Democratic Republic of Congo's confirmed ​Ebola cases have risen above 4,000 for the ‌first time in the current outbreak, government data showed.

The epidemic, the world's second-largest, has been described as the fastest-spreading ​on record.

Experts believe infections started circulating months before ​the outbreak was declared on May 15 ⁠and that the true number of cases could ​be much higher than the official tally.

The Central African ​country's public health institute said in its latest report that the total number of infections had reached 4,053, including ​1,850 deaths.

Cases have been recorded in five provinces ​in the country: Ituri, North Kivu, South Kivu, Haut-Uele and Tshopo.

A report ‌published ⁠in the journal Science last month concluded that Congo's outbreak had started in January, or even earlier, in Ituri. Researchers identified more than 500 suspected ​cases between ​mid-January and ⁠May 15.

Delayed detection, overwhelmed surveillance, military conflict, and a lack of vaccines and ​treatments for the species of the ​virus involved ⁠have allowed the disease to outrun containment efforts this time.

So far only West Africa's 2014-16 outbreak has ⁠been ​bigger, with over 28,000 cases ​recorded across Guinea, Liberia and Sierra Leone.