Virus family, morphology, and transmission of HIV, HBV, HCV, HSV, HCMV, HPV, RSV, VZV, and influenza virus. Virus family, morphology, and transmission of HIV, HBV, HCV, HSV, HCMV, HPV, RSV, VZV, and influenza virus. Nine human viruses are classified into DNA viruses (HBV, HCMV, HSV, HPV, and VZV), RNA viruses (HCV, RSV, and influenza virus), and retroviruses (HIV). These viruses are from 7 families: the Hepadnaviridae (HBV), the Papillomaviridae (HPV), the Herpesviridae (HCMV, HSV, and VZV), the Flaviviridae (HCV), the Paramyxoviridae (RSV), the Orthomyxoviridae (influenza virus), and the Retroviridae (HIV). Schematic views and electron micrograph images of viral particles are illustrated in boxes, where particle sizes measured as diameters and viral genome types (circular/linear dsDNA or linear RNA) are also indicated (Table 1). Human viruses are further characterized with the possible animal reservoirs. HIV is known to be transmitted from chimpanzees (HIV-1 groups M and N), gorillas (HIV-1 groups P and O), or sooty mangabeys (HIV-2) (11, 14, 15). Influenza viruses that infect humans originate mostly from birds, pigs, or seals (36, 401). Although the origin of HBV has yet to be clarified, bats might be a potential reservoir for HBV (47). HPV has been widely found in birds, reptiles, marsupials, and mammals, but cross-transfer between species is rare (54). Four human viruses (RSV [41], HCMV [64], HSV [74], and VZV [80]) circulate only in human populations and do not have any animal reservoir. In addition, it remains unclear whether HCV has any animal reservoir (27, 476). (The HCV electron micrograph image is republished from reference 20 with permission of the publisher. The HPV electron micrograph image was obtained from the Laboratory of Tumor Virus Biology at the National Cancer Institute [https://visualsonline.cancer.gov/]. The electron micrograph images for HBV, HCMV [by Sylvia Whitfield], HSV [by Fred Murphy and Sylvia Whitfield], VZV [by Erskine L. Palmer and B. G. Partin], RSV [by Erskine L. Palmer], influenza virus [by Erskine L. Palmer and M. L. Martin], and HIV [by Maureen Metcalfe and Tom Hodge] were obtained from the Centers for Disease Control and Prevention [http://phil.cdc.gov/phil/home.asp].)‏ Erik De Clercq, and Guangdi Li Clin. Microbiol. Rev. 2016; doi:10.1128/CMR.00102-15