penny August 24th, 2010
Distribution of dengue infestations (yellow) and dengue epidemics (red). (image source: [1])
News groups have reported a surge of dengue infections around the globe. One case was reported today in Australia (in the tropical Northern Territory), the first in over 70 years [2]. India has 434 new cases reported this week, with 1 death [3]. The Philippines was not spared, with reports of the number of deaths on the increase, from 387 people in 2009 and currently 315 people so far in 2010 since January [4].
Dengue has been recognized as a human disease for over 200 years. Life-threatening syndromes associated with dengue are dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). In the past 20 years, these diseases “emerged” as the most important vector diseases of humans worldwide [5]. To say they have “emerged” means that although these diseases have been around for a long time, the dynamics of these diseases have changed significantly such that it has become more difficult for us to control and prevent their occurrence. For instance, though we know that the epidemics are influenced by seasonal changes (wet weather being more favourable to the mosquitoes serving as vectors for the disease), the gaps of time between epidemics have shrunk from 10-15 years into as little as 3-5 years [6]. As with most infectious diseases, when the dynamics of infection change, we in turn should respond to these changes in order to control them, and protect ourselves from the harm they cause.
There are 4 different serotypes (genetic classifications) of dengue. A person can then be infected with dengue up to 4 times, since there is no cross-immunity. This poses a challenge to developing a vaccine that can be equally effective against all 4 serotypes.
Dengue virus. left: immature, right: mature (image source:[1])
What are the perceptions of the Filipino on dengue? If you ask some persons in a Manila street today what they know about dengue, you’d probably get some pretty straightforward responses, such as…
… it being a severe disease of children caused by mosquito bites,
… They might associate some faces of local government officials with ‘fogging’ activities [7] in their areas to fight dengue.
… They may have heard in the news that a number of people have died as a result of dengue.
If they didn’t know anyone close to them who was affected by dengue, chances are they really wouldn’t go much further than these responses. If you go further into the provinces you are more likely to meet someone who knows a person infected with dengue. Currently, dengue cases on the rise are noted in the Visayas and Mindanao. An assessment of the knowledge of students in Negros Oriental [8] showed that most respondents are unaware of the importance of indoor control measures (as opposed to ‘high-profile’ outdoor ‘fogging’, which generates a lot of publicity for politicians).
Fogging doesn’t work. Outdoor spraying to kill adult mosquitoes is less effective because not all the mosquitoes are outdoors. What remains most effective in control of dengue is to kill larvae: destroy the breeding sites of mosquitoes by draining water-filled containers and removing rubbish appropriately. Unfortunately, there is no consistent program in the Philippines to maintain a standard of sustaining the eradication of mosquitoes. Why? With such labor-intensive work comes the need for MONEY.
No money, no information campaign, no training, no end to the mosquitoes.
Without sustaining such projects mosquitoes reestablish themselves in a matter of a few years. If only there was constant funding so that such projects are not abandoned in developing countries such as ours, then these simple but highly effective control measures can continue. A program in Vietnam [9] was effective in controlling dengue. It involved support from the central government and action from the local community. Larval breeding sites were destroyed. The peculiar but effective use of Mesocyclops (a kind of crustacean which feeds on larvae of Aedes aegypti) to control the mosquitoes larval development in water-filled containers was successful to eliminate dengue. There has been recommendations that these techniques are transferrable to other South East Asian nations [10].
It is unfortunate that most efforts to fight dengue, even though highly effective, in tropical developing countries have either waned or been abandoned. Only in times as today where news banners headlines on deaths from dengue do we cast a spotlight on the problem. Sadly, such an attitude of nonchalance and apathy whenever there is no sensationalism contributes to the success of this disease. Mosquitoes become more cunning in hide-and-seek, the virus acquire more vigour against our therapies and efforts to find a vaccine. The wet weather comes and goes as do outbreaks, but our attitudes seem to remain the same. While disease dynamics become more efficient by virtue of evolution, our own complacence makes our battles against them a losing one.
The least we can do as citizens is to abide by ‘cleanliness’ standards to not contribute to the problem. An extra step would be to lobby for an effective AND consistent program to control the mosquito population. A concerted plan must be on the ready to prevent another inevitable outbreak.
[1] Mackenzie JS, Gubler DJ and Petersen LR. Nature Medicine 10, S98 – S109 (2004)
[2] http://www.abc.net.au/news/stories/2010/08/24/2991507.htm?section=justin
[3] http://timesofindia.indiatimes.com/city/delhi/34-new-cases-of-dengue-tally-434-now/articleshow/6423546.cms
[4] http://gulfnews.com/news/world/philippines/dengue-deaths-rise-in-philippines-as-authorities-deny-outbreak-1.671753
[5] Gubler DJ. Clinical Microbiology Reviews, July 1998, p. 480-496, Vol. 11, No. 3
[6] Gubler DH and Clark GG. Am. I. Tmp. Med. HYg.. 50(6) Suppl. 1994, pp. 50-60
[7] http://www.pcij.org/blog/?p=1201
[8] http://www.searo.who.int/en/Section10/Section332/Section1985_9819.htm
[9] Kay B and Vu SN. Lancet. 2005 Feb 12-18;365(9459):613-7.
[10] http://www.ecotippingpoints.org/our-stories/indepth/vietnam-dengue-mosquito-copepod-biological-control.html
Tags: dengue, philippines, virus
