Experts in global health have been expressing their dismay and concern over the dismantling of the United States Agency for International Development (USAID), which distributes tens of billions of dollars’ worth of overseas aid every year.

President Donald Trump’s administration has announced huge cuts to the agency’s workforce and the immediate suspension of almost all of its aid programmes.

The US government has announced a 90-day freeze on funding for aid projects while it undertakes a “review” to ensure they align with President Trump’s priorities.

Trump is a long-term critic of overseas spending and has said it needs to be brought into line with his “America First” strategy.

The administration has targeted USAID in particular, saying the agency’s spending is totally unexplainable and has singled out certain projects as examples of how the agency is, in its view, wasting taxpayers’ money.

Health experts, on the other hand, have warned of the spread of disease, as well as delays to the development of vaccines and new treatments as a result of the cuts.

As well as directly running many health programmes, USAID funds other organisations to carry out work on its behalf, and the freeze in funding has caused confusion among these groups too.

Waivers for the funding freeze have been issued for some humanitarian programmes, but the announcement has already caused widespread disruption to services.

Dr Tom Wingfield, an expert in tuberculosis (TB) and social medicine at the UK’s Liverpool School of Tropical Medicine, told the BBC it is hard to underplay the impact of the decision to dismantle USAID.

“People don’t appreciate the extent and reach of USAID. It goes towards under-nutrition, hygiene, toilets, access to clean water, which all have a massive impact on TB and diarrhoeal diseases.

“Diseases don’t respect borders – that’s even more the case where we have climate change and mass movement of people. Infectious diseases will spread.”

Dr Wingfield says TB kills 1.3 million people per year and makes a further 10 million people ill.

But four out of 10 people never receive any care and can therefore transmit the disease, he said.

“Whether it’s a research project or a clinic affected, then we run risk of further transmission.

“People will die directly because of cuts in US funding.”

It’s not just TB clinics that are at risk, but those providing care for people living with HIV.

Much of this work is done by non-governmental organisations, NGOs, who provide vital anti-retroviral medicines which can suppress the amount of HIV in the blood to undetectable levels, which helps prevent sexual transmission to other people.

Dr Wingfield says if treatment is disrupted, there could be serious problems.

“People with controlled HIV, if they miss meds, the virus in their blood increases and there’s a risk of onwards transmission.

“There is a risk of undoing all the progress to date.”

Frontline AIDS is a UK and South Africa-based organisation that works with 60 partners across 100 countries.

More than 20 of their partners have said they are affected by the US foreign aid freeze.

Communication around the freeze and subsequent waiver has caused “deep confusion”, the organisation told the BBC.

Many partners have had to suspend HIV care, treatment and prevention to vulnerable children and adults and lay off staff, it said.

“The majority remain in limbo and this is having a catastrophic impact on communities and organisations,” said John Plastow, Executive Director for Frontline AIDS.

It reported that one organisation in Uganda has said it will run out of its HIV testing kits, TB medicines and condoms in a month, which are mostly funded by USAID’s President’s Emergency Plan for AIDS Relief programme.

In South Africa, a large number of HIV services have stopped. Some provide aftercare and emergency contraception for women and girls who have been raped.

Prof Peter Taylor, director of international development studies at Sussex University, said one of the biggest issues with the freeze was an erosion of trust.

“Stopping things suddenly undermines people’s trust. People are bewildered and angry,” he said.

“The undermining of basic trust is the real cost and that is being magnified in many situations around the world.

“This is so damaging to the US global reputation.”

USAID also provides funding for crucial international clinical drug trials, which Prof Thomas Jaki, leader of the MRC Biostatistics Unit at the University of Cambridge, fears might now also be vulnerable.

“Unfortunately, there are quite a number of trials that are immediately affected by the USAID freeze – both in terms of running trials but also trials that are in set-up and are planned to start soon.”

He said he was “convinced” the US funding freeze “will detrimentally impact treatment development”, to an extent where exciting new treatments are delayed by years or even discarded.

“Clearly the impact in areas such as malaria and HIV will be particularly high as a notable portion of research in these areas is funded via this route,” Prof Jaki said.

Prof Rosa Freedman, professor of international law, conflict and global development at the University of Reading, said USAID provides up to 40% of the world’s development aid, which covers health as well as education and developing economic prosperity.

But health programmes is where the impact of a funding freeze – if it is prolonged or permanent – is likely to be felt most keenly in the months to come, she warns.

“This will be partly due to the prevention of further vaccines being distributed or funded by USAID.

“This could mean that preventable diseases, which we thought had been contained or even eradicated, could reappear or worsen, such as cholera and malaria.”

Prof Freedman said this could lead to a rise in healthcare problems around the world.

“Given the globalised and interdependent nature of our planet, the concern will be that these diseases could spread quickly and far.”