Taking the sting out of dengue
Chandra Devi Renganayar and Suzanna Pillay New Straits Times 13 Oct 13;
TRIALS: In 2008, it was reported that the Health Ministry would undertake an experiment to release genetically-modified mosquitoes to fight Aedes aegypti mosquitoes, the main carriers of the dengue virus. Was it a success? How effective have we been in efforts to control dengue fever? Deputy director-general of Health (public health) Datuk Dr Lokman Hakim talks to Chandra Devi Renganayar and Suzanna Pillay to get an insight into efforts to combat the scourge
Question: Where were the genetically-modified (GM) mosquitoes first released?
Answer: Our original proposed trial site was in Pulau Ketam, but our preliminary surveys indicated that the site was unsuitable for the trial. Instead, a trial site in Pahang was found to be ideal and the release was conducted in this site.
The trial, the first open release of male transgenic mosquitoes in Asia, was conducted on Dec 21, 2010, in an uninhabited forest (non-reserve forest land owned by the government off Jalan Tentera/Lebuhraya Bentong-Raub) in Bentong, Pahang.
Question: What was the outcome of the trial? Were the GM mosquitoes able to eliminate the Aedes aegypti mosquitoes as intended?
Answer: The goal of the trial was to understand the dispersal (that is, how far they fly) and longevity of the male OX513A strain dispersal, compared with the unmodified wild type strain under open field conditions. This was not a suppression trial and it was not done to determine the impact of the transgenic males on the Aedes population.
The Institute of Medical Research (IMR) released 6,045 transgenic male Aedes aegypti mosquitoes from the OX513A strain, along with 5,372 unmodified male mosquitoes from its laboratory strain. These two strains were marked with different-coloured fluorescent powder. Using stringent quality control, IMR ensured that the released mosquitoes were all male and cannot bite or spread diseases. The mosquitoes were recaptured using a network of adult traps.
The experiment was successfully concluded on Jan 5, 2011, in accordance with trial protocol. It was carried out in compliance with the National Biosafety Board's terms and conditions.
The dispersal and longevity of the GM Aedes aegypti and lab unmodified Aedes aegypti were similar, indicating that genetic modification (introduction of a single transgene) did not affect the biology of the mosquitoes. The longevity of the GM Aedes aegypti male was two days and the lab unmodified Aedes aegypti, 2.2 days.
Question: The experiment was reported in 2008 and, subsequently, that it was a suppression trial based on a successful field trial in the Cayman Islands. It was also reported that the field trial would be undertaken in collaboration with British-based Oxitec Ltd, an insect bio-tech company that had a proven GM technology.
Answer: Well, Oxitec did claim that their GM technology worked in the Cayman Islands. Based on this, they wanted to transfer the technology to Malaysia. But, this does not mean that we will apply this technology straightaway, especially if it is new to the country. Before any experiment is carried out in the field, it must be ensured that the site is appropriate for the release of the male transgenic mosquitoes. We need to do our own research.
The goal of the 2010 study in Bentong was to find out whether the behaviour of the transgenic mosquitoes was similar to normal mosquitoes. It was not a suppression trial to see whether the genetically engineered male mosquitoes would mate with the female mosquito population.
Question: Based on these reports, public perception was, and still is, that the experiment was to use genetically-engineered Aedes aegypti male mosquitoes to stop the spread of dengue. If this was not the purpose, why was it not clarified by the Health Ministry from the start?
Answer: When the experiment was completed in January 2011, the results of the findings were published in the IMR website and was picked up by some media organisations.
Question: What is the next move after the Bentong trial? Is the ministry planning to carry out the suppression trial and, if so, when will it take place?
Answer: There are no immediate plans for a suppression trial. As this involves research and development, it is best to ask IMR. I cannot answer for them.
Question: Doesn't IMR come under the jurisdiction of the ministry?
Answer: IMR answers to the director-general, not me. It is not under my jurisdiction.
Question: What is the dengue situation in the country? Is it on the rise?
Answer: The number of dengue cases from January to Sept 28 increased to 22,602 cases, a 38 per cent increase compared with 16,340 cases reported in the same period last year. A total of 1,149 dengue cases were reported between Sept 22 and Sept 28.
The total number of deaths from dengue also increased to 48, which reflects a 78 per cent increase from the 27 deaths reported in the same period previously.
Question: Why are we facing this situation, despite the many efforts taken to control dengue?
Answer: The increase in dengue cases is not specific to Malaysia, as other countries in the region have also reported an increasing dengue incidence. In fact, the increase is much higher in other countries in the region.
For example, Singapore and Laos have reported a 500 per cent and 1,000 per cent increase in dengue incidence compared with last year. It is a pattern in the region. You can see that the increase in Malaysia is much lower than these countries, as we have been able to control the increase through various measures.
Dengue is a cyclical endemic disease. This means there will be a cyclical rise and fall in the number of cases every few years, depending on the strain (of which there are four types) of dengue that is circulating and if the population has already built an immunity.
Source reduction measures through the elimination of mosquito breeding sites are the most effective method to control the spread of the disease. It should be noted that spraying insecticides and fogging are only a temporary means of controlling the adult mosquito population.
The public should check their premises for breeding sites and dispose of containers and stagnant water that may be a source of breeding mosquitoes.
Question: Where are the dengue hot spots in the country?
Answer: Dengue is predominantly an urban disease because of the abundance of the principal vector Aedes aegypti. Areas that have reported high numbers of cases include Selangor, Johor and the Federal Territories of Kuala Lumpur and Putrajaya.
Of the 244 dengue outbreak localities in the country, Selangor heads the list with 175 localities. Johor has 24 localities and the Federal Territory, 14. In the list of 20 dengue hot spots in the country, 19 were in Selangor and the other in the Federal Territory. The public can access the latest information on dengue hot spots from the ministry's website at http://idengue.remotesensing.gov.my.
Question: What are the obstacles in the fight against dengue?
Answer: Regional influences like rainfall and climate play a significant role in the transmission of the disease. These are beyond our control. However, the disease is also influenced by the cleanliness of our environment, which we can control.
The problem is compounded by people throwing rubbish indiscriminately. The lack of efficient solid waste management strategies also contributes to the increased availability of breeding sites.
We are trying to slow the rate of increase (in cases), but we need the public to do their part as well. We have had some success in engaging the people via our Communication for Behavioural Impact, or Combi, initiative. Localities with active Combi programmes are found to be less affected by the disease.
However, public participation is lacking in some highly urbanised localities like Kuala Lumpur, Selangor and Johor. Increased public participation and awareness in these areas is essential.
Question: What is the economic cost of dengue to the country?
Answer: Based on a study from 2002 to 2007, the immediate cost of dengue to Malaysia is between US$88 million (RM280 million) and US$215 million (RM683 million) per annum.
It is equivalent to between three per cent and seven per cent of the government's spending on healthcare.
Read more!
Posts
visitors since Nov 07