Taipei, Sept. 12 (CNA) The effective dispersal distance of the dengue-carrying mosquito Aedes aegypti, the primary vector in southern Taiwan, was found to be about 150 meters supporting the 200-meter spraying radius around confirmed cases set by authorities, according to a National Health Research Institutes (NHRI) study.<\/p>\n
“When an [mosquito-borne] outbreak occurs, we need to eliminate virus-carrying mosquitoes,” Huang Chin-gi (\u9ec3\u65cc\u96c6), an assistant investigator at the NHRI’s National Mosquito-Borne Diseases Control Research Center, said at a news conference Thursday in Taipei.<\/p>\n
“How far they can fly is crucial as it determines the scope of our control measures,” Haung added.<\/p>\n
NHRI data shows more than 98 percent of local dengue cases occur in southern Taiwan, while Centers for Disease Control (CDC) figures put this year’s tally at 12 local cases as of Sept. 8, all in the southern port city of Kaohsiung.<\/p>\n
Asked by CNA why Kaohsiung still saw a cluster of 12 cases if the mosquito’s effective dispersal distance is about 150 meters and spraying is done within 200 meters, Huang said outbreaks can persist due to factors such as insecticide selection and operator technique.<\/p>\n
Inappropriate insecticide selection and subpar field operations can allow transmission to continue even when the control radius is sufficient, according to Huang.<\/p>\n
“The control radius is only one part of a successful response,” Huang said, noting that other factors also determine whether an outbreak is contained, such as the timeliness of interventions.<\/p>\n
By collecting Aedes aegypti eggs from ovitraps — egg-laying traps for mosquitos — set across Tainan, Kaohsiung and Pingtung County, then rearing them to adults, researchers analyzed their genomes to analyze how far closely related, near-kin mosquitoes had dispersed.<\/p>\n
“For example, we can identify full-sibling relationships — offspring from the same mother and father — or half-sibling relationships sharing only one parent,” Huang said. “That lets us infer how far a mother might have flown to lay those eggs, or how far a father might have flown to mate with another female.”<\/p>\n
Analyzing genomes from 192 Aedes aegypti reared from ovitrap-collected eggs, Huang’s team found the median dispersal distance among closely related mosquitoes was 154 meters, with most values between 126 and 180 meters.<\/p>\n
While counties and cities in Taiwan set different outdoor chemical-spraying ranges around a confirmed patient’s residence, most use a 200-meter minimum radius, which is sufficient to contain Aedes aegypti’s 154-meter spread, Huang said.<\/p>\n
One “special” finding, Huang said, is that roads do not act as barriers — genomic data show mosquitoes cross streets freely — whereas administrative district boundaries within a city or county were linked to genetic differentiation among mosquito populations.<\/p>\n
“We found the separation [between administrative districts] is largely human driven,” he said, explaining that control measures such as source reduction and spraying create “pressure” on mosquito populations that pushes them apart.<\/p>\n
Since districts carry out control measures independently and at different times, mosquitoes that cross into a neighboring district are often killed before they can reproduce, reducing gene flow across the boundary and gradually creating genetically distinct populations even over short distances, Huang said.<\/p>\n
Asked whether districts can synchronize control measures, Huang said administrative districts are large and it’s impossible to complete all spraying and source reduction in a single day.<\/p>\n
He said this genetic differentiation can lead to different patterns of insecticide resistance among Aedes aegypti in neighboring districts.<\/p>\n
If an intercepted dengue-carrying mosquito can be genomically traced to its home district, responders can reference that district’s effective chemicals and deploy those agents immediately, he added.<\/p>\n
Starting in 2020, Huang’s team collected Aedes aegypti eggs and conducted a study spanning at least three years.<\/p>\n
An academic article from the research, titled “The Impact of Administrative Districts and Urban Landscape on the Dispersal of Aedes aegypti via Genetic Differentiation,” was published as a cover article in the international journal Molecular Ecology in February this year.<\/p>\n
(By Sunny Lai) <\/p>\n
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