ABSTRACT
Since 1976 an array of viruses have been either identified in tissue section using electron microscopy or isolated in cell culture from tissues of members of the orders Chelonia, Crocodylia, and Squamata (Essbauer and Ahne, 2001; Wellehan and Johnson, 2005). Except for a single report of a retroviral gene sequence (Tristem et al., 1995), there are no reports of viral infection of the tuatara (Sphenodon spp.), the only member in the order Rhynchocephalia. The majority of viruses identified in reptiles have been only circumstantially incriminated as causes of disease, with few studies fulfilling Koch’s postulates. In many of the older reports, viruses were identified using either electron microscopy or viral isolation. Several reptile viruses await isolation. Immunohistochemical staining has been used to identify viral antigens in tissue section. More recently, molecular techniques such as polymerase chain reaction (PCR) and in situ hybridization (see Chapter 7) are being used with increased frequency to identify viruses in tissues of reptiles or confirm identification of those isolated in tissue culture. This has revolutionized the ability to diagnose viral infections using small amounts of tissue or other biological samples such as mouth swabs and fecal samples. Many retroviruses have been identified in tumors of reptiles, but again, transmission studies have not been reported to confirm a causal relationship. In some situations, such as with western equine encephalitis virus, reptiles may serve as a reservoir host, with the virus being non-pathogenic in the infected reptile. Two species of turtles (Mauremys [formerly Clemmys] mutica and Chinemys [formerly Geoclemys] reevesii) were found to be infected with hepatitis B virus following inoculation with human sera that were positive for certain antigens of hepatitis B (Lee and Yoo, 1989), but natural infection has not been reported. Lastly, viruses of unknown disease potential have also been identified in reptiles. In this chapter, viral infections and viral diseases of reptiles will be discussed. DNA viruses (Herpesviridae, Adenoviridae, Poxviridae, Iridoviridae, Papillomaviridae, Parvoviridae, and Circoviridae) will be discussed first followed by RNA viruses (Paramyxoviridae, Retroviridae, Reoviridae, Togaviridae, Flaviviridae, Rhabdoviridae, Caliciviridae, and Picornaviridae).
