The growth cycle of influenza viruses as studied in touch preparations of the allantoic layer of chick embryos. 4. The growth cycle of influenza B virus: presence of basophilic inclusions in cytoplasm of CAM epithelial cells.

The infectious cycle of Influenza B virus occurring at the allantoic layer of embryonated eggs has been studied by means of cytological and immunofluorescence techniques utilizing touch preparations. The infectious cycle of the virus resembles closely that of Influenza A virus. Influenza B virus, regardless of the dose inoculated, affected the strata of the allantoic layer to a different extent. It totally destroyed the surface stratum (major growth cycle) in about 20 hours time when a 10(8) ID50 dose was inoculated and within 38 hours with a 10 ID50 dose. In the deep stratum, which remained denuded after the destruction of the surface one, most cells (90%) showed normal appearance and a small proportion (about 10%) appeared to be infected. This condition of a minor growth cycle of infection lasted till death of the embryos which occurred within 3--4 days as a maximum. At advanced stages of infection ulcerations (loss of epithelium) appeared which at no time were observed in a Influenza A virus infection.