Endocarditis-associated brain lesions in slaughter pigs

Left-sided valvular endocarditis (LSVE) is a common finding in slaughter pigs. The lesion is often associated with renal thromboembolism, but information on embolization to other organs is sparse. This study focuses on the presence and type of endocarditis-associated brain lesions (EABLs). The brains of 20 slaughter pigs with spontaneously arising LSVE and 11 controls were examined by sectioning half of a formalin-fixed brain into 4mm slices for histological examination. The aetiology of the endocarditis was determined by bacteriological and, in some cases, by fluorescence in-situ hybridization examinations. These examinations identified 11 cases of Streptococcus suis, six cases of Erysipelothrix rhusiopathiae, one Streptococcus spp. and two cases that remained aetiologically undetermined. One of the S. suis cases had a dual infection with S. suis in the aortic valve lesions and Streptococcus dysgalactiae subsp. equisimilis in the atrioventricular valve lesions. Renal infarcts were present in eight cases. Focal encephalitis was found in 12 cases, with the number of lesions ranging from one to 11. Most pigs had less than four microscopical lesions. Acute lesions were characterized by focal microabscesses without observable bacteria. Chronic lesions were characterized by astrocytosis and focal accumulation of mononuclear leucocytes. An infarct was observed in one animal. Perivascular inflammation was seen in 14 cases, mostly as two or three lesions, while focal leptomeningitis was found in eight cases. EABLs are therefore common in slaughter pigs with LSVE. The number of lesions per animal is small, which may explain the limited attention paid to this sequela of LSVE. EABLs have rarely been reported in domestic animals and mostly in patients with neurological signs. The frequent occurrence of EABLs in slaughter pigs suggests that this pathology should be investigated in other animal species with LSVE.