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What the community should know and what it can do

by Dr. K. D. P. Jayatilaka

The dengue epidemic in Sri Lanka is facing this year with more than 10,000 reported cases and excess of 60 deaths has caused panic and received the highest State attention. The country's President and the Prime Minister had expressed grave concern and urged the authorities concerned to treat it as a highest priority problem.

Everyone knows that, dengue fever is a disease caused by a virus and is transmitted from a patient to a healthy individual by a mosquito belonging to a species known as Aedes. Dengue Fever (DF) is now endemic, practically in all the tropical countries in the world.

The disease with its complicated forms viz. Dengue Haemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS) occur at different levels and some of these countries experience Dengue epidemics at varying intervals.

Countries like Thailand, Myanmar, Indonesia, Malaysia and Bangladesh in the region and some South Pacific countries have experienced explosive epidemics with hundreds of thousands of cases and thousands of deaths during the last decade. Four types of dengue viruses, dengue-1, dengue-2, dengue-3 and dengue-4, are identified in the world.

All these four types occur in the countries where dengue fever is endemic. About 30 to 40 years ago, dengue was considered a disease of the urban areas. But, since of late the disease has spread to more rural settings, due to the migration of the vector mosquito to these places in response to the creation of suitable breeding places, resulted with changes in the lifestyle of the population.

Biting habits

The main vector mosquito or the carrier of dengue in Sri Lanka is Aedes aegypti with Aedes albapictus playing a minor role. Aedes mosquitoes are daytime biters with peak biting behaviour during the early morning and late afternoon hours.

However, this does not mean that they do not bite during other times. They will bite inside as well as outside the houses. Mosquitoes which breed outside, enter the houses through doors, windows, grills and any other open spaces, whilst others breed inside and bite inside.

Inside houses very often they are found resting in dark areas such as closets, bathrooms, behind curtains and under beds mostly on soft surfaces. School buildings are favourite places for the mosquitoes to hide under desks and chairs. It is our experience that these Aedes mosquitoes inside buildings will bite at any time during the day and even in the nights.

The common description is that they bite like 'mad-dogs'. Usually the small children and ladies at home and the school children during school hours become the main victims for those mosquitoes. The use of mosquito repellents and protective clothing still has a place in avoiding their bites.

However, it is only a temporary solution. During an epidemic or at any time for that matter, small children should be made to sleep under mosquito nets. Out-door biting could occur anywhere.

Female mosquitoes usually mate only once but produce eggs at intervals throughout their life. Under natural conditions an adult Aedes mosquito could live for about two months. However, there are many natural dangers in the environment that make their lifespan shorter.

The female mosquito needs a blood meal, either human or animal for survival and for the maturation of eggs. The males normally live in the bush feeding on plant juices. The digestion of the blood meal and the simultaneous development of the eggs take 2-3 days.

After resting in a dark place either inside the house or on vegetation outside, the next need of the mosquito is to find a suitable place and lay the eggs. This may be inside or outside the house.

The cycle of taking a blood meal, maturation of eggs, find a suitable place and lay the eggs is repeated every 2-3 days during the lifespan of the mosquito. During the sucking of blood, the mosquito if infective will transmit dengue virus to the victim.

Breeding habits

Aedes mosquitoes breed in relatively clean water and are commonly known as container breeders. Any container, large or small which will hold relatively clean water for more than 7-8 days could be a potential breeding place.

There can be many such places inside and outside houses, which become sites for egg laying and for the adult mosquitoes to emerge.

To mention few inside a house are the receptacles of water for flower pots and indoor plants, flower vases containing water, containers to collect and store water, ant-traps etc. Outside the house there are many kinds of suitable places for Aedes breeding.

To mention, the more important sites in most residential compounds are the discarded plastic containers, discarded plastic bags and wrappings which could hold water, discarded coconut shells, discarded vehicle tyres, blocked roof gutters etc. for A. aegypti and place like tree-holes and leaf axils for A. albapictus.

These types of breeding places are found in plenty in vacant gardens and in garbage dumps, which are very common and frequent sites in our country today.

Another important place where water collects temporarily and cause breeding are the damaged surfaces with stagnant pools blocked with vegetation and other debris in the road drains which can hold relatively clean water during rainy periods.

