タヌキの肺吸虫症の1例 : 肺および付属リンパ節の病理学的所見

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　わが国の野獣のうち, イタチの肺吸虫感染は比較的多く報告されているが, タヌキのそれは至って少ない. われわれは1971～73年,宮崎県下で捕獲したタヌキ16頭を剖検し, うち1頭に大平肺吸虫の感染を認めた. 供試タヌキは右肺に8コ, 左肺に5コ, 計13コの虫嚢を有する重症例であり,各虫嚢には2匹または1匹ずつの虫体寄生を認めたが, なかには虫体が虫嚢外に脱出するものもあった. 虫嚢並びに周囲肺組織の病変は,先人により述べられている肺吸虫症の一般的病理所見にほぼ一致するが,本例では病変部の増殖性変化(すなわち結合織増殖)がすこぶる顕著であり,他面,侵入直後の虫体による出血巣も認められ,新旧病変の混在型である. 　本例では,付属リンパ節のうち右気管気管支リンパ節に,肺吸虫の幼若型と思われる小型虫の侵入を所見した.人体では脳その他諸器官に肺吸虫の異所寄生例が少なくないが,動物では著者の一人･波部の報告(イヌの気管支肺リンパ節)以外にあまり聞かない.従って, その意味からも本例は興味深い症例といえよう.In 1973, parasitization with Paragonimus ohirai was observed in a racoon-dog, Nyctereutes procyonoides viverrinus, caught in Miyazaki Prefecture. The lung and its lymph nodes were examined pathologically with the following findings. 1) The number of worm-cysts was eight in the right lung (three in the apical, two in the cardiac, and three in the diaphragmatic lobe) and five in the left lung (one in the apical and four in the diaphragmatic lobe), being thirteen in all. Each worm-cyst contained one or two flukes. Some flukes escaped from the worm-cyst and penetrated the surrounding tissue. Interstitial tissue proliferation was marked and connective tissue foci were formed distinctly around the worm-cyst. In the former, connective tissue proliferated in the walls of wormcysts and affected bronchi and extended to the interstitial tissue. The latter were produced by the organization of foci caused by migratory flukes. Both changes led to mild fibrosis. On the other hand, hemorrhagic foci were observed to have been formed by flukes under the pulmonary pleura immediately after penetration. In brief, new and stale lesions mixed with one another in the lung examined. 2) Microscopically, the wall of the worm-cyst was divided into two layers, an internal and an external. The background of the internal layer was granulation tissue characterized by a marked infiltration with lymphocytes, plasma cells, and histiocytes. The external layer was composed of a little stale connective tissue and infiltrated with a small number of lymphocytes and plasma cells. Infiltration with eosinophils was hardly noticed in both layers. In addition to fibrosis, such changes as atelectasis, pulmonary emphysema, and catarrhal pneumonia were shown around the worm-cyst. They were accompanied by mild hemorrhage and cell infiltration (eosinophils were very few in this case) . The bronchi were almost always affected (bronchitis and peribronchitis). In many arteries and veins, vascular walls were thickened and luminal deformity and stenosis obvious. 3) Fluke eggs were deposited not only in the worm-cyst but also in the wall of cyst, alveolus, alveolar wall, bronchial duct, pulmonary pleura, interstitial tissue, and focus of connective tissue proliferation. When the pattern of egg deposition was examined, eggs were deposited singly or in clumps of several eggs each, a relatively large number of eggs were scattered diffusely within a limited extent, and an extremely large number of eggs pushed aside part of the pulmonary tissue to form a focus of accumulation restrictedly. In a little cases, however, a typical nodule or granuloma was caused by fluke eggs. On the other hand, the foci of egg accumulation presented the same characters as those observed by the authors in the dog, although they were smaller in size (rice grain size) than the foci in the dog. 4) Of the lymph nodes attached to the lung, the right tracheobronchial lymph node was found to harbor fluke immediately beneath the capsule (or in the subcapsular sinus). Under the microscope was observed only the cut surface of the end of the fluke body, which was very small in size (155×75μ). Consequently, it was impossible to tell to what species this fluke belonged. The fluke may have been a juvenile type of Paragonimus. Around the fluke body was already formed a structure looking like the worm-cyst. It has been reported that the heterotonic parasitism of Paragonimus was noticed in the brain and other organs in human beings. Habe found such parasitism in the bronchopulmomary lymph node of a dog. There are few other papers dealing with the heterotonic parasitism in the field of veterinary medicine. In the present study, the right tracheobronchial lymph node exhibited a very conspicuous proliferative change, which seemed to have been induced by the organization of lesions caused by migratory flukes.

著者

芦沢広三
宮崎大学農学部家畜病理学教室

タヌキの肺吸虫症の1例 : 肺および付属リンパ節の病理学的所見

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