Sierra Leone has 2nd Ebola case after outbreak's end 

WHO declares West Africa Ebola-free 01:45

Story highlights

• New patient is an aunt of a woman who died of Ebola in Sierra Leone last week
• World Health Organization had declared an end to two-year Ebola outbreak in West Africa
• The outbreak killed about 11,300 people and infected 28,600 others

(CNN)A second case of the deadly Ebola virus has been reported in the West African nation of Sierra Leone in as many weeks -- just seven days after health officials declared a major epidemic in the region had ended.

The two cases are connected. The latest patient -- a woman being treated in the capital, Freetown -- is an aunt of a 22-year-old woman who died of Ebola last week in Sierra Leone, World Health Organization spokesman Tarik Jasarevic said Thursday.

The aunt, who had cared for her sick niece, tested positive for the virus after developing symptoms while in quarantine Wednesday, Jasarevic said.

The latest cases have links to the neighboring country of Guinea, where the 22-year-old first became sick, the WHO has said.

On January 14, the organization declared an end to the Ebola outbreak that killed about 11,300 people and infected 28,600 others, mostly in the West African countries of Guinea, Liberia and Sierra Leone.

Flare-ups, though, were anticipated. The declaration meant only that the three nations had reported zero cases for at least 42 consecutive days, or two 21-day incubation cycles of the virus.

"Lessons of the disease have taught us that countries that have experienced recent active transmission of Ebola remain at high risk of these small-flare ups, which is why strong prevention, detection and response systems must remain in place and communities must remain vigilant," Jasarevic said.

Flare-ups have happened before. Liberia was first declared free of Ebola transmission in May, but the virus has returned twice, with the latest case in November.

The WHO cautioned that the three countries remain at high risk of additional small outbreaks of the Ebola hemorrhagic fever.

Evidence shows that the virus disappears relatively quickly from survivors but can remain in the semen of a small number of male survivors for as long as a year, and in rare instances, be transmitted to sexual partners.