MALARIA EPIDEMICS DETECTION AND CONTROL FORECASTING AND PREVENTION |
ANNEX |
Table A True Epidemics
| Form of presentation | Main determinants | Parasites | Expected evolution | Primary control measures |
| Sudden or explosive epidemic 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 re-established, 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 re-established, 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 |