Are we doing enough things correctly to prevent epidemics?

Dengue control in Sri Lanka

By Dr. K. D. P. Jayatilaka

(July 03, Colombo, Sri Lanka Guardian) 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 due to the presence of the mosquitoe 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 accepted by the community. Also, it should be sustainable and continue with full participation of the community.

The basic principle in a Mosquito Borne Diseases Control Programme should be -:

Reduce the build up of mosquito densities,

Reduce the survival rate or the longevity of the mosquito.

Reduce or prevent man mosquito contact.

Identify and manage cases early.

Such a workable and a satisfactory Programme was put forward by the Epidemiology Unit – Sri Lanka, as the "National Plan of Action for Prevention and Control of 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 165 deaths and over 13,000 clinically / laboratory confirmed cases has occurred now and the whole country is in a panic. To me this looks like 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 faster than any other mosquito borne disease and all those who were exposed to any type of dengue serotype (Dengue 1, 2, 3 or 4) earlier are at the risk of developing complications like DHF (Dengue Hemorrhagic Fever) and / or DSS (Dengue Shock Syndrome) if they become sick with dengue again. There is no specific treatment for dengue unlike for malaria, but early management / treatment could reduce the mortality. Normally a second attack of dengue with complications carries about 50% mortality, but could be reduced to about 5% with early management. However a third or a fourth attack with another serotype will be very serious and fatal.

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, the risk factors involved, control measures envisaged and how the community should and could co-operate in the programme to make it a part of their daily life. The programme 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 Programme to prevent a bigger epidemic in the future if and when it comes.

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 causes 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 4 – 14 days with an average of 7 days. Hence, reduction of temporary breeding places should always be supplemented with reduction of temporary resting places. Otherwise even the few mosquitoes which breed in hitherto never thought of places will live up to their full life and 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 other breeding containers. However, combining these two activities i.e. reduction of breeding and resting places will be more meaningful and effective.

Discarded tyres are another very important place for breeding of A. aegypti mosquitoes. There are millions and millions of discarded tyres exposed to elements stacked at various bus depots, workshops of different government and private establishments and transport sections of defense and police forces etc. One discarded tire exposed to elements could produce more mosquitoes than 100 Bromelia plants. Larviciding these dumps at regular intervals of 2 weeks could be arranged by discussing with the authorities to train one or two of their staff and provide them with sprayers and the chemicals. There are so many thousands of used tyres exposed to elements stacked for sale at various places and 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 very effective as it is not practical. There are also so many discarded tires 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 such semi – permanent breeding sites. Action could be taken to collect them in different marked locations to be sprayed with a larvicide at two week intervals along with the permanent breeding places (mentioned in the plan but not practiced). The central organization should act in a manner of being friendly / helpful and take immediate action by visiting / treating that site to encourage such notifications. One mobile unit with 5 - 6 spray men and a supervisor could handle a large town or a portion of a big city if proper plans are drawn out. As discarded tyres is going to be a continuing problem, later on some permanent solution to handle them like recycling, e.g. to establish a plant to make asphalt for road construction etc. 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 programme is not very encouraging. Still some students in some schools have no real idea of breeding places, size and behavior of the dengue carrying mosquito and what the community could do to control / eliminate the breeding and resting places to reduce their density. School children are the best resource to make changes in the knowledge, attitudes and practices of the parents. School children if properly involved and guided will be a tremendous boon to the mosquito borne diseases control programmes (mentioned in the plan, but implementation?). Hence, the Department of Education too should be an important partner in the dengue control programme. 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 citizen of 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 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 tire with a corrugated asbestos roofing sheet is useless because the mosquitoes will still breed there if water is present. On a long term basis 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.(See Diagram)

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. Sometimes it is detrimental to a well run control Programme because it gives a false sense of security and a sense of dependency to 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, it should be repeated at 5 to 6 day intervals in the same area till the other more important community based activities are improved. Thermal fog affects the flying insects only 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. If 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 any time whether day or night. Also these days we see clean up operations being carried out practically in every area in the country. This is very encouraging as community participation is at its peak. However, 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. However, it is vaguely mentioned in the plan, but not practiced or encouraged at all. Only the importers of fly-wire advertise their products once in a way. Community education is very necessary to encourage this practice. Even the Architects and House Builders should be educated to become partners of the dengue control programme 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 good idea but it gives protection only when sleeping.

Lastly, an Effective Dengue Control Programme cannot be run only from air conditioned comfortable offices admiring a computer screen alone. Coordinating with other Government Departments and various Non Government Organizations is very essential to get their full corporation and participation in the dengue control activities and sustain it. 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 the 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 14 years with the Antimalaria Campaign, Sri Lanka.

-Sri Lanka Guardian