London, Aug 31 (IANS): Scientists have been left baffled with reports that malaria-carrying mosquitoes are disappearing in some parts of Africa, BBC reported.

Figures in the Malaria Journal say control methods like use of bed nets treated with insecticide are making a significant impact on the incidence of malaria in countries like Tanzania, Eritrea, Rwanda, Kenya and Zambia.

But researchers say they are uncertain if mosquitoes are being eradicated or whether they will return with renewed vigour.

For more than 10 years now, a team of Danish and Tanzanian scientists have been collecting and counting the number of mosquitoes caught in thousands of traps in Tanzania.

In 2004, they caught more than 5,000 insects. In 2009, that dropped to just 14.

The scientists say it was important that these collections took place in villages that were not using bed nets.

One possibility for the reduction in numbers was climate change.

Patterns of rainfall in these 10 years were "more chaotic" in these regions of Tanzania and often fell outside the rainy season.

The scientists say this may have disturbed the natural cycle of mosquito development.

Lead author of the study, Dan Meyrowitsch from the University of Copenhagen, says he is, however, not convinced that it is just the changing climate.

"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 there may have been some environmental changes in the communities that have resulted in a drop in the number of mosquitoes," he said.

The researchers are now unsure if mosquitoes will return to these regions.

If they do, a particular cause for concern is that young people who have not been exposed to malaria over the past few years, may be affected.

"If the mosquito population starts coming up again, 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," Meyrowitsch said.