Page 131 - Avian Virology: Current Research and Future Trends

124 | Brown and Eterradossi

et al., 2007; Turpin et al., 2008; Wei et al., 2013). Thus, it would South America and reciprocally that of South American AMPV-A
appear that AMPV-C have the broadest avian host range. and B in North America, especially as both continents share
Most of the information pertaining to the host range of AMPVs migratory flight paths.
has been drawn from different studies at different times in differ-
ent locations. However, between 2014 and 2018 the susceptibility
of SPF turkeys, chickens and Muscovy ducks to infection by Clinical features
each of the four subgroups was assessed in a series of controlled Field AMPV infection of meat turkeys is most often observed
experimental conditions (Brown et al. submitted). Globally these between three and 12 weeks of age with peak clinical respiratory
extensive experimental trials confirmed previous literature in signs occurring 2–3 days after infection. At the onset in galliformes,
that AMPV A, B, Turkey C and D were indeed well adapted to watery eyes and sneezing accompanied by a clear nasal exudate
turkeys and chickens, albeit that differences in seroconversion are observed. Thereafter, the nasal exudate becomes turbid, liquid
and transmission of viruses in these species could be observed. around the eyes develops a foamy appearance and often a dry
The Muscovy duck AMPV C was well adapted to Muscovy ducks tracheal cough develops (Eterradossi et al., 2015). Birds can also
however, both chickens and turkeys seroconverted and were show signs of depression. In galliformes, clinical signs culminate
positive by virus isolation despite a lack of detection of viral in swelling of the infraorbital sinuses. In the absence of secondary
RNA by RT-qPCR. Details of this study should bring a deeper bacterial infections these clinical signs will disappear within seven
understanding of the host range of AMPVs and give insight as to to ten days. Morbidity is usually 100% with mortality varying
how different subgroups become adapted to their preferred host from as little as 1% to as high as 60% in cases of poor management
(Brown et al., 2018). conditions and resulting secondary infections (Stuart, 1989; Van
The close relationships between AMPV C viruses and HMPV de Zande et al., 1998; Jones and Rautenschlein, 2013; Eterradossi
and the suggestion that HMPV and AMPV C originated from a et al., 2015). Field AMPV infection of breeding turkeys or chick-
common ancestor about 200 years ago (de Graaf et al., 2008b) ens is often much less pronounced and even benign in its early
means that cross species transmission has to be considered respiratory phase, which is suggested to be a result of better man-
however, to date there are no reports demonstrating respiratory agement conditions (Eterradossi et al., 2015). However, infection
disease in humans caused by AMPV. On the other hand, one during lay can result in a drop in egg production (10–30%) and
study has demonstrated clinical signs; viral antigen and genomic shell quality for up to 10–21 days.
RNA of HMPV in HMPV infected turkeys under experimental Similar clinical signs are observed in chickens and guinea fowl
conditions (Velayudhan et al., 2006). More investigations into following AMPV infections in the field however, in these species
this issue are need. early signs induced by virus-infection are less pronounced and can
sometimes be inapparent (Cook, 2000; Jones and Rautenschlein,
Transmission and spread 2013). That said, when complicated by secondary infections it
The transmission of AMPV is thought to be mostly due to direct can lead to swollen head syndrome (SHS) which is characterized
contact with excreting individuals or contaminated materials by severe oedema of the infraorbital and periorbital sinuses that
(Cook et al., 1991; Alkhalaf et al., 2002) and the virus is considered progresses subcutaneously over the head hence the ‘swollen head’
highly infectious. As a result, the density of the infected popula- appearance, a loss of equilibrium and torticollis due to inflamma-
tion plays an important role in its spread. Airborne transmission is tion of the middle ear. In SHS, mortality can reach as high as 20%
also suspected due to the replication of the virus in the respiratory (Morley and Thomson, 1984; O’Brien, 1985; Picault et al., 1987;
tract and observations in the field of spontaneous contamination Pattison et al., 1989; Buys et al., 1989b).
of different poultry houses during vaccination programs (France Egg-drop in breeders and SHS in chickens may often develop
anon). However, still to date only two studies focusing on this several weeks after the triggering AMPV infection. As a result,
issue have been reported and the results are conflicting (Giraud et seroconversion against AMPV may already be well established
al., 1986; Cook et al., 1991). and readily detected in supposedly ‘early’ serum samples collected
The potential for AMPV to be transmitted vertically has been in the first days when the egg-drop or swollen head signs become
shown through detection of viral RNA in the eggs of infected apparent. Under such a clinical course, a careful investigation of
flocks though no infectious virus was detected. Although no unnoticed mild respiratory episodes occurring in the preceding
viruses have yet been isolated from the reproductive tract the fact weeks may help unravel the original virus infection.
that several studies detected viral RNA in the reproductive tract The clinical signs observed in ducks following AMPV infec-
of laying turkeys and breeder chickens (Jones et al., 1988; Khehra tion are slightly different than those observed in turkeys, chicken
and Jones, 1999; Cook et al., 2000; Villarreal et al., 2007) means and guinea fowl and are somewhat more pronounced under
that this route of infection merits further investigation. experimental conditions. At the onset (2–3 days after initial
The mechanism of spread of AMPV over long distances is not infection) watery eyes accompanied by a clear nasal exudate
known. Wild birds have been implicated though the data are con- are observed and the ducks have a more nervous disposition.
flicting and based on different subgroups (Turpin, 2003; Delogu Thereafter heavy congestion in the respiratory tract develops and
et al., 2004; Turpin et al., 2008). If wild birds are involved in the rales not dissimilar to those of chickens following infection with
transmission of AMPV over large distances then it is surprising infectious bronchitis virus (IBV) can be heard. At this time the
to note the lack of report so far for North American AMPV-C in nasal exudate takes on a thick, cloudy appearance. Ducks tend