Studies in Viral Ecology by Christon J. Hurst & Christon J. Hurst

Author:Christon J. Hurst & Christon J. Hurst
Language: eng
Format: epub
Publisher: Wiley
Published: 2011-06-18T00:00:00+00:00

Chapter 9

Ecology of Viruses Infecting Ectothermic Vertebrates—The Impact of Ranavirus Infections on Amphibians

V. Gregory Chinchar

Department of Microbiology, University of Mississippi Medical Center, Jackson, MS

Jacques Robert

Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY

Andrew T. Storfer

School of Biological Sciences, Washington State University, Pullman, WA

9.1 Introduction

Although isolates from at least 15 viral families infect one or more classes of ectothermic vertebrates, only representatives of three families (Adenoviridae, Alloherpesviridae (order Herpesvirales), and Iridoviridae), naturally infect amphibians. With few exceptions most viruses within the order Herpesvirales and the family Adenoviridae infect mammals and birds (Fauquet et al., 2005). In contrast, all viruses within the family Alloherpesviridae infect either fish (e.g., Ictalurid herpesvirus 1) or frogs (ranid herpesvirus 1), whereas viruses within three genera of the family Iridoviridae (Ranavirus, Megalocytivirus, and Lymphocystivirus) infect ectothermic vertebrates. Within those three genera, megalocytiviruses and lymphocystiviruses infect only fish, whereas individual ranaviruses target amphibians, reptiles, or fish, and a few viral species appear able to infect members of different taxonomic classes (Moody and Owens, 1994; Mao et al., 1999; Chinchar et al., 2009; Jancovich et al., in press). For example, although Bohle iridovirus (BIV) naturally infects anurans (Cullen et al., 1995), it has also been shown to infect fish following intraperitoneal injection (Moody and Owens, 1994). Likewise, whereas Ambystoma tigrinum virus (ATV, family Iridoviridae, genus Ranavirus), and Frog virus 3 (FV3, family Iridoviridae, genus Ranavirus) infections are limited, respectively, to salamanders and frogs in nature, both will infect heterologous species, albeit at low levels, under experimental conditions (Clark et al., 1968; Schock et al., 2008).

In addition to these well-documented natural infections, amphibians have been suggested to serve as hosts for arboviruses of human concern, for example, Eastern equine encephalitis virus, West Nile virus, St. Louis encephalitis virus, and so on (Whitney et al., 1968; Klenk and Komar, 2003; Cupp et al., 2004; Densmore and Green, 2007; Burkett-Cadena et al., 2008). Although field and serological studies, as well as experimental infections, suggest at least limited amounts of virus replication take place in some frog species (Kostyukov et al., 1986), it is not clear whether infections of amphibians with Flaviviruses or Togaviruses lead to clinical disease, or whether infected amphibians act as virus reservoirs or amplifying hosts and contribute to disease in humans and other mammals. Partly this uncertainty may reflect the fact that some mosquito species that feed on amphibians do not readily feed on mammals or birds, and vice versa (Cupp et al., 2004), and the observation that viral titers in experimentally infected frogs are very low and transient (Klenk and Komar, 2003) and unlikely to result in mosquito infection following feeding. Because of this uncertainty, only viruses within the three aforementioned families that naturally infect amphibians and contribute to disease in those animals are listed in Table 9.1.

Table 9.1 Viruses Infecting Amphibiansa.

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