MADRID, Spain (AP) — Tens of millions of students stayed home on three continents, security forces went on standby to guard against large gatherings of people, and bars, restaurants and offices closed Friday to slow the spread of the coronavirus pandemic.

The virus edged ever closer to the world's power centers, with positive tests for the Canadian prime minister's wife, a top aide to Iran's supreme leader, a Brazilian official who met with President Donald Trump, and an Australian Cabinet minister who met with U.S. Attorney General William Barr and Trump's daughter, Ivanka.

Channeling wartime...