Disease-carrying mosquitoes found in 16 of Seoul's 25 districts

Mosquitoes capable of transmitting infectious diseases have been collected in 16 of Seoul's 25 districts — 64 percent of the city — with malaria-carrying mosquitoes found in 14 districts and dengue-carrying mosquitoes in five.

The Seoul Metropolitan Government's Institute of Public Health and Environment noted that collections were made only at designated sites within each district, meaning the insects could be present across all 25 districts. With peak heat easing and temperatures beginning to fall, mosquito activity is expected to rebound, and city health officials are urging residents to take extra precautions.

On July 23, The Herald Business analyzed a report on Seoul's disease-vector mosquito collection status for the fourth week of June, obtained by Seoul Metropolitan Council lawmaker Oh Geum-ran of the Democratic Party of Korea from the Seoul Institute of Public Health and Environment. The two species identified were the Anopheles sinensis — the malaria vector — and the Asian tiger mosquito, which can carry dengue fever. The institute has conducted mosquito collection annually since March.

A total of 41 Anopheles sinensis mosquitoes were collected. Yongsan-gu recorded the highest count at 10, followed by Songpa-gu with five, Jungnang-gu and Gangdong-gu with four each, Guro-gu and Geumcheon-gu with three each, and Dobong-gu, Yangcheon-gu, Yeongdeungpo-gu and Gangnam-gu with two each. Jung-gu, Dongdaemun-gu, Gangbuk-gu and Gangseo-gu each yielded one.

Seven Asian tiger mosquitoes were collected in total. Gwangjin-gu had the highest count at three, while Dobong-gu, Eunpyeong-gu, Yeongdeungpo-gu and Geumcheon-gu each recorded one.

When the institute released last month's disease-vector mosquito surveillance results, it said overall mosquito activity this year was similar to the average, but that malaria-carrying mosquitoes were collected about two weeks earlier than usual and mosquitoes that can carry overseas-imported diseases such as dengue fever were collected about one week ahead of schedule.

However, an institute official cautioned that collections are conducted only at specific sites within each district to track population trends, and that a high count in a given area should not be interpreted as that area being especially vulnerable to infectious disease. The data also implies that no part of Seoul can be considered entirely safe from disease-vector mosquitoes.

Malaria, classified as a Class 3 infectious disease, is transmitted through the bite of an Anopheles sinensis mosquito infected with the malaria parasite and does not spread directly between people. Early symptoms include headache, loss of appetite, chills and high fever, followed by shivering as body temperature rises.

Dengue fever is also a Class 3 infectious disease. It spreads through the bite of a mosquito infected with the dengue virus, primarily the Aedes aegypti mosquito. Transmission by the Asian tiger mosquito — commonly found in South Korea — is possible, but the virus has not been detected in Asian tiger mosquitoes living in the country to date. Symptoms include sudden high fever, headache, muscle pain, joint pain, leukopenia, thrombocytopenia and bleeding; in some cases the disease proves fatal due to shock and hemorrhage.

According to the Seoul Institute of Public Health and Environment, 278 Anopheles sinensis mosquitoes and 47 Asian tiger mosquitoes were collected across Seoul during the fifth week of last month.

Since the start of this month, however, mosquito numbers have dropped sharply. The total daily count of mosquitoes collected in Seoul averaged 600 to 800 from late June through mid-July, but fell to just above 500 in the first week of August.

An institute official said mosquitoes are most active at temperatures between 25 and 27 degrees Celsius, but sustained heat above 30 degrees since early August has accelerated their aging and shortened their life cycles. The official added that the hot weather has also dried up the puddles where mosquitoes breed, further reducing their numbers.

Regarding the broader trend, the institute warned that overseas-imported infectious diseases such as dengue fever are on a sustained rise in Seoul as international travel and exchange increase. A total of 83 cases of overseas-imported infectious diseases were recorded in Seoul through Aug. 12, among them 11 cases of malaria and eight of dengue fever — together the most common after syphilis, which accounted for 39 cases.

With the heat expected to ease and mosquito activity likely to pick up again, the institute urged residents to take preventive measures. "Remove any standing water near your home, wear long-sleeved shirts and long pants when going outdoors, and use mosquito repellent," an official said.