Interferon Inducers in Therapy of Infection with Encephalomyocarditis Virus in Mice. II. Effect of Multiple Doses of Polyriboinosinic-Polyribocytidylic Acid on Viral Pathogenesis

These studies were designed to evaluate the therapeutic efficacy of multiple doses of an interferon inducer, polyriboinosinic-polyribocytidylic acid, in encephalomyocarditis virus infection of mice. The results indicated that suppression of a detectable viremia was essential to the successful protection of mice from the lethal consequences of infection. The viremic phase of the infection could be delayed or partially suppressed without protection. The data strongly suggest that once the central nervous system had been seeded and virus replication had begun, inducer therapy was ineffective in altering the outcome of infection. This fact could be attributed in part to the low levels of interferon found in brain tissue after intraperitoneal administration of polyriboinosinic-polyribocytidylic acid. Also, animals that received the most effective regimen of the interferon inducer and that survived the infection were not protected against a second infection with the same virus, an observation suggesting that the incidence of circulating antibody to encephalomyocarditis virus is reduced after the initial infection.