Researchers get a handle on what made Typhoid Mary's infectious microbes tick

Stanford University School of Medicine scientists have shown how salmonella—a bacterial menace responsible for hundreds of thousands of deaths each year from typhoid fever and food poisoning—manages to hide out in immune cells, altering their metabolism to its own benefit.

Salmonella's ability to position itself inside infected people's cells for the long haul can turn them into chronic, asymptomatic carriers who, unknown to themselves or others, spread the infectious organism far and wide.

The findings could lead to new and better treatments for typhoid fever. Worldwide, there are 16 million to 20 million cases each year, resulting in about 200,000 deaths, although the disease is no longer common in developed countries. Scientists further estimate that there are close to 100 million cases of salmonella-induced gastrointestinal infections each year, the majority from food poisoning, resulting in more than 150,000 deaths.

"Between 1 and 6 percent of people infected with S. typhi, the salmonella strain that causes typhoid fever, become chronic, asymptomatic carriers," said Denise Monack, PhD, associate professor of immunology and microbiology and the study's senior author. "That is a huge threat to public health."

A classic case of a chronic, symptom-free carrier is the infamous Typhoid Mary, an Irish immigrant who made her living as a cook in and around New York City in the early 1900s. She infected about 50 people with typhoid fever. "To all outward appearances, she was perfectly healthy," Monack said.