax epidemic, followed by a P. falciparum epidemic. If the epidemic potential continues for one or two more years, the P. vivax epidemic will be bimodal
· In tropical Africa, the epidemic will be due to P. falciparum

· Self-limited in space to the areas affected by determinant factors and in time to the relatively short transmission season
· The epidemic year is often followed by one or two years of high transmission and then a period of no transmission, forming a paraquinquennial cycle
· In very arid areas, one or more paraquinquennial periods may be missed; epidemics may also be very focal, limited to particularly favourable microclimates

· Emergency supply of drugs and strengthening of diagnosis and treatment facilities
· If feasible, to be carried out before the epidemic peak: space spraying or reimpregnation of bednets, in areas where they are used
· Strengthening capabilities for epidemic risk monitoring and emergency preparedness for following years
· If predicted in time: Residual spraying to prevent epidemic

· Massive destruction followed by displacement of large numbers of people, due to war or natural disasters

· As above

· Major epidemic following destruction, but subsiding after reconstruction

· Strengthening case management facilities and drug supply
· Vector control in refugee camps and villages
· Aid to reconstruction of water-management works

· Failure of ongoing malaria control; return to previous or higher endemicity

· Strengthening case management and drug supply
· Emergency care of refugee populations
· Space and/or residual spraying, if feasible. in refugee camps

· Serious socioeconomic upheaval creating new endemicity aggravated by reconstruction efforts

· Identification and control of new areas of high risk
· Where endemicity already reestablished, revision of of malaria-control strategy

· Progressive invasion of a large area by a succession of local severe epidemics

· Invasion by an exotic and highly efficient vector of ecologically receptive areas

· The highly increased vectorial ability is likely to result in dramatic epidemics of P. falciparum

· Even if locally controlled, it is likely that the new vector will continue to invade neighbouring areas

· Emergency establishment of diagnostic and treatment facilities for P. falciparum and management of severe malaria
· Vector control aimed at eradicating the invader
· Mobilization of intercountry and international resources

· Periodic expansion of a dangerous vector beyond its normal area of distribution

· P. vivax and P. falciparum as determined by immune status of population.

· Periodic cycles of 1-3 epidemic years followed by spontaneous remissions

· Strengthening of care services and drug supplies
· Vector control, if feasible before epidemic peak.
· Monitoring of risk factors for the following years

· Reinvasion of an area by a previously eliminated vector

· P. vivax and P. falciparum, as determined by the ecology of the area and population immunity

· Differs from other failures of control as the eliminated vector has to invade in a similar way to an exotic vector, even if it does so more quickly

· Strengthening of care services and drug supplies
· Vector control to reduce epidemic impact in current season, if feasible in time
· Preparation for vector control in the future, taking into account the feasibility of new vector elimination in the light of the conditions of the current reinvasion

· Penetration by dangerous vectors and parasites following the construction of roads and railways or the colonization of neighbouring areas

· Invasion by P. falciparum., e.g., of tribal areas of Amazonia

· Limited outbreaks among project workers

· Vector control in labour camps and chemoprophylaxis
· Diagnosis and treatment

· Series of linked epidemics following new settlements

· Establishment and strengthening of health care services as settlements develop
· Vector control, residual spraying
· Source reduction in planned settlements

· Often increasingly dramatic epidemics among original populations

· Strengthening of health care services
· Vector control whenever feasible
· Technical collaboration with organizations of local peoples

· Serious focal epidemics in areas of increasing stability

· Colonization of tropical jungle areas by successful agricultural settlers

· In both south-est Asia and South America, early colonies have suffered severely from P. falciparum epidemics

· As agriculture expands, contact with sylvatic vectors decreases, immunity develops and endemicity is established

· Development of diagnostic and treatment facilities
· Vector control during epidemic phase
· Adoption of national strategy for control of endemic malaria

· Explosive growth of urban areas in the tropics; malaria outbreaks affect mainly new urban settlements

· P. vivax or P. falciparum, or both, depending on the area

· Reduction of transmission by urbanization or by heavy organic pollution in slums
· Endemicity in proximity to permanent breeding places

· As above

· Establishment of highly efficient forest vectors in neighbouring tree plantations

· Sylvatic vectors adapted to human environment have produced P. falciparum outbreaks

· Establishment of high endemicity in resident population and continued epidemic outbreaks in labour force

· Vector control may eliminate the invader

· Creation of foci of high apparent endemicity in relatively isolated communities with very high population turnover

· Open-cast mining for gold or gems in jungle areas (high transmission, high consumption of drugs)

· Epidemics of multidrug-resistant P. falciparum commonly observed

· Continued high attack rates among newcomers; localized permanent epidemics
· Intensification of drug resistance

· Guidance and support to diagnosis and treatment
· Vector control, impregnation of bednets, curtains and other materials

· Labour camps (tropical aggregation of labour)

· P. vivax or P. falciparum or both according to the area

· Similar to above, but less selection of drug resistance, due to less drug pressure

· Diagnosis and treatment
· Chemoprophylaxis, if accompanied by vector control

Table B Resurgences or Failures of Control

Form of presentation

Main determinants


Expected evolution

Primary control measures

· Explosive resumption of transmission

· Rapid and complete loss of protective effect of control measures similar to that following the interruption of mass chemoprophylaxis

· P. vivax and/or P. falciparum depending on remaining parasite reservoir and vectors, as indicated by previous endemicity in the area

· After the epidemic wave, the previous endemicity will be reestablished, if there have not been any ecological changes

· Vector control before the peak of the transmission season to reduce the intensity of the epidemic wave
· Adoption of control strategy for endemic malaria

· Interruption of vector control in areas previously subject to periodic epidemics where transmission has been interrupted for several epidemic cycles
· The first season of epidemic risk will find a highly non-immune population

· P. vivax and/or P. falciparum depending on remaining parasite reservoir and vectors, as indicated by previous endemicity of the area

· After one or more epidemic waves, the area will return to the previous meso- or hypoendemic situation and be prone to future epidemics as in the period before control was instituted.

· Strengthening health care facilities and drug supplies
· Seasonal vector control could reduce epidemic impact
· Establishment of monitoring of epidemic risk indicators
It is important not to re-establish the previous unsustainable and excessive control campaign

· Progressive return of endemicity

· Interruption of effective residual spraying in highly endemic area

· As above

· Relatively subdued focal outbreaks as transmission is resumed following new construction and progressive loss of insecticidal effect

· Strengthening of health care facilities and logistics
· Adoption of control strategy for endemic malaria