Arch Virol (2002) 147: 447–470
Ranaviruses (family Iridoviridae): emerging cold-blooded killers
V. G. Chinchar
Department of Microbiology, University of Mississippi Medical Center,
Jackson, Mississippi, U.S.A.
Accepted October 11, 2001
Summary. Although possessing novel replicative and structural features, the
family Iridoviridae has not been as extensively studied as other families of large,
DNA-containingviruses (e.g., poxviridaeand herpesviridae). This oversight most
likely reﬂects the inability of iridoviruses to infect mammals and birds, and their
heretofore low pathogenicity among cold-blooded animals and invertebrates. In
fact, the original frog virus isolates (e.g., frog viruses 1–3) would likely have
been considered orphan viruses since they were isolated from apparently healthy
frogs. However, recent disease outbreaks among commercially and recreation-
ally important ﬁsh, cultured and wild frogs, and endangered salamanders has
challenged this benign view and have implicated several members of the genus
Ranavirus as pathogens. This review explores three facets of ranavirus biology.
In the ﬁrst the salient features of ranavirus replication are summarized usingfrog
virus 3 as a model. Secondly, criteria for characterizingnew ranavirus isolates,
based on biochemical (viral protein proﬁles, DNA restriction fragment length
polymorphisms, and nucleotide sequence analysis), ecological (host range, tissue
tropism), and clinical considerations, are detailed. Lastly, the principal agents of
ranavirus-mediated disease and immune responses to these viruses are discussed.
In light of the above, it is clear that ranaviruses are no longer orphan viruses, and
that they have a signiﬁcant impact on diverse populations of ectothermic animals.
Although possessing several unique replicative and structural features [29, 31, 61,
90, 99], and known since the late 19th century for the wart-like disease that one of
them (lymphocystis disease virus, LCDV) causes in numerous species of marine
and freshwater ﬁsh , the vertebrate iridoviruses within the family Iridoviridae
have, until recently, generated relatively little research interest among virologists.