Towards inferring the global movement of beak and feather disease virus Beak and feather disease virus (BFDV) causes the highly infectious and often fatal, psittacine beak and feather disease (PBFD) that infects over 60 different psittacine species. Among these species are several that are at risk of extinction including the South African Cape Parrot (Poicephalus robustus), and the Echo Parakeet (Psittacula echo) (IUCN Red List of Threatened species, version 2011, iucnredlist.org/). BFDV is a circular single-stranded DNA (ssDNA) virus belonging to the family Circoviridae. The viral genome is bi-directionally transcribed and encodes at least two proteins; a replication associated protein (Rep) expressed from the virion strand and a capsid protein (CP) expressed from the complementary strand (which is present within a double-stranded replicative intermediate). Since it was officially described in a number of Australian psittacine birds in the 1970s (Pass and Perry, 1984), incidences of PBFD have subsequently been reported in various countries across Europe, Asia, North America and Africa and on several islands in the Pacific and Indian Oceans. Transmission is thought to include both horizontal and vertical modalities, the former through shedding of virus particles in feather dust, crop secretions, or faeces (Ritchie et al., 1991), and the latter from infected birds to embryonated eggs (Rahaus et al., 2008). Within individual wild-parrot flocks, incidences of BFDV can be higher than 41%, which suggests that it can be highly infectious and that horizontal transmission is likely the major route of transmission under natural conditions (Raidal et al., 1993). In the context of captive environments such as breeding facilities that supply psittacine birds (such as cockatoos, parrots, parakeets, and lovebirds) for the pet trade, horizontal transmission through environmental contamination is also probably the most prevalent mode of infection. Infection may be acute or chronic and typical PBFD symptoms include anaemia, depression and lethargy which ultimately lead to abnormal feather growth culminating in feather loss (Ritchie et al., 1989b). In severe cases, beak and claw deformities may be displayed (Pass and Perry, 1984). Symptoms may however be species-specific as beak and claw involvement appears to be more prevalent in cockatoos than in other psittacine species (McOrist et al., 1984 and Ritchie et al., 1989b). Possible beak deformities include elongation, transverse or longitudinal cracking, and palatine necrosis (McOrist et al., 1984, Pass and Perry, 1984, Ritchie et al., 1989a and Ritchie et al., 1989b). PBFD can present as a peracute, acute or chronic disease. Younger birds, neonates to fledglings, tend to suffer from the peracute and acute forms, in which sudden death can occur with no (peracute) or mild (acute) feather dystrophy (Doneley, 2003 and Ritchie et al., 1989a). The prevalence of the chronic form is higher in older birds and is not always fatal with infected birds potentially surviving for many years (Ritchie et al., 1989b). However, since the disease results in immune suppression, chronically infected birds often eventually succumb to secondary infections (Latimer et al., 1991, Ritchie et al., 1989b and Todd, 2000). Although BFDV has an almost global distribution and is found in both wild and captive bird populations (see Julian et al., 2012, Julian et al., 2013, Kundu et al., 2012 and Massaro et al., 2012), circumstantial evidence indicates that it may have originated in Australia (Pass and Perry, 1984) and spread to the rest of the world in modern times. Although the diversity of wild psittacine species in the Afro-Asian and Neo-tropical regions of the world remain largely under-represented in this analysis, it likely equals that of parrot diversity in Australasia (Forshaw, 2010). The Australian BFDV origin hypothesis is plausible for several reasons in addition to the fact that the diversity of wild psittacine species is relatively high in Australasia. For example, it is also notable that what is perhaps the first recorded description of PBFD occurred in a letter to an Australian journal in 1907, in which the author notes a personal observation from 1887 of wild Red-rumped Parrots (Psephotus haematonotus) in the Adelaide hills being unable to fly due to a complete loss of feathers ( Ashby, 1907). Another probable early reported case of a PBFD infection was that of a captive Sulphur-crested Cockatoo in Sydney, named Cocky Bennett, a bird so well-known locally that his death in 1916 at the estimated age of 120 years old (which is surprising given that it was likely infected by BFDV) warranted an obituary in the local newspaper ( Centre for Fortean Zoology Australia, 2011). Descriptions and photographs of Cocky from the early 1900s indicate that he was mostly featherless and had a severely elongated upper beak ( Nicholls, 1914), both of which are characteristic symptoms of PBFD. The origin of Cocky is uncertain and since Cacatua galerita were rare in the Sydney basin at that time, it is likely that he originated in the Moluccas ( Forshaw, 2010) where this species was much more common. As part of the aviculture and pet trade many parrots species have been trafficked around the world and in some cases these have established wild populations following escape or release from captivity (Bull, 1973 and Butler, 2005). In Europe where there are no native psittacines, wild exotic populations of these birds are now found the many of temperate regions (Chiron et al., 2009, Muñoz and Real, 2006 and Strubbe and Matthysen, 2009) and account for approximately 18% of Europes wild populations of exotic birds (Strubbe and Matthysen, 2009). As a result of this, in 2007 the import and trade of wild-caught exotic parrots in Europe was banned (Commission Regulation (EC) no. 318/2007). Whereas identifying when and where viruses like BFDV first arose can yield valuable insights into how such pathogens emerge, the identification of virus movement pathways and the estimation of virus movement rates can provide crucial information for both future disease forecasting efforts, and the formulation of governmental policies aimed at restricting the transport of avian viruses across national borders. For example, by identifying both key historical movement routes and the locations where the most important contemporary BFDV lineages first arose, it may be possible to impose modest sanitation measures and restrictions on future movements of psittacine birds in a targeted approach, leading to significantly reduced risks of spreading newly emergent recombinant BFDV strains or other avian pathogens around the world. Here we use all currently available BFDV genome sequence data from around the world to both infer the approximate geographical region where BFDV originated, and identify at least some of the historical global movements that have enabled this virus to achieve its present global distribution. sciencedirect/science/article/pii/S0042682213006557
Posted on: Wed, 19 Mar 2014 12:11:25 +0000
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