Sixty-three confirmed and probable cases have been reported in the Ebola outbreak in Uganda, including 29 deaths, the World Health Organization said Wednesday.

WHO chief Tedros Adhanom Ghebreyesus lamented that the outbreak, declared two weeks ago, was taking a deadly toll on health workers as well as patients.

There are six species of the Ebolavirus genus and the one circulating in Uganda is the Sudan ebolavirus -- for which there is currently no vaccine.

"So far, 63 confirmed and probable cases have been reported, including 29 deaths," Tedros told a press conference in Geneva.

"Ten health workers have been infected and four have died. Four people have recovered and are receiving follow-up care."

The east African nation's Health Minister Jane Ruth Aceng Ocero said that a 58-year-old anaesthetist had died of Ebola early Wednesday, following the deaths of a Tanzanian doctor, a health assistant and a midwife.

- Candidate vaccines -

Tedros said the vaccines used successfully to curb recent outbreaks of the Zaire ebolavirus species in the neighbouring Democratic Republic of Congo (DRC) did not provide cross-protection against the Sudan ebolavirus.

"However, several vaccines are in various stages of development against this virus, two of which could begin clinical trials in Uganda in the coming weeks, pending regulatory and ethics approvals from the Ugandan government," he said.

There are at least six candidate vaccines against the Sudan species, of which three have made it far enough to be tested on humans, producing so-called Phase 1 safety and immunogenicity data.

They could "proceed to be used in the field in a sort of ring vaccination campaign", WHO's chief scientist Soumya Swaminathan said.

She mentioned a candidate vaccine from the University of Oxford and another from the Sabin Vaccine Institute, and said which one goes into trials may depend on which one actually has doses ready to deploy.

"Realistically it may take another four to six weeks," she said.

Swaminathan said plans were also afoot for testing potential therapeutics.

- WHO sending specialists, resources -

The initial outbreak was discovered in the central district of Mubende.

There are gold mines in the Mubende area which attract people from across Uganda, as well as other countries, the WHO's Africa regional office said.

"The mobile nature of the population in Mubende increases the risk of a possible spread of the virus," it said.

Infections have since been found in Kassanda, Kyegegwa and Kagadi districts.

The WHO's Geneva headquarters has released $2 million from its contingency fund for emergencies and is working with partners to support the health ministry by sending additional specialists, supplies and resources, Tedros said.

Ugandan President Yoweri Museveni has vowed not to impose any lockdowns to tackle the disease, saying last week that there was "no need for anxiety".

- Haemorrhagic fever -

Ebola is an often-fatal viral haemorrhagic fever named after a river in DR Congo where it was discovered in 1976.

Human transmission is through bodily fluids, with the main symptoms being fever, vomiting, bleeding and diarrhoea.

Outbreaks are difficult to contain, especially in urban environments.

People who are infected do not become contagious until symptoms appear, which is after an incubation period of between two and 21 days.

Uganda has experienced several Ebola outbreaks, most recently in 2019 when at least five people died.

The neighbouring DRC last week declared an end to an Ebola virus outbreak that emerged in eastern North Kivu province six weeks ago.

The worst epidemic, in West Africa between 2013 and 2016, killed more than 11,300 people. The DRC has had more than a dozen epidemics, the deadliest killing 2,280 people in 2020.