Though the virus pushed into countries both rich and poor, its arrival in places with little ability to detect, respond and contain it brought concern it could run rampant there and spread easily elsewhere.

“We’re going to be trying to slow down the spread so that our hospitals are not overwhelmed in one big gulp, one big hit,” said Ian Mackay, who studies viruses at the University of Queensland in Australia.

In South Korea, workers sanitized public buses, while in China, banks disinfected banknotes using ultraviolet rays. In Germany, authorities stressed “sneezing etiquette,” while in the United States, doctors announced a clinical trial of a possible coronavirus treatment.

Around the world, as Christians marked the start of the holy season of Lent with Ash Wednesday, worshipers found churches closed and rituals changed by virus fears. Even in St. Peter’s Square, many of those gathered for Pope Francis’ weekly audience wore face masks and clergy appeared to refrain from embracing the pontiff or kissing his ring.