馬鼻肺炎ウイルスによる馬の異常産

Abstract

Abortion, stillbirth and neonatal death occurred in 5 of 8 pregnant mares in March and April on a ranch in Tochigi Prefecture, where 43 horses have been raised. The conditions were observed in the 9th through the 11 th months of pregnancy without premonitory symptoms.Two of 5 aborted fetuses were examined for diagnosis. Pathological changes observed were common to the 2 cases. Grossly, the lungs were highly congested and edematous. Hemorrhage was present in the spleen, kidneys, heart, oral and intestinal mucous membranes. The brain, liver and lymph nodes were congested. Microscopic changes in the lungs consisted of swelling, cytoplasmic vacuolation and formation of acidophilic or basophilic type A intranuclear inclusions in the bronchoalveolar epithelium. Cellular and serous exudation, as well as hemorrhage, were also observed in alveoli and interlobular tissue of the lungs. In the brain, there were perivascular cuffings, and nodular and diffuse microgliosis. The liver exhibited congestion, hemorrhage, cellular infiltration in acini, portal triads and interlobular septa.No significant pathogenic bacteria could be demonstrated in any of the fetuses examined. Equine rhinopneumonitis virus was isolated from the lung and lymph nodes of one case, and from the brain, lung, trachea, liver and intestine of the other case. Antibody titers determined by the virus-neutralization test conducted on serum samples collected at terminal stage of the epizootic were 1: 64 to 1: 256 for 10 brood mares and 1: 16 to 1: 256 for 15 rearing horses.From the results of these examinations, these abnormal parturitions were interpreted to have been caused by equine rhinopneumonitis virus.