South Korea has reported its first human-to-human transmission of a fatal tick virus, according to local health authorities. The country had its first tick-to-human case in 2013 and had seen a higher fatality rate for infected cases than was usual for the virus.

Health authorities confirmed on Wednesday that four medical staff in Seoul had become infected with what is known as severe fever with thrombocytopenia syndrome, or SFTS, according to the Korea Herald. They contracted it in September last year while attending to a 68-year old woman who suffered the same virus. All four were quickly cured, and only one developed serious symptoms, reported the Korea Herald. It is not known why authorities only announced it recently.

Symptoms of the virus include fever, vomiting, diarrhea and organ failure. Korea has had 36 reported cases of SFTS since its first case in 2013, and 16 have died so far. The recent fatality rate of nearly 50 percent is much higher than the usual 10 percent death rate from the virus, according to the Herald. There have not been any direct vaccines so far.

Human-to-human transmission was thought to be very rare, although it can be done via direct contact with an infected person. Health authorities have issued precautions only against tick bites previously but not against secondary infections, according to the Herald. “SFTS infectiousness is more of a problem than the Ebola virus in the country,” said Kim Song-han, professor of thoracic surgery at the University of Ulsan School of Medicine, according to MSN Korea. "It particularly requires attention because it can be spread via blood or mucosal secretions," he said. Kim advised medical staff attending to infected patients to don protective clothing such as gowns, gloves and masks.

SFTS has also been reported in China’s rural areas as well as Japan. Five cases of human-to-human transmission have been reported in China, with three involving infection within the family, Korea’s health authorities said, according to the Herald.