By Eduardo Gonzales, MD
Is it true that the number of dengue cases in our country have decreased? Is this due to the vaccine that was introduced last year? —firstname.lastname@example.org
This early, it certainly looks like the dengue outbreak in our country this year is not going to be as bad as last year. From Jan. 1 to May 20, our Department of Health (DOH) has recorded only 35,973 dengue cases, which is 31.8 percent lower compared to the 52,780 cases recorded during the same time period last year. Is this decrease in dengue incidence going to be a trend? And is it due to the dengue vaccine which was introduced last year?
The vaccine has little to do with the decrease in dengue cases
There is no way of telling whether this decrease in dengue cases is going to be a trend, let’s just wait and see, but it is safe to say that the dengue vaccine has little to do with it. In the first place, the DOH public vaccination program, which was launched in April 4, 2016, has so far reached fewer than half a million children, way below last year’s target of one million. This number of immunized children is still too small to significantly influence dengue incidence in the country.
Incidentally, the dengue vaccine (Dengvaxia) does not confer 100 percent protection. It only protects two-thirds (66 percent) of those who receive it, although among those who develop the illness after being immunized, it reduces the severe form of the disease by 93 percent and the hospitalization rate.
Dengue and its mosquito vector
Dengue is generally a mild, self-limiting febrile illness, but it sometimes complicates and gives rise to internal bleeding that can be fatal. It is caused by four types of Flavi viruses. These viruses are not capable of human-to-human transmission. They have to be transmitted to humans by either of two species of the mosquito genus Aedes: aegypti (the main vector in the Philippines) and albopictus.
The Aedesaegypti mosquito, minus its legs, is only three to four-millimeter-long. It stands out among mosquitos because it has white dots on its back and head and white stripes on its legs. Only the female mosquito bites and it does so because animal blood is needed for proper development of its eggs. The mosquito prefers human blood over blood of other animals and it loves to bite during the day. It acquires the dengue virus when it bites and feeds on the blood of a person with dengue. The virus then proliferates within, but does not harm, the mosquito. Eight to 11 days after feasting on infected blood, the mosquito becomes infective, can transmit the virus to any human it bites, and remains so for the rest of its life, which can be anywhere from 15 to 65 days.
The female Aedes mosquito, which has a flight range of up to 300 meters, breeds in stagnant water. It lays up to a hundred eggs at a time, in every place where non-running water exists: flower vases, jars, pots, bottles, drums, roof gutters, drains, old tires, tree cavities, plant stumps, etc. The eggs hatch into larvae (wrigglers) in a week. Another week later, the larvae transform into pupae, which become adult mosquitoes in one to three days.
Rainy season is peak season for dengue
With fewer than 36,000 cases so far this year, dengue may be down, but it is definitely not out yet. You should therefore keep your guard up this rainy season, the peak season for the disease. Remember that the best way to keep the number of dengue cases down is by stopping its mosquito vector from breeding and protecting people from getting beaten by the mosquito:
- Screen your house. Alternately, use mosquito nets, mosquito repellants, or mosquito coils (“katol”) and mats.
- Isolate persons with dengue fever in a screened room for at least five days from the onset of symptoms. This will prevent mosquitoes from biting the person and acquiring the virus.
- Eliminate all possible breeding places of mosquitoes in your neighborhood. Fill potholes; cover water containers and septic tanks; do not allow empty cans, soft drink bottles, spare tires, etc. to accumulate water; ensure that drains and gutters are not clogged and that water flows freely in sewage lines; and dispose garbage properly and regularly.
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