Failure to Immunize the Monkey Against Poliomyelitis by Prolonged Nasopharyngeal Spraying with Live Virus. ∗

In an attempt to explain the protection which a large number of children and the majority of adults enjoy against poliomyelitis it has been generally held that this immunity is acquired by repeated contact with subinfectious amounts of the active virus. It has also been suggested that this process of latent immunization is accomplished by small doses of virus entering the body through the upper respiratory tract. We have undertaken to verify experimentally the soundness of this hypothesis.

Four rhesus monkeys were subjected to extensive spraying of the nose and throat with a 10% emulsion of live poliomyelitis virus during a period of about 2 1/2 months. The treatments were given twice a week, so that each monkey received 20 sprays in all. The amount of virus consumed for each spray was approximately 1 cc. per monkey. At the end of the immunization period one of the 4 treated monkeys had died from extensive visceral tuberculosis; the autopsy showed a perfectly normal cord and histological examination revealed no lesions of poliomyelitis. From each one of the 3 remaining animals a sample of blood was obtained after a rest period of about one month following the last spray. These monkeys at the same time were inoculated intracerebrally with 1 cc. of a 10% virus emulsion to test for immunity, one normal control accompanying this test. All 3 treated monkeys developed typical poliomyelitis together with the control. Inasmuch as it has been suggested that the intracerebral inoculation is too severe a test to determine slight degrees of immunity, we have examined the sera of these 3 monkeys in the customary manner for the presence of virucidal substances. Equal quantities of serum and of 1% virus emulsion, 0.5 cc. in each case, were mixed, incubated for 2 hours at 37°C, left in the icebox overnight and the mixture, 1 cc., was then injected intracerebrally into a monkey; one control animal received a similarly prepared mixture of virus and salt solution.