PATHOLOGICAL STUDIES AND MOLECULAR DETECTION OF RESPIRATORY PATHOGENS ASSOCIATED WITH RESPIRATORY DISEASE COMPLEX IN COMMERCIAL CHICKEN
Loading...
Files
Date
2021-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
The present study was planned to study the incidence and pathology of common respiratory diseases of commercial chicken and to carry out the molecular detection of pathogens associated with respiratory disease complex.
A total of 639 birds with a history of suspected respiratory diseases were procured from various parts of Andhra Pradesh and representative samples were collected and subjected to pathological and molecular studies. Based on these studies, respiratory diseases were identified in 488 birds, accounting to an overall incidence of 76.36%. The major pathogens involved in respiratory disease complex in the present study were Newcastle disease virus (NDV), Infectious bronchitis virus (IBV), Fowl adenovirus (FAdV), M.gallisepticum (MG), M.synoviae (MS), Avibacterium paragallinarum, Pasteurella multocida and avian pathogenic E.coli (APEC). LPAIV and ILTV were not detected. Of these, respiratory disease caused by a single pathogen was identified in 136 (27.87%) cases and respiratory disease complex associated with multiple pathogens was identified in 352 (72.13%) of cases.
xxxii
Out of 488 cases, a total of 8 pathogens were detected either as a single infectious agent or as concurrent infections that resulted in respiratory disease complex. Among the single pathogen identified, NDV was detected in 159 cases (32.58%), followed by IBV in 72 cases (14.75%), FAdV infection in 31 cases (6.35%), M.gallisepticum in 190 cases (38.93%), M.synoviae in 108 cases (22.13%), A.paragallinarum in 14 cases (2.87%), P.multocida in 65 cases (13.33%) and avian pathogenic E.coli (APEC) in 308 cases (63.11%) occurring either as a single infectious agent or among concurrent infections.
Among the 136 cases caused by a single infectious agent, NDV was detected in 32 cases (6.56%), followed by IBV in 20 cases (4.10%), FAdV in 8 cases (1.64%), M.gallisepticum in 18 cases (3.69%), M.synoviae in 2 cases (0.41%), A.paragallinarum in 12 cases (2.46%), P.multocida in 25 cases (5.12%) and APEC in 19 cases (3.89%).
In case of concurrent infections, two to four pathogens were commonly involved in a single case and recorded in 72.13% of cases. Concurrent infection of two pathogens was recorded in 258 cases (52.87%) and three pathogens were recorded in 81 cases (16.60%). Isolation of quadruple agents involving NDV, MG, MS and APEC were identified in 13 cases (2.66%) of respiratory disease complex. Avian pathogenic E.coli was the most common organism involved in the concurrent infection in 289 (59.22%) cases.
In the present study, the clinical signs, gross and histopathological findings were almost similar in the respiratory diseases and it was difficult to diagnose the diseases based on the pathological studies alone especially when multiple agents were involved in a single case. Hence, molecular techniques were employed for confirmation of various respiratory pathogens.
Birds affected with different respiratory diseases showed signs of dullness, nasal discharge, gasping, coughing, open-mouth breathing, respiratory rales, dyspnoea, oedema of the face and eyelids, conjunctivitis, cyanotic combs and wattles, soiled vent and diarrhoea. Some birds also manifested paralysis and torticollis. A drop in egg production and egg quality in the flocks were recorded.
Grossly, in cases of respiratory disease complex caused by multiple etiological agents, the lesions recorded included congestion, haemorrhages and catarrhal to caseous exudates in trachea, thickened and cloudy air sacs with fibrinous to caseous exudates and edema, congestion and consolidation of lungs. Further, proventricular haemorrhages, haemorrhagic and necrotic intestines and caecal tonsils, pericarditis, perihepatitis, necrotic foci on liver, swollen and congested kidneys, congestion of ovaries, and egg peritonitis were noticed.
