Study On The Pathology Of Metagonimiasis In Experimentally Infected Cat Intestine

To study the basic pathological changes of small intestine in metagonimiasis, light- and electron microscopic studies were made, using a total of 21 cats which were experimentally infected with metacercariae of Metagonimus yokogawai. The metacercariae were obtained from naturally infected sweetfish (Plecoglossus altivelis) by digestion technique. The cats were divided in control, light-infection(10,000 metacercariae infected) and heavy-infection(50,000 metacercariae infected) groups. Cats were killed at the 5th, 10th, 15th day, and 4th, 8th and 10th week after the infection. And the small intestine was prepared for the study. Pathological studies comprised gross examination, worm distribution pattern, light microscopic examination and both transmission and scanning electron microscopic examinations. The results obtained were summarized as follows. 1. Gross morphologic changes were the most marked during the first 2 weeks after infection. The gross abnormalities were severer in the heavily infected animals. The changes were dryness and listlessness of serosal surface due to dehydration, mushy and/or watery intestinal content, effacement of transverse nodes and enlargement of mesenteric lymph folds and Peyer's patches. After 4 weeks of infection, these changes became less marked showing a tendency to return to normal. 2. The sectioned flukes were distributed from duodenum to proximal ileum. However, individual variation was marked in distribution. In the heavy-infection group, the locality of parasitism tended to extend more distally. 3. The locality of M. yokogawai in the intervillous space was mostly in the lower-most portion of intervillous space, where they compressed and eroded epithelial cells probably due to mechanical damage to the structure. Very rarely the worms were found in lumen of Lierberkuehn's crypt, and reaching, in two occasions, into proprial lymphoid tissue. 4. Light-microscopically the lesion was restricted in mucosa: Early mucosal changes were shortening, blunting, fusion, and thickening of the villi, crypt hypertrophy with consequent decrease of villus/crypt ratio, as well as stromal changes of edema, capilliary ectasia and marked inflammatory cell infiltration of lymphocytes and plasma cells. Goblet cells were markedly reduced in number as with depletion of its cytoplasmic content. In the later stages of infection, mucosa restored its normal configuration in spite of persistent parasitism of the worms. 5. At the infection stage of 5-15 days, there was significant shortening of the microvillous height with varible destruction of glycocalyx in electron microscopic examination. With lapse of infection time, microvilli became to restore the normal pattern. With these morphological changes, it appears that diarrhea in experimental metagonimiasis would be related to the decrease of absorptive surface of the small intestine particularly in the early phase of infection. The significant changes seen in villi and microvilli might be due to massive intrusion or invasion of Metagonimus worms into the crypts, causing direct mechanical and possible host-immune response to the small bowel mucosa.