HANOI, Vietnam – Tran Minh Giang has spent more than a third of his young life in a Vietnamese hospital, and it could be many months more before he can go home. All for a disease that in Asia is as common as chicken pox, and usually about as severe.

The 20-month-old was sickened by a particularly menacing form of hand, foot and mouth disease that has killed hundreds of young children across the region. They sometimes suffer high fever, brain swelling, paralysis and respiratory shutdown, even though they may have been infected by people with few or no symptoms.

When the strain hit Cambodia recently, doctors there had no idea what it was, and even now experts don’t fully understand why it can be so devastating. Seven months after becoming sick, Giang still breathes using a ventilator connected to a hole in his tiny throat.

“It may take time, maybe years, before he can recover. When he sleeps, his lungs don’t work,” his father, Tran Nam Trung, said Thursday while fanning the toddler.

The enterovirus 71 strain, or EV-71, raised fears earlier this week when it was detected in some lab samples taken after 52 of 59 Cambodian children died suddenly from a mystery illness that sparked international alarm. The World Health Organization said via Twitter on Thursday that its investigation has found most cases were caused by the disease.

An expert at the U.N. health agency earlier said it’s the first time EV-71 had been identified in Cambodia, but it’s a well-known pathogen elsewhere in Asia. In the first half of this year alone, 356 people in China and 33 in Vietnam have died from it.

The scale of the disease was clear last week on the crowded ground floor of a hospital in China’s hard-hit central Hunan province. Dozens of crying children were packed into two small rooms, sitting or lying on chairs with IV drips hooked to them. Hunan reported 33 hand, foot and mouth disease deaths in May, a quarter of the country’s total that month.

The disease has exploded across the region since 1997, when the first major outbreak was reported in Malaysia. Since then, Japan, South Korea, Singapore, Mongolia, Taiwan and Australia have all wrangled with it.

EV-71 is one of a group of viruses that cause the disease, but it has become a more dominant strain over the past decade in Asia. Still, only a small percentage of children infected experience severe symptoms, and experts aren’t exactly sure why. There is no vaccine or specific treatment to cure it, but severe cases are given supportive care and blood proteins are also sometimes administered intraveneously.

“There’s a buildup of that susceptible population, like many viruses, and this happens to be the children who have not been exposed to different types of enteroviruses before,” said Dr. Zarifah Hussain Reed, co-author of a WHO report on hand, foot and mouth disease.