Sheep caseous lymphadenitis: causative bacterial agents and their in vitro some antimicrobial susceptibility

ABSTRACT

Corynebacterium pseudotuberculosis [C. pseudotuberculosis] is the etiologic agent of caseous lymphadenitis. It is a serious, economically important disease for sheep production. This study was carried out on 762 sheep reared in private flocks [616 females and 146 males] with different ages at different localities in Assiut Governorate. The prevalence of the disease in sheep was 22.7% on the basis of clinical signs and 20.1% on the basis of bacteriological examination. The disease prevalence was significantly higher in females'sheep [25.3%] than that in males [11.6%]. Caseous lymphadenitis was highly significantly different among age groups. The high prevalence of caseous lymphadenitis was recorded in sheep of 1-2 years old [37.34], followed by animals of 2-3 years old [25.77%] and the low prevalence was in sheep under one year old [8.33%], this may be due to occurrence of maternal antibodies from colostrums. Parotid lymph nodes were the most common affected lymph node [11.81%], followed by superficial cervical lymph nodes [7.87%], while prefemoral lymph node was less affected [0.39%]. The superficial lymph nodes of the anterior body half showed the highest rate of infection then the posterior body half. C. pseudotuberculosis was the main causative agent of caseous lymphadenitis in sheep, where it was isolated either in pure form or in combination with Staph. aureus from 142 cases [82.1%] and 7 cases [4%] of the clinically infected sheep, respectively. On the other hand Staph. aureus was isolated as a sole pathogen from 4 cases representing 2.3%. All isolated strains of C. pseudotuberculosis were highly virulent to Guinea pigs and 97.3% of them were nitrate reduction negative. In vitro antimicrobial susceptibility test of C. pseudotuberculosis strains showed that Enrofloxactin and Ciprofloxatin had strong inhibitory effect on the isolates, while the most strains were highly resistant to Lincomyctin, Streptomycin, Amoxycillin and Penicillin. From the obtained results, it can be concluded that C. pseudotuberculosis is the main causative agent of caseous lymphadenitis in sheep. The superficial lymph nodes of the anterior body half show the highest rate of infection than the posterior body half. Enrofloxacin and Ciprofloxacin are the most effective drugs during in vitro tests