Viral Encephalitis of Equities and Domestic Ruminants in the Near East—Part II

Abstract

Virus was isolated from the sera of 2 recovered horses, and from one recovered and one exposed donkey, 6 weeks to 6 months after recovery from, or exposure to, natural infection. One donkey out of 3 inoculated intracerebrally with 2 rabbit-passaged strains of equine origin reacted mildly after 47 days. Two donkeys out of 3 inoculated with 2 rabbit-passaged avian strains of virus reacted after 39 and 49 days. The latter reaction was severe, with lameness and inco-ordination. The animal recovered, but relapsed 173 days after inoculation and finally died a month later, after showing severe unilateral conjunctivitis and facial paralysis. All 6 donkeys showed viraemia between 36 and 50 days after inoculation. The production of fatal encephalitis in a donkey by intracerebral inoculation of an avian strain strongly suggests an aetiological relationship between the equine disease and strains of virus isolated from wild birds. Of 2 caprine strains of virus, one appeared by complement-fixation to be identical with one equine and 2 ovine strains. The second caprine strain, inoculated intracerebrally, killed a donkey with characteristic histopathological lesions. After 3 tissue-culture passages this strain infected a sheep by multiple intradermal inoculation, causing death, 41 days after inoculation, with characteristic lesions of encephalitis. Three strains of Near East equine encephalitis (NEEE) virus were cultivated with the production of cytopathic effect (CPE), cither in primary lamb-testicle cells or in the MS line of monkey-kidney cells. Rabbits and a sheep were infected with these cultures. A Borna (Württemberg) strain was cultivated in the MS cell line with similar CPE, and it was possible to produce fatal encephalitis in a donkey and a sheep by intracerebral inoculation of a second tissue culture passage of this strain. The cytopathic effect of the strains on the MS line of monkey-kidney cells has certain characteristic features. The changes induced by Borna virus strains are indistinguishable from those caused by Near Eastern strains. In the form of extracts, homogenized with Freon or Arcton 112 or 113, a Near Eastern strain was twice filtered through Gradocol membranes of A. P.D. 20 mμ. Four German strains of Borna virus were also filtered through 20 mμ membranes of the same batches. Clearly the infective particle of Borna virus is not as large as was thought by earlier workers, and it is impossible to distinguish between Borna and NEEE by filtration results. A few rabbits were successfully immunized by repeated intravenous inoculations of live virus; in 2 instances the viruses were Near Eastern strains, and in another the Borna V strain. Intranuclear inclusions, indistinguishable from the Joest-Degen corpuscles of Borna disease, have now been identified in the neurons of rabbits inoculated with all current strains of NEEE virus, whether of equine, caprine, avian or arthropod origin. As far as the characterization of these virus strains has been taken, no differences are apparent that would justify preserving a distinction between NEEE strains and Borna virus. Accordingly, it is proposed that NEEE should be regarded as a synonym of Borna disease, unless fresh evidence is adduced to warrant a separation.