30 August 2011

The case of the disappearing mosquitos

The BBC reports that Malaria-carrying mosquitoes are disappearing in some parts of Africa, but scientists are unsure as to why.

Controls such as anti-mosquito bed nets are having a significant impact on the incidence of malaria in some sub-Saharan countries. However,researchers say mosquitoes are also disappearing from areas with few controls.

Data from countries 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 more than 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. 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 said "What we should consider is that there may be a disease among the mosquitoes, or there 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. "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."

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."

This is interesting stuff. I suppose it is too much to hope that the disappearance will be permanent. As the scientists fear I would expect a return and an explosion of malaria in those areas. Given the lack of exposure among children I fear there will be many more deaths


nursemyra said...

How interesting. I wonder what is causing the decline

jams o donnell said...

It is intriguing isn't it

CherryPie said...

Yes very intriguing.

jams o donnell said...

Quite fascinating Cherie

susan said...

It's a strange thing when something that ought to be good news actually isn't. Another serious danger would be malarial mosquitos moving northwards to places where nobody has immunity.

Steve Hayes said...

I wonder why it hasn't been more widely reported.

jams o donnell said...

I hope it isn't the case Susan

I couldn't say but I'm glad to have found the story Steve

beakerkin said...


Insects have peaks and valleys that are normal. In some years tent catipilars and Japanese beetles are all over the place. In other years I can't find one.

Nature is quirky.

jams o donnell said...

That's very true Beak but I daresay scentists would have taken that into account. If it were a normal population downturn I doubt this would have been news

beakerkin said...

Perhaps Jams

We kid ourselves that we grasp dynamic systems such as climate change and wild life changes.

The most interesting phenomena is alien species. We can almost figure out what happens in small places like Islands. What is unknown is what happens in larger ecosystems. Nature is not so predictable when we add more variables to the mix.

What happens to the bats and fish that depend on this food source? Did they adjust? That part of the matrix would be interesting.

We never grasp it all. Maybe existence would not be fun if we did.

jams o donnell said...

True we know so much but know so little. I hope that the Climate scientists are utterly wrong.

Alien species are quite a problem , potentually ecological disasters. Japanese knotweed and foreign crayfish spring to mind. It's the worst where there are no proper predators.

On a bright note our red eared sliders are gone from Hornchurch. Perhaps they were captured or did not survive a cold winter.

beakerkin said...


The cold did not kill those turtles as they survive here in Staten Island where it is much colder. It is unknown if they can breed in these climes. Thus far we have not seen any young. Their lifespan is entirely unknown, but mine is 34 and reports of 70 plus are likely.

More interesting was someone brought an alligator snapper into the UK and it was caught and placed into a local zoo. Reliable reports of 150 years are likely
and we really do not know much about them. Their common cousins have a very high ratio of plant matter in their diet.

In an ideal world science is depoliticized. I am leery of fads linking their way into research. Eugenics was once rationalized with
pseudo science. I am more concerned
with charlatans like Al Gore likening those who say wait a second to racists and others as deniers ala Holocaust denniers.

I also refuse to deal with the Green movement until it rids itself of people with ulterior agendas like Deb Fink. Mainstream people like you and I can bandy ideas from a common perspective. We don't have to agree on much but that is what liberal democracy is about. When the face of the green movement is someone like Jared Diamond I will listen and take them more seriously.

jams o donnell said...

Perhaps they were captured and removed. I don't read the local paper so I could have missed it.

I support a lot of things that the Greens support but as part and parcel of a wider view. Like any political/social issue/religion the green movement attracts plenty of nutters. But that is the way of things sadly

SnoopyTheGoon said...

Let's hope the little bastards went vegetarian forever.

jams o donnell said...

Now that would be good!