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In the early phase of experimental metagonimiasis in cats or dogs, non-specific villous changes were observed as shortening, widening, tip flattening, and fusion of villi, and as stromal edema. These changes reach their peak in 5-15 days after infection. Later than this period, these villous changes gradually returned to normal. The pathogenetic factor causing such villous pathology was investigated in the present study, mechanical destruction of enterocytes by worms as a main factor involved. A total of 8 domestic cats was experimentally infected with 5,000 metacercariae of Metagonimus yokogawai; then each cat was killed every day to 8th day after infection. Other 2 cats were killed as control. Three ㎝ long small intestinal tissue were taken from every 30 ㎝ from pylorus, and processed histologically. The observation results were as follows: 1. The intestinal lesions were limited to jejunum of the infected cats. At early phase of infection, the mucosal lesion were tortuous tissue defects or fibrinous exudates infiltrated by inflammatory cells at the upper portion of crypt of Lieberku¨hn. The reduction of villous length varied by individual cats. The sectioned worms were only very rarely observed in the crypt of Lieberku¨hn, unlike the cases of dogs. 2. By serial sections of jejunal tissues, that adult worms of Metagonimus yokogawai were found to make ulcer up to stromal tissue at villo-crypt junction. Enterocytes and goblet cells at the junction were degenerated and denuded by the retracting movements of anterior body of worms armed with tegumental spines. 3. The shallow ulcers which were formed by the worms were healed by syncytosis of enterocytes of nearby villus. By this healing process, adhesion of a villus to nearby one resulted in shortened, widened, or multilobed villi. And also intravillous epithelial tissue were resulted. From the above observations, the lesions of villi at the early stages of experimental metagonimiasis were considered as a result of uncompensated enterocytes deficit which was elicited by the mechanical destruction at upper parts of crypt of Lieberku¨hn or at villo-crypt junction.
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