Thermal, hematological, and serological responses of weanling horses following inoculation with equine abortion virus: its similarity to equine influenza.

Abstract: Manninger and Csontos reported that mares inoculated with equine abortion virus developed a transient fever 2 to 4 days after pharyngeal or intravenous inoculation and that an uninoculated horse in contact with the experimentally inoculated mares contracted a febrile disease resembling equine influenza. Also, mares that had aborted virus-infected fetuses were resistant to inoculation with equine influenza virus. From these observations, they proposed that virus abortions were a manifestation of infection of pregnant mares by the equine influenza virus. In reports on equine virus abortions, Kress recorded the occurrence of bronchopneumonia among horses in contact with mares that aborted and involvement of the respiratory tract of the aborted fetuses. From these observations it was thought that the disease was caused by a pneumotropic virus and that the equine influenza virus might have been the cause of the abortions. In an investigation of the relation of equine virus abortion to equine influenza, Manninger found that mares which were inoculated into the pharynx or intravenously with infected equine fetal tissue suspensions developed a hyperthermia and catarrhal symptoms which resembled equine influenza. Also, he found that mares which had recently aborted virus-infected fetuses were resistant to inoculation with equine influenza virus and that horses which had recently recovered from equine influenza were resistant to inoculation with the equine abortion virus. Interpretation of the cross-protection trials was based on the absence of febrile reactions and symptoms of respiratory catarrh. Hansen and Holst reported the occurrence of virus abortions which were preceded by an outbreak of respiratory disease with clinical manifestations of equine influenza. In view of Manninger's observations, they considered the abortions to be a sequel of the influenza infection. The study reported here was undertaken to determine whether an equine abortion virus, strain Kentucky-B, would induce the sypmtomatic response of equine influenza infection in young horses and to characterize the complement-fixation antibody response to intravenous and intranasal inoculation.