“STUDIES ON MAJOR RESPIRATORY PATHOGENS OF BROILER CHICKENS IN AND AROUND JUNAGADH” 2824
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Date
2019-06
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JAU, JUNAGADH
Abstract
The present research work was carried out to determine the etiological agents
responsible for respiratory distress with special reference to presence of LPAI (H9N2),
IB virus, ND virus and E. coli infection in broiler birds. The study comprised of
epidemiological information in relation to farm wise mortality and age wise mortality,
gross and histopathological examination of involved respiratory organs especially
trachea, bronchi, lung and air sacs, detection of LPAI (H9N2) virus, IB virus and ND
virus by RT-PCR, detection of avian pathogenic E. coli by PCR and also isolation as
well as antibiogram against E.coli from the birds affected with respiratory distress.
Studies on the farm incidence and age wise mortality among twenty five
broiler flocks having total population of 75,800 birds of second to fifth week of age
showed an average mortality rate of 3.25 percent ranging between 1.33 to 8.00
percent. The week wise mortality was found highest during third week of age
followed by second, fourth and fifth weeks of age.
Gross pathological lesions were predominantly found in organs of respiratory
system i.e. in trachea, bronchi, lungs and air sacs. The tracheal lesions observed were
severe congestion, excessive mucous exudate, presence of fibrino necrotic or caseous
cast in the tracheal bifurcation and extending in the bronchi and were pathognomonic
of respiratory distress. The lung lesions were mild to marked oedema and congestion.
In some of flocks affected during early age air sacs revealed thickening with fibrin
deposition. The liver and spleen in early infected flock showed congestion, mild
petechial haemorrhages and necrotic foci as well as pale and swollen kidneys.
Microscopic changes were most consistently seen in the trachea and bronchi
and variable from mild to severe in nature. In many cases trachea and bronchi showed
congestion along with infiltration of mononuclear cells in the mucosa and submucosa
and presence of fibrino necrotic masses in the lumen. The tracheal lesions were
mainly confined to mucosal glands and epithelial lining. Loss of cilia and hypertrophy
of mucous gland were noticed in early stages of the disease followed by degeneration
and desquamation of epithelium with infiltration of mononuclear cells leading to
thickening of tracheal mucosa. The microscopic lesions observed in bronchi were
fibrino necrotic masses in the bronchial lumen which were occluding the air passage.
The microscopic lesions observed in lungs were vascular engorgement and haemorrhages, smooth muscle hypertrophy and infiltration of mononuclear cells in
the parabronchi. Air sac lesions were marked by presence of fibrinous exudate and
mononuclear cells infiltration.
Molecular studies were carried out for detection of LPAI (H9N2), IB virus, ND
virus and avian pathogenic E.coli (APEC) from pooled tissue samples of bronchi and
trachea containing caseous plug of the twenty five broiler flocks. All the twenty five
flocks (100%) were found positive for LPAI (H9N2) virus as well as for pathogenic
E.coli, whereas IB virus, ND virus were detected in 4 (16%) and 8 (32%) farms
respectively. In addition to above it was also seen that out of twenty-five broiler
flocks, all the twenty five (100 percent) were positive for LPAI + APEC, three flocks
(12 per cent) were positive LPAI + APEC + IBV; seven flocks (28 per cent) positive
for LPAI + APEC + NDV; one flocks (4 per cent) positive for LPAI + APEC + IBV +
NDV.
To analyze the risk of secondary E. coli infection in case of respiratory distress,
isolation, identification and characterization of E. coli from pooled tissue samples of
caseous bronchial plugs from each flock was undertaken. Out of twenty-five tissue
samples processed for bacterial isolation, all the samples (100%) were found positive
for secondary E.coli infection. The antibiotic sensitivity test was carried out from all
the isolates obtained from affected flock. The isolates were found highly sensitive to
antibiotic disc colistin (Methane sulphonate) (100%) and meropenem (100%)
followed by levofloxacin (76.67%), ceftriaxone (64%), gentamicin (60%), amikacin
(60%), co-trimoxazole (40%), amoxycilin-clavunic acid (08%) and imepenem (08%).
Molecular characterization of E. coli was carried out for detection of presence
of four virulence genes i. e. iss, papC, tsh and vat. DNA was extracted from tissue
samples (caseous plugs) and subjected to PCR with gene specific primer pairs. Out of
twenty-five tissue samples, the iss gene, vat gene, tsh and papC gene found in 22
(88%), 13 (52%) , 15 (60%) and 8 (32%) in respiratory affected farm, respectively.