STUDIES ON THE PREVALENCE, PATHOLOGY AND MOLECULAR DIAGNOSIS OF DUCK VIRUS ENTERITIS IN ASSAM
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Date
2016-06
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Assam Agricultural University, Khanapara,Guwahati
Abstract
Duck plague or duck viral enteritis is an acute and contagious and economically important viral disease of ducks having high morbidity and mortality rate. A total thirty nos. of duck plague outbreaks occurring in certain district of Assam were attended during the period of February, 2014 to March 2016. Out of a total 5252 ducks at risk, 2956 (56.28%) were affected clinically and 2449 (46.62%) died. The overall morbidity and mortality were 56.28% and 46.62% respectively, however the cause specific mortality for DP in the present study was found to be 82.85%. Highest mortality was recorded in duckling (55.80%) followed by grower (51.24%) and adult ducks (35.43%) respectively.
In the present investigation, altogether 445 serum samples were collected from the ducks from affected as well as some other ducks from the surrounding areas of the outbreak from different parts of Assam. All the serum samples were subjected to indirect ELISA test for detection of the duck plague viral antibody. Out of the total 445 serum samples tested for detection of DP viral antibody, 171 (38.42%) serum samples showed positive in ELISA.
A total of 131 numbers of duck carcasses were subjected to necropsy examination. Externally, the carcasses were markedly emaciated, the vent was soiled with greenish-white faecal materials and occulo-nasal discharges were also observed. Grossly, the vascular changes were invariably present in all the visceral organs including the brain. The longitudinal folds of the esophagus showed presence of thick yellowish-white patchy diphtheritic membrane. In a few cases, the intestinal annular bands appeared as intensely reddened rings due to haemorrhages and were visible from external and internal surfaces. The liver was moderately enlarged with presence of scattered petechiae and focal greyish-white necrotic areas. The coronary vessels of the heart were engorged. There was presence of petechiael to echymotic haemorrhages in the epicardium particularly in and around the coronary groove, which give the heart a characteristics paint brush appearance.
Microscopic lesions were characterized by haemorrhages, congestion, degeneration and necrotic changes of the parenchymatous organs. Liver showed varying degrees of degeneration with multiple areas of focal coagulative necrosis. Intra-nuclear, eosinophilic inclusion bodies with a distinct halo were observed inside the degenerated hepatocytes. Congestion of the blood vessels in the myocardium, haemorrhages between the muscle fibres and epicardium of heart were evident. There were rupture of the blood vascular wall and escape of blood into the surrounding musculature. The intestinal annular band showed congestion, haemorrhages and depletion of the lymphocytic cell populations. Lymphocytic depletion was also observed in the spleenic and bursal follicles.
For in-situ demonstration of the DP virus Fluorescence Antibody Test was used. On fluorescent microscopy (FAT) DP virus was demonstrated in the liver, spleen, bursa of Fabricius, brain, thymus and intestinal annular band.
A total of 380 numbers of samples were collected from clinically affected (107) and dead ducks (273) for molecular diagnosis of the disease. Out of total 380 samples, 231 (84.61%) post mortem samples and 68 (63.55%) clinical samples showed positive for duck plague virus specific nucleic acid. Highest numbers of tissue samples that showed positive for PCR were liver (91.80%) and spleen (91.53%). In clinical samples 79.10 per cent was positive in whole blood, 40.91 percent was positive in cloacal swabs and 33.34 percent in tracheal swab.
In biochemical study, the ALT and AST activities in serum and tissues were significantly higher in DP affected ducks in comparison to the healthy ducks.
The virus could be successfully isolated in 9-11 day old duck embryos from the field samples. The infected CAM and the embryos showed extensive haemorrhages throughout the body. Embryopathy was observed within 4-8 days post infection.
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