New research could explain how Mary Mallon, infamously known as Typhoid Mary, carried the disease 100 years ago — and spread it — but had no signs of the infection herself, the L.A. Times is reporting.
A bacterium strain similar to the one in Typhoid Mary shows an ability to hide in the infected person’s immune cells, spreading the infection far and wide without showing any symptoms, a team of scientists from Stanford University and University of California, San Francisco have found.
The woman known as Typhoid Mary was an Irish immigrant to New York and worked as a cook in the early 1900s. She was eventually identified as the source to the typhoid outbreak while remaining healthy herself.
As many as 50 people died after being exposed to the disease carrier. She was arrested and quarantined until her death in 1938. It was not known how she could remain healthy while spreading the disease with no apparent symptoms.
“Between 1 and 6 percent of people infected with S. typhi, the salmonella strain that causes typhoid fever, become chronic, asymptomatic carriers,” Denise Monack, associate professor of immunology and microbiology at Stanford University and the study’s senior author, said in a statement. “That is a huge threat to public health.”
The team’s study was published in the journal Cell Host & Microbe.
The research involved experiments with mice. According to the Los Angeles Times,
“The trickery, revealed in experiments with mice, involves a receptor protein that affects how macrophages — the body’s Pac-Man gobblers of foreign pathogens — get the energy required to survive. The team found that the bacteria tend to hang out with a mellower macrophage associated with the later stages of infection. Enough of the bacteria survive the more aggressive wave of attackers during the inflammatory phase of the immune response to settle in with the more placid anti-inflammatory cells, according to the study. Once inside, the bacteria essentially hack the genetic programming that sets off production of glucose for the host cell, and its own survival.”
Researchers think the protein might be responsible for leaving patients with the asymptomatic infection.
"Mice whose genes were altered to be deficient in production of the transcriptional protein were a lot like Typhoid Mary — infected, but not sick. Six weeks later, levels of the tell-tale protein were nearly undetectable,” reports the LA Times.
Vaccinations for typhoid and improved sanitation standards for food and water ultimately led the disease to become rare in the United States.