The voice of Ari Greenwald, an emergency-medicine doctor in Toronto, played on thousands of Orthodox Jews’ smartphones on Wednesday, warning that the novel coronavirus “has been spreading throughout our community like wildfire.”

“This virus is so much smarter than all of us,” he said in a voice note that went viral on Orthodox WhatsApp. Greenwald then paused, and repeated himself: “So much smarter than all of us. It has been circulating in our community and across the world without anybody knowing it.”

Speaking to his “brothers and sisters,”Greenwald said that he is pessimistic about the pandemic’s spread among religious Jews, and urged them to self-isolate for at least 14 days. “The reality of cases in the community that I’m seeing from front lines, in our community, is at least 10 times higher than what you’re seeing published,” he cautioned. “I“We’re going to have to make difficult decisions and having funerals, because of the decisions we make today. I beg of you.”

Greenwald is one of many Orthodox physicians who have posted such videos on WhatsApp in recent days, amid news both about outbreaks in Hasidic enclaves in Brooklyn, Florida, Russia and elsewhere — and about the Orthodox continuing to gather for prayer, study and celebrations despite public-health advisories about the need for “social distancing.”

WhatsApp is the lifeblood of the Orthodox community. It is, in a way, the most kosher social media platform — how we communicate across extended families, synagogue communities, fields of work even. Increasingly, many Orthodox Jews get news primarily from Orthodox news outlets’ WhatsApp statuses — posts that remain live for 24 hours.

And now, as many recede into isolation, it is WhatsApp that has taken the place of every grocery-aisle conversation, every kiddush schmooze, every Shabbos table debate (though not on Shabbos, when use of electronics such as smartphones is forbidden).

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But the message seems not to have penetrated the most insular of communities. There were reports on WhatsApp of a wedding at Tiferes Mordechai in Boro Park, the Brooklyn neighborhood where 100 cases of coronavirus were confirmed on Tuesday. Nearby on 16th Avenue and 61st Street, according to a report on Twitter, a party was thrown in a yeshiva building.

The religious medical professionals sound increasingly desperate on the videos making the rounds. In one, Shloime Goldberg of Boro Park’s Chai Urgent Care, wearing both hospital scrubs and a black yarmulke, said: “Everyone must act as if they do have corona.” He asked that people isolate themselves and that only those who are over 60 or immunocompromised get tested, so as not to overwhelm local clinics.

In Baltimore, a group of Orthodox physicians created a video warning about what is coming. “Children are a major source of the virus,” said Dr. Adena Cohen. “We can’t have playdates.”

Much of the frustration has been towards those who continue to go to minyanim — the quorum of 10 required for group prayer, despite rabbinic rulings easing the mandate to do so. “These minyanim are going to kill people,” Ellie Bennet, an internist in Queens, N.Y., wrote in a WhatsApp text that was shared across Orthodox groups. “Elderly people from our neighborhood are on ventilators in the ICU because of these minyanim.”

Bennet wondered why community members only trust medical professionals on whether or not to eat on Yom Kippur or when to make a bris. “Why all of a sudden do you think it’s appropriate to ignore us?”

“You all trust me to treat you like family when you come to my office, so I’m speaking to you like family,” he added. “Stop the minyan. Stop the gatherings. Stay home and pray by yourself.”