MALARIA: Smelly chemicals confuse mosquitoes

1 June 2011 By James Gallagher

 Female mosquitoes follow a trail of carbon dioxide
Chemicals which interfere with a mosquito's ability to sniff out humans have been developed by US scientists, according to research in Nature.

It is hoped they could be used to develop the next generation of mosquito traps and repellents.
A UK expert said the discovery could be a "major step forward" if the chemicals were safe and cheap.
Blood sucking female mosquitoes use carbon dioxide in exhaled breath to track down humans.
They can detect minute changes in the concentration of the gas.
This knowledge is already used in carbon dioxide traps, but requires dry ice or gas cylinders - which mean they are rarely used in developing countries.
Researchers have been looking for chemicals which can disrupt or confuse a mosquito's carbon dioxide sense.

Deception
Scientists at the University of California, Riverside, tested smelly chemicals on three species of mosquito: Anopheles gambiae, which spreads malaria; Culex quinquefasciatus, which spreads filariasis and West Nile virus; and Aedes aegypti which spreads dengue and yellow fever.
The researchers say that these insects combined infect half a billion people each year, some in at risk countries will be infected multiple times in their lifetime, and cause millions of deaths.
The researchers identified three groups of chemicals, which disrupt a mosquito's carbon dioxide receptors.
One mimicked carbon dioxide and could be used as bait in insect traps, another prevented the mosquito from detecting carbon dioxide and the last group tricked the mosquito's brain into thinking it was surrounded by huge quantities of the gas - so it could not pick which way to go.

 

Anopheles gambiae is responsible for the vast majority of malaria cases in Africa Professor Anandasankar Ray, from the University of California, Riverside, said: "These chemicals offer powerful advantages as potential tools for reducing mosquito-human contact, and can lead to the development of new generations of insect repellents and lures.

"The identification of such odour molecules, which can work even at low concentrations, and are therefore economical, could be enormously effective in compromising the ability of mosquitoes to seek humans, thus helping control the spread of mosquito-borne diseases."
Carbon dioxide is not the only way mosquitoes can find their dinner however, as the smell of human sweat and skin can also be used.
Dr James Logan, from the London School of Hygiene and Tropical Medicine, said: "Whilst this is an exciting study, the authors are yet to show that the chemicals are capable of protecting a human being from being bitten.
"Although carbon dioxide is an important cue for mosquitoes, we know that mosquitoes respond differently to a trap releasing carbon dioxide than to a real human being, which releases a complex mixture of many attractive chemicals, heat, visual cues and moisture.
"The key question is - do the 'response modifying odours' actually protect a human being?"
The chemicals also need to be used at high concentrations, which could be hazardous to human health. The researchers say their next step is to develop safer chemicals.
Dr Nikolai Windbichler, from Imperial College London, said work needed to be done to ensure they were safe and could be produced at low cost.
He added: "These compounds have novel and desirable properties because they can confuse the mosquitoes' host seeking behaviour even when the substances are no longer present or the mosquitoes have left the area of application.
"This, if realised, could be a major step forward and could protect large groups of people or large areas, something that is not currently feasible with existing repellents."
Mark Stopfer, from the US National Institutes of Health, said the study offered "a promising line of defence."
http://www.bbc.co.uk/news/health-13614781

MALARIA: Malaysia follows Caymans with surprise GM mosquito trial

Shiow Chin Tan: 28 January 2011

 Flickr/CharlesFred: The mosquitoes were released in an uninhabited region of the remote district of Bentong

[KUALA LUMPUR] Malaysia became the second country in the world to release genetically modified (GM) mosquitoes into the wild in a trial whose timing has surprised international and local scientists as well as protesters.
The country's Institute for Medical Research announced this week (26 January) that around 6,000 GM male Aedes aegypti mosquitoes had been released at an uninhabited, forested site in the inland district of Bentong in Pahang state last month (21 December).
The trial passed all its regulatory hurdles last year. But the actual release took many by surprise — even the head of Malaysia's Genetic Modifications Advisory Committee, Ahmad Parveez Ghulam Kadir, admitted he was unaware that it had taken place.
In recent days local media had reported that the release had not yet occurred because of bad weather. Meanwhile the international press agency AFP had said that the release was delayed because of protests by nongovernmental organisations. It quoted a senior government official, Mohamed Mohamad Salleh, the biosafety department's director of research and evaluation, as saying that the trials had been postponed.
The trial also involved the release of 6,000 ordinary male mosquitoes and both groups were killed with insecticides in early January, with monitoring to continue for several months, said the institute in a press release.
Scientists are comparing the flying ranges and survival rates of the two groups.
Offspring of the mosquitoes die before reaching sexual maturity in the absence of the antibiotic tetracycline. It is hoped this strategy could be used to cut mosquito numbers and fight dengue fever, a disease whose incidence has risen dramatically in recent decades.
No further release can occur until post-trial monitoring is completed in accordance with the guidelines laid out by the advisory committee, with the results analysed and presented in peer-reviewed scientific journals or at meetings.
Releasing the GM mosquitoes in an inhabited area — which was part of the application the institute and its partner in the project, UK-based biotech company Oxitec, originally made — would have required the institute to gain the consensus and approval of local communities via a public forum at least two weeks before the release.
Lim Li Ching, senior biosafety researcher at the non-profit Third World Network, said: "In their interpretation of the conditions [of the approval] they did not have to organise a public forum for the release in an uninhabited area".
She said that the institute should have been more transparent about its actions considering the criticisms about excessive secrecy that surrounded trials done by Oxitec on the Caribbean island of Grand Cayman in 2009.
Ahmad Parveez emphasised that the release was small-scale (6,000 compared with Grand Cayman's three million), that the mosquitoes would all die within the monitoring period and that the goal was a modest one of data collection rather than trying to suppress the local mosquito population.
The campaigning organisation Genewatch UK recently published a report saying that the original risk assessment by the Malaysian GM Advisory Committee was incomplete and lacked full transparency because it did not list the potential hazards it had identified and its evaluations of their likelihood, consequences and estimated overall risk.

