Scientists have been left baffled as to why malaria- carrying mosquito's are disappearing in some parts of Africa.Controls such as anti-mosquito bed nets are having a significant impact on the incidence of malaria in some sub-Saharan countries figures show. However the incidence of mosquito's are also declining in areas with few controls as reported by Malaria journal researchers. It is unclear whether mosquito's are being eradicated completely or if their decline is due to environmental factors and they will then return.
Data from Eritrea, Tanzania, Kenya and Zambia shows the fast declining prevalence of mosquito's.Researchers are attributing this to effective implementation of control programmes such as the deployment of bed nets treated with insecticide.However teams of Danish and Tanzanian scientists say this that this is not the whole story. For over 10 years their research teams have been collecting and counting the number of mosquito's caught in thousands of traps in Tanzania, with over 5,000 caught in 2004. This figure has dropped to just 14 in 2009. These figures reflect collections carried out in villages where bed nets are not used.
Climate change has been considered as a major possibility for the major decline in numbers. Notably rainfall patterns were more chaotic in these regions of Tanzania and occurred outside rainfall season, which may have disrupted the natural cycle of mosquito development.Leading author of the study Professor Dan Meyrowitsch from the University of Copenhagen is not convinced that changing climate is the only reason.
"It could be partly due to this chaotic rainfall, but personally I don't think it can explain such a dramatic decline in mosquitoes, to the extent we can say that the malaria mosquitoes are almost eradicated in these communities."What we should consider is that there may be a disease among the mosquitoes, a fungi or a virus, or they're may have been some environmental changes in the communities that have resulted in a drop in the number of mosquitoes"
The research team also found anecdotal evidence that their discovery was not an isolated case.Prof Meyrowitsch added: "Other scientists are saying they can't test their drugs because there are no children left with malaria."They observed this in communities with no large interventions against malaria or mosquitoes. It may be the same scenario that the specific mosquitoes that carry malaria are declining very fast now"
Researchers are now unsure if mosquitoes will return to these regions. If they do, one particular cause for concern is the young people who have not been exposed to malaria over the past five or six years since the mosquitoes began to decline.
"If the mosquito population starts coming up again" says Professor Meyrowitsch "and my own assumption is that it will, it is most likely we will have an epidemic of malaria with a higher level of disease and mortality especially amongst these children who have not been exposed."