A fourth person in northern China has been diagnosed with the plague this month, officials confirmed, as a flea and rat eradication campaign was carried out by local government.

The Ulanqab government in central Inner Mongolia said on Wednesday that a herder who had been diagnosed with bubonic plague was currently being treated in isolation and was in a stable condition.

Another person was diagnosed with bubonic plague in Inner Mongolia’s Xilin Gol league on November 16, more than 400 kilometres (250 miles) away.

And in mid-November two patients from Inner Mongolia were moved to Beijing for treatment of the highly-contagious pneumonic strain of the plague.

The pneumonic strain can prove fatal in 24 to 72 hours and is the “most virulent form” of the disease according to the World Health Organisation (WHO), while the bubonic form is less dangerous.

The Ulanqab government said earlier that it had sprayed almost 200 acres of land last week as part of “rat- and flea-extermination work.”

Ulanqab officials didn’t disclose the specifics of how the latest patient caught the plague, but said the patient had been “active” in a plague-affected location prior to falling ill.

The plague germ Yersinia pestis can be transmitted to humans from infected rats via fleas.

Though the highly-contagious plague is rare in China, several cases have proven deadly in the past few years.

According to China’s National Health Commission, a total of five people have died from the plague between 2014 and September of this year.

In 2014, a man died of the plague in northwestern Gansu province and sparked the quarantine of 151 people.

The 30,000 people living in Yumen, the town where the man died, were also prevented from leaving, with police at roadblocks placed on the town perimeter.

In neighbouring Mongolia, a couple died of the bubonic plague in May after they ate raw marmot meat, another carrier of the plague germ.