DAKAR, Senegal — The World Health Organization says the death toll from the worst outbreak of Ebola on record has reached 887.

That’s an increase of 158 since the global health body released figures on July 31.

WHO said in a statement on Monday that there now have been more than 1,600 cases of Ebola since the disease emerged in Guinea earlier this year.

According to WHO, there now have been a total of 358 deaths in Guinea, 255 deaths in Liberia, 273 deaths in Sierra Leone and one in Nigeria.

The news comes as Nigeria announced Monday that it now had confirmed a second case in Africa’s most populous nation. Health Minister Onyebuchi Chukwu said the case is a doctor who had helped treat Patrick Sawyer, the Liberian-American man who died July 25 days after arriving in Nigeria from Liberia.

Test samples are pending for three other people who also treated Sawyer and now have shown symptoms of Ebola, he said. Authorities are trying to trace and quarantine others.

“Hopefully by the end of today we should have the results of their own test,” Chukwu said.

The emergence of a second case raises serious concerns about the infection control practices in Nigeria, and also raises the specter that more cases could emerge. It can take up to 21 days after exposure to the virus for symptoms to appear. They include fever, sore throat, muscle pains and headaches. Often nausea, vomiting and diarrhea follow, along with severe internal and external bleeding in advanced stages of the disease.

Sawyer, who was traveling to Nigeria on business, became ill while aboard a flight and Nigerian authorities immediately took him into isolation upon arrival in Lagos. They did not quarantine his fellow passengers, and have insisted that the risk of additional cases was minimal.

Nigerian authorities said a total of 70 people are under surveillance and that they hoped to have eight people in quarantine by the end of Monday in an isolation ward in Lagos. The emergence there is particularly worrisome because Lagos is the largest city in Africa with some 21 million people.