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al. (1983) described an asymptomatic orthoreovirus infection with multifocal acute hepatic fibrinoid necrosis, and orthoreo-
in quarantined psittacines. Numerous isolations of orthoreovi- viruses were isolated from the affected tissues.
rus from psittacine birds shortly after importation from seven Four reo-like viruses were isolated from clinically normal
different countries indicated that the virus was internationally wader species in a resting site in Germany, three isolates were
dispersed in psittacine species (Meulemans et al., 1983) and from dunlins (Calidris alpina) and one from a spotted redshank
implicated avian orthoreovirus as a potential disease agent associ- (Tringa erythropus) (Hlinak et al., 2006). Jones and Guneratne
ated with translocation of birds (Rigby et al., 1981). (1984) isolated an avian orthoreovirus from the droppings of a
Avian orthoreoviruses were isolated from live young Afri- clinically normal wedge-tail eagle (Aquila audax) in UK.
can grey parrots showing a wide range of non-specific clinical In 1996 orthoreoviruses were isolated from Common Eider
signs including depression, drooping plumage, loss of appetite, (Somateria mollissima) ducklings involved in a severe (99%)
diarrhoea, and respiratory symptoms (Sánchez-Cordón et al., mortality event in a breeding area in the Finnish archipelago
2002) as well as from dead young African grey parrots with (Hollmén et al., 2002). The viruses were isolated from the bursa
a disseminated necrotizing hepatopathy (Wilson et al., 1985). of Fabricius, and the affected birds had multifocal hepatic necrosis
Reovirus disease in psittaciformes in the Netherlands in 2002 and lymphoid necrosis suggesting the possibility of an immuno-
produced a high mortality in all age groups and affected para- suppressive effect. Later experiments that used the Common
keets and larger psittacines such as Eclectus parrots (Eclectus Eider isolate in Mallard ducklings found that it was infectious
roratus) and Amazon parrots (van den Brand et al., 2007). In for this species and caused focal haemorrhages in thymus, liver,
Amazon parrots, chronic respiratory signs were reported, and spleen, myocardium, and bursa of Fabricius without mortality
in cockatoos, non-specific clinical signs such as incoordina- (Hollmén et al., 2002).
tion, emaciation and diarrhoea were reported (Wilson et al., Avian reovirus was isolated from mortality events of emaci-
1985; Conzo et al., 2001). Sudden death and hepatomegaly ated American woodcock (Scolopax minor) during the winters of
were reported to be suggestive of orthoreovirus disease in 1989–1990 and 1993–1994 in Cape Charles, Virginia (Docherty
lories, lorikeets (Trichoglossus spp.), and in a less severe form, et al., 1994). The infection appeared to be systemic because virus
Senegal parrots (Poicephalus senegalus) and Jardine’s parrots was isolated from a variety of tissues including intestine, brain,
(Poicephalus gulielmi) (Pennycott, 2004). The most susceptible heart, lungs, and cloaca (Hollmén and Docherty, 2007).
species for orthoreovirus infection includes the African grey Many orthoreoviruses were detected in corvid species. In
parrots (Psittacus erithacus, Psittacus erithacus erithacus, Psittacus 2002, an orthoreovirus was isolated in southern Finland from
erithacus timneth) and the cockatoo (Cacatua alba); young birds a diseased wild hooded crow (Corvus corone cornix) that had
were the most severely affected (Spenser, 1991). Orthoreovirus neurological clinical signs, including abnormal flying with inco-
disease in New World South American psittaciformes was rare, ordination, abnormal postures, cramps, and paralysis (Huhtamo
and if affected, they would recover more easily when given et al., 2007). Mast et al. (2006) reported the presence of intra-
appropriate supportive care (Conzo et al., 2001). New World cytoplasmic, reovirus-like particles in the spleen and duodenum
psittaciformes were more resistant than the Old-World parrots of carrion crows (Corvus corone) found in a die-off event in
(those of Australian, Asian and African origin) to orthoreovirus Brussels, Belgium. Fatal haemorrhagic and necrotizing enteritis
diseases (Conzo et al., 2001). The association of orthoreovirus in American crows (Corvus brachyrhynchos) associated with a
with necrotizing hepatitis in the absence of other pathogens putative avian orthoreovirus was detected during surveillance for
had frequently been reported in psittacine birds, suggesting West Nile virus beginning in 2002 (Meteyer et al., 2009). Crow
orthoreovirus as the sole aetiology of the hepatic lesion (Conzo mortality associated with this syndrome has recurred repeatedly
et al., 2001). Orthoreoviruses acted as primary pathogens in in the USA since it was first reported, and similar mortality events
African Grey Parrots under experimental conditions without have been identified in eastern Canada since 2004 (Campbell et
concurrent bacterial or fungal infections (Graham, 1987). Van al., 2004, 2008; Stone, 2008) (Fig. 6.5).
der Brand et al. (2007) suggested that avian orthoreoviruses In 2011, orthoreoviruses were detected in the intestinal con-
might be widespread in psittacine birds and carriers of the tents of dead black-capped chickadees (Poecile atricapillus) in
virus could be a source of re-introduction to uninfected flocks. Minnesota (Mor et al., 2014). The birds were underweight, were
Climate, the introduction of new birds to a collection, and the dehydrated, and had watery and yellowish intestinal contents,
stress of transportation might be other factors contributing to but no significant lesions were observed. Molecular characteriza-
the development of the disease in psittacines (van den Brand et tion of the reoviruses showed 89.4–98.3% nucleotide identity to
al., 2007). Chicken orthoreovirus vaccines were found to be of turkey reoviruses (Mor et al., 2014).
little value for the Psittaciformes because the virus strains com- Recently, avian orthoreoviruses have been isolated from a
monly found in psittacine species were antigenically unrelated wide variety of free-ranging (wild) birds. In Great Britain, an
to those found in chickens (Gaskin, 1989). Orthoreoviruses avian orthoreovirus was isolated from a dead free-living magpie
were previously thought to be mildly pathogenic for budgeri- (Pica pica) (Lawson et al., 2015). The bird had hepatic and
gars (Melopsittacus undulatus). However, in Scotland and other splenic necrosis and the isolated orthoreovirus was identified
parts of the UK, high mortality was observed in different flocks as the aetiology of the lesions. An orthoreovirus was isolated
of adult breeding budgerigars since October 2002 (Pennycott, from the haemorrhagic intestine of a dead brown-eared bulbul
2004). The affected birds had splenomegaly and hepatomegaly (Hypsipetes amaurotis) in Japan (Ogasawara et al., 2015). A novel