新型節足動物媒介ウイルス感染症を示唆する子牛の先天性異常

A congenital abnormality of calves, suggestive of a new type of arthropod-borne virus infection.

• Y Kitano
• S Yamashita
• K Makinoda

抄録

鹿児島県では1990年10月から1991年10月にかけて約1000頭の先天性疾患の子牛が生まれ、流行のピークは1991年3月と7月であった。病理学的・血清学的に検査された85頭の異常子牛のうち、70頭がウイルス性疾患に罹患していたと考えられた。そのうち17頭に赤羽、中山、愛野、青竜、牛ウイルス性下痢粘膜疾患ウイルスに類似した病変が認められたが、血清中にはこれらのウイルスや感染性牛鼻気管炎ウイルスに対する抗体は認められなかった。このことから、南日本では新しいタイプのウイルス感染症が発生していることが示唆された。17頭の子牛のうち6頭は死亡し、他の子牛は脱力、吸啜困難、起立不能、めまい、眼瞼下垂、ふらつき、弱視、失明などの臨床症状を呈した。これらの症例は体が小さく、ドーム型頭部、脊柱管狭窄症、関節症、上顎後退、陥没眼、白内障、歯の不規則性や欠損を呈していました。剖検ではほぼ全例に水脳症が認められ、多くは脳の欠損と小脳低形成・閉塞を呈していた。そのうち2例は脳幹の低形成欠損を認めた。罹患臓器の病理組織学的検査では，グリア症，脳室の拡張に伴う大脳実質の喪失，リンパ球や血漿細胞などの丸い細胞による血管周囲塞栓，血管の増殖，脳幹の厚肉血管，中脳水道管の拡張，小脳皮質異形成，脊髄腹角の神経細胞の減少，骨格筋の筋異形成などが認められた．

About 1000 calves with a congenital disease were born in Kagoshima prefecture, Japan, between October 1990 and October 1991, the peaks of the epidemic being in March and July 1991. Of 85 abnormal calves examined pathologically and serologically, 70 appeared to have been suffering from a viral disease. Of these 70 animals, 17 had lesions bearing some resemblance to those of the diseases produced by Akabane, Chuzan, Aino, bluetongue and bovine viral diarrhoea-mucosal disease viruses-diseases known to occur in Kagoshima-but serum samples contained no antibodies to these viruses or to infectious bovine rhinotracheitis virus. This suggested the occurrence of a new type of viral infection in southern Japan. Six of the 17 calves were born dead and the others manifested clinical signs such as weakness, difficulty in sucking, inability to stand, vertigo, opisthotonus, staggering and weak eyesight or blindness. They were of small size and showed domed head, scoliosis, arthrogryposis, maxillary retraction, sunken eye, cataracts, and irregularities and defects of the teeth. At necropsy, almost all cases showed hydranencephaly, and many had cerebral defects and cerebellar hypoplasia or agenesis. Both cerebral and cerebellar lesions were seen in six cases, two of which showed a hypoplastic defect of the brain stem. Histopathological examination of the affected organs revealed gliosis, loss of cerebral parenchyma resulting from dilation of the ventricles, perivascular cuffing with round cells such as lymphocytes and plasma cells, proliferation of blood vessels, thick-walled blood vessels in the brain stem, dilation of mesencephalic aqueducts, cerebellar cortical dysplasia, decreased nerve cells in the ventral horn of the spinal cord, and myodysplasia of skeletal muscle.