SHANGHAI (Reuters) - China reported a third case of bubonic plague on Sunday after two other plague cases were revealed last week, but the disease remains rare despite its fearsome reputation and authorities say the cases appear unrelated.

A member of the plague prevention team under a local disease control and prevention centre holds rodents on a grassland in Serxu county, Garze Tibetan Autonomous Prefecture, Sichuan province, China August 28, 2019. Picture taken August 28, 2019. REUTERS/Stringer

HOW DOES INFECTION OCCUR?

Two patients from Inner Mongolia were quarantined in Beijing suffering from pneumonic plague, authorities said last week. A 55-year old man from the same region was later diagnosed with bubonic plague after eating wild rabbit meat, the health commission said.

Both types of plague are caused by the Yersinia pestis bacterium.

Bites from infected fleas are the most common cause of bubonic plague infection, but the pneumonic variant - where the bacterium is breathed into the lungs - is more dangerous because it is spread through coughing.

A rarer third variant of the diseases is septicaemic plague, which infects the bloodstream.

WHAT ARE THE RISKS?

Plague has killed tens of millions of people around the world in three major pandemics, with about a third of Europe’s population wiped out in the 1300s by bubonic plague, known as the Black Death.

The bacterium is believed to have originated in Yunnan in southwest China, where it remains endemic. Opium trade routes from Yunnan caused the third global plague outbreak in 1894, but it has since become increasingly rare.

Between 2010 and 2015 there were 3,248 cases worldwide, leading to 584 deaths - a fatality rate of 18%, according to the World Health Organization.

From 2009 to 2018, China reported just 26 cases and 11 deaths. By comparison, there were 12,082 cases of rabies over the same period, with a fatality rate of 96%.

The China Center for Disease Control said the plague is “an ancient bacterial infection that can be treated clinically with a variety of effective antibiotics” if caught early.

IS PLAGUE LINKED TO CLIMATE CHANGE?

The spread of plague in the 1300s has been linked by scientists to unstable climate conditions that caused the disease to evolve and spread more quickly to rats, fleas and humans.

Floods also contributed to the disease’s rapid spread via new water routes.

China says climate change has caused an increase in rodent populations throughout Inner Mongolia. A combination of heavier rainfall followed by longer summer droughts has allowed rats to thrive.

ARE THERE STILL RISKS?

China remains concerned about the risk of outbreaks as formerly remote plague-prone rural regions are integrated into the national economy.

The Center for Disease Control says Yunnan and the Qinghai-Tibet plateau in the far west are particularly vulnerable.

Qinghai officials said earlier this year the risk of plague spreading to regions with high population densities had increased because of urbanisation, new infrastructure and tourism.

Infectious diseases are also a sensitive issue for Beijing after an outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003, which many blamed on the failure by authorities to disclose information in a timely manner.