Fighting Dengue Fever With The Help Of A Mosquito Parasite

[Shiloh]

Source: http://www.medicalnewstoday.com/articles/148638.php

Fighting Dengue Fever With The Help Of A Mosquito Parasite
Article Date: 04 May 2009 - 2:00 PDT

Dengue fever is a terrible viral disease blighting many of the world's tropical regions. Carried by mosquitoes, such as Aedes aegypti, 40% of the world's population is believed to be at risk from the infection. What is more, previous exposure to other strains of the fever does not confer protection. In fact, subsequent infections are significantly worse, and can result in fatal dengue haemorrhagic fever. The lack of a functioning vaccine forced Scott O'Neill and Elizabeth McGraw to look for a more creative form of defence. Knowing that a parasite, Wolbachia pipientis, shortens the lifespan of host insects and could restrict dengue fever transmission by killing the insects before they can pass the infection on, O'Neill and his team successfully infected Ae. aegypti with a strain of the Wolbachia bacterium and shortened the mosquitoes' lifespan. But before insects carrying the bacterium can be released into the environment, the O'Neill and McGraw teams have to convince international governments that mosquitoes carrying the Wolbachia parasite could successfully limit transmission of the virus. McGraw and O'Neill had to find out how the bacterium affects the mosquito's physiology and behaviour and published their results in the Journal of Experimental Biology on May 1 2009 at http://jeb.biologists.org.

Knowing that Wolbachia slows down some insects' activity and speeds up others, the team decided to test how the parasite affects Ae. aegypti as they age and the infection takes hold. Working with uninfected and infected mosquitoes produced by Conor McMeniman, Oliver Evans and Eric Caragata used a system designed by Craig Williams to film the activities of male and female mosquitoes as they aged to find how the bacteria affected the insects' activity levels. According to McGraw, the experiments generated a huge amount of video data, so Evans teamed up with Megan Woolfit and David Green to pipe the data to a cluster of workstations to track the insects' movements and analyse their activity levels.

After a year of experimental design, data collection and analysis, it was clear that the infected mosquitoes were more active than the uninfected insects. Most surprisingly, as the mosquitoes aged and the infection took hold, it did not increase their activity levels further.

Having found that the insects became more active in response to their bacterial lodgers, Craig Franklin joined the team to help measure the insects' CO2 production to find how their metabolic rates respond to the parasite. Again, the insects' metabolic rates were higher than those of the uninfected mosquitoes.

So why are the infected insects more active than the uninfected insects? McGraw says there are three possible explanations; the insects are living fast and dying young; the insects are hungrier and consume more energy in their constant search for food; or the bacteria somehow affect the insects' tissues to change their behaviour and increase their metabolic rate. McGraw suspects that the last explanation is the most likely.

Having shown that the activity levels of Wolbachia infected mosquitoes respond to the bacterium, McGraw and O'Neill are continuing to test how the infection affects the insects' biting behaviour and whether a Wolbachia infection can become established in Ae. aegypti populations to limit their lifespans. Ultimately, McGraw and O'Neill hope to release infected mosquitoes into afflicted regions of the world to limit dengue fever transmission, but only once they are sure that the insects will do no harm to the environment.

REFERENCE: Evans, O., Caragata, E. P., McMeniman, C. J., Woolfit, M., Green, D. C., Williams, C. R., Franklin, C. E., O'Neill, S. L. and McGraw, E. A. (2009). Increased locomotor activity and metabolism of Aedes aegypti infected with a life-shortening strain of Wolbachia pipientis J. Exp. Biol. 212, 1436-1441.

Source:
Kathryn Knight
The Company of Biologists

 

[Shiloh]

Re: Fighting Dengue Fever With The Help Of A Mosquito Parasite

Source: http://www.heraldsun.com.au/news/br...tropical-disease/story-e6frf7kf-1225813589823

'Breakthrough' in deadly tropical disease

* From: AAP
* December 25, 2009 10:39AM

QUEENSLAND researchers believe they have found a way to to control the spread of dengue fever, which afflicts more than 50 million people worldwide every year.

The team at the University of Queensland's (UQ) School of Biological Sciences, led by Professor Scott O'Neill, is investigating infecting mosquitoes that transmit dengue fever with a bacterium that shortens their lifespan, limiting their ability to infect humans with the dengue virus.

Professor O'Neill said this approach may be even more effective than first thought.

"In a surprising development we have found that mosquitoes carrying this bacterium - known as Wolbachia - are resistant to a range of pathogens that cause disease in humans including dengue, Chikungunya and malaria parasites," Professor O'Neill said.

"What this means is our original proposed method for dengue control may be more effective than we had previously considered and may even be extended to a range of other diseases in the future."

There is no vaccine or cure for dengue fever, a painful and debilitating disease, also known as "breakbone fever", that afflicts more than 50 million people and kills more than 40,000 worldwide every year.

The virus is of greatest concern in tropical parts of the developing world but outbreaks are becoming increasingly common in north Queensland.

Last summer more than 900 cases were reported from the Cairns area and already this summer 12 dengue fever cases have been confirmed in Townsville.

