Abstract
The principal aim of this study was to compare a number of in vitro and in vivo systems, to establish the most suitable methods for detecting and quantitating anti-influenzal activity, and with these methods to compare the activity of different compounds. Eight strains of virus, two from each of the 4 sub-types, were used. For in vitro work two primary cell lines, chick embryo and calf kidney cells, and the allantois-on-shell system (AOS) were compared. Antiviral activity was assessed by yield reduction determination under either single or multiple cycle conditions, and by plaque inhibition and reduction tests. Chick tracheal organ cultures were also used on a limited basis to detect activity. For in vivo work mice were used, with activity determined by reductions in virus content of the lungs of infected mice, the results of which were compared with those of mortality tests. The effect of mouse lung passage history of virus on the results was also examined. The three in vitro systems used all proved satisfactory, with the AOS system the easiest to prepare. Plaque inhibition and reduction tests proved useful for detecting and quantitating activity, although single cycle tests were more suitable for comparing the sensitivity of different strains and the results obtained with different cultures. Multiple cycle tests gave rather variable results. In vivo the titrations of the virus content of lungs proved satisfactory for detecting and quantitating activity, and good agreement was obtained with mortality tests. With mouse lung passage history variation in results occurred, and highly adapted strains were found to be most suitable for comparative work. A total of 60 compounds were examined for activity, out of which only amantadine hydrochloride and Ribavirin proved sufficiently active for further work. The activity of amantadine hydrochloride varied in different systems and with different strains of virus. With Ribavirin minor variations occurred between systems, but all 8 strains examined were similar in sensitivity. Overall it was impossible to say which compound was more active, but the differences in activity between the two compounds were generally not great.