SANKHU, Nepal -- Nepal is desperately poor. Its hospitals are overcrowded with earthquake survivors who need urgent medical treatment, and the threat of infectious disease, given the dismal circumstances at the overstrained facilities, is real and mounting.

Dr. Christopher Barley normally treats wealthy patients, even royalty, at his Park Avenue practice in New York.

When the earthquake hit, he dropped everything and flew to Nepal.

CBS News Holly Williams caught up with him in the town of Sankhu, about 10 miles northeast of the hard-hit capital city of Kathmandu, trying to assess and treat a woman with a badly bruised leg.

Barley knows the country well. He built a hospital in a remote Nepalese village 12 years ago.

"It's actually quite heartbreaking for me to walk around and see this," he tells Williams as they walk through the rubble-strewn streets. "Unfortunately, for some reason, some of the poorest places are often hit the hardest."

Barley checks Sapta Maya Shrestha's head carefully for fractures. She was hit by falling bricks when her house collapsed.

"She's very lucky," he proclaims, before moving on to clean the wounds of Laxmi Nakami.

Nakami lost her home in the quake. Now she's living with ten other families in a disused chicken coop.

The 7.8 earthquake that struck on Saturday didn't just take thousands of lives, it destroyed families, entire communities, and centuries of history in the Himalayan nation.

With clean water in short supply, what Barley's really worried about now is infection and disease.

"Just about anything you can get in the tropics, they'll be getting," Barley warned of the coming weeks for the survivors. "The number of people that may die from that can be bigger than the original problem of the buildings falling down."

Williams says many people in Nepal share Barley's concerns. Over the last few days CBS News has seen thousands of people leave Kathmandu, concerned that the tent cities that have sprung up around the capital could become breeding grounds for infectious disease.