Dengue control in Sri Lanka :

Are we doing enough to prevent epidemics?

Dr. K.D.P. Jayatilaka

For a country like Sri Lanka, in the tropical belt of the Earth, mosquito borne diseases are a common occurrence. Already, few diseases like malaria, filariasis, dengue and chikungunea (Ross River Fever) are established and have become endemic in the country. Some new and more dangerous diseases may also be introduced in Sri Lanka, due to the presence of the mosquito vectors in the country and quick air travel from other parts of the world where these diseases occur.

In a tropical country, it is not possible under present conditions to completely eliminate the breeding of mosquito vectors or completely eradicate the disease when it becomes endemic. However, thinking in a realistic way, the diseases could be controlled and kept at levels, so that they will not cause epidemics and become public health problems.

For any mosquito borne disease control programme to be successful, it should be well managed and be accepted by the community. Also, it should be sustainable and continue with full participation of the community.

Such a workable and a satisfactory program was put forward by the Epidemiology Unit - Sri Lanka, as the “National Plan of Action for Prevention and Control Dengue Fever 2005-2009” after a number of consultation committee meetings of experts in different disciplines. Despite this effort, a major epidemic with more than 150 known deaths and over 10,000 clinically/laboratory confirmed cases has occurred now and the whole country is in a panic. To me this looks the ascending limb of the epidemic curve and it will come to a peak with more deaths and more cases before it declines to the normal endemic level.

Dengue is a killer disease which could kill people very fast than any other mosquito borne disease and all those exposed to any type of dengue serotype (Dengue 1, 2, 3 or 4) earlier are at the risk of developing complications like DHF (Dengue Haemorrhagic Fever) and/or DSS (Dengue Shock Syndrome) if they become sick with dengue again.

No specific treatment

There is no specific drug treatment for dengue unlike for malaria, but early management/treatment of the condition could reduce the mortality. Normally a second attack of dengue with complications carries about 50 per cent mortality, but could be reduced to about five percent with early management.

However, a third or a fourth attack with another serotype will be very serious and fatal. In Sri Lanka all four dengue virus serotypes exist.

Dengue control is vector (mosquito) control and that too could be brought down to larval (mosquito larva) control and community participation in various ways is very essential.

For these, the community should be given the correct information regarding the disease, behaviour pattern of the mosquito, the risk factors involved, control measures envisaged and how the community should and could corporate and participate in the program to make it a part of their daily life. The program should continue especially with long term measures whether there are dengue cases or not.

However, I feel that there are a few things which should be straightened up in the current program to prevent a bigger epidemic with many more deaths and many more cases in the future, if and when it comes.

Reducing breeding places

For reduction of vector densities, at present most of the activities are carried out to reduce the temporary breeding places connected with garbage and waste disposal and this is very good. But, dengue control is not the same as proper waste disposal. Improper waste disposal certainly creates more temporary breeding places for the vector mosquito which to a great extent is Aedes aegypti.

However, it appears that no attention is paid to reduce the resting places of the vector at least in areas where these activities are carried out. Normally Aedes mosquitoes rest in the dark places in the brush and the bush in the gardens and the road-side as well as inside houses and other structures.

It is extremely difficult to eliminate all these places but even reducing them wherever possible will be more meaningful. When these places are reduced or eliminated, the mosquito is exposed to more natural dangers, thus reducing its longevity or the survival period.

The extrinsic incubation period (development of the virus inside the mosquito) for the dengue virus is four to 14 days with an average of seven days. The idea of reducing the longevity of the mosquito is to destroy it before it becomes infective. Otherwise, even the few mosquitoes which breed in hither-to unsuspected places will live up to their full life to spread the disease if they get infected. Sometimes we see schoolchildren and volunteers creeping under the bush and the brush to collect the plastic cups and the breeding containers.

However, combining these two activities i.e. reduction of breeding and resting places will be more meaningful and effective, Hence, reduction of temporary breeding places should always be supplemented with reduction of temporary resting places.

Discarded tires are another very important place for breeding of A. aegypti mosquitoes. There are millions and millions of discarded tires exposed to elements stacked at various bus depots, workshops of different government and private establishments and transport sections of defence and police forces etc.

One discarded tyre exposed to elements to hold water could produce more mosquitoes than 100 Bromelia plants.

Larviciding these dumps at regular intervals of two weeks could be arranged by discussing with the authorities to train one or two of their staff and provide with sprayers and the chemicals.

There are so many thousands of used tyres exposed to elements stacked for sale at various places an these too are important breeding places for the Aedes mosquito. Advising the owners to cover those dumps with a canvas or a tarpaulin is not effective as it is not practical.

There are also so many discarded tyres thrown away by the road side and in vacant gardens which is nobody’s responsibility.

As a long term strategy, the community should be educated to notify a central organization regarding these semi-permanent breeding sites. Action could be taken to collect them in different marked locations to be sprayed with a larvicide at two weekly intervals along with the other permanent and semi-permanent breeding places (mentioned in the plan but not practised).

