The study was carried out at ICAR-Directorate of Poultry Research (ICAR-DPR), Hyderabad, India during 2018. The study was carried out with the approval of IAEC (IAEC/DPR/2017/7) and by following the guidelines of CPCSEA.
Experimental birds
Aseel, Ghagus and Vanaraja chicks hatched at hatchery and reared at farm of ICAR-DPR were used in this study. Birds were reared in battery brooders until 12 weeks with standard diet and
ad libitum water. All the birds were vaccinated against Marek’s disease, Newcastle disease, infectious bursal disease, infectious bronchitis and fowl pox by following regular vaccination protocol. No fowl cholera vaccine was done for the breeder or for chicks and were seronegative for
Pasteurella multocida (PM) specific antibodies confirmed by indirect ELISA with commercially available kit.
Pasteurella multocida A:1 isolate
The
Pasteurella multocida A:1 isolate maintained at avian health lab was used in the study. It was originally isolated from the fowl Cholera (FC) outbreak from broiler breeder flock. The isolate was confirmed by colony morphology, Gram’s staining and by PCR. The virulence was confirmed by inoculating in day-old chicks. The isolate induced death within 24 hrs and the organism was re-isolated from heart blood swab collected from chicks upon necropsy in brain heart infusion (BHI) agar (HiMedia labs, Mumbai, India; Cat # M210). The inoculum for the experiment was prepared as per the method of
Petersen et al., (2001). Briefly, single colony of virulent culture from BHI agar plate was inoculated into BHI broth and was incubated aerobically at 37°C for 24 hrs. The size of the inoculum was determined by plate- spread method to contain approximately 2.5 × 10
6 CFU/ml.
Experimental infection of chicken
A total of 72 birds, 24 from each breed (Aseel, Ghagus and Vanaraja) at the age of 12 weeks were divided into three groups for each breed (n=6/ group). One group of each breed was inoculated with 1 ml of BHI broth containing 2.5 × 10
6 CFU/ml through intraperitoneal route (I/P) and the other group was inoculated with same dose through intranasal route (I/N). The third group of each breed was kept as uninoculated control. The birds were kept in chicken isolators during the entire inoculation experiment following the institute bio-security guidelines. Birds were given standard diet and water
ad libitum.
Morbidity and mortality pattern
The inoculated birds were observed for any clinical signs, morbidity and mortality for 7 days. The dead birds were removed from the isolators and necropsy was performed (Bermudez and Stewart-Brown, 2003). PM specific lesions in different organs including liver, spleen, heart, lungs and wattles were examined. Swabs from liver and heart were taken for re-isolation of
P. multocida by standard procedure.
Histopathology
The organs showing PM specific lesions collected during necropsy were fixed in 10% buffered formal saline, processed and embedded in paraffin wax. The sections were made and stained with Hematoxylin and Eosin. The slides were analysed under light microscopy under high magnification (40x and 100x) for pathological changes.