Thursday, August 25, 2011

A Mosquito STD To Fight Dengue



Image: Dengue in the world

Global Spread of Dengue


# 5782


Last March in A Sexually Transmitted Disease Cure I wrote about attempts in Australia to infect mosquitoes with Wolbachia, a bacteria commonly found in fruit flies that – for reasons that aren’t entirely clear - inhibits a mosquito’s ability to transmit Dengue Fever.


It is thought that Wolbachia infection may up-regulate the mosquito’s immune system and interfere with viral replication, or perhaps it competes with the virus for vital nutrients in the host. 


Or perhaps some other mechanism is at work . . .


But what is known is that carrying the Wolbachia bacteria greatly inhibits the ability of some species of mosquitoes to carry and transmit the dengue virus.


Around the beginning of the year scientists in Queensland, Australia began releasing thousands of Wolbachia infected mosquitoes each week into the remote communities of Gordonvale and Yorkeys Knob.


The hope being that infected mosquitoes would eventually supplant the uninfected native mosquito population.  Helping this project along is the way that Wolbachia is transmitted among mosquitoes. 


You see . . .  among mosquitoes, Wolbachia is essentially an STD, a sexually transmitted disease


When an infected male mosquito mates with an uninfected female, the resultant fertilized eggs will fail to mature due to an abnormality known as cytoplasmic incompatibility (CI). Only the offspring from the union between already infected parents survive.


Since the Wolbachia infection is passed down from one generation to the next, that is expected to give the Wolbachia infected mosquitoes quite an evolutionary advantage.


Yesterday, in a pair of studies published in the Journal Nature, we learn of the promising early results of this field experiment. 


First, a paper that describes the ability of the wMel Wolbachia strain to infect caged mosquitoes and to block transmission of serotype 2 (DENV-2) Dengue.


The wMel Wolbachia strain blocks dengue and invades caged Aedes aegypti populations

T. Walker,P. H. Johnson,L. A. Moreira,I. Iturbe-Ormaetxe, F. D. Frentiu, C. J. McMeniman, Y. S. Leong, Y. Dong, J. Axford, P. Kriesner, A. L. Lloyd, S. A. Ritchie, S. L. O’Neill & A. A. Hoffmann



Next up, the results of the field release of hundreds of thousands of infected mosquitoes in Australia.


Successful establishment of Wolbachia in Aedes populations to suppress dengue transmission

A. A. Hoffmann, B. L. Montgomery, J. Popovici, I. Iturbe-Ormaetxe, P. H. Johnson, F. Muzzi, M. Greenfield, M. Durkan, Y. S. Leong, Y. Dong, H. Cook, J. Axford, A. G. Callahan, N. Kenny, C. Omodei, E. A. McGraw, P. A. Ryan, S. A. Ritchie, M. Turelli  & S. L. O’Neill



The bottom line:  Within a matter of a few months the Wolbachia infected mosquitoes overran the uninfected mosquito population in these two test environments.


While extremely encouraging, more tests are needed, including confirmation that this process works against all dengue serotypes. The Gates Foundation is providing further funding to support the release of Wolbachia mosquitoes in Australia, Vietnam and Thailand.


Other attempts to defeat Dengue and Malaria include the development of genetically modified Mosquitoes. For more on that field of endeavor, you may wish to revisit:


The Cayman Island Mosquito Trials

The Latest Buzz On GM Mosquitoes 

Malaysia: `Terminator’ Mosquito Field Test On Hold

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