The Journal of Medical Microbiology, Vol 13, Issue 2 297-306, Copyright © 1980 by Society for General Microbiology
Influenza virus infection of newborn rats: virulence of recombinant strains prepared from influenza virus strain A/Okuda/57
C. Teh, R. Jennings and C. W. Potter
Infant rats were infected intranasally with wild influenza virus strains,
attenuated strain A/Okuda/57 or recombinants prepared from these parents.
The growth of viruses in the turbinates or lungs, and the ability of virus
infections to potentiate subsequent bacterial infection by Haemophilus
influenzae (HIb) were measured. The two wild strains of virus and a
recombinant strain WRL105, known to be virulent for man, reached titres of
10(5.1)--10(6.5) EBID50/ml in the turbinates of infant rats 48 h after
infections; infection by these viruses was followed by HIb bacteraemia in
77--92% and meningitis in 58--75% of animals. In contrast, virus strains
known to be attenuated for man grew to lower titres in infant-rat
turbinates and promoted a lower incidence of systemic infection by HIb than
the virulent strains. A comparison of the various results of infection of
infant rats with influenza virus strains of known pathogenicity for man
indicated that the subsequent incidence of HIb bacteraemia was the most
discriminating measurement of virus virulence; the range of yields of
attenuated virus in rat turbinates overlapped that of virulent strains.
These results, together with those of previous studies, indicate that the
behaviour of influenza viruses in infant rats is an indication of virus
virulence for man, and could provide a test of virulence that would
facilitate the development of live attenuated virus vaccines for human use.
