Babies were left without clean clothes after bouts of diarrhoea and fed from the same unwashed bottle for days in US Border Patrol (USBP) custody, while many young children were left “totally fearful” by detention, according to a paediatrician who examined them.

Guards also prevented children from washing their hands or brushing their teeth and some two dozen showed signs of respiratory infections, Dolly Lucio Sevier found when she examined 38 children being held at USBP’s central processing centre for migrants and asylum seekers in McAllen, Texas, known as Ursula.

She told The Atlantic that keeping children from washing was “tantamount to intentionally causing the spread of disease”. Children had not been permitted to bathe or change their clothes since crossing the border despite being held for up to a month, Dr Sevier told the magazine.

Several children she examined, including a toddler who was panting hoarsely throughout, were “totally fearful but then entirely subdued in her presence”, she added – as opposed to young children in normal circumstances who, though they may be shy at first, “shouldn’t be fearful of a stranger”.

This Dr Sevier took as evidence of trauma, “because [it] is such an unusual behaviour”.

'Dangerous' overcrowding of migrants in US border facilities Show all 6 1 /6 'Dangerous' overcrowding of migrants in US border facilities 'Dangerous' overcrowding of migrants in US border facilities Photos of detained migrants crowded into cells at the US border - with one holding up a sign reading simply "help" - have been released as part of a new report warning of "dangerous" overcrowding. The memo was sent to the Department of Homeland Security by its Inspector General, containing photos taken at border facilities in the Rio Grande Valley over a week in June DHS/OIG 'Dangerous' overcrowding of migrants in US border facilities Eighty-eight adult males held in a cell with a maximum capacity of 41, some signalling prolonged detention to OIG Staff on June 12 DHS/OIG 'Dangerous' overcrowding of migrants in US border facilities Overcrowding of families observed by OIG on June 11, at a border patrol facility in Weslaco, Texas DHS/OIG 'Dangerous' overcrowding of migrants in US border facilities Migrant families overcrowding a border patrol facility on June 11 in McAllen, Texas DHS/OIG 'Dangerous' overcrowding of migrants in US border facilities Fifty-one adult females held in a cell designated for male juveniles with a capacity for 40 at Border Patrol’s Fort Brown Station DHS/OIG 'Dangerous' overcrowding of migrants in US border facilities Migrant families overcrowding a border patrol facility on June 11 in McAllen, Texas DHS/OIG

She was prevented from entering the areas where children were locked up to find the ones most in need of medical care, she claimed.

The Independent has contacted US Customs and Border Protection (CBP), USBP’s parent agency, for comment.

The interview was released a day before Donald Trump was due to address a Fourth of July “Salute to America” event in Washington DC, marking the anniversary of the declaration of independence in which the fledgling states asserted that “all men are created equal, that they are endowed by their creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness”.

People detained after migrating illegally or seeking asylum “are living far better now than where they came from, and in far safer conditions”, the president tweeted on Wednesday. He added: “No matter how good things actually look, even if perfect, the Democrat visitors will act shocked & aghast at how terrible things are. Just Pols.”

Tightening immigration rules and creating a merit-based system was the way to solve the border crisis, Mr Trump said.

In her interview, Dr Sevier recounted a meeting with a 17-year-old girl whose four-month-old son had had diarrhoea for some days, and had soiled his clothes. The girl told her that guards had refused him fresh garments so she scrounged two additional nappies and fashioned them into a tunic for the infant. Underneath it he was sticky and dirty, Dr Sevier said, and covered in fluff from the nappies.

A 15-month-old baby with a fever had been detained for three weeks and was fed from the same unwashed bottle for several days, Dr Sevier was told, before a guard replaced it. Denying people the chance to clean their baby’s bottle “is unconscionable and could be considered intentional mental and emotional abuse”, she wrote in an official medical declaration shown to The Atlantic.

The revelations, and Mr Trump’s tweets, followed a report by the homeland security watchdog on Tuesday that detailed inhumane conditions at five CBP facilities in the Rio Grande Valley area of Texas. It described overcrowding as “dangerous” and quoted a senior centre manager as calling the situation a “ticking time bomb”.

The office of the inspector general (OIG) found that “at one facility, some single adults were held in standing-room-only conditions for a week” and most were still wearing the clothes they arrived in “days, weeks and even up to a month prior”.

A diet consisting only of processed sausage sandwiches had left some people constipated and in need of medical help, OIG said, while two sites did not provide hot food for children until the week inspectors arrived.

That report came just weeks after OIG investigated centres run by Immigration and Customs Enforcement and ordered urgent improvements after finding makeshift nooses in some cells, plus staff serving spoiled food and wrongly putting people in isolation.

Border officials have struggled with a lack of space and money in the face of a rise in crossings, particularly by families. On Monday, the president signed legislation to provide $4.6bn (£3.7bn) to improve conditions.