Health

Whooping cough increases autism risk in infants, Trinity research finds

‘Impossible to put a number’ on level of risk, says TCD immunologist who supervised research

Immunologist Kingston Mills of Trinity College Dublin. Photograph: Nick Bradshaw
Immunologist Kingston Mills of Trinity College Dublin. Photograph: Nick Bradshaw
Seán Duke
Sat Feb 08 2025 - 06:00

Infection with whooping cough in infants increases their risk of developing autism spectrum disorder, according to a new study led by scientists at Trinity College Dublin (TCD).

Although the researchers identify whooping cough – also known as pertussis – as a risk factor for autism in a study published by iScience, they say it’s difficult to pinpoint the precise risk involved.

“It is impossible to put a number on this, or to define how much is down to whooping cough,” said immunologist Prof Kingston Mills, who supervised the research led by Dr Eoin O’Neill along with Prof Marina Lynch.

“There have been a few reports showing associations between viral or bacterial infections in pregnancy and autism in offspring,” Prof Mills said.

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Whooping cough is a highly infectious bacterial disease affecting the respiratory tract.

“Furthermore, children that have recovered from severe pertussis as infants often have neurodevelopment defects and learning difficulties.

“This is the first report to show a direct link between infection and development of ASD and the first to provide mechanistic insight,” he added.

[ Autism: Why are so many children being diagnosed these days? ]

Autism diagnoses have been increasing worldwide since the 1990s. Researchers believe this is due in part to increased awareness, widening of the diagnosis criteria and reporting of the condition.

However, scientists also believe environmental factors, including infections during pregnancy or in early neonatal life, are also contributing to this increase.

A viral infection in pregnant women in the first trimester, and bacterial infection during the second trimester have been linked with an increased likelihood of an autism diagnosis in children, Prof Mills noted.

Meanwhile, scientists also know autistic children are more likely to have had neonatal or early childhood infections compared with the general population.

“We showed that early in life, when the immune system is still immature infection with whooping cough is not confined to the respiratory tract, and bacteria spread to the brain,” he said.

“This results in inflammation in the brain, which negatively impacts immune cells that have a positive effect on neurons. This infection-induced inflammation gives rise to neurodevelopment defects, which results in ASD-like behaviours later in life.”

In Sweden, he said, there was a steep rise in whooping cough incidence between 1984 and 1994 after pertussis vaccination programme was halted which was associated with an increase in ASD numbers.

“The resumption of the pertussis vaccination programme in Sweden in the mid 1990s, following the development of a new pertussis vaccine, was associated with a decline in the prevalence of ASD at a time of global increases in the incidence of autism,” he said.

“This abrupt fall in ASD rates contrasted markedly with worldwide trends during the same period, confounding expected increases in ASD recognition, diagnosis and reporting over time.”

“Vaccination against whooping cough in pregnancy should not only prevent pertussis in the neonatal offspring, who are most susceptible to severe disease, but may also reduce the possibility of developing ASD later in life,” said Prof Mills, who is working on developing a new pertussis vaccine that will be delivered nasally.

Once translated to humans this vaccine holds hope of eliminating community spread of bacteria that has been resurgent in recent years, he said. “It also holds hope of reducing the indigence of neurodevelopment and learning defect seen in children that have recovered from whooping cough.”