A total of four Koreans have died since last month after contracting a deadly virus often transmitted by ticks, according to health authorities. All of the deceased patients were aged 70 or older.

The disease, called severe fever with thrombocytopenia syndrome, was first reported in China in 2009. It has an incubation period of six to 14 days and symptoms include fever, diarrhea, multiple organ failure and leukopenia. 

The first patient who died of the disease this year contracted the virus while working at a farm on Jejudo Island, the Health Ministry said. The 74-year-old died on June 14. Since then, three more patients have died in Gyeonggi and South Gyeongsang provinces.

To prevent the disease, health authorities advised people to wear long sleeves when working on farms and to not lie down on lawns without a mat from April to November. In China, the disease has a fatality rate of 12 percent.

On top of SFTS, a number of infectious disease cases have been reported this month. Two people have been infected by dengue fever, a mosquito-borne disease, while nine people have contracted malaria in Gangwon Province, according to the Health Ministry.

 By Claire Lee (dyc@heraldcorp.com)