It should have been one of the happiest times any family gets to experience.

Thorsten, 34, from Hamburg and his wife had just celebrated the birth of their son, John. Baby and mother had come home from the hospital and were apparently doing well.

But as the grief-stricken father explained in a May 9th Facebook post seen by thousands in recent days, the joy of a new baby was to be short-lived.

“About 14 days after he was born John became restless, started stretching and having shivering spells,” Thorsten wrote.

The midwife advised the young parents to bring John to a doctor the following day.

That evening, the parents brought John to hospital where he was immediately whisked to paediatric intensive care.

Four days later came the diagnosis: the baby had herpes encephalitis. The herpes virus had made it into his brain and was causing dangerous inflammation.

“John got a herpes virus from somewhere that was able to spread into his brain because the blood-brain barrier wasn't yet developed,” Thorsten explained on Facebook.

“We wanted to make people aware of the treacherous consequences of an infection,” said Thorsten S. Photo: DPA

For John, the prognosis is bleak. Large parts of his brain have been damaged or destroyed by the infection, despite the doctors' best efforts, and he might yet die of the illness.

But Thorsten insists that “we don't want any sympathy. We want something more important.”

He asks simply that anyone with active cold sores stay away from babies.

“If you keep this in mind you could save a child's life and spare him suffering,” he wrote.

Too weak to fight

“[A newborn's] immune system isn't strong enough yet to fight the virus,” confirmed Antje Vogler, head of a paediatric unit in Pasewalk, Mecklenburg-Western Pomerania.

Babies infected with herpes turn pale, become unresponsive, and may suffer seizures or cramping as well as a fever, she went on.

While it's rare for babies to become infected, herpes encephalitis is caused by the more common Type 1 herpes virus that causes cold sores – not the rarer Type 2 genital herpes.

“Before we were affected by it we had no idea that herpes could be so dangerous for babies,” Thorsten told news agency DPA.

The Facebook post was originally intended for friends and family only, but soon spread beyond those circles to tens of thousands of readers across Germany and beyond.

“If our Facebook post or the media coverage can save even one child, John's hard path will have gained meaning,” Thorsten said.