DAKAR, Senegal — Senegalese authorities on Monday were monitoring everyone who was in contact with a student infected with Ebola who crossed into the country, and who has lost three family members to the disease.

An Ebola outbreak in West Africa has killed more than 1,500 people in Guinea, Liberia, Sierra Leone and Nigeria. The university student is Senegal’s first case of the dreaded disease.

The 21-year-old left Guinea on Aug. 15, just days after his brother died of the disease, according to Guinea’s Health Ministry. It said that the brother apparently caught Ebola in Sierra Leone.

The student traveled by road, crossing into Senegal despite a border closure. He arrived in Dakar, the Senegalese capital, on Aug. 20, according to the World Health Organization, and was staying with relatives on the outskirts of the city. The agency said that on Aug. 23, he went to a medical facility seeking treatment for fever, diarrhea and vomiting – all symptoms of Ebola but also many other diseases.

But he concealed from doctors that he had had contact with infected people. He was treated instead for malaria and continued to stay with his relatives before turning up at a Dakar hospital on Aug. 26.

Senegal’s Health Ministry said Sunday that it has since traced everyone the student came into contact with, and they are being examined twice a day.

The Health Ministry in Guinea said that since the young man left home, his mother and a sister have died of the disease, and two other brothers are being treated for it.