The case adds some credence to what looked like dodgy-looking statistics being bandied about over recent days.
The Madrid hospital where the nurse works is being investigated by the European Commission after the 40-year-old woman was taken ill.
She had been treating two Spanish missionaries who were flown home after contracting the virus in Liberia.
Ebola is highly contagious and sufferers must be completely isolated to prevent spreading.
Madrid healthcare officials said that she had been wearing appropriate safety clothing while treating the patients.
The disease is at its most contagious in its final, terminal stages, however it can take up to three weeks for symptoms to take effect.
Although the World Health Organisation has not imposed any official travel restrictions, some airlines have suspended flights to the worst affected countries.
A mixture of spread patterns and airline traffic data has been cobbled together this week to predict a 75% chance the virus could be imported to France by October 24, and a 50% chance it could hit Britain by that date. More modest predictions suggested that France’s risk is still 25%, and Britain’s is 15%.
However, in developed countries, it is unlikely that the disease would have the same effect as in West African regions, where more than 7,200 have been affected and at least 3,400 people have died so far.
Deadly outbreaks have been reported in Guinea, Nigeria and Senegal, but Sierra Leone and Liberia have been the worst affected.
European and American Ebola sufferers have been flown home for treatment, but this is the first case to have been contracted outside of Africa.
The woman’s husband has also been put in to isolation.