A Study On Intestinal Lesions Of Experimentally Reinfected Dogs With Metagonimus Yokogawai

The intestinal lesions were studied in dog metagonimiasis by reinfection. The metacercariae of M. yokogawai were collected from naturally infected sweetfish. A total of twenty dogs were divided into three groups; control, primary infection and reinfection groups. The 18 dogs were infected with 10,000 metacercariae; the 5 dogs in primary infection group were killed at the 5 days in 1 week, 4 weeks, 6 weeks after the infection. The remaining 13 dogs were kept for nine weeks, and challenged again with 5,000 metacercaricae. The reinfected dogs were killed at the 1 day, 3 days, 5 days and 1 week, 2 weeks, 4 weeks, 6 weeks, 8 weeks respectively. The chronologic changes of the intestinal lesions in both groups, the worm recovery rate, and distribution patten were examined by gross observation, light and scanning electron microscopies. The results were summarized as follows: 1. Worm recovery rate in primary infection group ranged from 19.8% to 37.8%. The rates were 6.3% to 16.3% in reinfected dogs within 5 dats. And the ratio of young worms collected to old ones was 1:1.83. In primary infection group, the collected worms were distributed in upper portion of the small intestine, while the distribution of worms shifted down to the lower portion of the small intestine in reinfection group. 2. In primary infection group, gross pathologic findings of intestinal mucosa began to appear in the 5th day and the 1st week after infection. The changes were effacement of transverse folds, watery or serous intestinal content, and enlargement of Peyer's patches as well as mesenteric lymph nodes. After the 4 week of infection, these findings returned to normal. In the reinfection group, these findings did occur again, but were lighter in degree when compared with primary infection group in early phase of infection. Again the gross changes returned to normal in two weeks which resolved earlier than in promary infection groups. 3, By histopathologic observations, mucosal changes such as blunted, adhered villi with hyperplasia of crypt epithelium, stromal changes, edema, and inflammatory cell infiltration were observed. These regressed mucosal changes were returned to almost normal, except for inflammatory cell infiltration. The reinfected dogs showed less severe lesions of the small intestine, with shorter period of the changes especially in aspect of villous changes. 4. By the scanning electron microscopy, the histopathological findings of villi lesions were also confirmed. From the above results, it was inferred that the so-called spontaneous and/or self cure phenomena were of negligible importance in metagonimiasis in dogs. In the chronologic observations of pathologic process in intestine, it was also suggested that the host immunity tend to recover the intestinal integrity. And early invasion of young worms to the Lieberkuhn's crypt was considered as the primary cause of lesions of villi.