Malaria is a major public health problem in most countries of Africa. Over the past two decades, epidemics of plasmodium falciparum malaria often with high case fatality rates have been common in areas of unstable transmission in Africa. A large number of epidemics were reported in highland areas in East and Great lakes countries during the period 1985-1995.
In 1997-1998 when all countries in the sub-region Africa experienced malaria epidemic due to El Nino, Southern Oscillation (ENSO) now occurs at least yearly in several East Africa and Great lakes countries during the malaria transmission season.
Malaria epidemics occur in the western highlands, the arid and semi-arid lowlands of northern epidemiological zones in Kenya. The epidemics are associated with unusual climatic conditions especially rainfall and other factors such as suitable temperatures that favour breeding and longer survival of the malaria vectors.
Prediction methods for epidemics to alert implementers to either undertake epidemic prevention measures like Indoor Residual Spraying (IRS) or prepare to control the epidemic are still at developmental stages. Resources are scarce in developing countries finding it difficult to keep buffer stocks especially drugs to respond to outbreaks when routine services are without.
Once the epidemic has been detected the only cost effective measure is to institute case management activities. In the highlands, malaria prevalence above the epidemic threshold level last 4-6 weeks. Since the year 2000, major epidemics have been observed in the malaria epidemic prone districts. Malaria epidemics are some of the most serious public health emergencies with which health officials have to deal.
Malaria epidemics occur unexpectedly in areas where the health system is often unprepared to deal with the problem. They affect highly vulnerable populations (all age groups) with only limited immunity to malaria. This situation is exacerbated by public outcry and intense political pressure to intervene rapidly and decisively.
Epidemic conditions take few weeks to build up allowing time for preventive action. When it occurs, it takes several weeks to reach to its peak, effective control maybe possible if implemented in the early stages of development. The most important factor in reducing the impact of an epidemic is a timely response implementation of effective control measures as soon as it has been detected.
The longer an epidemic goes undetected with no measures for its control, the higher the cost of morbidity and mortality (Delacollette, 1999). Control measures are inherently costly. Implementation of control measures within a short delay after the epidemic has been detected might have some benefit. The maximum impact is however, when measures are implemented at the very early stages, usually within two weeks of onset, when deaths can be minimised.
Malaria upsurge is an annual event in the western highlands of Kenya which generally occurs between June and August. In some zones, the upsurges outdo the epidemic threshold. Widespread outbreaks of malaria epidemic involving the western highlands occur periodically and have been recorded between 1918 and 1950s when epidemic malaria was a scourge of the economically important Kenyan highlands.
Between 1950s and late 1980s the highlands enjoyed a free malaria epidemics period. This was as due to WHO driven eradication programme of the late 1950s which was terminated in the late 1960s (Republic of Kenya, MOH, 2001).
The most spectacular observed event in many occasions had been a dry spell preceding the outbreaks. The long rain season starts in April or May but the heat wave prevailing during the dry spell persists up to June or July. This is the most important factor that facilitates massive build up of vector density thus increasing the vectorial capacity.The increased transmission level of malaria in an area of susceptible population usually results in malaria epidemics.
The table below shows the association of anomalous weather conditions with malaria epidemics in Nandi District, Kenya. (Correlation of a 10-year retrospective data study- DOMC/WHO 2002)
Kenya northern arid and semi-arid lowlands are low malaria transmission areas. Malaria epidemics occur only during prolonged periods of flooding as observed during the EL Nino in 1998.
The temperatures are always right for the malaria vectors to breed when water is available and prolonged flooding makes such conditions to prevail. Other periods have short rain spells that do not enable build up of malaria vectors to levels that can result in malaria upsurge reaching the epidemic threshold proportions.
The national policy advices IRS in the epidemic prone Western highlands of Kenya in order to prevent the malaria upsurge.
Kenya National Strategic Plan of 2014-2018 identifies epidemic preparedness and response as a key approach to the control of malaria in the country. It proposes the development of a cost-effective monitoring system that includes forecasting, early warning and detection.
This will either lead to early recognition of epidemics and immediate implementation of control measures or the implementation of preventive measures before the epidemic starts. These efforts will improve the management of epidemics and reduce morbidity and mortality during epidemics.
The key to decisive reaction in the prevention and control of malaria is ‘preparedness.’ This means that effective surveillance and case detection will remain key to instituting response measures in the meantime. This is because the development of early warning systems is still in its developmental stages. However, so far this strategy has not worked well for the malaria epidemic response and containment in Kenya.
The strategy recommends that 80% of detected epidemics be contained within reasonable time. Due to the current health information systems (HIS) performance, it has been very difficult to detect epidemics as they build up, yet this is the ultimate requirement for effective response so as to significantly affect the magnitude or even avert it.
This scenario has made the Ministry of Health to modify its approach to malaria epidemic management. Since 2005, there has been a shift from the “preparedness and response” approach to the epidemic prevention and control approach.
The use of Indoor Residual Spraying (IRS) as a lead intervention in averting malaria epidemics in the highlands is a priority for the Ministry of Health. The NMCP, previously the Division of Malaria Control has been implementing well timed and coordinated IRS campaigns in 16 districts viewed to be highland epidemic prone. The counties are tabulated below:
Due to the heavy resource needs for the IRS campaigns, the Government of Kenya opted to scale up coverage in the 16 counties. The initial approach was to prioritise high risk areas within the counties and eventually progressively spiral to the entire counties. Due to increased support from the WHO, Global Fund and USAID, tremendous progress in terms of coverage has been realised. This is depicted in the IRS figure alongside.
The success of the malaria epidemic control relies on the choice of intervention to be undertaken at every stage within the epidemic cycle. The preparedness and response strategy requires the retention of buffer stocks of drugs, blood banks and infusions.
However, it is difficult to estimate the resource requirements including the right placement. This is heavily hinged on effective and prompt diagnosis as well as case management.
Long lasting insecticide-treated nets (LLINs) and insecticide-treated bed nets (ITNs) can be useful in containing epidemics among the nomadic communities. The two are effective since they are tools that can be easily carried or used anywhere provided they are used correctly.
Other vector control methods may also be employed. However, due to the acuteness of the epidemics, there is often a very short lead time to enable a credible response to be mounted.
The use of methods such as environmental management, house screening and biological agents of control is practically difficult. The methods may fail to produce the rapid desired effects on transmission in epidemic situations.
Ideally, these vector control options should be implemented on a routine basis as part of the community strategies and as control approaches to reducing malaria causing vectors. It is important to note that these methods have been implemented in Kenya over time.
However, due to lack of capacity to sustain them, they have yielded limited results in terms of malaria epidemic control. Only one county, Trans-Nzoia county has been able to utilise this strategy widely under a programme referred to a 'healthy villages'.
In other areas such as in lowlands, arid and semi-arid, the prediction of malaria epidemics is very difficult. This also makes the epidemic control difficult. Although vulnerability assessment of factors such as prolonged drought, preceding heavy rainfall and flooding can provide forecast, the expansive nature of the settlements and nomadic nature of the population makes it difficult to institute any epidemic prevention strategy.
The common approach has been to focus on effective diagnosis and prompt treatment of cases. It is important to note that the use of ITNs/LLITNs is also very useful among internally displaced persons during floods.
Article Prepared By
J Sang - Division of Malaria Control
Ministry of Health