Cross Immunization Experiments with the Poliomyelitis Virus and that of Encephalomyelitis in Horses

Abstract

During the summer and fall of 1930 and 1931, an epizootic of an acute encephalomyelitis broke out among the horses and mules in the rural districts of California. 1 Meyer, Haring and Howitt 2 report the recovery of a filterable virus as the causative agent and describe hemorrhage, oedema and acute inflammatory lesions in the brain with slight involvement of the cord. Since there were certain similarities between the equine malady and human poliomyelitis and since outbreaks of both forms chanced to occur simultaneously during 1930 in California, a series of cross immunization experiments were undertaken with both viruses.

Serum was obtained from each of 11 monkeys that had recovered from experimental poliomyelitis, either entirely or with muscular atrophy of certain extremities. According to previous tests these serums neutralized the poliomyelitis virus in vitro. Equal parts of the encephalomyelitis virus (20% brain suspension diluted 1 to 25 with saline) and the undiluted serums were mixed, incubated 2 hours at 37°C. and held in the icebox over night. 0.3 cc. of each mixture was then injected intracerebrally into a series of guinea pigs, 2 for each serum. Control animals were also inoculated with the same amounts of normal monkey serum and 1 to 25 virus. Temperatures were taken daily. All of the animals showed a typical rise in temperature followed by symptoms of the disease. Prostration and death occurred after 4 or 5 days, showing a complete absence of neutralization.

The serums of 4 rabbits and of one monkey recovered from encephalomyelitis neutralized the latter virus in vitro. Each serum was used in a second series of in vitro neutralization tests, prepared with the poliomyelitis virus in the proportion of 1 cc. of serum to 0.3 cc. of 5% virus.