A terrifying flesh-eating disease that can claim limbs is “exploding” in parts of Australia — but doctors are stumped as to how it’s transmitted and where it originates, according to reports.

The disease, known as the Buruli ulcer, usually starts off as a single, painless red lump — resembling a bug bite — on the arms or legs and slowly enlarges over weeks to months.

It’s caused by the bacterium Mycobacterium ulcerans and can destroy skin or soft tissue, according to the Centers for Disease Control and Prevention.

In worst cases, the disease — which comes from the same family as leprosy and tuberculosis — can cause irreversible deformity, bone infections or amputation.

Buruli ulcer is not the “most aggressive” flesh-eating disease, Daniel O’Brien, deputy director of the department of infectious diseases at Barwon Health in Victoria, told the Washington Post.

The tropical disease has reached epidemic levels in Victoria, a southeastern state in Australia and home to Melbourne – and is “rapidly increasing in number” as well as “becoming more severe in nature,” according to the Medical Journal of Australia.

Reported cases of Buruli ulcer in Victoria surged 51 percent from 2016 to 2017, which recorded 275 cases, according to O’Brien. The number of “severe” cases has doubled in the last five or six years, he added.

Last year, there were at least 2,209 cases of Buruli ulcer reported — with the majority of the cases from West and Central Africa, according to the World Health Organization.

Australia and Nigeria have reported an increase in cases, the WHO said.

“The numbers are exploding,” O’Brien said.

Buruli ulcer can be fully cured with antibiotics — but many people don’t even know they’re infected because symptoms can take up to six months to show.

The disease was first recognized in Victoria in 1948, but doctors are still baffled by where it lives in the environment and how it’s transmitted to humans.

“It is difficult to prevent a disease when it is not known how infection is acquired,” the Medical Journal of Australia said.

Warning: graphic image