As an investigation into an Ebola family cluster in Liberia's capital continues, the World Health Organization (WHO) said today that no other cases have been detected anywhere else in West Africa, except for the three recently reported cases. But another United Nations (UN) agency revealed that the mother of the first patient in the cluster showed signs of an earlier infection.

The first case detected in the cluster involved a 15-year-old boy who died from his infection on Nov 23. In its weekly update on the region's outbreak, the WHO said five of the boy's family members are in an Ebola treatment center and that illnesses have been confirmed in the boy's 8-year-old brother and their 40-year-old father.

Investigations into the source of the cluster are in early stages, the WHO said. It added that so far 149 contacts have been identified, including 10 healthcare workers who had close contact with the teen before he was isolated.

Questions surround virus source

Meanwhile, other details about the illness cluster surfaced in a Nov 23 situation update from UNICEF (UN Children's Fund), which was posted by ReliefWeb. Blood tests on the mother found high levels of Ebola antibodies, hinting at a recent recovery from the disease.

The group said elevated antibody levels were also seen in blood samples from the woman's 2-month-old baby, which UNICEF said tentatively suggests they came from the mother and not a recent infection.

Authorities still haven't pinned down the source of the teen son's infection, and possibilities include transmission from a survivor, exposure to an undetected transmission chain, or reintroduction from wildlife. Earlier this week a WHO official said a missed transmission chain source was unlikely, since Liberia was so far along in its enhanced surveillance period after being declared free of the virus on Sep 3.

The Ebola virus is known to persist in immune-protected body areas of survivors, such as testes, with semen and sexual transmission being the main concerns. At a media briefing earlier this week, Bruce Aylward, MD, MPH, the WHO's assistant director-general in charge of Ebola outbreak response, said that in seven other Ebola flares, health officials couldn't rule out Ebola transmission from a survivor.

He said the "inevitable, but rare" transmission instances typically don't lead to many infections or transmission generations, but added that such cases show the importance of quick detection and response in the three West African outbreak countries.

Contacts offered vaccine

UNICEF said the Ebola vaccine will be offered to contacts and contacts of contacts. The report didn't specify which vaccine. Given the ring vaccination nature of the measure, it is likely VSV-EBOV, which was shown to be so effective in Guinea's ring vaccination trial that it was extended to Sierra Leone.

Contacts of a Scottish nurse who survived Ebola and was recently hospitalized with a related meningitis complication were also offered VSV-EBOV.

The WHO said the new cases in Liberia underscore the importance of robust surveillance measures to detect reintroduction or reemergence in currently unaffected areas. Sierra Leone was declared free of the disease on Nov 7, and Guinea began its countdown to Ebola-free status on Nov 16.

West Africa's overall outbreak total is now at 28,601 confirmed, probable, or suspected cases, the WHO said today. The death toll is 11,299.

See also:

Nov 25 WHO situation update

Nov 23 ReliefWeb report

Nov 20 CIDRAP News story "Family case cluster ends Liberia's Ebola-free status"