How to eradicate Dengue virus from Sri Lanka


By a special correspondent-
Sri Lanka is in the grip of a severe epidemic of Dengue fever and Dengue haemorrhagic fever. The epidemic did not happen over a short period. Dengue has been in Sri Lanka since 1962. However, it was not a major public health problem. The disease was progressing at a very slow rate. Since about 2004, the numbers of cases have started going uprated dramatically since about 2008.
There have been great efforts to stop the spread of dengue in the country for several decades with singular lack of success, with the ever increasing spread of the decease as seen in the graph below. It is therefore evident that the approach to the problem and the means adopted are questionable, including the highly questionable proposals of large scale use of chemicals recently advocated and adopted.
See Graph 1
In recent years, there has been a National Dengue Control programme involving most government departments, the police and even the armed forces, coordinated at the highest level. However, all these efforts have been directed towards the elimination of the mosquitoes and not finding the means of controlling and eliminating the root cause, which is the Dengue Virus.
See Graph 2
BI = No of positive containers/No of premises inspected x 100
As the blue line in Graph 2 shows, their efforts have not been in vain, when reviewed only by the success in reducing the mosquitoes. The Breteau Index (BI) which is an index of the presence of mosquito breeding sites, has continued to fall until 2012. But during the same period the dengue cases have continued to rise (red line).
However, the same strategy to control dengue is continued to be followed today because;
=there appears to be no viable alternative and
*it is the recommended strategy; namely to reduce and eradicate aedes mosquito breeding sites.
See Graph 3
Should we continue with this strategy?
As Graph 3 shows, every year, since 2012, the annual cases have been going up. Although there have been periods of high and low incidence of cases, the pattern has been the same every year. In addition to the ongoing routine programme of dengue control, special 3, 5 or 7 day eradication programmes are also instituted periodically. We can use the pattern of dengue incidence during the past five years to test whether the special eradication programmes have any effect.
See Graph 4
Graph 4 shows in blue the pattern of average dengue cases during the years 2002 – 2015. The red line indicates what happened in 2016. The dates on the horizontal axis (29th Mar., 15th Jun. etc.) are for 2016 and special programmes for eradication of breeding sites started thereon. The reader can seeif the special programmes have been successful or not, in 2016, from the way the red line has moved with the blue line in spite of the special programmes.
It is therefore time to institute an alternative method of control or even eradicating dengue from Sri Lanka. Before such a strategy is even considered, a certain mindset has to be eliminated as regards the public and bureaucrats. They seem to think the only way dengue can be controlled is to prevent the breeding of aedes mosquitoes”.
If one analyses the dengue cases since 2004, some features were observed.
See Graph 5 and 6
See Graph 7
*The more densely populated a district is, the more intensely will the epidemic spread in that district
*The more populated a district is the faster the disease will spread in that district
*The more cases there are in a month the more cases there will be in the next month
These are the features of an infectious disease
Knowing that dengue in Sri Lanka behaves as an infectious disease we can adopt the measures that are traditionally used to control an infectious disease; when there is neither an effective treatment nor an effective vaccine. That measure or strategy is isolation.
Isolation works by preventing the transfer of the disease-causing organism from a sick individual to a healthy individual by whatever means. The transfer may be by touch, sneezing and coughing or by an insect
In epidemiology, there is a concept named Effective Reproductive Rate. (R) What this means is that in infectious disease epidemics, the behaviour or progress of the epidemic depends on, among other things, how many healthy persons a sick individual will pass on the disease to. If the sick person infects only one other person (R=1), the disease will continue to affect the community but will not become an epidemic. If the sick person (on average) passes on the disease to no one (R<1 but=”” disappear.=”” disease=”” hand=”” healthy=”” if=”” infects=”” more=”” on=”” one=”” other=”” person=”” sick=”” slowly=”” surely=”” than=”” the=”” will=””>1), there will be an epidemic.
This, in effect, means that in order to stop the epidemic (of dengue or any other disease), we do not have to isolate every case. Graph 6 shows (in theory), what would happen if we reduced the average number of healthy people thaHow to eradicate Dengue virus from Sri Lankat a dengue patien
t infects. As the graph shows, how soon we eradicate dengue will depend on how effective we are in isolating dengue patients. (50% isolation will eliminate dengue in 6 generations or 4 months).
