A new approach to dengue
“Dengue season” is upon us, what with the onset of the rainy season. This is because the rains and floods create stagnant pools of water where mosquitoes bearing the dengue-causing organism breed. But in truth, as the Department of Health says, dengue is a year-round threat, since many households still harbor locations and containers where water may collect—drums, pails, tires, ponds, fountains, gutters, even vases—which even at the height of summer may host mosquito populations.
The main “vector” or driver of dengue is the female Aedes aegypti mosquito which bites during the day, and, less commonly, the night-biting Aedes albopictus. (Both types are found in the Philippines.)
Although it has not yet made the list of the 10 most common causes of death in the Philippines, dengue is a major public health problem in the Philippines. Among Asian and Pacific countries, according to World Health Organization (WHO) data, the Philippines racked up the highest number of reported dengue cases, numbering 37,895 as of 2013, with 740 infections reported per week, resulting in 172 deaths (so far).
The WHO also ranks dengue fever as “the most important mosquito-borne viral disease in the world—and the most rapidly spreading—with a 30-fold increase over the past 50 years.” The global dengue burden currently stands at 390 million infections a year, with Southeast Asia bearing the “greatest dengue burden in Asia.”
Dr. Ma. Rosario Capeding of the Research Institute of Tropical Medicine, in an online article, said the average age of infection among Filipinos is 12 years old, with 36 percent of annual dengue infections afflicting children between one and nine years old.
Given the data, and the expenses incurred not just in hospitalizations, treatment, lost productivity and in lives lost but also in dengue-control measures, tests, public information drives, eliminating dengue has become an urgent public health imperative. Any measure that promises to bring an end to the scourge of dengue should thus be welcomed and encouraged.
* * *
One such proposed measure was presented last week at a recent “Dengue Dialogues” sponsored by the Australian Embassy, and featuring Prof. Scott O’Neill, lead scientist and program leader of the “Global Eliminate Dengue Research Program.”
What O’Neill had to say was, to put it mildly, exciting, provocative, promising—even if the mild-mannered O’Neill spoke about it in even tones and sober scientific terms. Although, I must add, he took the rather unusual approach of annotating an animated video to explain his and his international team’s work.
Quite simply, while most efforts to eliminate or control a disease focuses on protecting people from infection—vaccines being the most common and most successful approach—the measures being taken and studied by the “Eliminate Dengue” team turns the concept on its head. Instead of trying to reach the human subjects under threat, the team attempts to make mosquitoes, which spread the disease, incapable of infecting people with dengue.
They hope to do this by “infecting” Aedes aegypti and Aedes albopictus mosquitoes with the bacterium Wolbachia, described as an organism that occurs naturally in up to 70 percent of all insect species, but not the dengue-carrying mosquitoes.
* * *
How do they propose to do this? Already, the team, based initially in Monash University where O’Neill is dean of the Faculty of Science, has successfully transplanted Wolbachia from the fruit fly into the dengue-carrying mosquitoes, and demonstrated that “when Wolbachia is present in the (mosquitoes) it reduces their ability to transmit dengue viruses.”
What the team does in Australia (in Cairns, the only site in Australia where dengue exists) and in other locales like Vietnam and Indonesia (and soon in Thailand, China, Singapore, Brazil and Colombia) is to release mosquitoes infected with Wolbachia over a period of 12 weeks into the “wild” mosquito population where the two kinds of insects breed and spread the Wolbachia infection. Through collection receptacles, the team members then test the mosquitoes. Through this process, they have invariably found their captured mosquitoes to be dengue-free.
This brought up questions of environmental impact and even a possible “mutation,” from an audience made up largely of academics and health authorities. One scholar from UP Manila wanted to know if the experiment would not result in a “mutant strain” of Wolbachia. Over the eight years the experiment has been undertaken, said O’Neill, they have found “no evolution to weaker or mutant forms.”
Another audience-member wondered if the spread of Wolbachia in place of the dengue-causing virus would not have an adverse environmental impact. “Wolbachia is already pervasive in the environment,” said O’Neill, and the potential of transfer to humans of the bacterium “already exists,” to no apparent effect. (The bacterium lives only within insect cells.)
* * *
O’neill, who trained as a medical entomologist, said his interest in Wolbachia has been long-standing, although initially he was exploring the use of Wolbachia in malaria control. But when studies showed this approach to be “too ambitious,” he began searching for other ways to use Wolbachia and soon focused on dengue.
O’Neill said it may take about three years before the Wolbachia approach to dengue elimination would be ready to roll out to populations under continued threat of dengue. How about a possible collaboration with the Philippine government? “Can the government afford it?” he asked, conceding that health authorities here may have other priorities, although when he met with Health Secretary Enrique Ona, “he seemed to be quite interested” in the program.
