Southern Leyte has declared itself to be in a “state of calamity,” the fourth province to do so in recent weeks, because of the spread of the mosquito-borne tropical disease dengue. Such a declaration allows the provincial government to access funds set aside for disasters or calamities, and use them to pay for interventions that can help address the epidemic.
The Department of Health (DoH) has reported that between Jan. 1 and Aug. 3, more than 188,000 dengue cases have been recorded nationwide. This was more than double the number of cases recorded during the same period last year. There have also been 807 deaths, up from 497 in 2018, resulting from severe dengue cases.
This situation prompts one to question whether the government made a mistake in stopping the mandatory vaccination of public school children against dengue. In the same line, should we now ask our government officials to reconsider their action against the controversial Dengvaxia vaccine that used to be administered by DoH?
The DoH’s National Dengue Task Force, which monitors people previously vaccinated with Dengvaxia for possible ill-effects, is not inclined to recommend reusing Dengvaxia for mass immunization. It has noted that in Central Luzon this year, there were cases where even those already vaccinated still got sick from the dengue virus.
The task force noted that of the 172,000 people vaccinated in Central Luzon, 98 have gotten sick since the start of the year. Seven of the 98 even received the complete cycle of three doses of the vaccine. The Food and Drug Administration (FDA) has canceled the Certificate of Product Registration of Dengvaxia, but this has been appealed by the vaccine manufacturer.
The are more ways than one to fight dengue, and while vaccination can still be a future option, I believe people should now be looking at more practical ways to get rid of dengue mosquitos. After all, as with some cases with vaccination, viruses eventually evolve or develop new strains that are immune to vaccines. Getting rid of breeding sites must thus be the priority.
Mind you, it is not only dengue that’s on the rise. There are other cases of mosquito-related diseases being recorded like malaria, chikungunya virus, yellow fever, and Japanese encephalitis, among others. There are vaccines for malaria, yellow fever, and encephalitis, but I am uncertain if we are doing mass immunization. The same for dengue.
Getting rid of breeding sites will help minimize the problem. But “search and destroy” need not be harsh to the environment. It shouldn’t be “toxic” to people, either. The use of chemicals may be necessary in some cases, but to the extent possible, I still advocate for “natural” methods of eliminating the threat.
Households are encouraged to be vigilant of stagnant water and should urgently remove them. Moreover, they need to make sure that screens are used for windows, and in some cases, mosquito nets for sleeping. Use natural mosquito repellants whenever possible, either on the body or in homes. And be aware of emerging technologies against pests like mosquitoes.
More than a year ago I wrote about the US government’s approval — through the Environmental Protection Agency (EPA) — of an anti-mosquito paint that was made in Japan. Back then, I already noted that this product would be a big step in terms of “vector control” as a way to beat malaria and other mosquito-borne diseases like dengue.
I am uncertain, however, how much the paint costs. But I still believe that painting walls with anti-mosquito paint may be more cost-efficient and effective in dealing with mosquito-transmitted diseases than with periodic spraying of insecticides inside our homes or in our surroundings, or applying chemical-based insect repellants on our bodies.
The “technology” for the US-approved anti-mosquito paint was reportedly first developed in Africa to prevent the spread of malaria. The product has also been reportedly approved and commercially launched in Malaysia and Singapore. I await its introduction here. That is, if it is scientifically proven to be highly effective against mosquitoes.
Homes and public buildings will require or need painting, anyway. In choosing paint, even if “treated” paint costs a bit more, wouldn’t this be a more cost-effective approach to fighting malaria and dengue and similar diseases? If such a product can be made available here, then I am sure it will be a viable option in the fight against mosquito-borne diseases.
Another interesting option is the use of “predatory crustaceans” like copepods and varieties of fish that eat mosquito larvae. When they are placed in container habitats, decorative ponds, and pools, they prey on mosquito larvae, thus effectively preventing mosquito development. Copepods in large water-storage tanks successfully limited dengue transmission in Vietnam.
The choice of organisms, however, must be backed by scientific study. Moreover, such organisms must be localized and should not be introduced into the natural habitat. This is to avoid such organisms from preying on other fish and other creatures in natural bodies of water. The World Health Organization (WHO) warns that “only native larvivorous fish should be used because exotic species may escape into natural habitats and threaten the indigenous fauna.”
But WHO also noted that “biological control organisms” can be effective when bred and distributed into water-storage containers or wells. It added that a variety of fish species have been used to eliminate mosquitoes from larger containers used to store potable water in many countries, and in open freshwater wells, concrete irrigation ditches, and industrial tanks.
Other literature indicate that goldfish, guppies, bass, bluegill and catfish also prey on mosquito larvae. An option are birds such as purple martins, swallows, waterfowl (geese, terns, ducks), and migratory songbirds, which also eat both the adult and aquatic stages of mosquitoes. What would be ideal, of course, is the use of edible fish and fowl for the purpose.
Dengue and other mosquito-borne diseases are a problem. Dealing with them will not be easy. Vaccines, if proven effective and safe, should always be an option. But in the immediate, we should vigilantly employ a variety of methods, preferably more natural than chemical, in homes, schools, places of work, and in farms that can help prevent outbreaks and epidemics.
Marvin Tort is a former managing editor of BusinessWorld, and a former chairman of the Philippines Press Council.