With the onset of the rainy season or with scattered showers these receptacles collect water to cause breeding of large numbers of Aedes mosquitoes, increasing vector density which is the requirement to start an epidemic of dengue fever.

Female mosquitoes lay their eggs singly on the damp surfaces just above or near the water line. These eggs are very small, barely visible to the naked eye. A single female lays 20-30 eggs at a time. Mosquitoes have for distinct stages in their life cycle: egg, larva, pupa and adult.

The eggs once in contact with water develop through the larval stages to become adult flying mosquitoes in 7-8 days. Aedes larvae can be identified by the way they rest in water. i.e., at an angle to the surface, whereas Anopheles larvae rest parallel to the surface.

This differentiation is useful in identifying Dengue mosquito larvae in areas where both Anopheles and Aedes breed, as both are clean water breeders. Very often the eggs get attached to the surface above the water level and could stand drying even up to 3 months, to go through development in the normal way after coming into contact with water.

The same process could occur if the ground water pools become dry. This special property of the Aedes eggs to stand drying up is important in the building up of vector densities to cause epidemics of dengue fever.

Hence, it is important to remember that when emptying the containers either inside or outside the house and refilling them with water, even after a time, the old eggs clinging to the walls of the container could develop and turn into adults. In carrying out the control and cleaning activities it is important to remember this special feature of the Aedes eggs.

The sides of the container should be brushed and rinsed well before putting water to it again. Studies have shown that about 40% of the eggs in a breeding container could cling to the sides to start a fresh life later even after few months. Larva and pupa cannot stand drying whereas the eggs can.

Transmission of the disease

When an Aedes mosquito takes a blood meal from a dengue patient the dengue virus in the blood also enters the mosquito's intestine with the blood. The virus multiply (replicate) inside the mosquito for about a week causing the mosquito to becomes infective.

After that, each time this infective mosquito bites a susceptible human being, some of this virus enters the new person and develop to cause the disease.

This development period, of the dengue virus inside the person till the appearance of clinical signs could vary from 2-14 days (average 7-10 days) is known as the incubation period. Once a mosquito becomes infective, it will keep on transmitting the disease for the rest of its life.

Sometimes the virus could be transmitted to the next generation of mosquitoes through the eggs, known as the transovarial or vertical transmission, but this does not play an important part in an epidemic. As mentioned earlier there are four different types of dengue viruses.

When a human is infected with a particular type, that person will develop a long lasting immunity to that particular type of virus only, but he/she could still get infected with any one of the other 3 types. When this happens, i.e., a person who is already sensitized to one type of dengue virus gets infected with another type; the person can develop complications that could be even fatal.

Clinical features

Everyone in the country is now very familiar with the clinical signs and symptoms of dengue fever, even to extent of over diagnosing the disease.

However, classical dengue fever which is also known as 'Break-bone fever' is characterized by a sudden onset fever for 3-5 days (rarely more than 7 days), intense headache, severe muscle, joint and bone pain, pain behind the eyes, loss of appetite, mild diarrhea with some vomiting, may be accompanied with a mild rash noticeable in fair skinned persons.

Very often this type of symptoms are similar to common viral flue and the patient recovers without even knowing that he had an attack of dengue fever.

Uncomplicated dengue cases recover within 5-7 days. Recovery may be associated with prolonged tiredness and depression.

However, if a person who had dengue earlier gets infected with another sero-type of dengue virus there is always a chance of his getting complications (sometimes fatal) known as dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS).

In this case, the condition could worsen suddenly with marked weakness, appearance of dark patches on the skin, bleeding from nose and gums, vomiting or diarrhea with blood. Sometimes the skin may become pale, cold and the appearance of a bluish tinge (cyanosis) on the extremities with rapid pulses and low blood pressure indicate the patient has got the dangerous complications of DHF/DSS.

At this stage, the liver and other internal organs could get damaged and the fatality is about 40-50% in untreated or mistreated cases. With good treatment and management the death rate could be brought down to less than 5%.

Currently the proportion will go up with repeated epidemics, as the chance of a sensitized person getting infected with another type of dengue virus is more. Dengue patients harbour the dengue virus till they develop immunity and recover.

There are no drugs to kill the germ at present as in malaria. Hence, as a control measure, patient (man) vector contact should be avoided.

