A fishmonger who died this week of Ebola may have carried the virus from Congo into Rwanda as well as Uganda, the World Health Organization (WHO) said, as health workers struggled to track down people she could have infected.

The woman was one of almost 1 700 victims of the current 11-month outbreak of the highly contagious disease, which the WHO upgraded to an international health emergency on Wednesday and which has so far been effectively confined to northeastern Democratic Republic of Congo.

Three people died in Uganda last month. But they did not spread Ebola further there, and Rwanda has never had a recorded case.

The Congolese fishmonger vomited multiple times at Mpondwe, a market across the border in Uganda on July 11, a few days before she died, the WHO said on Wednesday, citing a Ugandan Health Ministry report. A second fishmonger died of Ebola in Congo on Tuesday after spending time at the same market, it added.

The ministry suspected that, while infected, the woman also went to the Congolese city of Goma and Gisenyi in Rwanda on business, the WHO said on Thursday.

Rwanda's health minister was not immediately available for comment.

'NO SIGNS OF LETTING UP'

A vast campaign of vigilance and vaccination, with almost 75-million screenings, has so far kept the outbreak confined.

The emergency committee of international health experts that advises the WHO had three times declined to declare an emergency - a rare designation aimed galvanising global support.

But the cases of the fishmonger and of a pastor who died this month after travelling to Goma, a city of 2-million and a gateway to other countries in the region, served to galvanise it into action.

"The committee is concerned that a year into the outbreak, there are worrying signs of possible extension of the epidemic," Wednesday's committee report said.

Jonathan Ball, a professor of molecular virology at Britain's University of Nottingham, said the latest cases and continued spread of the epidemic showed current efforts were not effective enough.

Despite the availability of an effective vaccine and an extensive pool of experts, the outbreak "is showing no signs of letting up", he said.

Health workers fronting the vaccination campaign have also faced hostility from at-risk communities where some equate Ebola with witchcraft - the sort of resistance that the Ugandan ministry said workers trying to trace people who may have come into contact with the woman fishmonger were having to deal with.

Healthworkers so far knew of 12 people at high risk of catching Ebola from her. But one fish store owner who she had dealt with had locked up his shop and could not be traced, nor could his four attendants or brother, and fellow traders were refusing to share his phone contact, the ministry said.

So far, tests on traders at the market had however not found any infected with the virus, said ministry spokesperson Emmanuel Ainebyona. The team continued to monitor the traders.

Ball said concerted action was needed to bring the outbreak to a close, in particular political and civil stability and increased and effective engagement with affected communities.