The central organization should act in a very friendly and a helpful manner to take immediate action by visiting/treating that site to encourage such notifications.

Other measures

One mobile unit with four to five spray men and a supervisor could handle a large town or a portion of a big city if proper plans are drawn out. As this discarded tyres are going to be a continuing problem, later on some effective long term solution to handle them, e.g. like recycling to make asphalt for road construction could be made available at National level. (Nat. Geographic Magazine June 2008, ‘Oil boom in Siberia’. Page 78)

Participation of schools in the dengue control program is not very encouraging. Still some students in some schools have no correct idea of breeding places, size and behaviour of the dengue carrying mosquito and what the community could do to control/eliminate the breeding and resting places to reduce their density.

Schoolchildren are the best resource to make changes in the knowledge, attitudes and practices of the parents. Schoolchildren if properly involved and guided will be a tremendous boom to the mosquito borne diseases control programs (mentioned in the plan, but implementation?) Hence, the Education Department too could be an important partner in the dengue control program.

Community participation

They will have great ideas of community level projects if they really get involved.

It is even worth introducing lessons on basic knowledge regarding vector borne diseases and their control as a subject in the school curriculum, because the people in Sri Lanka will face this as a problem indefinitely.

Some of the video clips shown as community educational messages are sometimes misleading and confusing. e.g. a pigeon sized Aedes mosquito emerging and sitting on a normal size coconut shell, is very misleading. Some members of the community have got the wrong idea that dengue mosquitoes are a special variety and are as big as pigeons.

It must be remembered that A.aegypti is the smallest compared to other diseases carrying Anopheles and Culicine mosquitoes. Also, cutting or puncturing of discarded tyres or filling them with sand is quite misleading and discouraging as only a person who attempts it will know the difficulty.

Also, covering a tyre with a corrugated asbestos roofing sheet is useless because the mosquitoes will still breed there if water is present. It is better to educate the community to inform a central organization to arrange its removal to a marked dumping area to be treated with a larvicide. Later, on the long term solution mentioned earlier could handle the tyre dumps.

See the diagram below:

Thermal fogging or ULV space spraying is an emergency measure used in a crisis situation and should not be considered a routine dengue control activity. If there is a good effective dengue control program that crisis or emergency situation will not arise.

Sometimes it is detrimental to a well run control program because it gives a false sense of security and a sense of dependency in the community resulting in their neglecting the more important day to day activities which should be carried out to reduce mosquito densities.

However, if it is done in an emergency situation, the procedure should be repeated at five to six day interval in the same area till the other more important community based activities are improved.

Thermal fog affects only the flying insects (mosquitoes) and is very short lasting. Another generation of mosquitoes will come out of the breeding places after a few hours and can get blood from dengue patients, if there are any in the community.

When thermal fogging is done it is useful to direct the fog or smoke inside houses and out-houses too, as many mosquitoes will be resting in those places. A hungry mosquito will bite at time whether day or night.

Clean up operations

Also these days we see clean up operations being carried out practically in every area in the country. This is very encouraging as the community participation is at its peak.

It is very important; we have to make sure that these activities are repeated at least once a month in the future.

To reduce man vector contact, screening the houses with fly wires is the most effective way to keep the mosquitoes out.

It is vaguely mentioned in the plan, but not practised or encouraged at all.

Majority of Sri Lankans have got so used to mosquito bites and getting bitten by mosquitoes either inside or outside houses has become part of our culture. Only the importers of fly-wire advertise their products once-in a way. Community education is very necessary to encourage this healthy and not so expensive practice. Even the architects and house builders should be educated to become partners of the dengue control program and their assistance is necessary to encourage the community to use this very important and comfortable preventive strategy. In most countries where mosquito borne diseases are a problem it is mandatory to have provision for insect screening to get approval for a building application. Sleeping inside mosquito nets is a very good practice, but it gives protection only when sleeping.

Lastly, an Effective Dengue Control Program cannot be run by sitting in air conditioned comfortable offices admiring computer screens. Coordinating with other Government Departments and various Non-Governmental Organizations is very essential to get their full cooperation and participation in the dengue control activities and sustain it. Their physical participation is necessary in planning and implementing the activities. They will have even better ideas of how to get best results when using their resources. All decision makers and managers should be in the field most of the time with the community to educate and guide them to participate in mosquito reduction activities in a correct and a meaningful way.

The writer has functioned as the Senior Specialist Medical Officer - Vector Borne Diseases Control and Consultant Malariologist in Papua New Guinea for 17 years in addition to his 14 years in different capacities with the Anti-malaria Campaign, Sri Lanka.

Basic principles in mosquito borne disease control

* Reduce the breeding places to prevent build up of mosquito (vector) densities,

* Reduce the survival rate or the longevity of the mosquito.

* Reduce or prevent man-vector (mosquito) contact.

* Identify and manage cases early.