In a statement on Saturday, the UN health agency said it learned on September 10 of the death of a person in Tanzania’s commercial capital, Dar es Salaam, two days earlier.
On September 11, WHO was “made aware of unofficial reports” the individual had tested positive for Ebola.
“Identified contacts of the deceased were unofficially reported to be quarantined in various sites in the country,” the agency’s statement said.
It added that WHO had also learned of two other non-fatal suspected infections, one of which reportedly tested negative, but despite repeated requests was provided with no further information from the country’s authorities on any of the three cases.
“To date, clinical data, results of the investigations, possible contacts and potential laboratory tests performed … have not been communicated to WHO,” the statement said.
“The limited available official information from Tanzanian authorities represents a challenge,” it added.
The Tanzanian government formally informed WHO on September 14 that it had no confirmed or suspected cases of Ebola. Health Minister Ummy Mwalimu told reporters on the same day that officials had investigated two recent cases of unknown illnesses, but they were not Ebola.
“There is no Ebola outbreak in Tanzania as we speak, people should not panic,” Mwalimu said.
There was no immediate reaction to WHO’s statement on Saturday by Tanzanian authorities, meanwhile, but health experts described the agency’s choice of language as highly unusual.
“WHO, almost to a fault, is very reluctant to call out countries and name them in a critical way,” Lawrence Gostin, faculty director at US-based Georgetown university’s O’Neill Institute for National and Global Health Law, told Al Jazeera.
“The fact that they have done it in relation to Tanzania is an indication both of how worried they are about the outbreak and the violation of legal and ethical norms the Tanzanian government has committed by refusing to cooperate with WHO,” Gostin added.
An ongoing Ebola outbreak in Democratic Republic of the Congo (DRC) – which shares a border with Tanzania – has killed more than 2,000 people to date. Dar es Salaam – home to some six million people – lies some 1,750km (1,080 miles) away from the epicentre of the epidemic in DRC.
“The thought that Ebola could be spilling over into other countries and spreading in those countries is truly terrifying,” Gostin said.
“If it went to a large commercial centre like Dar es Salaam with international travel routes and a very dense population it’s hard to overestimate how serious a global health problem that would be.”
WHO said on Saturday it was not aware of “signs of widespread transmission” linked to any of the three suspected cases but urged health authorities in Tanzania to monitor developments closely.
“Investigations, including with the support of WHO collaborating centres, should continue to reach a diagnosis and further inform the risk assessment,” the agency’s statement said.
WHO spokesman Tarik Jasarevic added the agency was ready to help Tanzanian officials in the event an outbreak was confirmed in the East African country.
“WHO is standing by to facilitate the delivery of various supplies, including vaccines and therapeutics – this will occur upon request by the government,” Jasarevic told Al Jazeera.
Ashish Jha, director of the Harvard Global Health Institute, meanwhile said Tanzania needed to be “completely open and transparent about what has happened so far” with WHO.
“Open about who has been tested, what the results have shown, who is being monitored as possible contacts, and their health,” Jha told Al Jazeera.
“Tanzania should submit their samples for secondary, confirmatory testing. If all the results are negative, this would be very reassuring,” he added.
Authorities in East and Central Africa have been on high alert for possible spillovers of Ebola from DRC, where a 13-month outbreak has seen more than 3,000 cases registered.
The outbreak was officially declared in August 2018 and has predominantly been confined to DRC’s eastern North Kivu and Ituri provinces.
A handful of cases were confirmed in neighbouring Uganda earlier this year after infected patients crossed the border, but all of those individuals either died or were sent back to DRC for specialised treatment.
On Saturday, DRC health officials announced they planned to introduce a second vaccine – manufactured by US-based firm Johnson & Johnson – to tackle the virus, which spreads through contact with bodily fluids of those infected.
It will complement another vaccine produced by US pharmaceutical giant Merck, which has been administered to more than 220,000 people in a bid to curtail the outbreak.
Jasarevic said WHO was “continuing to work” with Merck and researchers to increase the availability of vaccines for Ebola.
When asked if an outbreak in Tanzania would stretch available resources too thin, he said there was “sufficient supply” for ongoing response efforts.
Despite the inoculation programme, attempts to end the epidemic have repeatedly been hampered by security issues in eastern DRC. There have been regular attacks on medical teams trying to tackle the haemorrhagic fever amid mistrust within some communities over the outbreak and response efforts.
The epidemic is now the second-deadliest on record behind a 2013-2016 outbreak in West Africa that killed more than 11,300 people.
WHO, which in July declared this outbreak a “public health emergency of international concern”, was heavily criticised for its sluggish response to the earlier crisis in West Africa.