New bug kills young to stop dengue

An experiment by British biotechnology company Oxitec Limited has yielded mosquitoes genetically engineered to prevent the spread of dengue fever by killing their own offspring.

The mosquitoes, formally termed aedes aegypti RIDL strain, transmit a lethal gene to their offspring which kills them before they reach maturity. Only male mosquitoes carry the gene.

The engineered mosquitoes were first released in the Cayman Islands in 2009 in a 25-acre area. A report published yesterday (October 30) revealed signs of success.

According to the traps, genetically engineered male mosquitoes accounted for 16 percent of the total male population in the test area, while 10 percent of the larvae contained the lethal gene. Scientists concluded that although genetically engineered males were half as successful at mating as normal mosquitoes, their activities would still suppress the population in dengue-endemic areas.

A larger trial on Grand Cayman island in 2010 reduced the targeted mosquito population by 80 percent for three months, Oxitec has reported.

“The results, and other work elsewhere, could herald an age in which genetically modified insects will be used to help control agricultural pests and insect-borne diseases like dengue fever and malaria,” the US’ New York Times reported today.

The insects have also been released in Brazil and nearby Malaysia.

Dengue is reported in between 50 and 100 million cases each year, and accounts for an estimated 25,000 deaths. According to Oxitec, dengue threatens 50 percent of the world’s population and costs the global economy US$4 billion annually.

The new bug could prove useful to the Maldives. Though it ranks number one on South-East Asia’s list of malaria-free zones, the Maldives continues to combat dengue fever annually.

This year, hospitals documented the highest number of fatalities when Ahmed Shinah of Vaadhoo in Gaaf Dhaal Atoll succumbed to the disease in July. An Oxitec report shows a steady increase in cases weekly since 2009.

Director General of Health Services Dr. Ibrahim Yasir said health officials are aware of Oxitec’s experiment but are awaiting confirmation that the mosquitoes are a valid solution.

“We have heard about it, but we are not discussing the experiment at a policy level right now,” Yasir said. “We are waiting to see how it works in other countries first.”

Yasir was unable to say if the Maldives would be able to genetically modify its own mosquitoes, but noted that the environmental parallels between Malaysia and the Maldives gave officials confidence in Malaysia’s results.

“We will not pilot the experiment here, but I think the way they are exploring it in Malaysia will help us decide if it safe for the Maldives. It could certainly be a cutting edge solution to dengue,” Yasir said.

The Maldives is particularly vulnerable to the impact of dengue. Using Maldives as an example, Oxitec reported that dengue cases had occurred more frequently this year than in the two years previous in tourism-dependent countries. Travel warnings were issued by various government and international health organisations for these areas.

The economic impact of even a warning can be significant for tourism-dependent countries such as the Maldives, Oxitec claims. A paper by Mavalankar et al. found that French Réunion lost 40 percent of its tourism traffic in the year following the 2005-2006 chikungunya oubreak. The paper estimated that a country such as Thailand could lose US$363 million annually for every four percent drop in tourism traffic.

Deputy Director General of Tourism Hassan Zameel said dengue had never been reported on resorts in the Maldives, and was not expected to become a concern.

“Of course dengue is a problem if it becomes widespread and cannot be controlled, but the government has given this lots of thought and emergency mechanisms are in place,” he said, adding that emergency procedures were carried out effectively for the outbreak in July and August.

“Cases are mostly reported on local islands. Resorts have their own methods involving sprays and smoke to counter the spread of mosquitoes. They’re doing very well at controlling it. But I don’t think it will be an issue moving forward,” Zameel added.

Oxitec lately opened a new facility to serve further experiments in Brazil and Malaysia. However, the program is also being criticised for possible health and environmental risks.

Unlike an antibiotic, mosquitoes cannot be recalled once they have been released. Some scientists interviewed by the Times said the insects could develop a resilience to the gene and survive. Todd Shelly of Hawaii’s Agricultural Department said 3.5 percent of the insects in a lab test survived the gene and matured into adulthood.

The mosquitoes are also sorted by hand according to gender, leaving room for error which could be signficant when thousands are released over an area.

One possible solution is modifying female mosquitoes, which do not carry the lethal gene, to stay grounded.

Chief Scientist at Oxitec Dr. Luke Alphey deemed the new approach safe because it releases only males, while only females bite people and spread the disease. He said it should have little environmental impact, reports the Times.

Meanwhile, authorities in Florida, United States hope to conduct an experimental release of the bugs in December.