Molecular detection and epidemiological characterization of Pasteurella multocida associated with respiratory disease in sheep in Salah Alden province, Iraq

This study investigated the cultural, molecular, and epidemiological aspects of Pasteurella multocida in sheep affected with respiratory infections. Data were collected from 130 sheep that exhibited severe respiratory illness from various locations across Salah Alden province, Iraq. Nasal swabs were obtained from the sheep, cultured, identified by biochemical tests, confirmed by polymerase chain reaction (PCR), and subjected to antibiotic susceptibility testing. Seasonal patterns were analyzed, a relationship between clinical signs and infection status were established, and geographical distribution of infection sheep was assessed. The results indicated non- hemolytic colonies on blood agar that were Gram-negative and non-motile coccobacilli measuring 1-3 mm in diameter. The biochemical assays revealed positive oxidase, catalase, and indole tests, while the Simmons citrate and methyl red tests were negative, confirming the presence of P. multocida. The infection rate of P. multocida among the clinically affected sheep was 33.1% (43/130) and no significant sex difference was observed in the detection rate. Significant age-related differences were observed in the detection rate, with higher rate (62.1%) in sheep aged less than 1 year, followed by the age range of 1 to 2 years (37.8%), and the lowest (17.2%) in sheep greater than 2 years of age. The PMOut gene primers successfully amplified the 219 bp fragment from all culture positive samples, confirming the presence of P. multocida. The detection rate was higher in autumn (45.2%) and winter (38.7%) compared to spring (28.1%) and summer (21.4%) seasons. The main clinical signs correlating with P. multocida infection were fever, nasal discharge, and cough. The distribution of P. multocida positive cases in the Salah Alden province varied greatly among districts Tikrit revealing highest detection rate compared to Shirqat, and Tuz Khurmatu. Antibiotic susceptibility testing showed that all isolates were highly sensitive to gentamycin (100%) and completely resistant to penicillin, rifampin, and cloxacillin (100%). in conclusion, this study establishes that P. multocida is a major contributor to respiratory infection in sheep within the studied province with significant influence of age, season, and geography. The use of the PMOut gene for rapid and accurate identification along with epidemiological and antimicrobial testing data, provides valuable information for the development of effective disease control measures.