Duck plague is an acute, highly contagious and fatal disease of domestic ducks and water fowls¹. The first report of duck plague was recorded in Netherlands in 1923 and later from other countries². Duck plague is caused by Anatid herpes virus 1 belonging to Herpesviridae family, alpha herpesvirinae sub family and genus Mardi virus³. In India, the disease outbreak was recorded in West Bengal⁴, Karnataka⁵, Uttar Pradesh⁶, Kerala⁷, Tamil Nadu^8-9 and Assam¹⁰. More than 25 outbreaks were recorded in various districts of Assam state in India during the period from August 2012 to December 2015¹¹. The present study reports the occurrence of duck viral enteritis outbreak in the Cauvery delta region of Tamil Nadu.

Three ducks were received for necropsy at the Department of Veterinary Pathology, Veterinary College and Research Institute, Orathanadu. These ducks were reared in the Cauvery delta region with flock containing 3000 birds which were not vaccinated. During necropsy, gross lesions were recorded. Tissue samples like intestine, oesophagus, spleen, kidney and liver were collected in sterile container for polymerase chain reaction (PCR). The tissue samples like oesophagus, intestine, lungs, proventriculus, liver, pancreas, kidney, spleen and bursa of Fabricious were collected and fixed in 10% formalin for histopathological examination. The tissues samples were routinely processed, sectioned (4 pm thickness) and stained with Haematoxylin and Eosin (H&E) stain¹².

Grossly, oral and oesophageal mucosa showed adhesion of yellowish diphtheritic membrane. (Fig. 1). Liver revealed multiple white necrotic foci on entire surface. (Fig. 2). Heart showed petechial haemorrhages on the epicardium (Fig. 3). Lungs, trachea, ovary and kidney were congested. In one bird intestine mucosa revealed annular band haemorrhages (Fig. 4). Intestinal mucosa in another bird revealed annular band haemorrhage, multiple petechiael haemorrhages, annular band with yellowish diphtheritic adhesion and also multiple diphtheritic button ulcers of 2-3 mm diameter (Fig. 5).

The DNA was extracted from the homogenized tissue samples (intestine, oesophagus, spleen, kidney and liver) by Phenol chloroform method of DNA extraction to rule out duck viral enteritis. PCR reaction was carried out as per reference¹³ from the extracted DNA to rule out the Duck viral enteritis virus (DVEV). Primers for DVEV DNA-directed DNA polymerase gene (Forward primer - 5'-GAA-GGC-GGG-TAT-GTA-ATG-TA- 3'and reverse primer - 5'-CAA-GGC-TCT-ATT-CGG-TAA-TG 3') was used in this study The total reaction mixture contained - 12.5 pl amplicon Red Dye master mix, 10 pM forward and reverse primers each, 2 pl of template DNA and nuclease free water up to 25 pl. PCR was performed in a Bio-Rad thermo cycler with the following conditions: 94^OC for 2 min followed by 35 cycles each of denaturation at 94^OC for 1 min, annealing at 55^OC for 1 min, synthesis at 72^OC for 2 min and final extension at 72^OC for 7 min. The PCR product was electrophoresed on 1.5% agarose gel in Tris EDTA buffer stained with 0.5pg/ml of ethidium bromide and visualized under Bio-Rad gel doc system, for desired size of band with DNA ladder (100bp DNA Ladder, BIO-HELIX). The result was positive expected amplicon size of 446 bp was seen for the specific primers (Fig. 6).

Histopathologically, intestinal mucosa revealed fibrinous exudate with desquamated epithelial cells and inflammatory cells. (Fig. 7). In another bird, intestinal mucosa showed adhesion of fibrinous exudate with clumps of bacteria and inflammatory cells (Fig. 8). Oesophageal mucosa showed ulceration with focal necrosis of gland. Liver showed diffuse moderate sinusoidal congestion. Pancreas revealed focal necrosis. Lungs, kidneys and ovary showed moderate congestion. Spleen showed multifocal congestion with mild lymphoid depletion. The bursa of Fabricious revealed moderate lymphoid depletion (Fig. 9).

Lesions of DVE are associated with disseminated intravascular coagulopathy and necrotic/degenerative changes in mucosa and submucosa of gastrointestinal tract in lymphoid and parenchymatous organs. These collective lesions, when present, are diagnostic of DVE¹⁴. Grossly, diphtheritic lesion in oesophagus was in agreement with earlier reports⁹, ¹⁰, ¹⁴, ¹⁵, . Necrotic foci in the liver were in agreement with earlier findings^14-15. Epicardial haemorrhages were in agreement with previous reports¹⁰, ¹⁴, ¹⁵. Intestinal annular bands appear as intensely reddened rings visible from external and internal surfaces. Later, the entire band becomes dark brown and tends to separate at its margins from the mucosal surface. The multifocal necrosis of gut-associated lymphoid tissue causes ulceration covered by fibrinous pseudomembranes¹⁴. Similar lesions of intestinal annular of band haemorrhages, diphtheritic lesions and button ulcers were observed in the present report. The confirmatory diagnosis by PCR was in accordance with earlier reports^9,13,15. Histopathological lesions like diphtheritic enteritis were similar to earlier reports¹⁴. Lymphoid depletion in the bursa of Fabricious was in agreement with recent experimental report¹⁵.Congestion and haemorrhage in parenchymatous organs were similar to earlier reports⁹, ¹⁴, ¹⁵.

The present study reports the occurrence of duck viral enteritis infection in Cauvery delta region of Tamil Nadu. The affected ducks suffered from diphtheritic lesions in oral cavity, oesophagus and intestine resulting in decreased feed intake and body weight which led to increased mortality with severe economic loss to the farmers who were rearing ducks. Hence, the duck rearing farmers and veterinarians need to be aware of vaccination for duck viral enteritis in ducks and other waterfowls.

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