Last year, WHO spent about US$71 million on Aids and hepatitis. On malaria, it spent US$61 million. And to slow tuberculosis, WHO invested US$59 million.

Still, some health programmes do get exceptional funding – the agency spends about US$450 million trying to wipe out polio every year.

On a recent trip to Guinea where WHO director-general Dr Margaret Chan praised health workers in West Africa for triumphing over Ebola, she stayed in the biggest presidential suite at the Palm Camayenne hotel in Conakry. The suite has an advertised price of €900 (US$1,008) a night. The agency declined to say who picked up the tab, noting only that her hotels are sometimes paid for by the host country.

But some say that sends the wrong message to the rest of the agency’s 7,000 staff.

“We don’t trust people to do the right thing when it comes to travel,” said Nick Jeffreys, WHO’s director of finance, during an in-house seminar on accountability in September 2015 – a video of which was obtained by the AP.

Despite WHO’s numerous travel regulations, Jeffreys said staffers “can sometimes manipulate a little bit their travel”. He said the agency couldn’t be sure they were always booking the cheapest ticket or that the travel was even warranted.

“People don’t always know what the right thing to do is,” he said.

Ian Smith, executive director of Chan’s office, said the chair of WHO’s audit committee said the agency often did little to stop misbehaviour.

“We, as an organisation, sometimes function as if rules are there to be broken and that exceptions are the rule rather than the norm,” Smith said.

Earlier that year, a memorandum was sent to Chan and other top leaders with the subject, “ACTIONS TO CONTAIN TRAVEL COSTS” all in capital letters. The memo reported that compliance with rules that travel be booked in advance was “very low” and also pointed out that WHO was under pressure from its member countries to save money.

Travel would always be necessary, the memo said, but “as an organisation we must demonstrate that we are serious about managing this appropriately”.

In a statement to the AP, the UN health agency said “the nature of WHO’s work often requires WHO staff to travel” and said costs had been reduced 14 per cent last year compared to the previous year – although that year’s total was exceptionally high due to the 2014 Ebola outbreak in West Africa.

But staff are still openly ignoring the rules.

An internal analysis in March, obtained by the AP, found that only two of seven departments at WHO’s Geneva headquarters met their targets, and concluded the compliance rate for booking travel in advance was between 28 and 59 per cent.

Since 2013, WHO has paid out US$803 million for travel. WHO’s approximately US$2 billion annual budget is drawn from taxpayer-funded contributions from its 194 member countries, with the US the largest contributor.

After he was elected, US President Donald Trump tweeted: “The UN has such great potential,” but had become “just a club for people to get together, talk, and have a good time. So sad!”

Some health experts said while WHO’s travel costs look out of place when compared to some of its disease budgets, that doesn’t necessarily mean that travel expenses are inflated.

Michael Osterholm, an infectious diseases expert at the University of Minnesota, has frequently been flown to WHO meetings – in economy class – on the agency’s money.

“This may just speak to how misplaced international priorities are, that WHO is getting so little for these disease programmes,” he said.

During the Ebola disaster in West Africa, WHO’s travel costs spiked to US$234 million. Although experts say on-the-ground help was critical, some question whether the agency couldn’t have shaved costs so that more funds went to West Africa, where the three stricken countries couldn’t even afford basics like protective boots, gloves and soap for endangered medical workers or body bags for the thousands who died.

Dr Bruce Aylward, who directed WHO’s outbreak response, racked up nearly US$400,000 in travel expenses during the Ebola crisis, sometimes flying by helicopter to visit clinics instead of travelling by jeep over muddy roads, according to internal trip reports he filed.

Chan spent more than US$370,000 in travel that year, as documented in a confidential 25-page analysis of WHO expenses that identified the agency’s top 50 spenders. Three sources who asked not to be identified for fear of losing their jobs told the AP that Chan often flew in first class.

Until February, WHO said the travel policy “included the possibility for the [director general] to fly first class,” but that Chan flew business class and requested the policy be changed.

“There’s a huge inequality between the people at the top who are getting helicopters and business class and everyone else who just has to make do,” said Sophie Harman, an expert in global health politics at Queen Mary University in London.

Other international aid agencies, including Doctors Without Borders, explicitly forbid their staff from travelling in business class – even having the charity’s president fly in economy class, a spokeswoman said. With a staff of about 37,000 aid workers versus WHO’s 7,000 staffers, Doctors Without Borders spends about US$43 million on travel a year.

“When you spend the kind of money WHO is spending on travel, you have to be able to justify it,” said Dr Ashish Jha, director of the Global Health Institute at Harvard University. “I can’t think of any justification for ever flying first class.”

Jha warned that WHO’s travel spending could have significant consequences for fundraising. Several weeks ago, WHO asked for about US$100 million to save people in Somalia from an ongoing drought. In April, it requested US$126 million to stop the humanitarian catastrophe in Yemen.

“If WHO is not being as lean as possible, it’s going to be hard to remain credible when they make their next funding appeal,” Jha said.