Pathological studies on white spots of the liver in fattening pigs

Hepatic lesions were found in fattening pigs derived from a farm where swine had been suffering from the multiple occurrence of white spots in the liver. They were examined at a slaughter-house for 18 months. The white spots were classified into three patterns on the basis of the macroscopic appearance; that is a compact, a mesh-worked, and a lymphonodular pattern. Histologically, the following 3 kinds of lesions were seen: (1) Eosinophilic interstitial hepatitis accompanied with intralobular necrosis, arteriolar degeneration, boring focus, granuloma and the existence of Nematoda larvae. (2) Fibrosis accompanied occasionally with infiltration of a few eosinophils and lymphocytes. (3) Lymphofollicular hyperplasia. As to the relationship between macroscopic and histologic patterns, compact white spots were generally produced by eosinophilic interstitial hepatitis. The mesh-worked pattern consisted of eosinophilic interstitial hepatitis or fibrosis, and the lymphonodular pattern of lymphofollicular hyperplasia. The incidence of eosinophilic interstitial hepatitis was relatively high over a period from July to December and rather low over a period from January to June. That of fibrosis was considerably high all the year round. Lymphofollicular hyperplasia showed no distinct seasonal incidence. Intestinal ascarids were frequently detected over a period from August to October. Pigs having CF antibody against Ascaris suum increased in number over a period from August to December. From these results, the cause of the multiple occurrence of white spots in the liver was regarded as A. suum infection.