Mosquitoes 'disappearing' in some parts of Africa

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.

'Chaotic rainfall'
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."

By Matt McGrath Science reporter, BBC World Service
http://www.bbc.co.uk/news/health-14685612

Malaria claiming more British birds

Malaria is killing growing numbers of British birds including nightingales, sparrows and chaffinches, say scientists who claim climate change is fuelling the disease. 

Twenty years ago few British species showed regular signs of infection but now some 30 types are infected, monitoring projects have found.

The problem is linked to a rapid growth in mosquito populations, which is attributed to a rise of about 1C in global average temperature.

The proportion of house sparrows infected has risen from less than 10 per cent to 30 per cent, according to Laszlo Garamszegi, of the Doñana biological station near Seville in Spain.

He carried out malaria infection analysis into over 3,000 species around the world, comparing recent information to that dating back to 1944. The study is published in the journal Global Change Biology.

He said: "It does show trends we ought to be worried about."

The avian version of malaria cannot be passed to humans.

Ben Sheldon, professor of ornithology at Oxford University, said: "There is very convincing evidence that a wide range of biological processes are altering in response to climate change."
http://www.telegraph.co.uk/earth/wildlife/8700698/Malaria-claiming-more-British-birds.html

Spermless mosquitoes hold promise to stop malaria

Scientists have created spermless mosquitoes in an effort to curb the spread of malaria.


Experts say that this is an important first step toward releasing sterile males into the wild to reduce the size of mosquito populations.

Malaria kills around one million people worldwide every year, and in Africa alone, accounts for 20% of all childhood deaths.

The work is reported in Proceedings of the National Academy of Sciences.

Insect sterilisation isn't new: scientists have attempted to control the sleeping sickness-carrying tsetse fly by exposing them to radiation to render them sterile.

A similar approach has been successfully used against the potatoes weevil in Japan and the tropical screwworm that attacks cattle.

Frail fly
However, exposing mosquitoes to radiation has tended to leave male mosquitoes frail, and unable to compete in the frenzied mating aerobatics that Anopheles gambiae - the world's most efficient malaria vector - enjoys.

Now scientists have developed an alternative route to mosquito sterility.

Entomologist Flaminia Catteruccia from Imperial College London enlisted the help of her graduate student Janis Thailayil in the search for how to make male mosquitoes sterile but leave them otherwise unharmed.

Mr Thailayil injected 10,000 mosquito embryos with tiny fragments of RNA designed to turn off a gene - called zpg - that is essential for normal sperm development.

After months of laborious work, the researchers created around 100 spermless mosquitoes, and showed that females were just as willing to mate with these males as with fertile ones.

Dr Catteruccia explains that female mosquitoes mate only once in their lives. If scientists can trick them into thinking that they have successfully mated, then they will continue to lay their eggs without knowing that they have not been fertilised.

"You [could] in principle release large numbers of sterile males over many generations… and eventually all the females will have mated with the sterile males and…you can really reduce the number of mosquitoes," explained Dr Catteruccia.

This would gradually reduce the number of hatching mosquitoes. And hopefully help eradicate what many consider to be the single most dangerous insect species for mankind.

However, Dr Catterucci warns that this is only a proof of principle. The method her team used to create the spermless males would be far too labour-intensive to flood wild populations with enough spermless males to have any effect on their numbers.

However, knowing that females don't notice whether they are receiving sperm or not is still an important step, she said.


By Jennifer Carpenter

Science reporter, BBC News


http://www.bbc.co.uk/news/science-environment-14422440

The Origin of Malaria: The Hunt Continues

ScienceDaily (July 22, 2011) — The agent of malaria has been found in the greater spot-nosed monkey, also known as putty-nosed monkey (Cercopithecus nictitans), a small African primate derived from a line different to that of humans, gorillas and chimpanzees. This discovery challenges current thinking on the origin of the parasite and introduces a key element in the fight against malaria: knowing how it has adapted to the human species will make it possible to target its weaknesses.

This work stems from research carried out by CNRS researchers in association with other organizations(1) and is published on the 4 July 2011 in the journal PNAS.


Malaria, also known as paludism, is one of the greatest global scourges. This pathology, which causes a million human deaths each year, is especially rampant in Africa. The question of whether the primary infection originated from rodents or birds has long remained unanswered. Also found in gorillas, it was thought that the parasite was specific to hominids(2).

By working on the subject, a team of CNRS researchers headed by Franck Prugnolle and François Renaud of the Laboratoire MIVEGEC(1)(CNRS/IRD/Université Montpellier 1), jointly with the Centre International de Recherches Médicales de Franceville in Gabon, and in collaboration with other organizations(4), has demonstrated the presence of Plasmodium falciparum, the agent of malaria, in the greater spot-nosed monkey (Cercopithecus nictitans), a small African monkey derived from a line different to that of humans. The origin of the parasite probably predates the origins of the African hominids line.

The presence of Plasmodium falciparum in this Old World Monkey opens the way to the analysis of the genome of the parasite found in this species. Comparing its sequence with that (already known) of falciparum in humans will enable researchers to discover the molecular signatures of the human parasite and to find out how it has adapted to humans. Knowing the weaknesses of the parasite will be a major asset in combating malaria.

(1)Centre International de Recherches Médicales de Franceville au Gabon, IRD, Université Montpellier 1, Université de la Méditerranée, Université de Toulouse, University of California and Université de Brazzaville.

(2)The hominids line comprises two branches: humans and large monkeys (gorillas, chimpanzees and orangutans).

