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Impact of Climate Change on Mosquito Proliferation, Dengue Outbreaks and Mitigation

Posted Jan 09 2010 12:00am

British Virgin Islands

An Environmental Officer (not an Environmental Health Officer) of the British Virgin Islands’ Conservation and Fisheries Department asked me for my views on The Impact of Climate Change on Mosquito Proliferation, Dengue Outbreaks and Mitigation.

The thoughts that question generated swirled like a hurricane through my head.  Being the person that I am, I put fingers to keyboard right away to capture everything firing between the synapses.  This is what I came up with, raw and unfiltered.


All things being equal, older teenagers and young adults are most vulnerable to Classic Dengue Fever (a first encounter with the disease); then infants and the elderly for obvious reasons of either underdeveloped or compromised natural immunity.  However, the fact remains that everyone in the British Virgin Islands can potentially succumb to infection. And indeed, Dengue cases dot the complete age spectrum from the very young infant to the middle-aged.

That being the case, more precise variables for determining vulnerability need be examined, namely location and mobility.  In regards to location, records show that on Tortola, the majority of Dengue Cases fall within a precise swath from East End/Long Look along the Blackburn Highway – through Baughers Bay, Purcell Estate, Pasea, the Greater Road Town area to include Lower Estate and Huntum’s Ghut – to Harbours.  Of course, sporadic cases turn up in other parts of Tortola, but still generally in coastal communities to West End and on the North Shore.  Very few cases occur at higher elevations.

The suggestion I would put forward to explain this phenomenon is two-fold.  The coastal communities are more urbanized and thus heavily populated by day – when the Dengue mosquito is most active – in comparison with the those on the Ridge Road, for example. Hence, by the law of averages, it is reasonable to expect that closer human contact and activity make it easier for the Aedes aegypti mosquito to successfully transmit the Dengue virus around.

However, there is the issue of the socioeconomic structure, and more specifically water management, in the Virgin Islands.  Persons residing at the highest elevations are not consumers of pipe-borne water and have no expectation of such.  Consequently, they depend strictly on cisterns.  They have no need to hoard water in arbitrary containers like drums, pails, tubs and the like as a backup supply.  The reverse is true for persons living in the low-lying communities.  They depend primarily on the pipe-borne, municipal supply and use the odd containers as backups.

It is this tendency that invariably leads to the over-abundance of open containers in a community, containers that contribute to the high mosquito Indices that are found in densely populated areas.  This in turn, predisposes the Aedes aegypti to carry a sufficiently high viral load that serves to trigger a Dengue outbreak in those very communities.


Over the past five years, there has been a rapid growth in housing activity in already heavily populated coastal communities on Tortola, British Virgin Islands.  This trend places such a burden on water consumption patterns that the hoarding of water has increased and with it mosquito density.  As much as the Vector Control Unit of the Environmental Health Division has succeeded in keeping down mosquito breeding in those critical spots, all it takes to reverse those gains is a rainfall event.

Rainfall in excess of 2 inches over a few days causes results in a dramatic upsurge in Aedes aegypti (and other species) mosquito breeding due to an abundance of containers that householders make available to them.  With between 80-90 percent of containers found on private premises being left open to receive rainfall and the apathy and lack of knowledge on the part of community members in handling them, the likelihood of a Dengue outbreak occurring today as compared to five years ago has improved substantially.

It does not help either that rising global temperatures are speeding up the larval and pupal stages of the mosquito’s development.  Indeed, accounting for things like turbidity, alkalinity, availability of particulate matter and predation, the warmer the water, the faster the aquatic stages will be.  This drastically cuts into the response time for the curbing of a mosquito infestation following a rainfall event.

For these reasons, Dengue infections have trended upwards over time so much so that 2007/2008 were some of the worst years on record.  This trend closely mirrors the situation in the Caribbean and the rest of the Americas on a whole.


The crux of the matter of controlling Dengue is not just one of Climate Change actions in terms of reducing global temperatures, dampening the intensity and frequency of storms, and mitigating the encroachment and intrusion of sea water unto arable lands and into aquifers with the attending side effects of desertification and threats on food security and human survivability.  What would matter more are the social communication methodologies geared towards engendering mass community awareness of and direct involvement in the activities to curb the prevalence of Aedes aegypti.

The basic community actions called for are…

1. Source Reduction through country-wide clean up campaigns (removing all open containers, wanted and unwanted, from the environment)

2. Motivation of householders to conduct their own weekly premises inspections and to maintain good sanitation

The Vector Control Unit will continue to…

1. Conduct daily premises inspections to teach householders how to do self-inspections

2. Monitor the human environment and to search for and destroy mosquito breeding places

3. Manage breeding places identified using Physical, Biological and Chemical Control methods

4. Disseminate mosquito control information to the public through close community interactions (meetings, demonstrations) and the media

5. seek to bring all four variables above to bear in a Social Communication strategy that will eventually make the householder more responsible for Dengue management in the Territory

6. expand this concept to the sister islands on a full-time basis, unlike what obtains at present

The Climate Change debate is of course so much broader than Vector Control.  Explore the expanded issues for now at takepart.com where Danny Jensen speaks the Inconvenient Truth about the extent to which The Caribbean is One of the Most Vulnerable Regions to Climate Change.

As part of his argument, Jensen cites the two-part video Islands on the Edge –  A Look at Climate Change in the Caribbean.  These videos draw on the expert opinion of some of the most prominent of Caribbean Scientists alive today, scientists like Dr. Sam Rawlins.

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