Wednesday, March 02, 2011

A Sexually Transmitted Disease Cure



# 5349




No, not a cure for a sexually transmitted disease.


A sexually transmitted disease (well, among insects) that may actually help eradicate the dengue virus in the Aedes Aegypti mosquito.


At least, if tests being conducted in Australia prove successful. 


The disease is Wolbachia, an common bacterium carried in the reproductive system of many of the world’s insects, but not found in mosquitoes that commonly transmit dengue fever.    


Exactly what it is about Wolbachia that helps prevent the transmission of dengue isn’t known.


It may be that the bacteria up-regulates the mosquito’s immune system and interferes with viral replication, or perhaps it competes with the virus for vital nutrients in the host.  Or maybe something else . . .


But what is known is that Wolbachia infection greatly inhibits a mosquito’s ability to carry and transmit the dengue virus.


So two months ago scientists in Queensland, Australia began releasing 5,000-6,000 Wolbachia infected mosquitoes each week into the Cairns suburbs of Gordonvale and Yorkeys Knob.


It is hoped that over time Wolbachia infected mosquitoes will supplant the uninfected mosquito population, either slowing or (hopefully) halting the transmission of dengue.


Helping this project along is the way that Wolbachia is transmitted among mosquitoes. 


You see . . . it’s 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 should over time give the Wolbachia mosquitoes quite an advantage in the wild. 


As the Wolbachia bacteria is already found in the majority of the world’s insects (it is probably the most common reproductive parasite in the insect world), scientists believe there to be little danger in introducing it into the dengue mosquito population.


Today, early surveillance of these Cairns neighborhoods are showing 20% of mosquitoes captured and tested to be infected with Wolbachia.  


This from ABC News (Australia).



'Good start' to dengue eradication trials

By Brad Ryan and Kristy Sexton-McGrath

Updated Wed Mar 2, 2011 12:54pm AEDT

Scientists say a trial in far north Queensland aimed at stopping mosquitoes from transmitting dengue fever is showing early signs of success.


(Continue . . .)



For more on the science behind all of this, we turn to a PLoS Pathogens research article, published in April of 2010, by Zhiyong Xi  et al. called:


The Endosymbiotic Bacterium Wolbachia Induces Resistance to Dengue Virus in Aedes aegypti

Genetic strategies that reduce or block pathogen transmission by mosquitoes have been proposed as a means of augmenting current control measures to reduce the growing burden of vector-borne diseases.


The endosymbiotic bacterium Wolbachia has long been promoted as a potential vehicle for introducing disease-resistance genes into mosquitoes, thereby making them refractory to the human pathogens they transmit. Given the large overlap in tissue distribution and intracellular localization between Wolbachia and dengue virus in mosquitoes, we conducted experiments to characterize their interactions.


Our results show that Wolbachia inhibits viral replication and dissemination in the main dengue vector, Aedes aegypti. Moreover, the virus transmission potential of Wolbachia-infected Ae. aegypti was significantly diminished when compared to wild-type mosquitoes that did not harbor Wolbachia.


At 14 days post-infection, Wolbachia completely blocked dengue transmission in at least 37.5% of Ae. aegypti mosquitoes. We also observed that this Wolbachia-mediated viral interference was associated with an elevated basal immunity and increased longevity in the mosquitoes. These results underscore the potential usefulness of Wolbachia-based control strategies for population replacement.



Quite interesting, these results were not shown to extend to the the aedes albopictus mosquito, a lesser vector of Dengue.



Experiments with other strains of Wolbachia have shown similar inhibition in the transmission of chikungunya and malaria as well, making these discoveries potentially even more valuable.


The tests going on in Queensland will hopefully show us over the couple of years just how viable this novel approach to dengue control really is.

No comments: