Persistence of Influenza Virus in Different Biological Systems and its Possible Implications

The results of a study into the persistence of influenza virus, pursued by these authors since 1969 at the Gamaleya Institute of Epidemiology and Microbiology, USSR Academic of Medical Sciences, are briefly outlined. The first stage of these experiments indicated the possibility of producing and continuously maintaining a latent influenzal infection in cell cultures previously considered insusceptible to influenza viruses. It was demonstrated that the latent viral persistence mechanism in such systems is conditioned by the disturbed assembly of viral ribonucleo-protein (RNP). A consistent pattern has been recognized, according to which either an acute or latent influenzal infection may be produced within the same “influenza virus-L 929 cells” system depending on the ratio of defective to standard particles in the infecting viral preparation and on the multiplicity of inoculation. At the second experimental stage, a combined strategy was devised to demonstrate that the persistence of influenza virus in mammals may result from all known natural ways of its introduction: (1) recovery from the disease; (2) immunization with living virus; and (3) by vertical (mother-fetus) virus transmission. If the first two ways lead to a latent infection, the third route not infrequently gives rise to a slowly developing influenza infection in the progeny characterized by an unusually long incubation period, a slowly progressive course, peculiar damage to organs and tissues, and a fatal outcome.