"Sporadic cases of Ebola virus disease in Europe are unavoidable," said Zsuzsanna Jakab, regional director for Europe at the World Health Organization.
"This is due to travel between Europe and affected countries," Jakab said in a statement.
"However, the risk of spread of Ebola in Europe is avoidable and extremely low," she said, adding that European nations were "among the best prepared in the world".
Six people have now been quarantined at a Madrid hospital, including a nurse who was diagnosed with Ebola on Monday in the first case of transmission of the disease outside Africa.
The nurse, in her forties, had cared for two elderly Spanish missionaries who died from the virus following their return from west Africa.
"There is a risk of accidental contamination for people exposed to Ebola patients," Jakab said.
"This risk can be and must be mitigated with strict infection control measures," she said.
"Health care workers are on the frontline of the Ebola fight and they are those most at risk of infection."
Jakab said they need to be "protected and supported by all means".
Among the six people hospitalized in Madrid are the woman's husband, considered at "high risk" by Spanish authorities, and two other nurses.
Officials said they were monitoring as a precaution 52 other people — mostly health workers — who had been in contact with the infected nurse.
"All countries have protocols and procedures that must be implemented when a case is suspected and it is important that these are followed diligently. WHO is, as always, ready to provide help and support where requested," said Jakab.
Ebola has killed 3,439 people in west Africa since the start of the year, according to the latest WHO toll, with health workers making up around six percent of the victims.