Linfadenite caseosa como causa de paralisia de membros pélvicos em ovinos no Estado do Rio Grande do Sul Caseous Lymphadenitis as a Cause of Hind Limb Paralysis in Sheep in Rio Grande do Sul State

Background: Caseous lymphadenitis (CL), an infectious disease of sheep and goats caused by Corynebacterium pseudotuberculosis, is characterized by pyogranulomas, white to greenish-yellow contents with aspect of rennet-coagulated cheese, and concentric laminations. Transmission occurs through direct contact with animals showing superfi cial lesions, via iatrogenic, or by respiratory route from aerosols. This paper reports the association of pyogranulomatous spondylitis with caseous lymphadenitis in two sheep, in Rio Grande do Sul State, southern Brazil. Cases: Two male sheep, 7- and 6-months-old, Texel (lamb 1) and mixed Texel (lamb 2), respectively, were submitted to necropsy. Affected sheep were reared under semi-intensive system in the same group, and had not been tail-docked. Both lambs showed weakness, diarrhea and paralysis of hind limbs. At necropsy, sheep had good body conditions, pale mucous membranes and large numbers of Haemonchus sp. worms within the abomasum. Lamb 1 showed serous fat atrophy and two abscesse-like lesions, one measuring 3.0 cm in diameter in the left apical lung lobe and other affecting the last lumbar vertebrae body. In lamb 2 there were three lesions like abscesses, a thoracic lesion involving the 13th vertebrae and the 1st lumbar vertebrae, a 3.0 cm in diameter lesion in the left axillary region, and a 1.5 cm lung lesion in the left apical lobe, apart of a calcifi ed nodule with 0.5 cm in diameter in the diaphragmatic lobe. Histologically, these lesions were characterized by areas of caseous necrosis with foci of mineralization associated with peripheral infl ammatory infi ltrate rich in neutrophils surrounded by macrophages, epithelioid cells and occasional multinucleated giant cells and plasma cells and peripheral abundant fi brous connective tissue proliferation. In the vertebral bodies these lesions were partly surrounded by fi connective tissue, and in lamb 1 reached the dura mater, while in lamb 2, it extends to the spinal cord with pyogranulomatous myelitis, characterized by foci containing large amounts of neutrophils, surrounded by macrophages and epithelioid cells. There was thickening of blood vessel walls, with macrophages within or around them. Spinal cord injury affects both gray and white matter, with peripheral axonal spheroids. Corynebacterium pseudotuberculosis grew in pure culture upon microbiological tests from samples of lung and vertebral lesions from both cases. Discussion: This paper describes, originally, caseous lymphadenitis as a cause of hind limb paralysis in sheep in Rio Grande do Sul State, Brazil. The association of the macroscopic and histological fi ndings with the isolation of C. pseudotuberculosis allowed us to relate pyogranulomatous spondylitis with caseous lymphadenitis. The spondylitis and spinal cord compression and/or myelitis may explain the hind limb paralysis. The spread of the pathogen was probably hematogenous to the lungs and the other parts of the body. The hematogenous osteomyelitis caused by bacterial infection affects often young animals in the area of vascularization of the growth plate and epiphyseal articular complex. The blood vessels of these sites allow the bacterial installation due to slow fl ow and the blood turbulence in the larger descending vascular branches, but also due to lowed phagocytic capacity and discontinuity between endothelial cells. These factors, in addition to the antiphagocytic action of Corynebacterium pseudotuberculosis in endothelial cells may explain the location at spinal lesions of caseous lymphadenitis in these sheep.