Environment &Epidemiology Bill Brieger | 31 Dec 2009 06:51 am
Facing Malaria on Mount Kenya
The recently concluded climate change summit on Copenhagen did not stress health, let alone malaria, as much as other consequences of climate change. The Inter-governmental Panel on Climate Change has let us know a reason why attention to malaria in the climate debate may be somewhat confused:
Climate change may “have mixed effects on malaria; in some places the geographical range will contract, elsewhere the geographical range will expand and the transmission season may be changed.”
Kenya is one of those areas that has been reporting increases in the geographical range of malaria – particularly into the highlands.
Li and colleagues have been examining the Western Highlands over the period 2003-05 and documented variability of mosquito breeding sites by season and year. Their findings point to ways to improve larval habitat modifications as an important part of integrated vector management in such areas of seasonal and focal mosquito breeding.
An integrated approach to malaria control also is credited for a “pronounced reduction and possible interruption of malaria transmission in 2 highland areas of Kenya for a 1-year period and provides evidence that interruption of transmission was related to widespread annual IRS insecticide treatment and use of ACT as first-line treatment for uncomplicated malaria. Although both areas remain at risk for recurrence of malaria epidemics, our study provides evidence that interruption and eventual elimination of malaria in areas of unstable transmission may be achievable.”
The Mount Kenya highlands have been studied by Chen et al. who were concerned about possible increases in malaria cases reported over the past 10-20 years there. They found that, “Local malaria transmission on the Mount Kenya highlands is possible due to the presence of An. arabiensis. Land use pattern and land cover might be the key factors affecting the vector population dynamics and the highland malaria transmission in the region.” Human factors appear to play an important role –
On the Mount Kenyan highlands, the population has increased at least 25% over the past 20 years. Population density in Karatina and Naro Moru areas is estimated at 530 persons per square km, much higher than those in the further north areas, e.g., only 81 persons per square km in Nanyuki. With the increasing population on the highlands, enhanced human activities including deforestation, farming and livestock rearing could create more vector habitats. For example, at the site northwest to Karatina, hundreds of anopheline larvae were found in ditches holding spring water for crops in a field. The vectors emerging from this kind of habitat can play an important role in local malaria transmission.
More recently researchers from the Kenya Medical Research Institute with support from DfID “found that the average temperature in the Kenyan Central Highlands had risen from 17C in 1989 to 19C today.” Specifically the group reported that …
Before the 1990s malaria was absent from the region because the parasite that causes it can mature only above 18C. However, malaria epidemics began among the population as average temperatures went over the 18C tipping point. The number of people contracting malaria during these epidemics has increased seven-fold in the past decade. In 2005, malaria-carrying anopheles mosquitoes were discovered in Naru Moro, more than 6,175ft (1,900m) above sea level.
Climate change may partly explain malaria increases in Kenya’s highlands, as may more local human activities. The important lesson is that such epidemic-prone areas need to be closely monitored. A timely mix of control interventions can then be judiciously applied. As Noor and colleagues recommend:
As malaria interventions go to scale effectively tracking epidemiological changes of risk demands a rigorous effort to document infection prevalence intime and space to remodel risks and redefine intervention priorities over the next 10-15 years .