The risk from the deadly Ebola outbreak has been raised to the highest level for the Democratic Republic of Congo, the World Health Organization said Friday, as the toll continued to rise.

There are now 82 confirmed cases and seven confirmed deaths in the DRC, with almost 750 suspected cases and 177 suspected deaths, the WHO said.

The outbreak, which experts suspect was circulating under the radar for some time, was caused by the less common Bundibugyo strain of Ebola, for which there are no approved vaccines or treatments.

The WHO is prioritising certain existing treatments to see how effective they might be in combating the strain.

Uganda situation 'stable'
WHO chief Tedros Adhanom Ghebreyesus said the situation was "especially challenging" as health workers scramble to catch up with the spread of the virus and track down contacts of everyone thought to be infected, in highly insecure areas.

"We know the epidemic in DRC is much larger" than the confirmed cases, he told journalists at the WHO headquarters in Geneva.

Tedros said the situation in neighbouring Uganda was "stable", with two cases confirmed in people who travelled from DRC and one death.

Intense contact tracing appeared to have prevented further spread, he added.

While a US national who was working in the DRC has tested positive and been transferred to Germany for care, Tedros said another US national deemed to be a high-risk contact had been transferred to the Czech Republic.

Rwanda's health ministry announced Friday that any foreign nationals who had travelled through the neighbouring DRC would be refused entry.

Rwandan nationals and foreigners with Rwandan residency would be allowed in, subject to a mandatory quarantine period "in line with public health protocols".

In the Netherlands, Radboud University Hospital said Friday it had admitted a patient with a "low suspicion" of Ebola and had put him in isolation pending the result of diagnostic tests.

Virus 'rampant'
Ebola is a deadly viral disease spread through direct contact with bodily fluids. It can cause severe bleeding and organ failure.

The WHO upgraded its risk assessment level from high to very high for the DRC, while keeping the regional risk level at high and the global risk level at low.

The assessment determines the potential impact of a public health threat and the necessary response measures, with WHO advice set to follow.

"The potential of this virus spreading rapidly is very high, and that changed the whole dynamic," said the WHO's emergency alert and response director Abdi Rahman Mahamud.

Speaking from the field, Anne Ancia, the WHO's representative in the DRC, said the case numbers would keep rising until all the response operations could be put in place.

The virus has been "rampant and silently disseminating for a few weeks already", she said.

"We are sprinting behind" playing catch-up, with the spread "not yet under control", she added.

With no treatments or vaccines available, finding contacts and isolating them for 21 days was the only way to disrupt transmission, she said.

WHO's Africa regional director Mohamed Yakub Janabi said Ebola had had a silent early phase, when symptoms resemble malaria or typhoid, meaning transmission can remain undetected.

Ancia said rising case numbers at this stage was a "good sign" because it showed that surveillance and active discovery of cases were working.

Treatment trials planned
There have only been two previous outbreaks of Bundibugyo, in Uganda in 2007 and the DRC in 2012.

With no approved treatments or vaccines for Bundibugyo, WHO chief scientist Sylvie Briand said the UN agency was prioritising all existing tools that might be useful in combating the outbreak.

The WHO research and development branch's technical advisory group on treatments has prioritised two monoclonal antibodies for clinical trials: Regeneron 3479 and Mapp Biopharmaceutical's MBP134.

It also recommended evaluating the oral antiviral obeldesivir in clinical trials as post-exposure prophylaxis for people who are high-risk contacts.

Briand said it looked "promising" as something that might be able to prevent infected contacts from going on to develop disease from that infection.

As for vaccines, the Ervebo vaccine works against the Zaire strain of Ebola but there is "very little evidence of cross-protection for Bundibugyo", said Briand.

While a Bundibugyo-specific equivalent has been worked on, even if prioritised it could take six to nine months to develop.