by Dr Pradeep Kariyawasam Former Chief Medical Officer of Health, Colombo. Dengue outbreaks have been taking place in the country for 60 or more years, but the large-scale epidemics began only in the 21st century. There are basic understandings and actions that health officials…
by Dr Pradeep Kariyawasam Former Chief Medical Officer of Health, Colombo. Dengue outbreaks have been taking place in the country for 60 or more years, but the large-scale epidemics began only in the 21st century. There are basic understandings and actions that health officials must take if we wish not to see them taking place every year. First, not all patients who get dengue fever are reported to the Health Authorities as some may get only a mild fever and, after a few days, the fever will go away. Secondly, the vast majority will get treatment from their General Practitioners, and they may not be reported to the area Medical Officer of Health. Thirdly, there is a structural failure in dengue control in this country. Sri Lanka has fought dengue with “ad hoc measures” for over 50 years, relying on periodic “Mosquito Weeks” instead of sustained, year-round surveillance, preventive and control action. The success of Sri Lanka’s Malaria Control Programme was mainly due to the fact that it had dedicated staff throughout the country to eradicate the disease. Take for example the Epidemiology of Dengue Control Units of the Ministry of Health. They have no dedicated staff in the field to take measures needed to prevent the diseases spreading, especially in major urban centres run by Local Authorities. The issue of understaffing at the Local Authorities is an impediment that has not been addressed by the Ministry. Dengue spreads to other parts of the country from Colombo through the transport system. Trains and buses operating from the bus stands in Fort and railway yards in Maradana and Fort areas took, not only the persons who contracted the disease, but also infected Aedes mosquitoes. Those state employees, or students from outstations, who get ill in urban areas, go home to rest, in the majority of cases. That is why Matara, Puttalam, Kurunegala, Anuradhapura, and Kandy became dengue hotspots years ago. As the Chief Medical Officer of Health, I campaigned hard to have all field officer vacancies filled to carry out preventive measures, but the appeals fell on the deaf ears of the provincial and government officials. Colombo’s Public Health Department needed around 450 field officers (Public Health Inspectors, midwives, health instructors, mosquito control assistants) to inspect the city’s 80,000 premises but only had about 180 — leaving inspections badly under-resourced. There were budget constraints that prevented public education campaigns through television and newspaper advertisements. However, I must note that major NGOs and private firms helped me immensely and carried out educational programmes. The International award-winning Green Star programme was launched with their help. It was launched 25 years ago. The first lesson we have forgotten is that social mobilisation is a must for dengue prevention and control. Unfortunately, hardly any residents have realised the need to keep their premises clean. We cannot expect that from them when garbage mounds are visible everywhere and roadsides are not kept clear of rank vegetation. The Green Star programme was created to motivate the residents to keep their premises mosquito free while the Council took measures to clear the areas of garbage and vegetation. To recognise the efforts of the residents we pasted a ‘Green Star’ sticker on their walls, and they were proud to have one. This programme replicated in areas outside Colombo, too. The second lesson we have forgotten is that timing of starting dengue prevention work is a key aspect of a successful programme. We have two rainy seasons, although the weather pattern has changed, and we find that sometimes it rains much harder at other times. But it is important to start dengue prevention programmes much before the beginning of the rainy seasons. We used to get information on rainfall from the Department of Meteorology. So, the authorities, local or central, must start programmes in the latter part of April and September and see that all possible rainwater collection sites, utensils, etc., are removed. Canals and drains should be cleaned, biochemicals should be sprayed into gabion walls. More than 10 years ago when the government took action to clear the canal system, and with this kind of spraying, we found that hardly anyone had dengue fever in those areas. Shramadana campaigns are unheard of today, but these must be restarted as the government, or the Municipal or Urban Councils, cannot do everything alone. Social mobilisation is again the key to all this. It is said that the dengue virus has changed and the herd immunity cannot cope with the new type of virus. Years ago, a study was done in the eastern part of the city in the Wanathamulla area, where it was found that nearly 95% of the children in that area had dengue antibodies in their blood. Although that area was notorious for dengue, later only a few dengue patients were found there although I don’t believe that the mosquito density decreased. For dengue to spread, herd immunity should be low and mosquitoes should be abundant. But reducing mosquito numbers too effectively can lower community herd immunity, creating conditions for sudden major outbreaks as had been found in Singapore’s experience where reduced Aedes populations combined with imported dengue viruses which caused increased transmission. What should be remembered is that the number of Aedes mosquitoes that bite, the number of times they bite, and within which a particular period, determine how a person is infected. A lot of people wait for a vaccine to be given to them rather than spending time outside their garden destroying mosquito breeding places to prevent them getting the disease. There is a single dose vaccine, named Butantan, which covers all four virus types and could be given in one dose. But it is a long way off from reaching this country so, therefore, every effort should be made to reduce the mosquito population first. Fourth Lesson we have forgotten is that prevention is the best way to keep away hundreds entering hospitals with dengue fever. Source reduction, larvicide, repellents (DEET), insecticide-treated nets/strips, and remember that Aedes mosquitoes also transmit Chikungunya, Zika, and Yellow Fever — making vector control non-negotiable. What is needed is a formal partnership between public health officials and communities, as in the past. In Colombo, there were 300 Community Development Councils at the time of my retirement. Today only a handful are there. They provided hundreds of volunteers for our educational and preventive and control programmes. There was no cost to the Council as everything was looked after by the NGOs and CSR projects of the private sector firms. Schools willingly participated in most of our programmes and in return we taught them recycling and gave them bins to collect the stuff. All the departments in the Colombo Municipal Council helped even in a small way by sending their staff during a weekend for these programmes. These actions should be restarted. Staff members and volunteers were then appointed into Street Committees, which were given lots of 100 to 200 premises to check for breeding and create awareness. The inspections were carried out once a month. In the same manner they created Dengue Free Zones in housing schemes, settlements, schools and large land parcels in the areas allocated to them using the people living in and around these areas. Unfortunately, there was no continuation of such programmes. A lot of people request fogging in their areas believing that it could get rid of the epidemic. I see a lot of fogging being done during the present epidemic, too. However, using one machine and carrying out these programmes is dangerous as such action could spread the disease into newer areas. As soon as the mosquitoes get the smell of the smoke they fly into neighbouring regions. I have been advocating that if we fog then use at least 4-5 machines and block out an area and fog from the periphery into the centre, usually into the infected area. That way it is difficult for the mosquitoes to escape. Mapping is also a key aspect of dengue control. I used GIS mapping for this purpose 20 years ago and that helped us to investigate the reasons for the outbreaks, the direction of the spread and analyse the successes and failures of our programmes. I believe the Colombo Municipal Council is continuing with GIS mapping and we have a proper Epidemiologist now. But it is good if the officers come out and tell the public where the disease is and the direction of the spread as we did 20 years ago. At least then people will take an interest in cleaning up their premises. The Wolbachia issue: The Wolbachia bacteria were released in 2018 in Colombo and Nugegoda areas and the programme went on for several years. That has been successful in many countries. There is an attempt to restart the programme again, and I believe it should be started in between monsoon periods to mop up the remaining infected mosquitoes. Even for this we need the help of the community to breed and release the Wolbachia infected mosquitoes to the environment. Every year the epidemic is on the wane towards the end of July and that is a natural phenomenon. In the same manner every year in the May-July and November-January periods we either have smaller outbreaks or epidemics. Therefore, considering the past experience we can see that this epidemic will also go away in a few weeks. But the most important thing is to prepare for the next epidemic as all over the world the number of patients and epidemics is increasing.
