Sterile Mosquito Bred To Fight Dengue Fever Shows Promise In Field Trial

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Main Category: Tropical Diseases
Also Included In: Infectious Diseases / Bacteria / Viruses
Article Date: 01 Nov 2011 - 0:00 PDT


A new study published in the journal Nature Biotechnology on 30 October finds that introducing genetically sterile mosquitoes into the wild shows promise as a way to help fight the dengue-carrying mosquito Aedes aegypti. The publication follows a presentation of the results at an annual meeting of the American Society of Tropical Medicine and Hygiene in Atlanta last November.

The study was conducted by researchers from Oxitec, the company in Oxford, UK that developed the genetically sterile mosquito, and the Mosquito Research and Control Unit (MRCU) in Grand Cayman on the Cayman Islands, where the open field trial took place.

Dengue is a mosquito-borne viral infection that causes a severe flu-like illness that sometimes develops into a lethal complication called dengue haemorrhagic fever. It occurs in tropical and sub-tropical parts of the world, mostly in urban and semi-urban areas.

There is no specific treatment for dengue, but the right medical care can save the lives of people who develop the lethal complication.

The only way to prevent the disease from spreading is by controlling the mosquitoes that carry the virus. These methods currently centre on the use of insecticides, together with other practical ways of reducing mosquito breeding sites.

However, despite these methods, the disease has spread dramatically in recent decades and the World Health Organization (WHO) now estimates that two-fifths of the world's population is at risk. Around 50-100 million new cases are reported worldwide every year.

The study reports the results of an early stage of the the first open field trial to test an alternative way to control the Aedes aegypti mosquito and reduce its numbers. The trial used a genetically sterile mosquito strain whose sterility can be suppressed by feeding the insect with an antidote. This provides an effective way to breed large numbers of the sterile strain.

The idea is that a large number of sterile males are bred and then released into the target environment where they seek out and mate with wild females, competing with wild males in the process. When a wild female mates with a sterile male, she will have no offspring, thus reducing the population of the next generation.

By repeatedly releasing enough sterile males, then the hope is that this will eventually reduce the virus-carrying mosquito population to below the minimum level needed to support dengue transmission.

This method is considered a safer alternative to insecticides because male mosquitoes don't bite or spread disease, and only mate with females of the same species.

However, some environmental groups have expressed concern about this GM approach. For instance the ETC Group in Ottawa, Canada, and and EcoNexus of Oxford, UK, who suggest that releasing the transgenic insects in the wild to reduce the native population will create an "empty niche" that could be filled by other equally, if not more dangerous, insects. The other concern is there could be an as-yet unexplored consequence to organisms further up the food chain.

In the study published in Nature Biotechnology, the researchers report the first stage of open-air field tests in the Cayman Islands.

They demonstrate that thousands of genetically modified sterile male mosquitoes, released across 10 hectares on Grand Cayman Island for a 4-week period, mated successfully with wild females and fertilized their eggs.

The presence of transgenic larvae showed that the genetically sterile males survived and were capable of finding mates, leading the researchers to conclude that:

"These findings suggest the feasibility of this technology to control dengue by suppressing field populations of A. aegypti."

Oxitec's facilities in the UK produced the sterile male eggs, and the MRCU on the Cayman Islands then hatched and released them.

The second stage of the trial, not reported in the study, but mentioned at the conference last November, released millions of genetically sterile male mosquitoes. This apparently resulted in a population collapse of 80% reduction in the target area.

Dr Luke Alphey, Chief Scientific Officer and Founder of Oxitec, told the press at the conference that:

"Oxitec considers that this approach could be used in many countries to help control the Aedes aegypti mosquito and hence prevent dengue fever."

Written by Catharine Paddock PhD
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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