The African boy never made it to the hospital. Blood was spurting from every orifice and when the driver opened the ambulance door, infected bodily fluids gushed onto the sand.

"I was scared," Ross Donaldson recalls about his time in Sierra Leone caring for the sick. "At any moment, if you slip up, the consequences are fatal."

His new book, The Lassa Ward: One Man's Fight Against One of the World's Deadliest Diseases , describes the brutal conditions in a part of the world long devastated by civil war. The boy was a victim of the Lassa fever Donaldson went to study. In the same family as Ebola, it's an acute viral hemorrhagic illness transmitted to human beings from rats, and then from contact with an infected person or medical equipment.

The sole treatment for Lassa fever is the anti-viral drug ribavirin, effective only if given early enough. In its first stages the symptoms are mild, however, and Lassa is often mistaken for less dangerous diseases.

Still a medical student when he arrived in Kenema, Sierra Leone's third largest city, Donaldson, now 33 and a Los Angeles resident, was shocked by the unremittingly grim poverty. The hospital had no equipment for diagnosis or treatment. "People were dying for lack of a $20 Ambu bag," he said, referring to the ventilator used in resuscitation. Medicine flown in by relief organizations was often unavailable at the medical center, stolen by health workers who resold the stuff in the markets, trying to feed their families.

For much of the time, Donaldson felt deep frustration. Though medical care was theoretically free, the staff at the next-door maternity hospital refused to treat anyone without a wad of cash up front. One pregnant woman suffering eclamptic seizures was left to die on a stretcher until a foreign doctor, aided by Donaldson, performed an emergency Caesarian section.

Donaldson was abruptly left in charge of the Lassa ward when the director was called away. He quickly learned how little training the caregivers had when one recommended treating viruses with antibiotics (only effective for bacterial infections).

Attempts to control Lassa fever at the source went strangely awry, as people didn't stop eating the infected rats even when warned. "It's such a sweet meat, it can't be wrong, they told us," Donaldson explains. When cats were brought in to contain the rodents, the protein-starved villagers waited until they fattened up, and then ate the cats, too. "There's a disjunct between knowledge and practice," says Donaldson. "But it's really no different in Los Angeles, where I've had the same conversations regarding smoking."