Investigation of an outbreak of caseous lymphadenitis in goats

Abstract

Caseous lymphadenitis (CLA) is a chronic and sub-clinical disease of sheep and goats with high prevalence in domestic animals. It is caused by Corynebacterium pseudotuberculosis biovar ovis. An outbreak of CLA in superficial and visceral forms was observed in Barbari and Jakhrana goat herds maintained at ICAR-CIRG, Makhdoom (UP) in July, 2016. A total of 147 goats was affected by the infection of external lymph nodes and two cases in Barbari goats showed internal abscess on necropsy. Biopsy pus samples were collected and identified the organism after Gram's staining. All biopsy samples were inoculated to blood agar and subjected to biochemical (catalase, oxidase and nitrate) tests. Isolation of DNAfrom culture and 16S rRNAgene-based PCR for C. ovis was carried out for confirmatory diagnosis. Gross and histopathological studies were conducted in cases of internal abscess. Antibiotic sensitivity tests were conducted for all the isolates obtained during the study. External lymph nodes were predominantly affected involving pre-scapular and post-scapular (94), pre-femoral (44) and mandibular lymph nodes (9). After incising abscesses, white thick pus oozed out. In Grams ’stained smears, the organism was pleomorphic rods arranged in Chinese letters. On blood agar, round, raised, greyish colonies were observed and biochemical examination showed catalase positive and oxidase negative. The 16S rRNA genebased PCR confirmed the presence of C. ovis. In two cases, visceral abscess was observed with oozing pus from affected lungs. Histopathology of affected lung tissue showed infiltration of inflammatory cells including neutrophils, lymphocytes and macrophages within infected tissue and concentric fibrous layers separated by inspissated caseous exudate. Based on morphology, biochemical tests and PCR, causal organism was confirmed as C. ovis and based on 16 antibiotics tested for sensitivity, ciprofloxacin was the only antibiotic found to be effective against isolates.