By Joshua McElwee

VATICAN CITY (Reuters) - Pope Francis is alert and cheerful as he battles double pneumonia in hospital, Italian Prime Minister Giorgia Meloni said on Wednesday after paying a visit to the ailing leader of the 1.4-billion-member Roman Catholic Church.

The 88-year-old pope is undergoing treatment at Rome's Gemelli hospital, where he was admitted on Friday after struggling with breathing difficulties for several days, in what was first described as bronchitis.

"I am very happy to have found him alert and responsive," Meloni, the first known hospital visitor for Francis, said in a statement. "We joked as always. He hasn't lost his proverbial sense of humour."

Francis has the onset of double pneumonia, the Vatican said on Tuesday, complicating his treatment. Double pneumonia is a serious infection that can inflame and scar both lungs and makes breathing more difficult.

The Vatican had said previously that the pope had a polymicrobial infection, which occurs when two or more micro-organisms are involved, adding that he would stay in hospital as long as necessary to tackle a "complex clinical situation".

A Vatican official, who did not wish to be named because he was not authorised to speak about the pope's condition, said on Wednesday Francis was not on a ventilator and was breathing on his own.

The official said the pope had been able to get out of bed and sit in an armchair in his hospital room, and was continuing to do some work.

The Vatican is expected to give a further update on the pope's condition later on Wednesday.

Messages of support for Francis have come in from around the world, the Vatican's official media outlet reported. Pilgrims at the Vatican on Wednesday for the pope's cancelled weekly audience expressed hope for his recovery.

"We will pray for him so that he can recover as soon as possible," said Gianfranco Rizzo, a pilgrim from Bari, Italy.

The pope has been plagued by ill health in recent years, including regular bouts of flu, sciatica nerve pain and an abdominal hernia that required surgery in 2023. As a young adult he developed pleurisy and had part of one lung removed.

All the pope's public engagements have been cancelled through Sunday and he has no further official events on the Vatican's published calendar.

'TARGETED THERAPY'

Gemelli hospital, Rome's largest, has a special suite for treating popes, and is known especially for often treating the late Pope John Paul II during his long papacy.

Francis spent nine days at Gemelli in June 2023, when he had surgery to repair an abdominal hernia.

Outside the hospital on Wednesday, people were leaving flowers and personal notes under a statue of John Paul II, wishing Francis a speedy recovery.

Victoria Darmody, a tourist from England, said she came to the hospital just to be near the pope. "We were hoping to go to the papal audience today but felt this was the right place to be instead," she said.

Andrea Vicini, a Jesuit priest and medical doctor, said it was notable that the Vatican's statement on Tuesday referred to the pontiff as having the onset of pneumonia and not bronchopneumonia. The latter would indicate an infection that is more widespread, he said.

"It (sounds like) it's more localized and has not spread," said Vicini, a professor at Boston College, who said he did not have details of the pope's case beyond the Vatican's public statements.

"If they identified the pathogen, as I expect they would have done, they will have a very targeted therapy," he said. "I am optimistic. It seems they are controlling what is happening."

Work at the Vatican was continuing as the pope was in hospital. One senior official, Cardinal Michael Czerny, was expected to depart on Wednesday for a five-day visit to Lebanon.

The Vatican's top diplomat, Cardinal Pietro Parolin, returned to Rome as scheduled on Wednesday from a trip to Burkina Faso.

(Additional reporting by Gabriele Pileri and Alvise Armellini; Writing by Gavin Jones and Crispian Balmer; Editing by Cristina Carlevaro and Janet Lawrence)