http://www.scidev.net/en/news/malaysia-follows-caymans-with-surprise-gm-mosquito-trial.html

MALARIA: Malaysia to release GM mosquitoes into the wild

Shiow Chin Tan
2 November 2010

An OX513A mosquito

Malaysia will soon take the controversial step of releasing genetically modified (GM) mosquitoes into the wild as part of an experiment to test their survival in natural conditions.
The move was approved by the country's National Biosafety Board last month (10 October) and will make the nation the first major country in the world to release GM Aedes aegypti mosquitoes for field testing — second only after the Cayman Islands in 2009.
The mosquitoes, known as OX513A, have been developed by Malaysia's Institute for Medical Research (IMR) and the UK-based biotech company Oxitec to control the dengue virus, which is transmitted by A. aegypti.
A total of 4,000–6,000 male GM mosquitoes are expected to be released within the next couple of months, along with a similar number of unmodified male mosquitoes.
The male GM mosquitoes mate with normal females to produce larvae that are unusual because of an extra enzyme they produce. This enzyme accumulates in the larvae to a level where it becomes toxic and kills them. The larvae's only hope for survival is if the antibiotic tetracycline is present — because it mops up the enzyme.
The developers hope male GM mosquitoes will compete with normal males for females so that repeated releases cut numbers of A. aegypti in dengue-prone areas.
The mosquitoes will be released in the inland districts of Bentong in the state of Pahang, and Alor Gajah and Melaka in the state of Malacca, according to the National Biosafety Board. Each location will have two release phases: the first at a site 0.5–1 kilometres from the nearest human settlement, and the second at an inhabited site.
They will be recaptured using mosquito traps, which will be monitored for at least one month, while the inhabited release sites will also be fogged with insecticide when the experiment is over.
The board made its decision after its Genetic Modifications Advisory Committee (GMAC) analysed the risk factors for the experiment. The issue was opened for public consultation from 5 August to 4 September.
Ahmad Parveez Ghulam Kadir, head of the GMAC, told reporters last month (29 October) that the committee had been concerned that lab tests had shown that three per cent of the offspring of male GM mosquitoes and normal females actually survive into adulthood rather than dying as larvae as intended.
Ricarda Steinbrecher, a geneticist and co-director of EcoNexus, a UK-based non-profit research organisation, said that it is not clear how the offspring of the male GM mosquitoes survive into adulthood and do not die as 'programmed', but it raises the possibility that they could breed and pass on this — as yet unknown — mechanism for overcoming the lethality.
"I would suggest that it is far too early for any open field releases. More data are needed from laboratory experiments. Furthermore, trials in field cages [large outdoor enclosures made from netting, i.e. confined field trials] are needed," she said.
The advisory committee had also been worried that female GM mosquitoes might accidentally be released. The technicians separate the male from the female GM mosquitoes based on the size of the pupae — the stage after the larval stage — and is therefore not completely accurate.
Because of this, Parveez said, the board has insisted that scientists sort through the pupae twice — first mechanically and then manually.
The 'self-limiting' strategy theoretically poses little threat of genes being released uncontrolled into the environment because of the death of the offspring. But future strategies, in which the aim is to overwhelm mosquito populations with those that are resistant to disease, are more controversial because the mosquitoes survive and breed.
A Malaysian geneticist, who declined to be named, said he hopes the experiments will be carried out under rigorous safety protocols.
"We have the best laws on biosafety in the world, but the problem is the enforcement," he said.
Liow Tiong Lai, health minister of Malaysia, told a press conference last month (10 October) that the Malaysian government views the GM mosquitoes "as one of the most efficient and fast ways of getting rid of the Aedes mosquito from our local environment".
http://www.scidev.net/en/news/malaysia-to-release-gm-mosquitoes-into-the-wild.html

MALARIA: Yellow Fever Mosquito Shows Up in Northern Europe

In the latest display of mosquitoes' predilection for modern travel, entomologists have found a small colony of the tropical species Aedes aegypti—also known as the yellow fever mosquito—in the Netherlands. The insects were found on and near two facilities of a company that imports used tires and presumably originated in the hot southern part of the United States. Aedes aegypti is an important vector not just of yellow fever but also of two other viral diseases, dengue and chikungunya.
http://www.sciencemag.org/cgi/content/summary/329/5993/736

MALARIA: Getting the mosquito to do the work

Malaria pathogens are transmitted to humans by the bite of female Anopheles mosquitoes. The juvenile stages of these mosquitoes develop in a variety of water bodies and are key targets for vector control campaigns involving the application of larvicides. The effective operational implementation of these campaigns is difficult, time consuming, and expensive. New evidence however, suggests that adult mosquitoes can be co-opted into disseminating larvicides in a far more targeted and efficient manner than can be achieved using conventional methods.
A recent field trial with the dengue vector, Aedes aegypti, exploited the obligate behaviours of adultmosquitoes to transfer a potent larvicide between resting and oviposition sites.
An impressiveimpact on the juvenile population was mediated by 1) a highly effective and persistent insecticide, 2)the predictability of sites where adult mosquitoes could be exposed, 3) a limited aquatic habitat and 4) sufficient mosquito density. The use of adult females as larvicide-disseminating vehicles resulted in the very precise targeting of the insecticide; only those aquatic habitats visited by adults were contaminated and, the more popular the site, the greater the number of transfer events.
http://www.malariajournal.com/content/9/1/142