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Koreans face itchy — and potentially fatal — autumn as mosquito numbers surge

Published: 25 Sep. 2024, 15:31

LEE SOO-JUNG
[email protected]

Researchers classify collected mosquitoes at a laboratory in Suwon, Gyeonggi in April. [YONHAP]

Korea is seeing a rise in the number of mosquitoes nationwide in autumn, along with an increase in the number of mosquitoes that can transmit the Japanese encephalitis virus (JEV) caught by health authorities earlier this month.

The Seoul Metropolitan Government said on Tuesday that it collected approximately 25,900 mosquitoes from 54 sites across the city through a digital mosquito monitoring system between Sept. 1 and Sept. 14.

Per single day, 1,850 mosquitoes were tallied on average, a 6.3 percent increase from last month’s 1,739.7 mosquitoes daily.

Generally, mosquitoes thrive in summer from June to August because they have higher chances of survival when outdoor temperatures range between 15 and 30 degrees Celsius (59 and 86 degrees Fahrenheit). Periodic rain also helps them survive.

However, this year’s long-lasting heat wave and unpredictable downpours accompanied by record-breaking precipitations appear to have altered their peak season. In July and August, daily highs frequently reached 33 degrees Celsius.

A report from the JoongAng Ilbo on Tuesday said this year’s extraordinary weather made them relatively inactive in July and August compared to previous years.

The report also noted that the recent retreat of sweltering heat waves and a drop in daily temperatures seemingly triggered a rebound in their population this month.

The daily average of mosquitoes trapped by the Seoul city government surged from 1,287 in May to 2,282 in June.

The figure dropped slightly to 2,023 in July and 1,739 in August before rising again to around 1,850 in the first half of September.

“Extreme heat waves made water in puddles evaporate faster," said Prof. Lee Dong-kyu, a biological science professor at Kosin University. He also noted that such conditions "shortened their life span."

Mosquitoes usually lay eggs in puddles or areas filled with water.

A recent increase in the population of Culex tritaeniorhynchus mosquitoes prompted health authorities to raise the alarm because the species can spread JEV to animals and humans.

The state-run Korea Disease Control and Prevention Agency (KDCA) said it caught 301 Culex tritaeniorhynchus mosquitoes in the first week of September. The agency saw a twofold increase from the previous year’s average of 150.

Also, the specific type of mosquito accounted for nearly 54 percent of the 557 mosquitoes caught by the KDCA in the first week of September. The ratio has grown recently, recording 36 percent in July and 50 percent in August.

"Culex tritaeniorhynchus mosquitoes used to be most active in August to September. However, intense heat waves and downpours in recent years made their activities peak in September," Prof. Lee said.

He added that the mosquitoes "are usually observed to be active even after October.”

JEV is a mosquito-borne infection that can accompany symptoms ranging from fever to neuropsychiatric disorders. Its fatality rate is reportedly to be around five to 30 percent.

“Climate change advanced the date of issuing JEV advisories by three months and JEV warnings by one month compared to 1975,” the KDCA said.

An official from the KDCA said research to identify a correlation between the increase in the Culex tritaeniorhynchus mosquito population and this year’s weather is currently underway. The report is expected to be published at the end of this year.

BY LEE SOO-JUNG, JEONG EUN-HYE [[email protected]]