Molecular Identification of Major Bacterial and Viral Pathogens of Chickens and the Public Health Importance of the Pathogens in Commercial Poultry Farms in Bishoftu and Mojo, Central Ethiopia
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Date
2023
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Addis Ababa University
Abstract
The importance of poultry production is increasing in Ethiopia where high-quality protein and contained costs make poultry a valuable food resource. However, it entails some problems linked to rural, backyard and intensively reared flock proximity and pathogen circulation. The growing poultry production particularly in large-scale commercial intensive systems is challenged by occurrence of diseases of economic and public health importance. This study was planned to investigate the presence of important pathogens in chicken with a direct and indirect public health importance (Campylobacter, Salmonella, Newcastle Disease Virus (NDV), Infectious Bursal Disease Virus (IBDV), Infectious Bronchitis Virus ((IBV), and Avian Metapneumovirus (aMPV)), in poultry farms in Bishoftu and Mojo, Central Ethiopia. Respiratory tract and cloacal swabs and bursa of Fabricious and kidney tissue imprints on FTA cards were collected in 2021 from a total of 500 chickens from 16 farms (1 broiler and 15 layer farms) and tested using PCR-based molecular methods for pathogen detection and sequencing method for species and strain identification. To generate farm-level data, the samples were pooled per farm, shed/flock, and sample type (matrix) where each swab pools contained ten swabs and each tissue smear pools contained variable number of imprints (two to five tissue smear pools). Based on their tropism for specific body system/part or tissue, twenty cloacal pooled samples were tested for Campylobacter and Salmonella species identification using genus-specific PCR. On the other hand, forty cloacal and respiratory swab pooled samples, and fourteen bursal and kidney tissue imprint pooled samples were tested using reverse transcription PCR, for different viral agents. Among the total twenty cloacal pooled samples tested, 70% (14/20) of them were positive for Campylobacter spp., where 71.4% (10/14) of the positive samples belonged to Campylobacter jejuni species, 21.4% (3/14) belonged to Campylobacter avium and 7.1% (1/14) to Campylobacter helveticus. But, all the twenty cloacal swab samples tested for Salmonella spp. became negative. On the other hand, among the total 16 farms tested for viral pathogens, one farm was positive (6.7%) for NDV (among 15 layer farms tested for NDV) with a Lasota vaccine strain, genotype II; another one farm was positive (6.25%) for IBDV (out of a total of 16 layer and broiler farms covered in the study), resulting in strains similar to those present in vaccines, Winterfield-2512, belonging to genogroup A1a; two farms were positive (12.5%) for IBV, resulting in a 4/91-like strain/793B (GI-13 lineages); but there were no farm tested positive for aMPV. In this study, Campylobacter jejuni was a predominantly isolated (71.4%) Campylobacter species in chickens in the study area, whereas species such as C. avium and C. helveticus were newly reported in Ethiopia, revealing a variability that needs to be monitored in light of the public health significance of this pathogen. On the other hand, the present findings suggest a low presence of viral pathogens (3/16,18.75% farm and 6/54,11.11% sample pool) probably due to the implementation of vaccination strategies, which is also testified by the detection of vaccine strains. The detection of high total prevalence of pathogens (35.2% (19)) for sample pools, and 81.2% (13) for farm), and particularly of a public health important campylobacter jejuni which has a high zoonotic importance, can imply high transmission potential of the pathogens from poultry host to human being indicating high risk of acquiring the infection. The high rate of detection of an important zoonotic pathogen, campylobacter (70% sample pools), in this study with wider farm coverage (80% farms) and among different host factors, management conditions, vaccination protocol and treatment schemes used, coupled with the poor biosecurity practices encountered during the field data collection, suggested a high risk of pathogen introduction to human population and greater dissemination potential. It was the limitation of laboratory facilities and budget related constraints that hinder further extensive investigation of the problems in both chicken and human population, covering wider areas and farms and coming up with detection of the circulating pathogens at their presence and at the same time investigating other public health important zoonotic pathogens of poultry like avian influenza virus and E.coli bacteria. In the future, extensive PCR-based detection of important pathogens circulating among poultry and human population should be carried out to have a clear epidemiological picture of distribution of these pathogens and to let design an appropriate intervention measures for control and prevention of the pathogens. Keywords: aMPV, campylobacter; chickens, IBV; IBDV; NDV; poultry; public health, salmonella.
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Keywords
aMPV, campylobacter, chickens, IBV, IBDV, NDV, poultry, public health, salmonella