The deaths of monkeys at the Hong Kong Zoo due to a bacterial infection remain mysterious.

In the last 10 days, a total of 12 monkeys died while autopsies revealed a large amount of bacteria that cause rot.

According to the authorities they probably came from contaminated soil. Workers digging soil near the cages are believed to have brought in contaminated soil through their shoes, Hong Kong’s Minister of Culture, Sports and Tourism told local broadcaster RTHK.

The risk of the infection spreading to humans is “quite low”, Dirk Pfeiffer, a veterinary epidemiologist at the City University of Hong Kong, told the BBC. He added that soil contamination is often underreported in Asia, but “it’s always a concern if multiple mortalities suddenly occur in captive animal populations where this has never happened before.”

The 11 monkeys found dead earlier include endangered tamarins, as well as common squirrel monkeys and a De Brazza monkey.

Authorities said they died of melioidosis, an infectious disease that can be spread through contact with contaminated soil, air or water. It is caused by Burkholderia pseudomallei, a strain of soil-dwelling bacteria endemic to tropical and subtropical regions.

The 12th monkey died on Tuesday, and initial results showed it too had “similar damage … to the tissues of its organs,” officials said.

Authorities said the health of the remaining 78 mammals at the zoo was “normal”. However, the mammal department has been closed since October 14 for disinfection and cleaning.

The Hong Kong Zoo and Botanic Garden is the oldest park in the city and is located in its center, covering an area of ​​14 hectares.

Animal rights group Peta said it was concerned about the risk of zoonotic diseases such as monkeypox, which can be transmitted from animals to humans. ​