February 4, 2011

Researchers Discover New Malaria Mosquito

Scientists have discovered a new type of mosquito that is unlike any that have been documented before and could complicate the fight against malaria even further.

Scientists from France collected mosquitoes from ponds near villages in Burkina Faso over a four-year period and said they identified some as a subtype of Anopheles gambiae -- which is responsible for most malaria transmissions in Africa. The new subtype is highly susceptible to infection with the malaria parasite and, because it likes to nest outdoors rather than inside, it can evade control measures more easily.

"They are very susceptible to the human malaria parasite, we know they belong to a species that has an exquisite preference for human blood, and we know they are abundant in the population," said Ken Vernick, who discovered the mosquito with colleagues at the Unit of Hosts, Vectors and Pathogens at the French National Center for Scientific Research in Paris.

Vernick said that it was not yet clear how much malaria transmission was coming from the new mosquito, but the team of researchers feared that the insect could be a major factor in the spread of the disease.

Vernick told Reuters in a telephone interview that it is "unlikely they're harmless," referring to the new type of mosquitoes.

Scientists said the new type may have evaded classification for some time since it rests away from human habitation where most scientific collections tend to be made.

Dr. Michelle Riehle, from the Pasteur Institute in Paris, France, one of the discoverers of the new mosquito, said when they examined the insects in the lab, they had found many to be genetically distinct from any A. gambiae insects previously recorded.

The team grew the unique subtype in the lab to study their susceptibility to the malaria parasite. Their findings showed that the new type of mosquito was especially vulnerable, more so than indoor-resting mosquitoes.

But Vernick cautioned that the new 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," Vernick said. "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, reporting their findings in the journal Science, said the new subtype could be quite a recent development in mosquito evolution and they urge for further studies to better understand the consequences for malaria control.

They also highlighted the need for more diverse strategies in the collection of insects and other specimens. The subtype is likely to have been missed because scientists in the past have only collected mosquitoes in and around homes, whereas the new subtype is found away from homes.

Dr. Gareth Lycett, a malaria researcher from the Liverpool School of Tropical Medicine in the UK, who was not involved in the discovery, said the findings could have important implications on the fight against 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," Lycett 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," he said.

"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," he added.

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

The WHO has called for faster research and development of new anti-malarial drugs and said last year that the international community could stop malaria deaths by 2015 if it contributed to massive investments in the fight against the disease.

But according to Vernick, discoveries such as this one add to the "never-ending battle" against the disease. "The parasite is smarter than all the immunologists that study it... and the mosquito is smarter than all the vector biologists that study it."

Malaria threatens up to half the world's population. Most of its victims are children under five in poor countries in sub-Saharan Africa.


Image Caption: The new mosquito is a subtype of Anopheles gambiae, which is responsible for most malaria transmissions in Africa. Credit: CDC


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