The prominent histopathological lesions in cases of respiratory disease complex observed were haemorrhagic tracheitis, oedema, pulmonary congestion and pneumonia, fibrinous airsacculitis, fibrinous pericarditis and perihepatitis, haemorrhagic
proventriculitis, catarrhal enteritis, lymphoid depletion in caecal tonsils and spleen, tubular epithelial cell degeneration, congestion, interstitial nephritis and urate tophi in kidneys, perivascular cuffing and glial cell proliferation of brain. In NDV and concurrent infections (IBV, P.multocida, MG, MS and APEC) grossly congestion, haemorrhages and catarrhal exudates in the trachea, congestion of lungs, proventricular haemorrhages, haemorrhagic and necrotic intestines and caecal tonsils were noticed. Further, necrotic foci on the liver when co-infected with P.multocida, fibrinous to caseous exudates in the air sacs, pericarditis, perihepatitis and egg peritonitis in concurrent infections of MG, MS and E.coli were found. Microscopically, tracheitis, airsacculitis, pneumonic changes, exudates in the parabronchi and lymphoid depletion in the spleen and caecal tonsils were noticed. Ultrastructurally, trachea showed total loss of cilia and epithelium, large vacuoles in the cytosol and pyknotic nuclei with margination of chromatin and in lungs erythrophagocytosis, loss of cell membrane of Type II pneumocytes, few lamellar bodies and electron dense bodies in the cytosol were noticed. In IBV and concurrent infections (NDV, MG and APEC), birds showed grossly congestion, edema and caseous exudates on the tracheal mucosa, thickened air sacs with fibrinous to caseous exudates and edema, congestion, consolidation and pneumonia of lungs. Kidneys were swollen, congested or haemorrhagic and ureters were distended with urates. Cystic oviduct, egg peritonitis and mild fibrinous pericarditis and perihepatitis were also found. White chalky urate deposits were found on the pericardium, liver and kidneys. Microscopically, tracheitis, airsacculitis, exudates in the parabronchi and haemorrhages and degenerative changes in the kidneys and interstitial nephritis were noticed. Ultrastructurally, tracheal tissue homogenates showed round electron dense virions of approximately 100 nm in diameter. In FAdV and concurrent infections (MG and APEC), congestion and thickening of the tracheal mucosa, thickened air sacs, edema in lungs, ascites, hydropericardium, swollen liver with necrotic foci, swollen haemorrhagic kidneys, fibrinous pericarditis and perihepatitis were noticed. Microscopically, tracheitis, airsacculitis, congestion and edema in lungs and intranuclear basophilic inclusion bodies in liver and kidneys were found. Ultra structurally, virus particles exhibiting oval or hexagonal configurations arranged in crystalline arrays were found in the hepatic cells. In M.gallisepticum and concurrent infections (MS and APEC), catarrhal to caseous exudates in the nasal passages, trachea, bronchi and air sacs and congested and consolidated lungs were noticed. In severe infections, fibrinous exudate was deposited on the pericardium and liver. Microscopically tracheitis, airsacculitis, pneumonia and lymphoid aggregates in the trachea, lungs, liver and kidneys, pericarditis and perihepatitis were noticed. In M.synoviae and concurrent infections (MG and APEC), congestion of trachea and lungs, accumulation of catarrhal exudates in the air sacs, mild fibrinous exudate
on the pericardium and liver were seen. Microscopically, mild tracheitis, airsacculitis and congestion and edema of lungs were noticed. In birds infected by P.multocida and concurrent infections (APEC), congestion throughout the carcass, petechial haemorrhages on coronary fat and epicardium, congestion of liver, intestines, kidneys and ovaries and necrotic foci on the liver, fibrinous pneumonia, pericarditis and perihepatitis were noticed. Microscopically, congestion, fibrinous exudates in the parabronchi, thickening of parabronchial septa, degenerative changes in the heart and necrotic changes in liver were evident. In A.paragallinarum and APEC concurrent infections, the birds revealed swelling of eyes and face, conjunctivitis and a serous to mucoid discharges from nostrils and sinuses, congestion of trachea, edema and congestion of lungs, thickened air sacs and fibrinous exudates on the pericardium and liver. Microscopically, severe sinusitis, mild tracheitis and airsacculitis were noticed. In avian pathogenic E.coli infected birds trachea and lungs were severely congested and edematous and polyserositis with fibrinopurulent pericarditis, perihepatitis, airsacculitis and egg peritonitis were noticed. Out of 60 E. coli isolates, virulent genes viz. iss, vat, tsh and papC were found in 48(80%), 43(71.6 %), 31 (51.6%) and 18(30%) of isolates respectively.
In the present study molecular detection of the respiratory pathogens viz. NDV, IBV, FAdV, LPAI, ILTV, M. gallisepticum, M. synoviae, A. paragallinarum, P.multocida and avian pathogenic E.coli (APEC) was carried out by PCR/RT-PCR. Of these, except LPAI and ILTV other pathogens were detected on PCR in the affected birds. Based on the pathogen under study, the amplicons of appropriate base pair sizes were detected by agar gel electrophoresis. Further, nucleotide sequencing and phylogenetic analysis of F gene of NDV, S1 gene of IBV and hexon gene of FAdV was also carried out. On sequencing and phylogenetic analyses, the 6 NDV samples (NDV/GVM/AP1- 6) were grouped with the isolates of Tamil Nadu, Nagpur, Assam, West Bengal and Bareilly belonging to genotype XIII. On amino acid analysis, fusion protein cleavage site amino acids at positions 112 and 116 (RRRKR) and a phenylalanine (F) at position 117, indicated that the NDV strains are of virulent type of strains. The IBV samples IBV/GVM/AP-1, 2 and 3 were grouped with vaccine strains M41, H120 and other respiratory IBV strains and IBV/GVM/AP- 4, 5 and 6 were grouped with nephropathogenic strain of IBV-470 and other nephropathogenic IBV strains. The two FAdV samples (FAdV/GVM/AP-1 and 2) isolated from the respiratory disease complex cases were grouped along with fowl adenovirus strain E.
The present study indicated that respiratory disease complex is a major problem in commercial chicken and it has a potential to cause severe economic losses in poultry.
Description
THESES