Protection of weanling hamsters from experimental infection with wild‐type parainfluenza virus type 3 (para 3) by cold‐adapted mutants of para 3

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Abstract
Parainfluenza virus type 3 (para 3) was adapted to replicate at 20° C, a nonpermissive temperature for wild-type (wt) para 3. Serial passage at 20° C resulted in the generation of cold-adapted (ca) and temperature-sensitive (ts) mutants. These mutant viruses have been characterized both in vitro and in vivo [Belshe and Hissom (1982): Journal of Medical Virology 10:235–242; Crookshanks and Belshe (1984): Journal of Medical Virology 13:243–249]. We now report the evaluation of three mutants (clone 1150, passaged 12 times in the cold [cp12], clone 1146, passaged 18 times in the cold [cp18], and clone 1328, passaged 45 times in the cold [cp45]) for their ability to protect hamsters from infection by wild-type para 3. Ether-anesthetized male syrian hamsters were intranasally vaccinated with either wt para 3 (clone 127) or one of the ca para 3 mutants and on day 28 postvaccination; each animal was intranasally challenged with 105.0 pfu of wt para 3. On days 1, 2, 3, and 4 post-challenge, 4 to 13 hamsters from each group were sacrificed, and the quantity of para 3 in the nasal turbinates and lungs was determined. Wt virus induced protection from challenge. cp12, cp18, and cp45 reduced the peak titer of wt replication in the lungs by > 100-fold, tenfold, and tenfold, respectively. The duration of virus replication was shortened also by intranasal vaccination with the mutants. These data give evidence of an inverse relationship between the degree of protection induced by vaccination with coldadapted mutants and the number of passages of the virus in the cold.