Study on frequency of lungs and mediastinal lymph nodes infection in caseous lymphadenitis in sheep

A total of 468 sheep carcasses of both genders were inspected randomly since the first of January and February 2006 in Khosroushahr (a city of suburb of Tabriz, East Azerbaijan province, Iran) abattoir. Considering the infection of lungs and mediastinal lymph nodes is the most visceral infection of CLA, the aim of present study was to determine frequency of visceral form of CLA and its relation with superficial lymph nodes infection.197 cases containing 153 (77.7%) male and 44 (22.3%) female had prominent enlargement in size of one of the lymph nodes such as prescapular, prefemoral, inguinal, suprammamary or mediastinal For evaluation of causes, lymph nodes were removed intact with surrounded tissue. In all suspected samples of CLA, lungs were inspected and removed for more studies. The samples for diagnosis of CLA were sent to microbiology and pathology departments at 4˚C in ice container. Standard bacteriological culture methods for isolating of Corynebacterium pseudotuberculosis and tissue preparations for histopathological sections were performed. Statistical analysis of data was done by SPSS (version 16) software. Based on the results, in 63 (13.46%) carcasses Corynebacterium pseudotuberculosis were isolated and in 94 (20.08%) of them, histopathological study revealed pathognomonic sings (lamellated exudates or onion- ring) of CLA. 34 (17.25%) of lungs revealed CLA in microbial culture or histopathological study, that 11 (32.3%) cases only with histopathology, 8 (23.5%) cases only with microbiological culture and in 15 (44.1%) of them, both microbiological and histopathological studies confirmed CLA. In 16 (26.7%) of cases, the pathogenomonicsigns of CLA were revealed in mediastinal lymph nodes macroscopically, that increased to 26(24.7%) in histopatholgical study. Microbiological culture on mediastinal lymph nodes revealed 31 (32.6%)cases contain pure agent of CLA (P<0.05). Based on statistical tests, correlation rate between the bacteriologicalculture and histopathological studies was positive (r=0.196) and significant (P= 0.006).