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close this bookMalaria Epidemics, Detection and Control Forecasting and Prevention (WHO - RBM - WHO - OMS, 1998, 90 p.)
View the document(introduction...)
Open this folder and view contentsI. GENERAL CHARACTERISTICS OF MALARIA EPIDEMICS
Open this folder and view contentsII. EARLY DETECTION AND CONTROL OF EPIDEMICS
Open this folder and view contentsIII. EPIDEMIOLOGICAL SURVEILLANCE, FORECASTING AND PREVENTION OF EPIDEMICS
View the documentREFERENCES
View the documentANNEX

ANNEX

Table A True Epidemics

Form of presentation

Main determinants

Parasites

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

Parasites

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