Contrary to UN predictions – Malaria-carrying mosquitoes are disappearing in some parts of Africa, but scientists are unsure as to why.
Figures indicate controls such as anti-mosquito bed nets are having a significant impact on the incidence of malaria in some sub-Saharan countries.
But in Malaria Journal, researchers say mosquitoes are also disappearing from areas with few controls.
They are uncertain if mosquitoes are being eradicated or whether they will return with renewed vigour.
Data from countries such as Tanzania, Eritrea, Rwanda, Kenya and Zambia all indicate that the incidence of malaria is dropping fast.
Researchers believe this is due to effective implementation of control programmes, especially the deployment of bed nets treated with insecticide.
But a team of Danish and Tanzanian scientists say this is not the whole story. For more than 10 years they have been collecting and counting the number of mosquitoes caught in thousands of traps in Tanzania.
In 2004 they caught over 5,000 insects. In 2009 that had dropped to just 14.
More importantly, these collections took place in villages that weren’t using bed nets.
One possibility for the reduction in numbers is climate change. Patterns of rainfall in these 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.
But the lead author of the study, Professor Dan Meyrowitsch from the University of Copenhagen, says that he is 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 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”
The researchers are 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.”
False Alarm: Global Warming Increases Malaria, Dengue Fever Threat, UN Says
Global warming will put millions more people at risk of malaria and dengue fever, according to a United Nations report that calls for an urgent review of the health dangers posed by climate change.
Increases in rainfall, temperature and humidity will favor the spread of malaria-transmitting mosquitoes over a wider range and to higher altitudes, according to the 2007-2008 Human Development Report, released today. That could put 220 million to 400 million additional people at greater risk of the disease that kills about 1 million a year, mostly in Africa.
THE IPCC AND TECHNICAL INFORMATION. EXAMPLE: IMPACTS ON HUMAN HEALTH
1. This evidence is presented to the Select Committee to provide a perspective on the role of the Intergovernmental Panel on Climate Change (IPCC) in compiling and assessing technical information.
2. I am a specialist in the natural history and biology of mosquitoes, the epidemiology of the diseases they transmit, and strategies for their control. My entire career, more than thirty years, has been devoted to this complex subject. My research has included malaria, filariasis, dengue, yellow fever, St Louis encephalitis and West Nile encephalitis, and has taken me to many countries in Africa, the Americas, Asia, Europe and the Pacific. I spent 21 years as a Research Scientist for the United States Centers for Disease Control and Prevention (CDC). At present, I am a Professor at the Institut Pasteur in Paris, and am responsible for a new unit of Insects and Infectious Disease.
3. I have been a member of the WHO Expert Advisory Committee on Vector Biology and Control since 1998, and a consultant for several WHO Scientific WorkingGroups. I have worked for the World Health Organization (WHO), the Pan American Health Organization (PAHO) and other agencies in investigations of outbreaks of mosquito-borne diseases, as well as of AIDS and Ebola haemorrhagic fever and onchocerciasis. I was a Lead Author of the Health Section of the US National Assessment of the Potential Consequences of Climate Variability and Change, and a contributory author of the IPCC Third Assessment Report (see below). I have been Chairman of the American Committee of Medical Entomology of the American Society for Tropical Medicine and Hygiene, and of several committees of other professional societies.
4. The comments that follow mainly deal with the Health Chapters of IPCC Working Group II (Impacts, adaptation and vulnerability) in the second and third Assessment Reports, in which mosquito-borne diseases have figured prominently. But first I need to give you some background on mosquito-borne diseases. I will use malaria as an example. […]
The natural history of mosquito-borne diseases is complex, and the interplay of climate, ecology, mosquito biology, and many other factors defies simplistic analysis. The recent resurgence of many of these diseases is a major cause for concern, but it is facile to attribute this resurgence to climate change, or to use models based on temperature to “predict” future prevalence. In my opinion, the IPCC has done a disservice to society by relying on “experts” who have little or no knowledge of the subject, and allowing them to make authoritative pronouncements that are not based on sound science. In truth, the principal determinants of transmission of malaria and many other mosquito-borne diseases are politics, economics and human activities. A creative and organized application of resources is urgently required to control these diseases, regardless of future climate change.