Within 48 hours after simple oropharyngeal exposures of cynomolgus monkeys to poliomyelitis virus, histological signs of infection were found in ganglia supplying the exposed mucous membranes. At 3 days, virus was found in the Gasserian, petrosal-nodose, and superior cervical sympathetic ganglia. Lesions were most extensive and severe in the Gasserian. Virus continued to be detected daily from the 3rd to the 8th day, inclusive, in the Gasserian but not on the 9th; from the 3rd to the 6th day, inclusive, in the petrosal-nodose but not on the 7th, 8th, or 9th; on the 3rd and 6th days only, in the superior cervical sympathetic; and on the 5th day only, in the celiac.
In all the ganglia examined, the histological signs of infection increased to a maximum on the 5th day, and thereafter declined. In the sympathetic ganglia, a secondary late increase was observed on the 7th day.
During the first 7 days, no signs of infection were found in the CNS in 84 per cent of the animals examined, and in the remainder such lesions as were found were probably not significant. In control animals permitted to survive, the median period before the onset of symptoms of poliomyelitis, when these occurred, was 9 days (range 7 to 16 days), and in the animals with symptoms typical extensive lesions were found in the CNS. In two control animals failing to show symptoms and sacrificed at 26 and 30 days respectively, histological signs of infection were present in the Gasserian and other ganglia but none in the CNS.