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days and can reach 10% and occasionally be as high as 30% (Hess, et al., 1988; Shivaprasad et al., 2001; Hess, 2013; Moura-Alvarez
2013). Clinical signs include poor growth, apathy, prostration, et al., 2013). Limited studies have been conducted to understand
ruffled feathers and huddling behaviour. Concurrent infections the epizootiology and association of aviadenoviruses and diseases
often occur in flocks affected by IBH, which might explain the in turkeys. The prevalence of aviadenovirus in turkey flocks asso-
difficulties in reproducing the disease experimentally (Schachner ciated with poult enteritis complex has been recently described in
et al., 2018). Brazil (Moura-Alvarez et al., 2013), UK and Hungary (Kajan et
GE is mainly caused by FAdV-1 and -8 (Ono et al., 2003; al., 2010; Marek et al., 2014a). However, the serotypes affecting
Okuda et al., 2004) and is commonly found in slaughtered broiler these turkey flocks are not described (Kleine et al., 2017). Studies
chickens (Okuda et al., 2004). conducted in Germany in 2012 demonstrated the prevalence of
HPS is caused by FAdV-4 and occurs in broiler birds of 3 to TAdV-2 and -4 in turkey flocks clinically presenting with enteritis
5 weeks of age of either sex and occasionally in 10- to 20-week- and poor growth, respectively. TAdV-5 and members of species
old layers and breeder pullets. HPS outbreaks are rare in older FAdV-B and FAdV-E were identified in flocks with clinical signs
birds and in other species of poultry. HPS outbreaks have been of hepatitis, splenitis, enteritis and polyserositis. In addition, a
reported in quails, pigeons, black kites, ducks and recently in member of species TAdV-D was isolated from flocks showing
ostriches (Asthana et al., 2013; Changjing et al., 2016; Pan et al., clinical signs of HPS and increased mortality (Kleine et al., 2017).
2017b). Some studies suggest that broilers, regardless of breed, The negative impacts of EDS in egg production have been
are susceptible under field conditions. It has also been shown recognized since 1976. The natural hosts for EDSV are ducks
that the course of disease under natural conditions or after oral and geese, though it extends its host range to other avian spe-
inoculation range from 7 to 15 days (Asthana et al., 2013). The cies such as coots, grebes, herring gulls, owls, storks, swans, and
mortality rate can range between 20–80% depending on location. quail. EDSV in chicken is thought to have originated from ducks
For example, outbreaks in broiler farms in Pakistan ranged from (Smyth, 2013), probably through contaminated vaccines grown
20% to 75% and in India from 30% to 80% (Asthana et al., 2013). in duck cells or embryonated eggs or during blood collection
Emerging cases of severe IBH/HPS have been recently (McFerran, 1979). Some studies showed that EDSV isolated
reported in China, and IBH cases in Spain (2011–2013) and from ducks failed to cause any drop in egg production from laying
Korea (2007–2010) (Zhao et al., 2015; Oliver-Ferrando et al., hens, though egg weight decreased (Brugh et al., 1984). EDSV
2017). In particular IBH/HPS outbreaks that are associated with infection compromises eggshell quality and causes loss of egg
virulent FAdV-4 are reported in high numbers from China and production. Chickens of all ages and breeds are susceptible to
since 2015 increases in economic losses due to high mortality infection, though disease tends to be most severe in heavy broiler-
have also been reported (Li et al., 2016; Zhang et al., 2016; Ruan breeders and hens producing brown eggs. There are rare reports
et al., 2017). Although FAdV-4 seems to be the predominant that the egg drop syndrome virus (EDSV) has caused either a
serotype in China, other serotypes – such as FAdV-1, FAdV-2, drop in egg production or respiratory tract disease in other spe-
FAdV-8, FAdV-10 and FAdV-11 have also been isolated from cies, e.g. turkeys, ducks, geese, and quail (McFerran, 1979; Ivanics
flocks with clinical signs of IBH (Zhao et al., 2015; Changjing et et al., 2001). EDSV can be transmitted vertically through the egg,
al., 2016). after which the virus remains latent until progeny reaches sexual
HE outbreaks were first reported in some states of the US maturity. Virus is then shed through the eggs and faeces infecting
during 1960s. This disease affects confined as well as free-range susceptible contacts. Virus can be also transmitted horizontally
turkey flocks. Currently, HE is distributed worldwide where during lay. Horizontal transmission between flocks can occur by
turkey production takes place (Pierson and Fitzgerald, 2013). displacement of contaminated egg trays. Indeed, outbreaks often
HEV varies in pathogenicity from no clinical signs and death to occur in common egg-packing stations. Transmission and out-
severe clinical outcomes with mortality ranging between < 1% to breaks can occur when domestic birds have direct contact with
over 60% (Dhama et al., 2017). HEV can infect and cause disease wild birds or through water supply contaminated with wildfowl
in chickens, peafowl, bobwhite quail and chukars (McFerran droppings (Smyth, 2013).
and Smyth, 2000). Infection of chickens and pheasants with EDS 76 was successfully eradicated from Northern Ireland by
pathogenic virus causes MSD and hence its alternative name, constant monitoring (through HI test) and removal of contami-
MSD virus (MSDV). MSD has been reported in all geographic nated and adjoining pens until all birds (40 weeks of age) were HI
locations with confinement pheasant operation. Infections in negative. Eggs from grandparent and parent flocks were found to
chickens are common based on serology (Dhama et al., 2017). be EDSV-free (McFerran, 1979).
Disease outbreaks caused by aviadenoviruses have been EDSV is distributed worldwide in ducks and geese, but clinical
reported in other poultry species such as quail, turkey, pigeon, cases of EDS have been reported mainly in Europe, Asia, Africa
goose and ostrich (McFerran and Smyth, 2000; Changjing et al., and Latin America (Bishop and Cardozo, 1996; Ivanics et al.,
2016). The pathogenicity of aviadenoviruses in turkeys remains 2001; Biđin et al., 2007; Ezema et al., 2010; Cha et al., 2013; Kang
unclear to date. These viruses have been isolated in clinical cases of et al., 2017). EDS outbreaks have also been reported in flocks of
respiratory and enteric diseases. IBH caused by aviadenoviruses ducks in Canada and domestic birds (chickens and ducks) in the
in turkey seems to be responsible for lower hatchability rates (Guy USA (Schloer et al., 1978; Villegas et al., 1979; Brash et al., 2009).