Epidemics and current situation

Occurrence of dengue epidemics with its complicated forms of DHF/DSS is related to the increase in the mosquito densities (vectors) which in Sri Lanka is principally Aedes aegypti. Any epidemic has its natural curve. The number of cases/deaths will start going up (ascending curve), reaches a maximum (peak), and then will come down (descending curve) on its own even without any control measures.

However, by applying emergency control measures at the beginning, the number of cases/deaths could be reduced. Total elimination of mosquito population is not possible but it could be kept well under control by a carefully planned, sustainable, well monitored, long-term, control programme with the greater participation of the community.

When the vector population is kept low by reducing eliminating the breeding places, epidemics will not occur. Dengue will still be there, but a lower rate (endemic) and is not going to be public health problem. Another very important activity I noticed during the dengue epidemics in the last 3 years is the amount of community education activities carried out in the electronic and written media.

So many valuable advices with illustrations were given during these sessions and it is taken for granted that the community which plays the major role in the dengue control programme will understand, accept and follow what the learned panel discussed.

Unfortunately the condition remains the same as the attitude and practices of the community had not changed. I have never seen any officer or health worker visiting the community even on a sample basis to check whether the people have understood, accepted and are following what was discussed. Or to find out how much the community know about the condition and what their attitudes and practices are.

In the area I live (a lane in Kohuwala), we have not noticed any Health Worker visiting houses to discuss the problems faced by the community with regard to the dengue epidemic and to motivate them.

In this area, vector breeding appears to be quite high and a few patients were admitted to hospitals with complicated dengue fever. In my opinion a disease like dengue cannot be controlled from air-conditioned rooms looking at computer screens.

The staff involved in the programme from top downward must go to the community and work with the community to motivate and change some of their attitudes and practices which cause the breeding of dengue vector.

The control programme should be integrated to involve the Central Government, Local Governments, NGOS and the Community, which plays the major role. Certain routine field surveys and observations like Container Index, House/Premises Index and Bretau Index at Indicator areas will give early warnings of vector density buildup for impending epidemics.

It is accepted practically in all endemic countries, a Container Index over 20 will always give rise to epidemics of dengue fever. High-risk areas should be identified and priority and special attention should be given to them. What we often see is crisis management during an epidemic. It is called the 'soda bottle phenomenon'. When the epidemic goes down, may be due to natural causes all activities slow down to a halt.

Control activities mostly for the community

1. Reduction of vector densities.

(a) Reduction of breeding places-This is the most important, useful and easy to perform dengue control activity the community could participate in their own house, in their own garden and in their own area. There are many receptacles and containers inside and outside most houses, which can breed Aedes mosquitoes.

These containers should be either eliminated or emptied, rinsed/brushed and refilled once a week to prevent the breeding and emergence of adult mosquitoes. Containers which are too heavy to handle e.g. receptacles for large flowerpots, containers for water plants etc. inside some houses are a bit problematic but still they too could be treated either by introducing chemical larvicides like Abate or Actallic granules or by introducing few larvaevorus fish like gambusia or guppy.

Some salt could be added to ant traps. However, the more important breeding places are in the garden and these should be attended to once a week. Epidemics occur mainly due to explosive breeding of vectors in places outside the house during rainy periods. Plastic containers and plastic bags should be collected, burnt, buried, or put to separate bags and send to the dump yard.

To prevent breeding in tree holes and discarded tyres in the garden, such could be filled with sand to prevent water collection if the numbers are small. If there are large numbers of unused tyres, such as in collection stations or used tyre dumps, some type of organized programme like spraying at regular interval with a larvaecide should be arranged with the assistance of the authorities.

The community should make it their responsibility to identify these large breeding places and bring to the notice of the authorities for regular treatment.

(b) Larveciding with chemicals like Abate, Actallic either in granular form or spraying is possible but operational problems will be there due to the great variation of breeding places and the necessity to repeat every 2-3 weeks.

The same applies to the use of BTI as a larval control measure. However, there measures have a place in controlling larval breeding in specific places like tyre dumps, motor repair places and second hand part sites which collect water, construction site etc. Spraying these sites at regular intervals should be the responsibility of a central organization, but identifying and reporting should be the responsibility of the community.

(C) Destroying the adult mosquito during an epidemic or to abort an epidemic when vector densities build up is possible with ULV spraying using chemical pesticides like Malathion, Permithrin, or Deltametherin. However, this is a temporary measure.

