Craig Saffoe, curator of the great cats at the Smithsonian’s National Zoo, had warned his staff in advance that Shera, the African lion, might not pull through.

She had been infected with covid-19’s highly contagious delta variant. She was lethargic. She wouldn’t eat or drink. And her kidneys were failing.

As the 335-pound animal lay anesthetized on the floor of her enclosure, with a stomach tube down her throat and an intravenous line in a blood vessel for fluids, there seemed to be little improvement.

The staff worried: Was she was suffering too much? Should they wake her up? Or should they euthanize her?

It was a critical moment last month, as the zoo fought a dangerous covid outbreak that sickened nine of its lions and tigers — three of the lions seriously — and almost killed 16-year-old Shera, who had been at the zoo for 14 years.

It was one of the larger covid outbreaks at an American zoo, and it almost led to the first death of a lion from the disease in the United States, the zoo’s chief veterinarian said.

In June, two lions at India’s Vandalur Zoo reportedly died after being infected with covid. In January, two white tiger cubs died of it in a zoo in Lahore, Pakistan. And big cats around the United States have been sickened.

The National Zoo believes its animals were probably infected unwittingly by one of their caretakers who had the virus but no symptoms.

Asked if the zoo subsequently tested caretakers for the coronavirus, a spokeswoman emailed: We “tested when indicated. We also respect the privacy of those tested and do not release testing results.”

(The zoo announced Thursday that it has canceled its Halloween Boo at the Zoo event and its holiday ZooLights show because of the pandemic.)

Last month, the Atlanta zoo reported that 18 of its 20 western lowland gorillas may have contracted the virus.

Gorillas have also been infected at the San Diego zoo. Tigers have tested positive at zoos in Norfolk and the Bronx. And on Wednesday, the Agriculture Department announced that a bearcat and a fishing cat at a zoo in Illinois had the virus.

At the National Zoo, the first signs of trouble appeared on Sept. 10, when its male lion, Jumbe, developed a cough, Saffoe said in a recent interview.

But the cough could have been caused by something as simple as a hairball, he said, and the keepers were unsure what it meant.

“Taking care of … animals is much like taking care of children,” he said. “Your kid gets a runny nose. Is it a cold? Is it sinuses? We’re more or less like the parents of that kid. We want to gauge when it’s appropriate to get the vets involved.”

The next day, though, when Shera and the other female lions, Amahle and Naba, came back into their enclosures after being outdoors, they all started sneezing.

A lion’s sneeze is similar to a human sneeze. “Sneezing is sneezing,” Saffoe said. “It’s just funny when you hear it from a big cat. It’s loud,”

But “that was an abnormal behavior,” he said. “That’s when we got suspicious.”

“Given the climate that we’re in, everybody starts thinking the same thing,” he said. “I started thinking, ‘This [has the] potential to be something as bad as covid.’ But I don’t think anybody was … ready to say: ‘This is covid.’”

Don Neiffer, the chief veterinarian, said in a recent interview: “We couldn’t say it. We didn’t want it to be [covid, but] we assumed it was covid until proven otherwise.”

The following week, tests on fecal samples showed six lions and three tigers were probably infected. For unknown reasons, the tigers weathered the infections much better than the lions, he said.

Neiffer was worried about the animals. He was also worried about the staff.

“These folks see these animals in many ways as their extended family,” he said.

“They’re not going to do anything … to jeopardize” them, he said. “One of the first thoughts I had was, ‘I hope nobody on this team blames themselves' … Because I know they did everything they were supposed to do, and they did it correctly.”

Over the next few days, conditions worsened, especially for three lions — Shera, and males Shaka and Jumbe.

They were lethargic, seemed nauseous and wouldn’t drink or eat.

“Shera would not even get up and come for food,” Neiffer said.

He worried about dehydration, and pneumonia setting in.

A week passed with little improvement. On Sept. 18, the three lions were so sick that the zoo decided to anesthetize them to administer fluids and antibiotics, get blood samples, and examine them more closely.

It was a complex procedure that had to be carefully choreographed.

It was a Saturday morning. Saffoe was about to attend his daughter’s soccer game when he got the call and headed to the zoo. Extra veterinarians were summoned. Jobs were assigned.

One at a time, the lions were darted with anesthesia and treated in separate enclosures. The animals were poked with a pole to make sure they were asleep.

“We did Shera first, because she was the animal of most concern,” Saffoe said. Then Jumbe and Shaka.

It was critical to get fluids into the animals.

“If you don’t have enough fluids in your body, nothing works,” Neiffer said. “None of the organs. None of the immune response. … We had to get fluids into those cats or they were gong to die.”

But time was short. The anesthesia would soon wear off. Saffoe squeezed the fluid bags to force liquid into the animals while the vets worked.

“For the big cats … we can’t keep that fluid line going once the animal is awake,” he said. “So you have to push all of those fluids in” before it wakes up.

Each lion got six to eight bags, he said.

They also got shots of antibiotics and anti-nausea drugs. Nasal and throat swabs were taken, and blood was drawn. A tube was inserted through Shera’s mouth and into her stomach to introduce more medication.

When Shera’s blood was analyzed during her procedure, it showed that she had gone into renal, or kidney, failure, Neiffer said.

“Renal failure is actually a potential consequence of covid in humans,” he said. Plus, Shera’s blood and been sampled and tested before she got sick and there was no indication of kidney failure. It had to have been be caused by covid, he said.

As Shera’s procedure ended Saturday, Neiffer was very worried. He hoped the medicine and fluids worked. But he said he wondered if Shera might become the first lion in the country to be euthanized because of covid.

By Monday, Sept. 20, when Shera was not much improved, the staff decided to anesthetize her again, examine her and repeat the process.

She was still very sick. Saffoe, the curator, had called and emailed nine people on his staff to prepare them for the worst. “You get ready for it,” he said.

Once Shera was anesthetized that day, the staff pondered her condition.

She was no better.

“If the … animal is not responding to therapy, we have to make the collaborative decision on whether it would be more humane to not wake her up,” Saffoe said.

But she was also no worse.

“With the animal anesthetized, we were literally having a conversation with the vet: ‘What do you think? Do you want to wake her up? Do you want to keep trying?’” he said.

“We agreed: ‘Lets wake her up,’” he said.

Shera came around, but the next day, Tuesday, Sept. 21, she remained extremely ill and had to be anesthetized and treated again.

The zoo thought about doing the procedure a fourth time on Friday, Sept. 24, Neiffer said.

But Thursday afternoon she seemed a bit improved.

“And Friday morning … she was not the same cat,” Neiffer said. “I didn’t think she was on death’s doorstep. … And we made the decision not to do a fourth immobilization.”

“And, knock on wood,” he said. “She really hasn’t looked back.”

“It doesn’t mean she’s out of the woods,” he said. “It doesn’t mean she won’t have issues. It doesn’t mean we won’t be having a difficult conversation” about her future.

“But we all feel 100 percent better,” he said.