The Kenyan man had travelled from the Democratic Republic of Congo through Uganda before arriving in Nairobi on 3 October. He later died, becoming Kenya’s first recorded Ebola death in the current outbreak.
Although both patients passed through Entebbe airport on the same day, health officials have not established whether they met, used the same facilities or had any other contact.
«One of the issues we are currently investigating has been some sort of interaction between the two cases at the airport,» Mankoula told journalists on Thursday.
Investigators are also examining whether the two infections could have a common source.
The WHO said it was too early to determine where the Nigerian woman became infected.
«The source of exposure is still not known. The travel history of the patient is still being pieced together,» said Dr Patrick Otim, a WHO emergency response official.
He said investigators had struggled to obtain a complete account of her movements because opportunities to interview her were limited while she remained in hospital.
Nigeria’s Centre for Disease Control and Prevention (NCDC) said it was carrying out genomic sequencing, which could help investigators understand whether the infection is related to other cases.
«The investigation is reconstructing the full travel and exposure history. Genomic sequencing is given a high priority,» said Dr Pavel Ursu, the WHO’s representative in Nigeria.
Ugandan health officials previously said the woman had travelled to eastern DR Congo for business, where the current Ebola outbreak began.
However, the WHO, Africa CDC and Nigeria’s health ministry said they had not received verified information confirming that she had visited the country.
Uganda has maintained that it has no confirmed active Ebola cases and says the woman’s travel through the country does not necessarily mean she contracted the virus there.
Meanwhile, Africa CDC said Nigeria had identified additional people who may have been exposed to the woman, beyond the 44 contacts initially reported.
«Most of those contacts, they are from the healthcare workers in different facilities where this case has been receiving treatment. We have also some few family members,» Mankoula told journalists on Thursday.
He said Nigerian authorities were working to identify and quarantine those considered at high risk, but declined to give an updated figure before the government released its findings.
«The position of the country [is] to bring those high-risk contact and put them on quarantine,» he added.
Dr Ursu said the woman was receiving a high standard of clinical care and that her condition was stable.
In Kenya, the first group of people quarantined after possible exposure to Ebola will begin returning home on Sunday after completing 21 days of monitoring without developing symptoms.
Health Director-General Dr Patrick Amoth said all nine confirmed infections were linked to the first patient, with no evidence of wider community transmission.
«We are not out of the woods,» he warned, urging the public to remain vigilant but not panic.
He said the remaining eight patients remained in isolation and were responding well to treatment.
The developments have renewed concerns about the movement of infected people across international borders, particularly between the DR Congo and neighbouring Uganda, where thousands of people cross daily for trade, work and family visits.
Dr Otim warned that the long and porous border between the two countries made it difficult to screen everyone entering or leaving, as many people used unofficial crossing points.
The WHO’s regional director for Africa, Dr Mohamed Janabi, called for «regional vigilance» and urged countries to strengthen surveillance, investigate infections and protect frontline health workers.
Ebola is a serious viral disease that spreads through direct contact with the blood or other bodily fluids of an infected person, or with contaminated objects. It does not spread through the air like flu.
The virus can cause fever, severe weakness, vomiting and diarrhoea, and can be fatal. People are not considered infectious before they develop symptoms.
Health authorities say tracing contacts quickly, isolating suspected cases and providing early treatment are crucial to preventing further transmission.
