BRUSSELS — For Europe, the coronavirus could not have arrived at a worse time.

This was the year — with Britain out, terrorism waning and the migrant crisis at an ebb — that the European Union had hoped to repair and revive its cherished goal of open internal borders.

But cases of the virus have emerged nearly daily in new European countries — in Spain, Greece, Croatia, France, Switzerland and, on Wednesday, in Germany. Many of them can be traced back to Europe’s largest outbreak, in Italy, where more than 300 people are now infected.

[Update: Nigeria records Sub-Saharan Africa’s first case of coronavirus.]

As the cases spread and multiply, calls for closing borders have grown louder, most predictably from the far right and populists who were never fans of the bloc’s open border policy

So far no country has taken that drastic step, but privately European officials warned that this could change quickly. On Wednesday, the bloc’s top official for communicable diseases said that Europe needed to prepare more broadly for the kind of crisis that has hit northern Italy.