Phylogenetic analysis of FAdV isolates
A phylogenetic tree was constructed based on the partial hexon gene of
FAdV sequence alignment of the 46 isolates (Figure 6). The FAdV isolates
were distinctly divided into five general clusters: FAdV-A, FAdV-B,
FAdV-C, FAdV-D, and FAdV-E. The phylogenic tree’s topology indicated
that two different FAdV genotypes with different genomic evolutions
circulate in Kurdistan. The FAdV/Kurdistan/2013 and FAdV/Kurdistan/2020
belonged to FAdV-E close to USA isolates. On the other hand, the
FAdV/Kurdistan/2015 belonged to FAdV-D closer to the Chinese FAdV
isolate.
DISCUSSION
Iraqi Kurdistan contains more than 1300 poultry farms, and intensive
farming and deficient control strategies have led to the spread of new
viral infections. Thus, epidemiologic research is crucial to monitor
disease outbreaks and develop vaccines. FAdV outbreaks have become a
considerable concern for poultry farmers globally
(Cizmecigil et al., 2020). IBH causes
mortality resulting in production and economic losses. A higher number
of FAdV clinical cases have been reported in recent years, and multiple
FAdV strains have been isolated from sick birds in many countries
(Mittal, Jindal, Tiwari, & Khokhar,
2014; Schachner et al., 2018). There is
no published data about FAdV in Kurdistan chickens, reinforcing the
requirement for molecular surveys on this emerging infectious agent in
poultry and studying its fundamental role in clinical diseases. This
study describes an IBH outbreak in Kurdistan/Iraq broiler flocks.
In this study, sudden high acute mortality of 8% to 15% started at two
days to four weeks of age in affected broiler flocks. IBH can infect
chickens of all ages; however, young chicks were more susceptible during
the first two weeks, even when immunologically intact. There is an
apparent age effect with avian adenoviruses. As the host’s age
increases, the multiplication of the viruses within the host is
restricted, and mortality decreases
(Rahimi & Haghighi, 2015). There was no
accumulation of straw-colored fluid in the pericardial sac, indicating
no relation with HHS. This outcome is probably because of the different
viral strains and serotypes of FAdV causing infection in this study,
which agrees with previous studies
(El-Tholoth & Abou El-Azm, 2019;
Mittal et al., 2014). Mortality during
IBH outbreaks is generally between 2% and 10% of the flock, but up to
30% has been described in case of coinfection with other
immunosuppressive causative agents
(El-Tholoth & Abou El-Azm, 2019). Typical
necropsy observations such as an enlarged and pale liver, enlarged and
hemorrhagic spleen and kidneys, and clinical findings were detected in
this study’s IBH cases (Ahamad, Selvaraj,
Sasikala, & BabuPrasath, 2016; Nakamura
et al., 2011). Also, a pale and enlarged pancreas and greenish diarrhea
were observed in some chicks, as reported by others
(Ahamad et al., 2016).
The most critical histopathological finding in liver sections of
diseased birds is the presence of intra-hepatocytic inclusion bodies.
These are large basophilic intranuclear inclusion bodies surrounded by a
pale halo (Anjum, Sabri, & Iqbal, 1989).
Many hepatocytes were degenerated and appeared swollen with vacuolated
cytoplasm. Infrequently, there was necrosis of some scattered
hepatocytes. Moreover, there was lymphocytic and heterophilic hepatitis
(Nakamura et al., 2011). These
inflammatory infiltrates appear clearly around the central vein.
Additionally, there was widening and infiltration of sinusoids with
lymphocytes, heterophils, and histiocytes.
Histopathological sections of testicles from infected birds revealed
degeneration of spermatozoa, spermatids, Sertoli cells, and Leydig
cells. In the interstitial tissue, there was intertubular hemorrhage and
large vacuoles. Also, there was dilation of the seminiferous tubular
lumens containing necrotic debris and devoid of spermatozoa. Lesions in
the testicle are reported for the first time in the present study.
In the present study, the isolates’ phylogenetic analysis revealed the
circulation of two different genotypes in Kurdistan. Both Kurdistan FAdV
had different genomic evolution. The FAdV/Kurdistan/2013 and
FAdV/Kurdistan/2020 belonged to FAdV-E close to USA isolates. On the
other hand, the FAdV/Kurdistan/2015 was closer to the Chinese FAdV
isolate, proposing possible virus spreading from these areas, perhaps
through trades and primary breeders or breeder substitutes. Circulation
of two genotypes of FAdV in Kurdistan may hurt the clinical disease
because some strains of different serotypes can reproduce IBH and
hydropericardium syndrome simultaneously
(Zhao et al., 2015).
Immunosuppressors such as IBDV, chicken infectious anemia virus (CIAV),
and Marek’s disease virus (MDV) are factors that facilitate IBH
outbreaks propagation or worsen clinical manifestations of FAdV
infections (Morshed, Hosseini, Langeroudi,
Fard, & Charkhkar, 2017; Niczyporuk,
Woźniakowski, Samorek-Salamonowicz, & Czekaj, 2013). However, several
studies showed that IBH might occur as a primary disease
(Gomis et al., 2006;
Ojkic et al., 2008).
CONCLUSION
This study is the first molecular characterization and histopathological
examination of FAdVs in Sulaymaniyah broiler farms. FAdVs could be
emerging infectious agents in Kurdistan poultry flocks, causing severe
disease in young chicks. More research is needed to evaluate fowl
adenoviral serotypes’ prevalence and pathogenicity in poultry flocks in
Iraq. Identification of FAdV serotypes is essential in epidemiological
studies of the disease outbreaks, development of preventative measures,
and adoption of vaccination strategies. There is also a need for future
development in molecular methods to identify adenovirus strains’ origins
in IBH.