Senegal confirmed its first case of Ebola today, becoming the fifth country in West Africa to detect the virus that has killed more than 1,500 people in the current outbreak as it rages ever faster through the region.

The day after the World Health Organization warned that the incurable disease could infect at least 20,000 people, the Senegalese health ministry said a young man was being treated under quarantine in the capital Dakar.

The patient is a university student from Guinea, the source of the outbreak, and initially failed to tell medical staff that he had come into contact with Ebola patients there. It is unclear how he arrived in Senegal, which officially closed its border with Guinea a week ago — highlighting the difficulties of containing the epidemic in a region with porous frontiers and weak infrastructure.

The presence of the disease in Senegal is particularly concerning as it is a tourist destination and major travel hub for the region.

Riots broke out in Guinea's second largest city after a market was sprayed with disinfectant in an attempt to curb the spread of the virus.

People attacked medical workers and the hospital in Nzerekore, near the border with Liberia, while reportedly shouting, "Ebola is a lie." But it was also claimed that some feared that the spray would infect them with the dreaded disease.

Police fired tear gas reportedly in response to gunfire from rioters, while workers from the local Red Cross were forced to flee to a military base.

It is not the first time that health workers and facilities have come under assault from those mistrustful of claims about the disease. In some communities, residents are in thrall to rumors that Ebola is either a hoax or was invented by the West. Earlier this month, 17 Ebola patients fled from a Monrovia clinic after it was stormed by armed gunmen claiming the virus was a fiction — further frustrating efforts to halt its spread.

'It's a grave situation… the horizon is getting wider and wider by the day'

The disease, which is spread by contact with bodily fluids of infected individuals, has so far infected some 3,000 people, killing 1,552 according to figures released by the WHO on Thursday. Guinea, Liberia, and Sierra Leone — three deeply impoverished countries — have been worst hit, with a handful of cases reported in Nigeria.

The WHO said that the outbreak was accelerating, with the highest increase in cases this week — more than 500 — since it was first detected in March. Almost 40 percent of the total number of known cases had occurred within the last three weeks, it reported.

Liberia has suffered the biggest rise in infections, but the WHO said Sierra Leone and Guinea had also seen their worst tolls of any week so far.

"There are serious problems with case management and infection prevention and control," the report said. "The situation is worsening in Liberia and Sierra Leone."

Neither of the two countries had sufficient capacity in treatment centers to handle the growing flood of cases, it added.

In Liberia's Bong County, one of the epicenters of the West African outbreak, health workers said that they were unable to cope with the march of the disease, which is spreading to ever more communities.

The Ebola strain sweeping through West Africa has mutated repeatedly.

Bong County health administrator Fatorma Jusu told VICE News said the area was in desperate need of treatment centers and experienced staff, adding that they had no more beds for Ebola patients. Nine medical workers had themselves contracted the disease, he said, eight of whom had died.

"The situation is out of hand," Jusu said. "It's a grave situation… the horizon is getting wider and wider by the day."

"We do not have treatment facilities," he said, adding that people were dying in their communities and therefore spreading the disease further, with the rate of infection rising. Health workers were able to attend to very few cases, Jusu explained. "All the rest are dying."

On Thursday, scientists from Harvard University said the Ebola strain sweeping through West Africa had mutated repeatedly throughout the current epidemic, a fact that further complicate treatment for the disease that as yet has no known cure. Findings published in the journal Science also indicated hundreds of genetic mutations, making this outbreak different from any in the past.

A small number of patients, mostly in the US and Europe, have received the experimental drug ZMapp, which today was reported to have been 100 per cent effective in trials on monkeys, even at the later stages of the disease.

The US National Institutes of Health announced on Thursday that human trials would begin next week on a new vaccine being developed by its National Institute of Allergy and Infectious Diseases (NIAID) and GlaxoSmithKline. The vaccine is also to be tested separately in Britain, Gambia and Mali.

Anthony Fauci, director of NIAID, said the detected mutations made it imperative the disease was halted now.