Wilson da Silva

Science journalist, feature writer and editor.

Jul 15, 2002
Published on: Science | AAAS
3 min read

By Wilson da Silva

Bacterial infections can trigger high levels of a brain steroid that can make infants too drowsy to awaken when they encounter difficulty breathing, suggests new research on lambs. 

Although a link between infections and sudden infant death syndrome (SIDS) has been previously suspected, this is the first time a clear mechanism has been found that might explain such a link.

SIDS usually occurs while an infant is sleeping at night. An emerging theory holds that the condition is caused by bacterial toxins, encountered by virtually all infants in the first year of life. Researchers have proposed several theories to explain how these toxins might kill infants, but so far there has been little experimental evidence to back them up.

Now, physiologist Saraid Billiards of Monash University in Melbourne, Australia, has found that even a mild bacterial infection can cause brain steroid levels to rise dramatically, leading lambs to become extremely drowsy and difficult to wake. In a trial involving 12 lambs, a mild infection with Escherichia coli caused levels of the steroid allopregnanolone in the blood to rise by 50%. 

Results were even more dramatic in the brain, where levels of allopregnanolone, which is known to have sedative and anaesthetic properties, increased two- to threefold. If the same occurs in humans, even a mild infection could blunt infants’ ability to awaken, Billiards says. “If they develop breathing problems while they’re asleep that cause their blood oxygen to fall, they don’t have the appropriate arousing response that allows them to wake.”

John Newnham, director of the Women and Infants Research Foundation in Perth, Australia, says the finding is an important step towards understanding SIDS. “This helps us with the idea that infection is involved.” The research has been accepted for publication in the journal Pediatric Research later in the year.