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188 | Kibenge et al.

turkey-origin avian reoviruses, the sequence differences on gene reverse genetics system for mammalian orthoreovirus strains
segments S3 (Kapczynski et al., 2002; Sellers et al., 2004), S1 (Day type 1 Lang (T1L) and type 3 Dearing (T3D) has been devel-
et al., 2007), and S4 (Patin-Jackwood et al., 2008) may simply oped, based on bacteriophage T7 RNA polymerase, which can be
reflect reassortment of genome segments between isolates of the supplied transiently by recombinant vaccinia virus (rDIs-T7pol)
same species (but not those of different species). However, one or by cells that constitutively express the enzyme (Kobayashi
of the turkey-origin avian reoviruses (strain NC/SEP-R44/03) et al., 2007; Boehme et al., 2011). The efficiency of virus rescue
grouped closely with S1 sequences from Nelson Bay orthoreovirus was enhanced in a second-generation system by combining the
(NRV), which is a different Orthoreovirus species (isolated from cDNAs for multiple reovirus gene segments onto single plasmids
fruit bats in Australia (Gard and Compans, 1970) (Day et al., to reduce the number of plasmids from ten to four, using BHK
2007). cells that express T7 RNA polymerase increased the efficiency
The genotypic differences in some cases have been sufficient of viral rescue to reduce the incubation time required to recover
to support establishment of separate new species within the infectious virus and eliminate biosafety issues associated with use
genus Orthoreovirus (Huhtamo et al., 2007; Dandár et al., 2014; of recombinant vaccinia virus. Kawagishi et al. (2018) recently
Ogasawara et al., 2015; Kalupahana, 2017). Phylogenetic rela- reported the development of a plasmid-based reverse genetics
tionships within the avian reoviruses based on the σNS (S4) gene system free of helper viruses and independent of any selection for
is illustrated in Fig. 6.4 (only isolates for which sequences of all the fusogenic orthoreovirus NBV. Kawagishi et al. (2018) used
three most variable genes: λB (L2), σC (S1), and σNS (S4) (Liu the system to generate viruses deficient in the cell attachment pro-
et al., 2003) were available in the GenBank database were used to tein σC and were able to demonstrate that σC is dispensable for
construct the phylogenetic trees). cell attachment in several cell lines, including murine fibroblast
The σNS (S4) gene phylogenetic tree clearly shows two main L929 cells but not in human lung epithelial A549 cells, and plays
clusters consisting of the species Avian orthoreovirus (ARV) iso- a critical role in viral pathogenesis. They also used the system to
lated from domestic or wild poultry (chickens, turkeys, ducks, rescue NBV that expresses a yellow fluorescent protein. Most
geese, pigeon, quail), and the species Wild bird orthoreovirus recently, Wu et al. (2018) used a novel duck reovirus strain TH11
isolated from wild birds (Pycno-1 passeriformes and the corvid in the ten plasmid-based reverse genetics system based on bacte-
orthoreovirus Tvärminne avian virus) (Fig. 6.4). The isolates of riophage T7 RNA polymerase in BSR-T7/5 cells and production
the Wild bird orthoreovirus species are very similar to Nelson Bay of infectious virus was shown by inoculation of cell lysate derived
orthoreovirus species in the phylogenetic tree for segment L2 from transfected cells into 10-day duck embryos.
(figure not shown). In fact, Tvärminne avian virus (Huhtamo et
al., 2007; Dandár et al., 2014) and American crow orthoreovirus
(Kalupahana, 2017) may represent a separate new species within Pathogenesis
the genus Orthoreovirus. In the σNS (S4) tree (Fig. 6.4), ARV The host range of avian reoviruses includes all domestic and wild
further splits into three genotype clusters: the chicken/turkey poultry (chickens, turkeys, ducks, geese, pigeon, quail) (Jones,
isolates genotype I, the duck/goose isolates genotype II, and the 2013) and a wide range of free-ranging (wild) birds (Huhtamo
chicken isolates from Hungary genotype III. The chicken/turkey et al., 2007; Kalupahana, 2017). Avian orthoreovirus was first
genotype I is more heterogeneous with chicken isolates from isolated from chickens with chronic respiratory disease (Fahey
China, USA, and Canada forming subgroup Ia and the turkey and Crawley, 1954). This initial isolate was originally termed the
isolates from USA and Hungary and other chicken isolates from Fahey-Crawley agent, and was later characterized as an orthoreo-
USA and Canada in subgroup Ib. The duck/goose genotype II virus (Petek et al., 1967). Subsequently, avian orthoreoviruses
has two main subgroups: subgroup IIa consisting of the classical were isolated from a variety of clinical presentations in chickens,
Muscovy reovirus (classical MDRV) strain ZJ2000M in which including viral arthritis/infectious tenosynovitis (Glass et al.,
σC is encoded by S4 and not by S1 and σNS is encoded by S3 1973; Jones et al., 1975), runting-stunting syndrome/malabsorp-
and not by S4 (Kuntz-Simon et al., 2002; Yun et al., 2013), as tion (van der Heide et al., 1981; Page et al., 1982; Robertson et al.,
usually described for avian reoviruses, and subgroup IIb consist- 1984), cloacal pasting (Deshmukh and Pomeroy, 1969), hydrop-
ing of other Muscovy, Mallard and Pekin duck and goose isolates ericardium (Bains et al., 1974; Spradbrow and Bains, 1974; Jones,
(Fig. 6.4). 1976), myocarditis and pericarditis (Mustaffa-Babjee et al., 1973),
and hepatitis (Mandelli et al., 1978). Orthoreoviruses have been
Reverse genetics conclusively demonstrated to cause viral arthritis/infectious ten-
Roner et al. (1990) first reported that mammalian orthoreovi- osynovitis in chickens (van der Heide, 1977). However, it is not
rus RNA was infectious by transfecting a combination of viral exclusively associated with viral arthritis and tenosynovitis (van
ssRNA, viral dsRNA, and in vitro-translated viral ssRNA prod- der Heide, 2000), but can be associated with a variety of diseases
ucts with Lipofectamine into cells that were then infected by a including gastroenteritis (Deshmukh and Pomeroy, 1969), myo-
helper reovirus of a distinct serotype. This allowed the rescue carditis and pericarditis (Mustaffa-Babjee et al., 1973), respiratory
of temperature-sensitive reovirus mutants, opening the way to disease (Fahey and Crawley, 1954), feathering abnormalities,
Reoviridae reverse genetics (Roner et al., 1997). More recently, a hepatitis (Mandelli et al., 1978), hydropericardium (Bains et
new helper virus-independent reverse genetics system has been al., 1974; Spradbrow and Bains, 1974; Jones, 1976), ruptured
established for mammalian orthoreoviruses. A plasmid-based gastrocnemius tendon (Jones et al., 1975), cloacal pasting in