Asymptomatic carrier

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Typhoid Mary in a 1909 newspaper illustration

An asymptomatic carrier (healthy carrier or just carrier) is a person or other organism that has contracted an infectious disease, but who displays no symptoms. Although unaffected by the disease themselves, carriers can transmit it to others.[1]

In humans, HIV goes through a long latency period, during which the host is asymptomatic.[2] Many carriers are infected with persistent viruses such as EBV and Cytomegalovirus that only rarely progress to a disease state. Herpes simplex viral infection may also be asymptomatic and can be spread without the originally infected person realising they are infected.[3]

C. difficile has also been shown to be spread by asymptomatic carriers, and poses significant problems in care home settings.[4]

Mary Mallon, known as "Typhoid Mary", was an asymptomatic carrier of typhoid fever.[5] 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. There was at the time no way of eradicating the disease, and an attempt was made to restrict her from continuing to work as a cook to avoid spreading it to others.


  1. ^ "Dictionary Definition". Retrieved 20 August 2013. 
  2. ^ Siliciano, Robert F. "HIV Latency". Cold Spring Harbor Laboratory Press. Retrieved 20 August 2013. 
  3. ^ "Asymptomatic Herpes". Retrieved 20 August 2013. 
  4. ^ Riggs, M. M.; Sethi, A. K.; Zabarsky, T. F.; Eckstein, E. C.; Jump, R. L. P.; Donskey, C. J. (2007). "Asymptomatic Carriers Are a Potential Source for Transmission of Epidemic and Nonepidemic Clostridium difficile Strains among Long-Term Care Facility Residents". Clinical Infectious Diseases 45 (8): 992–998. doi:10.1086/521854. PMID 17879913.  edit
  5. ^ "Scientists get a handle on what made Typhoid Mary’s infectious microbes tick - See more at:". Retrieved 20 August 2013.