Following more than a month during which no new Ebola cases were reported in the country, Liberia was officially declared Ebola-free on Saturday.
In a triumphant statement announcing an end to an epidemic that claimed the lives of more than 4,700 Liberians, the World Health Organization called the West African nation’s success in eliminating the deadly virus “a monumental achievement.”
Neighboring Guinea and Sierra Leone are still struggling to contain the deadly outbreak, though they have slowed the progress of the virus considerably, from hundreds of new cases per week at the epidemic’s peak this summer to just nine cases each last week.
Ebola has killed more than 11,000 people in the region, according to WHO estimates.
A country must go 42 days without reporting any new cases of the virus in order for the WHO to declare it Ebola-free. Liberia’s last known Ebola patient, 44-year-old Ruth Tugbah, died on March 27.
According to the WHO, 42 days is twice the virus’s maximum incubation period, the interval beginning when a person is first infected and ending when he or she begins displaying symptoms. The underlying rationale is that waiting twice the maximum incubation period should provide a margin of security to cover missed cases and other potential sources of infection.
However, some evidence has emerged since epidemic’s start that suggests that the virus may persist longer than 42 days.
The WHO has said that Ebola can survive in the semen of male survivors months after they stop displaying symptoms, and even after the virus is no longer present in their blood. Although it is not proven, the organization says it is likely that Ebola can be transmitted through the semen of otherwise cured men.
In March, fears that Ruth Tugbah may have contracted the virus sexually prompted Liberian health officials to urge Ebola survivors to practice abstinence, or at least safe sex. The WHO also amended its guidelines to recommend continued surveillance after a country is declared free of Ebola.
Although it may not apply to all possible infections, the 42-day rule provides a sound public health basis for declaring a country Ebola-free, New York University epidemiologist Ann Kurth told PBS NewsHour at the time of Liberia’s last Ebola case.
The WHO declaration also comes on the heels of the discovery of high levels of the virus in the eye of a patient who had become ill months earlier, The New York Times reported.
That patient is Ian Crozier, a doctor who contracted the virus while volunteering at an Ebola treatment unit in Sierra Leone. Although he was released from Emory University Hospital in October, Crozier was recently readmitted after suffering vision loss and intense pain in his left eye. Testing showed that Crozier’s eye was teeming with the virus, though it was not present on the eye’s surface or in his tears, meaning he was not contagious.
The infection has caused Crozier’s eye color to change from light blue to vivid green, a rare effect of severe viral infections.
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Though new information like the possibility of sexual transmission of Ebola and discoveries like Crozier’s eye infection have experts urging caution, the 42-day rule remains the standard.
The White House congratulated Liberia on reaching the milestone Saturday. In a statement, Press Secretary Josh Earnest said, “We congratulate the people of Liberia on reaching this important marker, and once again pledge our commitment to ending the Ebola outbreak in West Africa.”
But Earnest also urged continued vigilance, saying, “We must not let down our guard until the entire region reaches and stays at zero Ebola cases. And we must all work together to strengthen capacity around the world to prevent, detect, and rapidly respond to outbreaks before they become epidemics.”