See Graph 8
This naturally raises the question; how do we isolate dengue patients? We do not actually “isolate” a dengue patient in the traditional sense. We isolate the dengue patient from mosquito bites.
One would notice that what is suggested is quite a radical departure from the accepted dogma. If we are to adopt the strategy proposed, two things are essential.
=There must be very strong commitment at the highest level to the new strategy.
=There is a need to mount an intensive health education campaign.
Some basic misconceptions have to be corrected. For example, that dengue is acquired from mosquitoes. Dengue is actually acquired from a dengue patient; the mosquito only “transports” the virus. All campaign literature must display the image of a dengue virus and not a mosquito.
Undoubtedly, there will be many who will object to the proposed solution. Some will say that what is proposed is not practicable. I should like to ask them what the aim of the present strategy is. It is aimed at preventing mosquito breeding? The final aim of the present strategy is also to prevent mosquitoes biting dengue patients. There is no harm done if aedes mosquitoes bite healthy people, unless of course the mosquitoes has bitten a dengue patient previously.
Only a little reflection is necessary to realise what a roundabout and wasteful method we employ to control dengue. Take the Colombo District as an example. There are 2,000,000 people there. Every month about 800 cases are reported from Colombo. When one infected mosquito bites a person (2,000,000 – 800) some 1,999,200 could be bitten by non-infected mosquitoes. What this means is that in order to prevent one mosquito biting a dengue patient we have to prevent the birth of (2,000,000/800) 2,500 mosquitoes.
Another argument that might be advanced is that the cooperation of the public cannot be expected. Once again if we take the Colombo District as an example, there are approximately 500,000 households there. What the authorities are now asking the public to do is keep these 500,000 premises free of mosquitoes breeding. What I am asking is to look after 800 patients. Which is easier? A further difficulty is that people find it difficult to eliminate all breeding sites from houses and gardens because some breeding sites are either inaccessible or hidden e. g. on the roof, in tree hollows and underground. Dengue -patients on the other hand are easily identified because of fever.
Finally, if evidence is required to prove that it is not mosquitoes that cause dengue epidemics, rather than individual dengue cases, the next graph from Singapore is sufficient:
Dengue and Dengue Haemorrhagic Fever Singapore 1966 – 2005
(Bowman LR, Donegan S, McCall PJ (2016) Is Dengue Vector Control Deficient in Effectiveness or Evidence?: Systematic Review and Meta-analysis. PLOS Neglected Tropical Diseases 10(3): e0004551. doi: 10.1371/journal.pntd.0004551)
Premises index = premises with breeding sites/total premises inspected x 100
When there were plenty of mosquito breeding ( premises index of 50 in 1966) there were fewer than 50 cases of dengue per 100,000. However, when the premises index was brought down to about 2 by 2005, there were 300 dengue cases per 100,000 population.
Even in Singapore, the authorities have now realised that control of mosquito breeding alone is not sufficient to eradicate dengue. From 2016 there is an additional bit of advice to people.
“You should apply insect repellent in the following situations:■
*You are a confirmed or suspected dengue patient, having a fever. Fever in dengue patients coincide with the presence of dengue virus in their blood, which could be inadvertently transmitted to family members and neighbours via Aedes mosquitoes.
■ *A family member or neighbour has contracted dengue.
*Your neighbourhood has been declared a dengue cluster. Click here for the list of active clusters. Use of repellent can minimise chances of being bitten by an infective mosquito.
■ *You are visiting a place that is a declared cluster or has high mosquito population”.
A Thought Experiment
If the following are true:
*We live in an island
*Dengue is caused by a virus
*The virus cannot lead an independent life outside man or mosquito
*Dengue is transmitted only by the bite of a mosquito.
Then the following will happen:
*If mosquitoes stop biting everybody no new dengue cases will appear after one week
*If mosquitoes stop biting all dengue patients no new dengue cases will appear after 5 weeks
*If mosquitoes stop biting half the dengue patients no new cases will appear after 16 weeks
(This is an abridged version of a larger document. The original document containing the development of the suggested strategy together with the sources of data, references etc. can be found in Please email any comments to
This report has been compiled by a MBBS Qualified Doctor with over 50 years service experience in public health in Sri Lanka and the UK. The data used for the compilation of the detailed report is from publicly available documents.
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