Tropheryma whipplei as a commensal bacterium.

Tropheryma whipplei is the bacterial agent of the well-known and rare Whipple's disease, mainly observed among Caucasians. This bacterium has recently been involved in other chronic and acute infections. For a long time, the only known source of the bacterium was patients with Whipple's disease; however, thanks to the advent of molecular biology, T. whipplei has now been detected in specimens from healthy individuals, mainly in stool and saliva samples. The prevalence of carriage depends on several factors, such as age, exposure and geographical area, reaching 75% in stool specimens from children less than 4 years old in rural Africa. T. whipplei is a commensal bacterium that only causes Whipple's disease in a subset of individuals, probably those with a still-uncharacterized specific immunological defect.