Various isolates from occurrences of lymphadenitis in small ruminants worldwide have been detected, including Corynebacterium pseudotuberculosis, Trueperella pyogenes, Actinobacillus licheniformis, Staphylococcus aureus subsp. anaerobius, Streptococcus spp., Micrococcus luteus, Bacillus cereus, and others. Although Corynebacterium pseudotuberculosis is recognized as the etiological agent of caseous lymphadenitis, other microorganisms are also considered important in some cases of (caseous) lymphadenitis. This research represents the first study on the epidemiological and microbiological aspects of lymphadenitis in sheep and goat flocks in Northeast Iran. A total of 4733 sheep and goats from 23 herds were studied. The prevalence ranged from 0% to 28.57%. The most commonly affected superficial lymph node was the submandibular lymph node. Ewes were more affected than males, and the most affected age group was between 2 to 3 years. Sheep were more affected than goats. Microbiological culture demonstrated that Corynebacterium pseudotuberculosis was the most common isolate detected, followed by Corynebacterium spp., Trueperella pyogenes, and others.

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