The poultry population in Mizoram, India, has increased five-fold in the last decade. With the increase in the density of population, the occurrence of disease outbreaks like IBD, NDV, MDV, coccidiosis have also been recorded frequently
(Rajkhowa et al., 2012, Bhutia and Singh, 2016;
Rajkhowa et al., 2018). However, the information regarding prevalence, epidemiology, pathology and molecular diagnosis of HHS in poultry population of Mizoram are lacking till date.
The present study has confirmed outbreak of HHS in 5 out of 15 poultry farms covering a chicken population of 2430. All the outbreaks were recorded during the summer months from March to June in broiler birds of 4 to 6 weeks of age. Similar findings were previously described by
Sawale et al., (2012), Palanivelu et al., (2014), Das et al., (2015) and Bhutia and Singh (2017). Clinically disease appeared suddenly with mortality of 18 to 25.2% in the birds. General signs of illness like dullness, depression, lethargy and huddling were observed in affected birds. Similar observations were earlier recorded by Palanivelu
et al., (2014), Bhutia and Singh (2017) and
Dutta et al., (2017).
At necropsy, the most consistent gross lesion observed in all the cases was hydropericardium characterized by the presence of 5-10 ml of clear to straw coloured fluid in the pericardial sac of the heart (Fig 1) and hepatitis. The heart showed congestion and focal petechial haemorrhage at the base of the epicardium. The liver was enlarged, congested and friable with rounding of the edges in the FAdV affected birds. There were focal areas of necrosis and focal to diffused petechial haemorrhages on the surface (Fig 2). Such lesions were earlier described as the characteristic lesions of HHS
(Meenakshi-Bal et al., 2005; Sawale et al., 2012; Thakor et al., 2012; Palanivelu et al., 2014; Das et al., 2015; Dutta et al., 2017). Enlarged, congested and friable kidneys were observed in all of the cases. In some cases there were focal necrotic areas and petechial haemorrhages on the surface of the kidneys (Fig 3).
Palanivelu et al., (2014) and
Das et al., (2015) also reported similar findings. The lungs showed moderate to severe congestion and edema in almost all the cases. The bursa of Fabricius was edematous and showed mild to severe degree of congestion. The spleen showed moderate to severe congestion and in some cases it was enlarged and friable. Congestion of thymus was observed in some cases. These findings are in accordance with reports from
Kumar et al., (1997), Meenakshi-Bal et al., (2005), Sawale et al., 2012, Palanivelu et al., (2014), Das et al., (2015) and
Dutta et al., 2017. Moderate to severe ascites was observed in dead birds of 3 farms along with the hydropericardium and hepatitis as earlier described by
Das et al., (2015).
Histopathological examination of the liver revealed mononuclear infiltration and moderate to severe congestion in portal area. Sinusoidal spaces were congested and dilated along with disorientation of the hepatic chords and vacuolar degeneration (Fig 5). Hepatocytes revealed cellular swelling and degeneration. Many of the swollen hepatocytes contained basophilic intranuclear inclusion bodies completely replacing the nucleus of the degenerating hepatocyte which is considered as pathognomonic lesion (Fig 6). These findings were found to be similar with the earlier reports of
Sawale et al., (2012), Thakor et al., (2012), Palanivelu et al., (2014) and
Dutta et al., (2017). Kidneys of affected birds showed infiltration of mononuclear cells in the interstitium, hypercellularity in glomerular tuft, congestion in the interstitium, marked degeneration, swelling, necrosis and desquamation of the renal tubular epithelium (Fig 7). Similar findings were earlier described by
Sawale et al., (2012) and
Palanivelu et al., (2014). The lungs revealed severe congestion of the parabronchiolar wall and mononuclear cell infiltration towards the lumen leading to compression of respiratory atria and air capillaries and dilatation of the inter-parabronchiolar septae due to oedema. The findings were similar to earlier reports by
Venkatesha et al., (2005) and
Dutta et al., (2017). Heart revealed congestion, lack of cross striations indicating degeneration and disintegration of the cardiac muscle fibres due to degeneration.
Sharma et al., (2014) and
Dutta et al., (2017) reported similar findings. Bursa showed congested and haemorrhagic areas and dilatation of the interfollicular septa due to oedema and lymphoid depletion in the germinal centre of the follicle (Fig 8). Similar observations were reported by
Thakor et al., (2012) and
Palanivelu et al., (2014). Microscopic examination of spleen showed severe congestion and haemorrhages in splenic parenchyma and depletion of the lymphocytes in the germinal centre of the follicle. This was similar to findings reported by
Meenakshi-Bal et al., (2005), Thakor et al., (2012) and
Dutta et al., (2017).
Following clinicopathological examination, all the outbreaks of HHS were further confirmed by detection of hexon gene of FAdV in liver tissue lesions by PCR. Out of 15 farms included in the study, 5 (33.3%) farms were tested positive for FAdV by PCR detection of a 1319bp region of hexon gene (Fig 4). PCR technique targeting the hexon gene of FAdV to confirm diagnosis of HHS was earlier described by Raue and Hess (1998) and
Shamim et al., (2009).
