Constant companion: clinical and developmental aspects of torque teno virus infections.

Torque teno virus (TTV) is a commensal human virus observed as a circular single-negative-strand DNA molecule in various tissues and biological samples, notably in blood serum and lymphocytes. TTV has no apparent clinical significance, although it might be very useful as a prospective tool for gene delivery or as an epidemiological marker. Human populations are ubiquitously infected with TTV; the prevalence may reach 100%. The majority of babies become spontaneously infected with TTV, so that by the end of the first year of life, the prevalence reaches 'adult' values. TTV positivity in healthy early infancy and the presence of TTV in umbilical cord blood samples have been reported. The mechanism of infection and the dynamics of TTV prevalence in infants with age remain understudied. Meanwhile, the potential diagnostic and prognostic value of TTV as a marker deserves special attention and study, along with the possibility, causes and consequences of placental transmission of TTV under normal or pathological conditions.