Abstract
Iridoviruses are large, variably host-specific, dsDNA viruses that infect invertebrates and poikilothermic vertebrates. Five genera are recognized, of which members of the genus Ranavirus have been shown to infect fish, amphibians and reptiles.3-5 Several accounts of iridovirus infection have been documented in chelonians.1,2,5-8 In the United States, only three cases have been reported; a Russian tortoise (Testudo horsfieldii), and a box turtle (Terrapene carolina) in which no pathology was described5 and a wild gopher tortoise (Gopher polyphemus) that had signs of respiratory disease8. Between July and October 2003, a captive Burmese star tortoise (Geochelone platynota) from Georgia, a wild gopher tortoise (Gopherus polyphemus) from Florida and five Eastern box turtles (Terrapene carolina carolina) from Pennsylvania were found to be infected with Ranavirus. Clinical signs were similar to those seen with herpesvirus infection and included palpebral edema, ocular and nasal discharge, and oral plaques. The most consistent histologic lesions were necrotizing and ulcerative stomatitis and/or esophagitis, and fibrinous and necrotizing splenitis. In addition, several animals had varying degrees of multicentric vasculitis or thrombosis, necrosis of hematopoietic tissues, and multifocal necrotizing tracheitis, conjunctivitis or gastritis. In some cases, basophilic intracytoplasmic inclusion bodies were observed within epithelial cells of the oral mucosa, esophagus, stomach and trachea, or within endothelial cells, macrophages and hematopoietic cells. In each case, a virus compatible with iridovirus was isolated in Terrapene heart cells. PCR was used to amplify a segment of the gene encoding the iridovirus major capsid protein.5,6 Approximately 400 base pair amplicons were sequenced and BLAST analysis indicated the most closely related virus to be Frog Virus 3, a Ranavirus. An iridovirus was isolated from an ill leopard frog (Rana utricularia) near the Burmese star tortoise enclosure with an identical sequence as the star tortoise iridovirus, suggesting that amphibians may serve as a reservoir host for a ranavirus transmissible to chelonians. The identification of a Ranavirus in box turtles and tortoises at widely separated sites over a 3-mo period either suggests an emerging disease or one that has been previously unrecognized.
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