UNDER THE MICROSCOPE
Dengue cases are rising in the Philippines, with about 208,965 cases recorded so far this year, higher than the 124,157 cases during the same period in 2023, a 68 percent increase. With a 20 percent symptomatic rate, actual dengue infections are five times higher. Ninety-three percent of Filipinos are seropositive for dengue antibodies, indicating high infection rates. There are 364 deaths so far this year, far too many. Nobody should die from vaccine-preventable diseases. The DOH has not yet declared a national epidemic, claiming it is up to local governments to do so.
Interestingly, the Philippines has not reported dengue statistics to the World Health Organization as of April 2024, yet, it reported it in the preceding year, leaving a knowledge gap on the state of dengue worldwide. This is unsettling, as it indicates hesitancy in conveying timely and accurate information that will affect WHO decisions and advice for dengue-affected countries. Dengue is creeping into the temperate regions as global warming promotes the proliferation of Aedes aegypti and Aedes albopictus mosquitoes, vectors for the dengue virus. In fact, the WHO has declared a Global Dengue Grade 3 Emergency, the highest grade, thus requiring substantial global response and resources. Yet the Philippines did not send in data.
Aside from the perceived hesitancy to share information on dengue statistics, the DOH is sticking to its declared 5S strategy: (1) Search and destroy mosquito breeding sites, (2) Use Self-protection measures, (3) Seek early consultation, (4) Say yes to fogging where needed, and (5) Sustain hydration.
Of the 5 S’s, two (Nos. 3 and 5) are actually after-the fact measures, when a person has already been infected with the dengue virus. The preventative measures don’t appear to have made a dent on dengue statistics, considering the yearly increase in cases.
The other measures are either difficult to implement or may be environmentally harmful, such as No. 4 and insects eventually develop resistance. For No. 1, mosquitoes can breed in the tiniest amounts of water, say in bottle caps or dried leaves, hence it is impossible to eradicate mosquito breeding grounds. The mountains of trash in our towns and cities likewise pose hazards of rain water accumulation. No. 2 can be problematic in a tropical environment, where heat and humidity cause people to wear less, thus, exposing more skin surfaces to mosquito bites. Insect repellents are likewise expensive.
As the saying goes, doing the same thing repeatedly and expecting a different result is insanity, to say the least. We need innovative and more effective measures aside from the 5S’s.
For an effective environmental management strategy, community members should be educated about vector control and make behavioral changes. Local governments must undertake education campaigns and provide resources for such efforts at the barangay level.
Other methods of reducing mosquito populations are available. Ovitraps are devices that encourage female mosquitoes to lay their eggs. A mesh traps the emerging adult mosquitoes from flying out. Sufficient numbers of ovitraps used and maintained properly, can effectively reduce mosquito populations. They can also be used for mosquito surveillance.
Bioinsecticides are a combination of biological controls and insecticides, like Bacillus thuringiensis israelensis (Bti), which can effectively kill mosquito larvae present in water. Pyriproxyfen and Methoprene (juvenile hormone analogues), prevent mosquito larvae from metamorphosing into adults.
Non-chemical approaches to mosquito control include predatory crustaceans called copepods that eat mosquito larvae, proven to limit dengue transmission in Vietnam. Many species of fish that eat mosquito larvae can be placed in bodies of water. Dragonflies, aquatic turtles and beetle larvae are also effective in killing Aedes aegypti.
Genetic approaches include genetically engineering female mosquitoes that cannot fly. These wingless females cannot “sing’ and court with male mosquitoes using their wing oscillation. These are also easy prey for their predators. Genetically sterile male mosquitoes are undergoing trials in Grand Cayman in the Caribbean in efforts to wipe out dengue fever.
Another novel approach is infecting mosquitoes with the bacteria, Wolbachia pipientis, which is known to shorten the lives of mosquitoes. A study in Singapore showed up to 90 percent reduction in mosquito populations with 77 percent of the people in the area less likely to be infected with dengue. Another Wolbachia strain kills the dengue virus in mosquitoes, and is thus a sort of dengue vaccine for mosquitoes.
In summary, there are other feasible methods that can be used to control dengue transmission without environmental or human consequences other than the 5S’s, all of which should be explored if we are serious about controlling dengue. That is, if we can’t have dengue vaccines approved, which are still proven the most effective measure so far. The aborted Dengvaxia vaccination campaign could have achieved its purpose, had it not been politicized and demonized to the point of causing vaccine hesitancy.