Only the flying adults will get knocked down. Another batch will emerge the following day. ULV spraying needs truck mounted equipment and will have to be repeated weekly at least for a month to get any beneficial effects. This activity, if it has to be done, should be well planned. Thermal fogging using diesel as it is done today has no effect in reducing the vector densities.

A small solution for household garbage problem.

Dumping household refuse at different places and the local authorities not having proper plans for refuse disposal is a problem beyond the control of the householder. This problem could be minimized, if each householder makes an attempt to use the soft kitchen refuse and garden refuse/grass cuttings etc to make compost in their own place.

Only a simple device (cage) made out of welded mesh, about 3ft.x 3ft.x4ft. lined on the sides and bottom with 2 or 3 empty manure or rice bags could be used for this purpose.

The pieces of welded mesh could be tied with thin wire to make the device. When the container becomes full with the collected refuse which might take about 2-3 months for a normal house, wet the contents and cover with another 2-3 manure bags. Some logs or bricks could be placed on top to keep the cover in place and leave it to mature.

It take about 3 months for the refuse to turn into compost. If a house has 2 of these compost makers the problem of soft kitchen refuse could be handled very easily. There would be the useful compost/manure in return. Whilst one compost maker is maturing the other one will get filled.

The welded mesh to make 2 devices will cost about Rs. 500.00 and it could be used for more than 10 years. The most important thing in this process is to change the behaviour of the inmates of the house including children to put the household refuse to two separate bags.

One for the soft matter, which will go into compost making and the other for solid things like plastic bags and containers, tins, bottles etc. for separate disposal. At the beginning it is a little difficult as everyone will make the mistake of putting plastic bags into the compost maker, but it will correct itself after some time. (The writer has used this method for the last 4 years in Sri Lanka and for about 6 years in another tropical country and no soft home refuse was thrown away or put out for the garbage collector.

The return was about 500 kg of good quality compost which provided fertiliser to the plants. There is no smell or breeding of other insects and flies in the compost maker, as the heat generated during the fermentation process will kill all insect larva.

Even fish and meat refuse could be added to the compost maker. For people living in flats and those who do not have any space in the garden to set up the compost makers, there will be a problem, but still something could be done jointly with the others. This method will not solve the household refuse and garbage problem completely, but will give a satisfactory solution to those who want to try and minimise the number of garbage bags thrown to the roadside dumps.

2. Prevent man vector contact

a). Screening of houses (windows, grills and other openings) with fly-wire screens still play a very important role in preventing the mosquitoes from entering the houses. However, still a few will come through the open doors and other openings. Screened doors with automatic door closures will reduce this problem to a great extent.

b). Mosquito coils, insecticide aerosols and insect repellents will be useful in keeping mosquitoes away for short periods. It is only a temporary solution.

c). As an epidemic control measure, it is a very important for dengue patients or suspected dengue cases to sleep under a mosquito net at least till the fever subsides to prevent infecting new mosquitoes. If the newly infected mosquito lives upto 8-10 days to go through the maturation of the virus, the next victim may be an inmate of the house or a neighbour.

3. Management of patients

(a) As mentioned earlier uncomplicated dengue fever could pass off for a normal viral flue. There is no specific treatment to destroy the virus. Recovery in these cases is usually uneventful.

However, complications could occur suddenly in some dengue patients and it is very important to be vigilant of the early warning signs and refer the patient immediately for institutional treatment. With complications, and delay in instituting the correct management, the fatalities of these patients could be very high.

4. Community organisation

(a) It is useful for the community to get organised to carry out dengue control activities in their own areas. Religious leaders and community leaders in the area should take the initiative in organising this activity.

Women's groups such as 'Mahila Samithies' and other welfare activity groups in the community or the particular area could participate and assist in organising most of the activities discussed under (1). Involving schoolchildren in these community activities will be very useful in implementing these programmes more successfully.

At the same time it gives the children a chance to show their capabilities in group work and improve their leadership qualities. Also, the child can motivate the parents and others in the family to get involve in these activities. With health workers working with the community the success of community involvement in dengue control programme will pay its dividends.

This cleaning up programmes should be continued once a week to get the benefits. Studies have shown that keeping the environment clean alone had reduced the vector density by 72 per cent. Source reduction through environmental sanitation should be the principal method of control of dengue fever.

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