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This virus has a 50% chance of killing you — and ticks that carry it are running wild

Published: 08 Aug. 2025, 18:52 Updated: 08 Aug. 2025, 18:54

Pictured is a Haemaphysalis longicornis tick, a carrier of severe fever with thrombocytopenia syndrome (SFTS). [YONHAP]

Ticks carrying a virus with a fatality rate as high as 47 percent are multiplying rapidly in Korea, with health officials warning that August and September mark the most dangerous months for infection.

The Korea Disease Control and Prevention Agency (KDCA) has urged the public to take extra precautions during outdoor activities, as cases of severe fever with thrombocytopenia syndrome (SFTS) cases are climbing sharply this year.

In its latest weekly health and disease bulletin, the KDCA reported findings from its 2024 surveillance of hard ticks, carriers of SFTS.

The disease, classified as a Class 3 infectious disease, infected 2,065 people from 2013 to 2024, killing 381 and resulting in a cumulative fatality rate of 18.5 percent. Individual cases have shown mortality rates ranging from 12 to 47 percent, placing SFTS among the most lethal infectious diseases.

Class 3 infectious diseases, designated by the Ministry of Health and Welfare, require urgent prevention and control because they are likely to spread suddenly and cause epidemics.

Tick numbers jump

From April to November of last year, KDCA researchers set traps at 16 sites nationwide, baited with dry ice. They recorded a tick density index — the number of ticks caught per trap — of 46.8, a 30 percent increase from 36.0 in 2023 and 13.9 percent higher than the 2020–2022 average of 41.1.

Different types of hard ticks [KOREA DISEASE CONTROL AND PREVENTION AGENCY]

Of the various Haemaphysalis tick species, those that transmit SFTS include Haemaphysalis longicornis, Haemaphysalis flava and Haemaphysalis japonica. In the latest survey, 97.3 percent of the ticks collected were Haemaphysalis longicornis.

The insects were most frequently found in grave sites, followed by grassy fields, scrublands and mountain trails.

August and September saw the most captures, coinciding with peak larval activity.

Inje County, Gangwon, had the highest share, accounting for 33.5 percent of all ticks collected. Samcheok, also in Gangwon, followed at 17.7 percent. Other high-density areas included Gochang in North Jeolla with 9 percent; Jeju with 8.1 percent; Dangjin, South Chungcheong, with 7.4 percent; and Cheongju, North Chungcheong, with 6.7 percent.

Climate change drives spread

Researchers linked the rise in tick density to warmer temperatures. In 2024, Korea’s average temperature was 14.5 degrees Celsius (58.1 degrees Fahrenheit), 2 degrees above the long-term average and 0.8 degrees higher than in 2023. April temperatures were particularly influential, with an average 2.8 degrees above normal and 1.7 degrees higher than the year before.

August 2024 saw the highest recorded average, maximum and minimum temperatures since observations began, a factor the KDCA said likely accelerated tick growth and reproduction.

“The average maximum temperature was 2.1 degrees higher than the previous year, which is believed to have affected the growth rate of hard ticks,” the KDCA said.

“Korea’s climate is shifting from temperate to subtropical, increasing the risk of vector-borne diseases such as those carried by ticks,” the researchers wrote, urging the public to follow preventive measures.

The hard tick's different developmental stages [KOREA DISEASE CONTROL AND PREVENTION AGENCY]

Cases on the rise

While tick numbers have increased, SFTS cases declined from 243 in 2020 to 198 in 2023 and 170 in 2024 — with annual deaths also falling from 38 in 2023 to 26 last year.

However, early 2025 figures suggest a reversal: 132 cases were reported from January to July, up 69.2 percent from the 78 recorded in the same period last year and 63.4 percent above the 2020–2023 average.

SFTS symptoms include high fever lasting three to 10 days, low platelet and white blood cell counts, nausea, vomiting and diarrhea. There is no treatment or vaccine.

The virus can also spread to humans through infected animals, including cats and dogs.

SFTS cases are most common in Korea, Japan and China.

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
BY SHIN SUNG-SIK [[email protected]]