Studies on respiratory diseases of pigs: III.—Persistence of Influenza Viruses in the Respiratory Tract

Abstract

Summary Chick embryos, 13 to 14 days old, have been shown to be very susceptible to infection with the virus of swine influenza when inoculated into the amniotic cavity. Such inoculation was found to be a more sensitive method of detecting the C.1. strain in pigs' lungs and nasal washings than inoculation of pigs, ferrets or mice. Experiments to ascertain the persistence of swine influenza virus in pigs have shown that a mouse adapted strain (C.1.) could be detected in nasal washings and lung suspensions of pigs only up to a week after inoculation. These results were obtained both when a clinical or a subclinical disease was produced by the virus alone, or when bacteria were mixed with a small inoculum of virus. A small experiment in mice gave similar results. A mild disease was set up in pigs by the inoculation of a recently isolated strain of human influenza A. The virus was recovered from a pig killed on the 7th day, but not from pigs killed on the 28th day and thereafter.