Senegal’s health ministry has confirmed a first case of Ebola, making it the fifth West African country to be affected by the outbreak.
Health Minister Awa Marie Coll Seck told reporters on Friday that a young man from Guinea was confirmed to have contracted the virus.
The man was immediately placed in quarantine, she added.
The current outbreak, which began in Guinea, has killed more than 1,500 people across the region.
At least 3,000 people have been infected with the virus. The World Health Organization (WHO) has warned it could get much worse and infect more than 20,000 people.
Senegal had previously closed its border with Guinea in an attempt to halt the spread of Ebola, but its frontiers are porous.
It had also banned flights and ships from Guinea, Liberia and Sierra Leone – the three worst-hit countries.
But the Guinean health services reported on Wednesday “the disappearance of a person infected with Ebola who reportedly travelled to Senegal,” according to Senegal’s health minister.
A young Guinean student later turned up at a hospital in the capital, Dakar, said Ms Seck, but he did not reveal that he had had contact with Ebola patients in his own country.
Senegal, a major transit hub for aid agencies, has a large Guinean population.
Separately on Friday, residents of Guinea’s second largest city, Nzerekore, rioted after its main market was sprayed with disinfectant in an attempt to halt the spread of the virus.
The exact cause of the riot is not clear – some people reportedly feared the spray would spread Ebola. Police responded by firing tear gas.
A 24-hour curfew is currently in place in the city, which is the capital of the Forest Region, where the Ebola epidemic has its epicentre.
However the BBC’s Alhassan Sillah in Guinea says the town has miraculously remained free of Ebola so far.
There have been relatively few cases in Guinea recently, with far higher infection rates in Liberia and Sierra Leone, and six deaths in Nigeria.
On Thursday, the WHO unveiled a plan aimed at stopping transmission of the virus in the next six to nine months.
Among its recommendations, it said countries affected should conduct exit screening to prevent the disease from spreading to a further 10 countries.
The plan calls for $489m (£295m) to be spent over the next nine months and requires 750 international workers and 12,000 national workers across West Africa.