Health authorities are assessing the effectiveness of using bacterial infection in mosquitoes to fight dengue fever, although eliminating breeding grounds remains the most effective method, entomologist Chen Chin-seng (陳錦生) said on Thursday.
Dengue fever has been on the rise with higher summer temperatures, and one known way of prevention is to control insect vector population by introducing sterilized mosquitoes infected with Wolbachia bacteria, said Chen, a university professor and consultant to the National Mosquito-Borne Diseases Control Research Center.
Wolbachia is one of the bacteria that infects mosquitoes and other insects, and it is a reproductive parasite, causing an infected male mosquito to render the female sterile while mating, Chen said.
Photo courtesy of the Kaohsiung Department of Health
This “enforced family planning for mosquitoes” used in Southeast Asian countries before requires scientists to infect both male and female mosquitoes with Wolbachia in a laboratory setting, he said.
Batches released outdoors might be able to replace the wild population, with females still capable of stinging humans, but with a lesser infection rate, and these mosquitoes have a shorter lifespan, Chen said.
Singapore wanted to utilize male mosquitoes’ polygamous habit of mating with multiple females to reduce the wild mosquito population, Chen said.
“However, results are different for the actual plans, and Singapore is 2.6 times the size of Taipei, while their program, which started in 2016, has seen limited success, due to the effects of neighboring Malaysia,” he said. “Singapore had a big dengue fever outbreak last year, and this year it has already had more than 5,000 cases.”
“Currently we have cultivated Taiwanese species of Wolbachia at our research center and have the technique to raise mosquitoes,” Chen said. “We need pilot tests on how best to release them outdoors, and find out the Wolbachia infection rate among several generations and related issues.”
“It could be possible to do so [infect mosquitoes] on Orchid Island (Lanyu, 蘭嶼), Green Island (綠島) and other islets to effectively reduce mosquito populations, but the whole of Taiwan is a quite large area, and we have tourists coming in and out, so mosquitoes could also enter the country in cargo ships from Southeast Asia,” he said.
In the past Taiwan tried to sterilize male fruit flies with X-ray irradiation, but that program did not manage to reduce the fruit fly population, Chen said.
The authorities spray insecticide around neighborhoods to deal with the outbreak and releasing bacteria-infected mosquitoes would not be successful, as the insecticide would also kill the released mosquitoes before they can spread Wolbachia, he said.
The most effective and economical way is still to eliminate the breeding pools, Chen said.
“No breeding for mosquitoes, then you have no need to kill them off,” he said.
The four steps remain the best way: local patrolling, removing pools of water, cleaning containers, and using a brush to wipe them dry, Chen said.
“One container usually contains several hundred mosquito eggs or larvae,” he said. “We can eliminate them by drying out and cleaning up these breeding pools.”
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