(3)Laboratoire "Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle"

(4)Université de la Méditerranée, Université de Toulouse, University of California and Université de Brazzaville.

http://www.sciencedaily.com/releases/2011/07/110722130301.htm

Mosquito-eating spider likes smelly socks

Not the most appealing-looking house guest,
but it could help combat malaria

Wednesday, 16 February 2011

By Victoria Gill
Science and nature reporter, BBC News

A spider that preys on the malaria-carrying mosquito Anopheles gambiae is attracted to the odour of sweaty socks, according to a study.

Scientists in the UK and Kenya used previously worn socks in an experiment to find out if the spider, like its prey, was attracted to human odours.

The jumping spider appears to have evolved an affinity for smelly human feet in order to help find its prey.
The team reports its findings in the journal Biology Letters.

They say that people might be able to "recruit" this East African jumping spider, Evarcha culicivora, in the battle against malaria by encouraging the arachnids to live in their homes.

Smelly experiment

Fiona Cross, from the University of Canterbury, and Robert Jackson, from the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya, carried out the study.

They were interested in this species because it is the only known predator that specifically preys on blood-carrying mosquitoes.

"We had a suspicion that human odour was attractive to the spiders before we even ran the experiment," Ms Cross told BBC News. "We generally find these spiders in the tall grass next to houses or other buildings occupied by people."

To test this suspicion, the team devised an aroma-based experimental set-up called an olfactometer.
They put each "test spider" into a small holding chamber into which air was pumped, either from a box containing a clean sock or one containing a worn (and therefore smelly) sock.

Each spider was able leave its holding chamber at any time and escape into an exit chamber, which did not have sock-scented air pumped into it.

The spiders supplied with the aroma of worn socks always remained in the holding chamber for longer than those exposed to the freshly washed sock.

Ms Cross said it was "unprecedented that a spider should find human odour attractive".

But, she added, the discovery tied in with some of the spiders' remarkable behaviour.

"When they smell blood, they can launch into feeding frenzies where they kill up to 20 mosquitoes in rapid succession, and not necessarily to eat all of them," she explained.

"We need to learn more about why they do this - they really do go quite crazy when they are in the vicinity of blood."

Anti-malaria arachnid

It may be a rather ugly, bloodthirsty little creature, but Evarcha culicivora could help in the ongoing and complex battle against malaria.

"It's something that's there in the environment for free," said Ms Cross. "So why not do what we can to find out about this remarkable predator?"

She and her colleagues are currently trying to find out what exactly people might be able to do to attract the spiders into their homes, without also attracting the mosquitoes.

The scientists say that, in malaria zones, people should welcome these particular creepy crawlies into their houses.

http://news.bbc.co.uk/earth/hi/earth_news/newsid_9398000/9398408.stm
(Submitted by Dawn Holloway)

New mosquito type raises concern

3 February 2011 Last updated at 19:02
By Jonathan Amos Science correspondent, BBC News

Scientists have identified a new type of mosquito.

It is a subgroup of Anopheles gambiae, the insect species responsible for most of the malaria transmission in Africa.

Researchers tell Science magazine that this new mosquito appears to be very susceptible to the parasite that causes the disease - which raises concern.

The type may have evaded classification until now because it rests away from human dwellings where most scientific collections tend to be made.

Dr Michelle Riehle, from the Pasteur Institute in Paris, France, and colleagues made their discovery in Burkina Faso, where they gathered mosquitoes from ponds and puddles near villages over a period of four years.

When they examined these insects in the lab, they found many to be genetically distinct from any A. gambiae insects previously recorded.

The team grew generations of the unique subtype in the lab to assess their susceptibility to the malaria parasite and this revealed them to be especially vulnerable, more so than indoor-resting insect types.

But Pasteur team-member Dr Ken Vernick cautioned that these mosquitoes' significance for malaria transmission had yet to be established.

"We are in a zone where we need to do some footwork in the field to identify a means to capture the wild adults of the outdoor-resting sub-group," he told BBC News.

"Then we can test them and measure their level of infection with malaria, and then we can put a number on how much - if any - of the actual malaria transmission this outdoor-resting subgroup is responsible for."

The researchers report that the new subgroup could be quite a recent development in mosquito evolution and urge further investigation to understand better the consequences for malaria control.

They also emphasise the need for more diverse collection strategies. The subtype is likely to have been missed, they say, because of the widespread practice of collecting mosquitoes for study inside houses. In one sense this has made sense - after biting, mosquitoes need to rest up and if they do this inside dwellings, the confined area will make them an easier target for trapping. However, the method is also likely to introduce a bias into the populations under study.

Commenting on the study, Dr Gareth Lycett, a malaria researcher from the Liverpool School of Tropical Medicine in the UK, said it was an interesting advance that might have important implications for tackling malaria.

"To control malaria in an area you need to know what mosquitoes are passing on the disease in that district, and to do that you need sampling methods that record all significant disease vectors," he told BBC News.

"You need to determine what they feed on, when and where, and whether they are infectious. And where non-house-resting mosquitoes are contributing to disease transmission, devise effective control methods that will complement bed-net usage and house spraying.

"A recent 12m-euro multinational project (AvecNET), funded by the European Union, and led by the Liverpool School of Tropical Medicine has the specific aims of doing just this."

According to the World Health Organization (WHO), there are more than 200 million cases of malaria worldwide each year, resulting in hundreds of thousands of deaths, most of them in Africa.

Malaria is caused by Plasmodium parasites. The parasites are spread to people through the bites of infected female Anopheles mosquitoes.

http://www.bbc.co.uk/news/science-environment-12352565
(Submitted by Dawn Holloway)