The numbers are mind-boggling: Over the past four months, half a million people are suspected of having contracted cholera in Yemen and 2,000 have died from the diarrheal disease.

The outbreak took off in earnest in late April, sweeping through this country of 27 million people on the Arabian Peninsula. Yemen has been engulfed in political strife for years, a factor that has greatly exacerbated the scale of this epidemic.

Cholera is caused by the bacterium Vibrio cholerae, which attacks the intestine. Most infections are mild, or even symptomless. But as many as 10 percent of infected people develop severe illness — vomiting and profuse, watery diarrhea that lead to a rapid loss of body fluids, which, in turn, can induce dehydration, shock and death.

This cholera outbreak is the largest currently underway in the world. Annually, between 3 million and 5 million people are infected with cholera and the infection claims an estimated 100,000 lives every year, according to the Centers for Disease Control and Prevention.

The Yemen case count has been declining since early July, the World Health Organization said Monday, with transmission slowing in previously hard-hit areas. Still, transmission continues in newly affected areas, and it’s estimated 5,000 new people are being infected daily.

The already under-resourced health care system is collapsing under the weight of the outbreak, the WHO said. Millions of people in the country don’t have sources of safe, clean water, and waste collection efforts have ceased in major cities, the agency said.

Meanwhile, 30,000 health care workers haven’t been paid for a nearly year — a situation denounced by the new WHO director-general, Tedros Adhanom Ghebreyesus.

— Text by Helen Branswell