The present study extends our previous discovery of partetraviruses in domestic animals. Although no clear association has been found between clinical disease and human partetraviruses, the relatively high prevalence of PARV4 in human blood products has raised safety concerns, especially since available evidence appears to support possible parenteral transmission of the virus [14, 36, 37, 38, 39] . Similarly, animal partetraviruses have not been found to be associated with any clinical diseases in the hosts, and are detected frequently in apparently healthy animals [19, 20, 21] . So far, these viruses were mostly detected in liver, spleen, lymph node and bone marrow, suggesting significant tropism for lymphoid tissue, although there is also a report of detecting PARV4 DNA at relatively high frequencies in other organs such as the heart, lungs and kidneys [12] . The development of immune electron microscopy and related techniques can determine the intracellular location and cellular tropism of partetraviruses in infected tissues, and success have been reported with the visualization of PARV4 particles in a high-titre-positive plasma sample [40] . This will aid efforts to target screening for subclinical disease in patients or animals with positive partetravirus detection by PCR or serology.