Dengue control: the unrealised promise of Wolbachia-infected mosquitoes

Sub: Sci

Sec: Health

Dengue Burden in India:

Dengue poses a significant threat to India’s economy, with direct costs amounting to approximately ₹28,300 crore annually and the loss of 5.68 lakh years of young life each year.
Existing vector control measures, including the use of insecticides and community education, have only shown limited success.
The safety and efficacy of India’s two dengue vaccine candidates remain unproven, and effective antiviral agents are yet to be discovered.
The female Aedes mosquito is the primary transmitter of dengue, chikungunya, and Zika viruses.
Biological vector control methods, such as sterile insect techniques, show promise due to cost-effectiveness but have limited success.

Wolbachia method to control mosquito population:

The Wolbachia method is simple. When Aedes aegypti mosquitoes carry Wolbachia, the bacteria compete with viruses like dengue, Zika, chikungunya and yellow fever.
This makes it harder for viruses to reproduce inside the mosquitoes. And the mosquitoes are much less likely to spread viruses from person to person.
This means that when Aedes aegypti mosquitoes carry natural Wolbachia bacteria, the transmission of viruses like dengue, Zika, chikungunya and yellow fever is reduced.
Wolbachia strain wMelPop:
- Studies demonstrated that the Wolbachia strain wMelPop could reduce the lifespan of the Aedes mosquito by half.
- Later, the wMel strain was used successfully to promote viral resistance without affecting the mosquito’s lifespan, making it a viable candidate for blocking dengue transmission.

Using wMel to Combat Dengue:

The wMel strain is introduced into mosquito populations through mechanical transfer (transinfection) and subsequent release in urban areas.
Two primary strategies are employed: population suppression and population replacement.
- In Singapore, infected male mosquitoes are released, leading to non-viable eggs upon mating with uninfected females, reducing the Aedes population by 90%.
- Australia’s population replacement strategy involves releasing infected mosquitoes to promote mating and ensure the dominance of wMel mosquitoes in the wild.
Results from Australia indicate a stable wMel genome and a significant reduction in dengue cases, moving towards dengue elimination.
A randomized controlled trial in Indonesia showed a 77% reduction in dengue infection and an 86% reduction in hospitalization in wMel mosquito deployment areas.

Long-term Impact and Classification:

The long-term effects of wMel releases on ecosystems are uncertain; however, Wolbachia does not infect humans or vertebrate animals.
Aedes mosquitoes, introduced to non-African ecosystems through the slave trade and increased global travel, are a recent addition.
The process of wMel transinfection is not considered genetic engineering, as it does not involve genome integration.

wMel Programs in India:

India currently lacks an active wMel mosquito release program.
The Indian Council of Medical Research – Vector Control Research Center (ICMR-VCRC) has developed two colonies of Puducherry wMel Aedes strains, pending government approval.
Recent findings indicate the natural presence of Wolbachia in Aedes mosquitoes in Northeast India, though its significance is unclear.

Source: TH