Effect of swine influenza virus on a sulphonphthalein dye

Abstract

WHEN swine influenza virus (Shope) is inoculated into the allantoic cavity of 11-day eggs simultaneously with a dye of the Sulphonphthalein group (thymol blue, bromphenol blue, bromcresol green, bromcresol purple, bromthymol blue, phenol red, cresol red, 0.3 ml. of a 1 per thousand solution), it is found after forty-eight hours that a notable decrease in the colour intensity of the allantoic fluid has occurred as compared with that of the allantoic fluid of eggs inoculated with dye alone. We also found that this change in intensity was much less when the dye was inoculated together with human influenza A. For this experiment we used a W.S. strain, which for years had been cultivated on eggs in this Institute. This is also true of the swine influenza strain used for the first experiment. There was but little difference in the hæmagglutination titres of these strains. With this colour reaction it is possible to differentiate between the two strains. We are as yet unable to explain the cause of the change in colour intensity. A quantity of the dye is discoloured or removed from the allantoic fluid. There is no change in the pH of the allantoic fluid during the development of the virus. ö © 1951 Nature Publishing Group.