Unraveling the puzzle of human anellovirus infections by comparison with avian infections with the chicken anemia virus.

Current clinical studies on human annelloviruses infections are directed towards finding an associated disease. In this review we have emphasized the many similarities between human anellovirus and avian circoviruses and the cell and tissue types infected by these pathogens. We have done this in order to explore whether knowledge acquired from natural and experimental avian infections could reflect and be extrapolated to the less well-characterized human annellovirus infections. The knowledge gained from the avian system may provide suggestions for decoding the enigmatic human anellovirus infections, and finding the specific disease or diseases caused by these human anellovirus infections. Each additional parallelism between chicken anemia virus (CAV) and Torque teno virus (TTV) further strengthens this premise. As we have seen information from human infections can also be used to better understand avian infections as well. Increased attention must be focused on the "hidden" or unrecognized, seemingly asymptomatic effects of circovirus and anellovirus infections. Understanding the facilitating effect of these infections on disease progression caused by other pathogens may help to explain differences in outcome of complicated poultry and human diseases. The final course of a pathogenic infection is determined by variations in the state of health of the host before, during and after contact with a pathogen, in addition to the phenotype of the pathogen and host. The health burden of circoviridae and anellovirus infections may be underestimated, due to lack of awareness of the need to search past the predominant clinical effect of identified pathogens and look for modulation of cellular-based immunity caused by co-infecting circoviruses, and by analogy, human anneloviruses.