Northwest China's Ningxia Hui Autonomous Region issued a level IV emergency response on plague prevention and control on Tuesday night, after one patient was confirmed to be infected with the zoonotic bacteria.

The case was originated in another region of the country, local authorities said in a notice, without detailing specific places.

Under the level IV warning, Ningxia will treat the patient with all its efforts and implement relevant epidemic measures to ensure there will not be further spread and transmission.

A level IV warning is the lowest level in the national emergency response mechanism for plague, according to media reports.

In April this year, the city of Baotou, in North China's Inner Mongolia, activated a warning against bubonic plague as one dead infected mouse was found.

The plague is a severe infectious disease that is highly transmissible and has a high fatality rate. It is a Class A infectious disease, the highest classification under China's Law on the Prevention and Treatment of Infectious Diseases.

Plague-infected rodents are a key source of the spread of the disease which is mainly transmitted among humans through bites from infected fleas.

According to the World Health Organization, plague is caused by Yersinia pestis, a zoonotic bacteria usually found in small mammals and the fleas they carry. Bubonic plague is the most common form and is characterized by painful swollen lymph nodes or buboes.

It can be a very severe disease in people, with a fatality ratio of 30 to 60 percent for the bubonic type and is always fatal for the pneumonic kind when left untreated, according to the WHO.

In August 2021, Ningxia also reported a confirmed case of bubonic plague in its capital city Yinchuan. The case was traced back to Inner Mongolia, with the patient in critical condition, triggering a level IV emergency response on plague prevention and control.