A multipronged approach
Eliminating a disease often requires solutions that rely on more than a single approach. True, many infectious diseases—such as smallpox—have been eliminated or severely limited through the use of vaccines, which protect humans against the encroachment of deadly organisms.
Polio is another disease that has been largely eliminated, save for pockets of Pakistan, Afghanistan and Nigeria. But health authorities and field workers, and a civic organization like Rotary International, are busy stepping up efforts to eradicate the disease and protect humanity.
But some diseases, especially those for which no vaccine has yet been fully developed or licensed for widespread use, require more than one approach. Take malaria, for example.
I remember my father telling me how, in the years just before the war, he would go around the resettlement areas in Polomolok, South Cotabato (there was just one Cotabato province then), urging the settler-farmers not to forget to use mosquito nets at night to protect themselves from malaria-bearing mosquitoes. Today, mosquito nets soaked in insecticide are still being distributed in malaria-endemic areas in Africa. And, since the malaria-carrying Anopheles mosquito was known to be low-flying, residents built their houses on stilts to keep them out of the mosquitoes’ reach. Today, travelers to malaria-endemic areas are also advised to avail themselves of prophylaxis (drugs to prevent transmission of a disease), although the drugs are not of practical use to long-time residents in these areas because of cost and adverse side-effects.
Then there is mosquito control, such as clearing one’s surroundings of stagnant water, especially containers like drums, tires, pails, ponds, fountains. The use of insect-repellant lotions and sprays (or repellant stickers) is also recommended. One public health measure is “fogging,” spraying areas like schools, playgrounds, or public plazas with insecticides, although this has been found to be a temporary measure at best, and expensive, too.
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DENGUE is a disease very much linked to malaria, mainly because it, too, is spread by a mosquito, although of a different type: Aedes aegypti (another mosquito, the Aedes albopictus, is also a dengue carrier, but is rarer).
At the moment a vaccine to protect against malaria or dengue is yet to be licensed, although the drug company Sanofi Pasteur says field trials for its dengue vaccine are nearing completion. In its Phase III study, the company said, field trials were conducted in Cebu and San Pablo, Laguna, with 3,500 Filipinos from two to 14 years old vaccinated against dengue. The subjects are now undergoing surveillance.
On Tuesday, I wrote about another approach to dengue elimination—introducing the bacterium Wolbachia, quite common in insects but not in the two types of dengue-transmitting mosquitoes, in wild mosquito populations. Once carrying Wolbachia, Prof. Scott O’Neill of the “Eliminate Dengue” program said, dengue mosquitoes have been shown to have lost their ability to transmit the virus.
At the moment, both the vaccine and the Wolbachia experiment are still a few years away from licensing or being adapted for a general population, although O’Neill said a vaccine would certainly be “compatible” with their program. “We are not competing,” he said, “we support each other.”
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MEANTIME, as the world awaits the results of studies and field trials and surveillance of both the antidengue vaccine and the Wolbachia antidengue program, there is still much that all of us—health authorities, local governments and ordinary citizens—can do to minimize the threat of dengue.
Speaking at last week’s “Dengue Dialogues” hosted by the Australian Embassy was Dr. Fe Esperanza Espino of the Research Institute for Tropical Medicine. She shared the results of two case studies that sought to study the “ecological, biological and social factors” that fostered the spread of dengue “vectors.”
The studies centered on two different areas of the country: Muntinlupa, which has seen rapid changes in land use and topography only in the last two decades or so, and Puerto Princesa in Palawan, which is also rapidly transforming from rural to urban, driven by tourism and commercialization.
One factor found to be driving the spread of dengue, said Espino, was the lack of basic services, most notably water delivery. Due to the lack of water in Muntinlupa, she said, many householders, even those living in “gated” communities, were forced to store water in receptacles like drums and pails. But when Maynilad began piping in water to residences, the number of water containers—as well as the number of dengue cases—was greatly reduced. “It was much easier for us to work with the informal settlers,” Espino said after the forum. “The gated community dwellers were less trusting; we had doors shut in our faces more than once.”
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IN Puerto Princesa, said Espino, the city was “at risk of emerging infectious diseases” due to the pressure of population growth and tourism, but with the cooperation of the local government, she added, “it is possible to intervene in the process of environment and social change.”
This was done mainly through training of specific communities at risk, informing residents about the basics of dengue infection, or, in Espino’s words, “not dengue control but vector management.”
Disease management and, perhaps, elimination, calls for more than a single “magic bullet.” True, vaccines that work on both humans and insects can bring infection, illness and death rates down. But just as effective is environmental control, basic services (such as water delivery), and heightened awareness.
