The diversity of viruses infecting humans.

Most human viruses have been discovered through the diseases they cause in animals, plants, bacteria or fungi. Recent finds include human bocaviruses, which now seem to have a global distribution, and cause respiratory tract disease in infants, and several new pathogenic human coronaviruses. The SARS coronavirus, genetically distinct from all previously known coronaviruses, caused a disease which was highly transmissible and very severe, eventually leading to 8000 cases worldwide with over 800 deaths. Many viruses which are transmitted to humans by invertebrates, such as insects or ticks, have the ability to infect and replicate in cells of both vertebrate and invertebrate origin. However human virology is a rapidly expanding field and recent technologies such as the polymerase chain reaction (PCR) amplification system have made it possible to look for previously unrecognized viruses which may or may not be involved in pathogenesis. For example viruses in the genus Anellovirus are found in 80% of human blood samples yet do not seem to cause any disease. This paper overviews known human vertebrate viruses, more recent discoveries, and recommends a systematic search for viruses which may already infect the human population but have so far remained undetected.