KUALA LUMPUR: NEW methods to stop the spread of dengue, such as genetically modified (GM) mosquitoes and vaccines, are still a long way from being effective, said World Health Organisation Collaborating Centre for Arbovirus Research and Reference director at Universiti Malaya Prof Dr Sazaly Abu Bakar.
Instead, simple tried and tested methods, such as using mosquito netting and wearing light clothing, could lower cases of dengue.
“The technique of using GM mosquitoes has weaknesses. The idea is to replace the mosquito population. But if you release GM mosquitoes in Kajang, for example, would the mosquitoes from Cheras stop coming to Kajang? Mosquitoes will come from other areas. When you drive around from Shah Alam to Petaling Jaya, for example, you may be carrying mosquitoes around in your car,” he said.
Dr Sazaly said that while the GM mosquito experiment might have worked inside the lab, there was no guarantee it would work in the real world.
“If you eradicate one type of mosquito, the others might be more aggressive,” he said.
GM mosquitoes were released in Malaysia on a trial basis in Bentong, Pahang, in 2010 under a project by the Health Ministry.
GM male mosquitoes were released to mate with the local Aedes aegypti mosquitoes so that they would not produce offspring that survive adulthood, leading to a reduction in the overall Aedes aegypti population.
According to the latest dengue situation update from the World Health Organisation for the Western Pacific Region, Malaysia was the only country that registered a substantial increase in dengue cases in the region over the last year.
“Regional dengue activity is variable. The recent trend for dengue is increasing in Cambodia, Laos, Malaysia and Singapore.
“Compared with last year, Malaysia was the only country where cases of dengue were substantially higher this year compared to the same period last year ,” stated the report, dated June 3.
Health Minister Datuk Seri Dr S. Subramaniam had recently said that dengue cases this year had risen to 42,229, compared with 12,143 in the same period last year. As of June 21, 82 people had succumbed to dengue nationwide, compared with 25 in the same period last year.
On the introduction of a vaccine, Dr Sazaly said it was “far from being ready”.
“The problem with a vaccine is that it still does not accord full protection. There is still a lot more for us to learn.”
Bloomberg has reported that pharmaceutical company Sanofi has been working on an experimental dengue vaccine.
Their results on 10,275 vaccinated children showed a 56 per cent reduction in dengue cases.
Sanofi’s study consisted of three injections administered at six month intervals and was conducted in Malaysia, Indonesia, the Philippines, Thailand and Vietnam between 2011 and last year on children aged 2 to 14.
Dr Sazaly, however, said efforts by the government to introduce GM mosquitoes and a possible vaccination programme in the future may not work.
“Do we want to vaccinate 10 million people when only 50,000 people are affected?
“It is a matter of cost. Who are we going to give the vaccine to? Children or adults? Most of those affected are young adults.
“It used to be that young children got the virus, and now it’s young adults.”
He said some tried and tested methods could be used to control dengue instead.
“It’s easy to avoid dengue — just don’t get bitten by mosquitoes. When at home, sleep in a mosquito net. Wear bright clothing, and, at dusk or dawn, don’t wear dark clothing. Primary schoolchildren should wear bright clothing. Perhaps khaki instead of dark blue. It has been scientifically proven that dark blue and black attracts mosquitoes.”
Dr Sazaly said people who had dengue fever had hundreds of millions of viruses in their blood. As mosquitoes are multi-biters, they should avoid getting bitten again, to avoid the spread of the disease.
He said the current spike in dengue cases was not extraordinary, as there was also a spike in March this year.
“The number will go down again after the rain comes. When it rains, stagnant water will overflow and the dengue larvae is carried away, thus the mosquitoes can’t breed.
“During the hot season, though, trapped water becomes stagnant. It becomes a breeding ground for mosquitoes.”
Even a spot of water the size of a 20 sen coin is enough for the mosquitoes to breed.
“The dry season is also when there is a lot of outdoor activities. Therefore, the exposure is higher.”
Dr Sazaly said methods such as fogging only had the ability to get rid of mosquitoes for about half an hour.
“The most (that the effect of) fogging will last is 30 minutes. After that, the mosquitoes will just come back. We never measure the efficacy.”
Dr Sazaly stressed that mosquitoes alone were not the problem. If no one has dengue fever, then the mosquitoes will be clean of the virus.
“That’s why during some years, we don’t have dengue fever — or an exceptionally low number of cases. The spread of the disease stops. If someone gets it, then it starts to spread again.”
He also refuted claims of a new strain of the virus.
“We are still seeing the DEN-1 to DEN-4 types. DEN-1 is still dominant. They are all equally dangerous.”
He said that the same weather patterns that led to the increase of Aedes mosquitoes also led to the increase of Japanese Encephalitis (JE)-carrying mosquitoes.
“In the cities, you will see high cases of dengue. Out of town, you have JE.
“JE exists in padi fields and water canals. It is different from dengue in the sense that the Aedes mosquito needs clean water.
“The Culex mosquito, which carries the JE virus, on the other hand, can breed in dirtier water,” he said.
“Malaysia is now an endemic country. It is even worse than an epidemic.”