Professor O'Neill said mosquitoes that carry the Wolbachia bacterium lived shorter lives and had a greatly reduced ability to transmit dengue virus between humans.

The research forms part of a large research program funded through the Bill and Melinda Gates Foundation Grand Challenges in Global Health initiative.

The UQ team's latest findings, are published in leading scientific journal Cell.

 

[Shiloh]

Re: Fighting Dengue Fever With The Help Of A Mosquito Parasite

Source: http://www.eurekalert.org/pub_releases/2009-12/cp-nti122109.php

Public release date: 24-Dec-2009


Contact: Cathleen Genova
cgenova@cell.com
617-397-2802
Cell Press
New tool in the fight against mosquito-borne disease: A microbial 'mosquito net'

Earlier this year, researchers showed that they could cut the lives of disease-carrying mosquitoes in half by infecting them with a bacterium they took from fruit flies. Now, a new report in the December 24th issue of Cell, a Cell Press publication, suggests that their strategy might do one better: The Wolbachia bacteria also makes the mosquitoes more resistant to infection by viruses that are a growing threat to humans, including those responsible for dengue fever and Chikungunya.

Once infected with Wolbachia, Aedes aegypti mosquitoes also become less suitable as hosts for a form of malaria parasite that infects birds, said Scott O'Neill of The University of Queensland. (The mosquitoes under study aren't natural carriers of human malaria.)

"This might be very powerful in reducing pathogen transmission by Aedes aegypti to humans, particularly for dengue and Chikungunya," O'Neill said. "Together with the previously described life-shortening effects, the results suggest we might be able to have a major impact on disease." That's if it can be shown that the Wolbachia infection can invade natural mosquito populations, he added, a question his team is working on right now.

There is no vaccine or cure for dengue fever, which is a painful and debilitating disease suffered by some 50 million people worldwide every year. Dengue haemorrhagic fever, the more severe form of the disease, kills more than 40,000 people annually. Chikungunya usually isn't fatal, but can cause symptoms similar to dengue. Human epidemics of Chikungunya have been cited in Africa, Asia and more recently in Europe, according to the CDC.

Wolbachia is already rampant in nature; the bacterium is estimated to infect up to 60 percent of all insect species. They are passed from mother insect to daughter or son through the insect egg and readily spread to high frequency in many species of mosquito. The species that are the major carriers of human disease don't normally carry them, but that's something O'Neill aims to change.

"We are currently conducting a series of experiments in contained outdoor greenhouse settings that are examining the ability of the Wolbachia infection to spread into natural mosquito populations," he said. "If these prove successful, we hope to move to open field testing within the next one to two years."

The idea would be to seed the natural mosquito population with Wolbachia by releasing mosquitoes that had been purposefully infected in the laboratory. Wolbachia bacteria have a good 'trick' to help ensure their spread, O'Neill explained. They are responsible for a developmental defect that makes the would-be offspring of pairings between infected male mosquitoes and uninfected females inviable. Since the bacteria is passed from mothers to their offspring, that means that infected females can actually have a reproductive advantage over uninfected ones, encouraging Wolbachia's spread from one generation to the next.

O'Neill said his team is working on computational models to determine just how many infected mosquitoes would need to be released for the infection to take hold in the wild.

The researchers don't yet know exactly how Wolbachia protects the insects from human disease-causing viruses. They have some evidence to suggest that the bacterial symbiont primes the insects' immune system. Wolbachia may also outcompete the virus by limiting resources such as fatty acids inside the mosquitoes.

Even if the strategy works in a natural setting, there's a chance the mosquitoes or the viruses could become resistant to Wolbachia's influence over time.

" We can predict from evolutionary theory that selection will push the system in the direction of resistance, but we do not know the speed with which this might occur," O'Neill said. "Even if it was effective for a few decades it might have a major impact on human disease."

###

The researchers include Luciano A. Moreira, The University of Queensland, Brisbane, Australia,2 Inaki Iturbe-Ormaetxe, The University of Queensland, Brisbane, Australia; Jason A. Jeffery, Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Brisbane, Australia; Guangjin Lu, Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Brisbane, Australia; Alyssa T. Pyke, Queensland Health Forensic and Scientific Services, Coopers Plains, Australia; Lauren M. Hedges, The University of Queensland, Brisbane, Australia; Bruno C. Rocha, Rene? Rachou Research Institute- FIOCRUZ, Belo Horizonte MG, Brazil; Sonja Hall-Mendelin, The University of Queensland, Brisbane, Australia; Andrew Day, The University of Queensland, Brisbane, Australia; Markus Riegler, The University of Queensland, Brisbane, Australia; Leon E. Hugo, Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Brisbane, Australia; Karyn N. Johnson, The University of Queensland, Brisbane, Australia; Brian H. Kay, Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Brisbane, Australia; Elizabeth A. McGraw, The University of Queensland, Brisbane, Australia; Andrew F. van den Hurk, Queensland Health Forensic and Scientific Services, Coopers Plains, Australia, The University of Queensland, Brisbane, Australia; Peter A. Ryan, Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Brisbane, Australia; and Scott L. O'Neill, The University of Queensland, Brisbane, Australia.