Researchers dengue fever breakthrough will halve life span of mosquitoes

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Source: http://www.news.com.au/adelaidenow/s...18-911,00.html

Researchers dengue fever breakthrough will halve lifespane of mosquitoes
By Janelle Miles

January 02, 2009 01:20am

A BREAKTHROUGH by Queensland researchers holds promise for the prevention of the mosquito-borne dengue fever virus which kills about 20,000 people worldwide each year.

The University of Queensland scientists have found a way to halve the lifespan of the Aedes aegypti mosquito, which spreads dengue fever.

Their discovery, reported today in the prestigious international journal Science, is being hailed as having the potential to reduce the incidence of the virus because only older mosquitoes are effective in transmitting it to humans.

UQ biologist Scott O'Neill said the scientists had found infecting Aedes aegypti embryos in the laboratory with a bacteria harmless to humans had halved their average lifespan.

The bacteria, wolbachia, occurs naturally in 20 to 60 per cent of all insect species, including fruit flies, but not the dengue mosquito.

Professor O'Neill, head of UQ's School of Biological Sciences, has been studying wolbachia for 20 years and received $10 million from the Bill and Melinda Gates Foundation to research its benefits in preventing dengue fever.

The virus infects about 100 million people around the world each year.

The scientists adapted the bacteria by growing them in mosquito cell culture before transferring them to Aedes aegypti embryos.

PhD student Conor McMeniman spent about 18 months using tiny needles to inject 10,000 embryos manually with wolbachia.

The next step will involve attempting to replicate the findings in a field cage in far north Queensland. "Mosquitoes live much longer in the lab than they do in the field and so we want to undertake outdoor experiments in Cairns in a more natural setting to see whether we get a similar reduction in lifespan," Professor O'Neill said.

Symptoms of dengue fever, which has four strains, can include a fever, headaches, especially behind the eyes, a rash, unpleasant taste sensation, extreme tiredness, muscle aches and pains and diarrhoea.

The most severe form of the virus, known as dengue haemorrhagic fever, can be fatal. Two Queenslanders died of dengue haemorrhagic fever five years ago.

Cairns is experiencing one of its worst outbreaks of dengue in years. More than 60 people have been infected since late November.
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Re: Researchers dengue fever breakthrough will halve lifespane of mosquitoes

Source: http://www.canberratimes.com.au/news...px?storypage=0

Scientists bite back in dengue fever fight
BY ROSSLYN BEEBY, SCIENCE AND ENVIRONMENT REPORTER
2/01/2009 6:29:00 AM

Australian scientists have developed a new, safe and quick way to control the spread of the mosquito-borne virus, dengue fever, by infecting mosquitoes with a common parasite found in fruit flies.

The vital breakthrough, which could save more than 20,000 lives a year in some of the world's poorest tropical countries, is the culmination of 20 years of ''dogged, plodding research'' for University of Queensland biologist Professor Scott O'Neill.

Using microscopic glass needles, Professor O'Neill and doctoral student Conor McMeniman, manually injected 10,000 mosquito embryos with wolbachia a bacterium which occurs naturally in the common fruit fly.

''It's very, very difficult work. We were injecting mosquito embryos less than 30 minutes old, using fine glass needles that you can only see, and use, when they're under a microscope. It's challenging, but the biology involved is quite elegant,'' Professor O'Neill said.

The wolbachia bacterium, which is harmless to humans and animals, halves the lifespan of the Aedes aegypti mosquitoes that spread the dengue virus.

The mosquitoes must be at least 12 to 15 days old before they can transmit the virus.

''It's only the older mosquitoes that transmit the virus to humans, so by reducing the lifespan, we can reduce the spread of dengue.''

''You'll still have mosquitoes flying around the place, but they'll die before they reach the stage where they can spread dengue when they bite,'' Professor O'Neill said.

The bacterium is passed on to the next generation through the female mosquito's eggs and quickly builds up in mosquito populations.

''It become hereditary, and the great thing is that it doesn't jump between individuals or skip a generation.''

The results of Professor O'Neill's findings are published today in the global journal Science, and there is already strong interest from media and governments in tropical countries where the virus affects 30million a year.

The research signals an early success for the Bill and Melinda Gates Foundation, which invested $10 million in the project as a part of an initiative announced five years ago by the Microsoft billionaire to fund research ''on diseases that disproportionately affect people in the developing world''.

There are no vaccines to control or prevent dengue fever, and health and environmental concerns have been raised about large-scale insecticidal spraying to control mosquito larvae. More than 40 per cent of the world's population 2.5 billion people are at risk of contracting the virus, which is known as ''breakbone fever'' or ''bonecrusher'' for its severely debilitating effects.

The next stage in Professor O'Neill's research is to conduct open release trials in an outdoor field enclosure in northern Queensland, to track how quickly the bacterium spreads.

''It's already worked in laboratory conditions, so we need to progress to the next level and verify how the life span is affected in populations released into a large, contained environment.''

Professor O'Neill said there was currently an outbreak of dengue fever in the district around Cairns, in northern Queensland, where 60 cases had been reported in the past month.

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Re: Researchers dengue fever breakthrough will halve lifespane of mosquitoes

Source: http://www.google.com/hostednews/ap/...ec-2wD95EH81G0

Exploiting nature to cut mosquitoes' life short

By LAURAN NEERGAARD ?

WASHINGTON (AP) ? Old mosquitoes usually spread disease, so Australian researchers figured out a way to make the pests die younger ? naturally, not poisoned. Scientists have been racing to genetically engineer mosquitoes to become resistant to diseases like malaria and dengue fever that plague millions around the world, as an alternative to mass spraying of insecticides. A new report Friday suggested a potentially less complicated approach: Breeding mosquitoes to carry an insect parasite that causes earlier death.

Once a mosquito encounters dengue or malaria, it takes roughly two weeks of incubation before the insect can spread that pathogen by biting someone, meaning older mosquitoes are the more dangerous ones.

The Australian scientists knew that one type of fruit fly often is infected with a strain of bacterial parasite that cuts its lifespan in half.

So they infected the mosquito species that spreads dengue fever ? called Aedes aegypti ? with that fruit-fly parasite, breeding several generations in a tightly controlled laboratory.

Voila: Mosquitoes born with the parasite lived only 21 days ? even in cozy lab conditions ? compared to 50 days for regular mosquitoes, University of Queensland biologist Scott O'Neill reported in the journal Science.

Mosquitoes tend to die sooner in the wild than in a lab. So if the parasite could spread widely enough among these mosquitoes, it "may provide an inexpensive approach to dengue control," O'Neill concluded.

Theoretically, it could spread: This bacterium, called Wolbachia, is quite common among arthropod species, including some mosquito types ? just not the specific types that spread dengue and malaria, the researchers noted. And Wolbachia strains are inherited only through infected mothers, with an evolutionary quirk that can help them quickly gain a foothold in a new population.

Next month, O'Neill's team begins longer studies in special North Queensland mosquito facilities that better mimic natural conditions to see how well the wMelPop strain persists as more mosquitoes are born, and what happens when they're exposed to dengue.

"By killing old mosquitoes, wMelPop could thus impact on dengue transmission," Pennsylvania State University specialists Andrew Read and Matthew Thomas concluded in an editorial accompanying the work, which they called "a major step."

It's possible that dengue viruses could evolve to incubate more rapidly if their mosquito hosts die younger, they noted, although that likely would be less of a problem than today's insecticide resistance.

Still, "determining whether it can remove enough infectious mosquitoes to be useful will be a challenge," the duo cautioned.