Asymptomatic carrier

An asymptomatic carrier (healthy carrier or just carrier) is a person or other animal which has become infected with a pathogen, but who shows no signs or symptoms. Although unaffected by the pathogen themselves, carriers can transmit it to others.

Typhoid Mary in a 1909 newspaper illustration

Typhoid fever

History

Mary Mallon, known as "Typhoid Mary", was an asymptomatic carrier of Salmonella enterica, the causative agent of typhoid fever. She worked as a cook for several families in New York City at the beginning of the twentieth century and she also cooked for the soldiers. Several cases of typhoid fever in members of those families were traced to her by the Health Department. It appeared that she "carried" the infectious agent without becoming sick. At the time, there was no way of eradicating the disease.