[Dengue virus serotype 2 strains isolated from the epidemic occurred in Santiago de Cuba in 1997].

Introduction: during the Cuban epidemic that occurred in Santiago de Cuba in 1997, there was observed increasing severity in the course of time, in terms of proportion of serious dengue haemorrhagic cases and deaths that could be due to the emergence of escape mutants to neutralization with greater virulent potential.

Objective: to study some biological attributes of a group of strains isolated at different points of time during the Santiago de Cuba epidemic in 1997.

Methods: nine DENV-2 strains were studied. The cytopathogenic effect, the viral growth in C6/36 HT and VERO cell lines, the virus plaque sizes, the sensitivity to temperatures, the neurovirulence in newborn mice and the influence of the pH in the union of the virus to the cell as well as in the multiplication medium were all evaluated.

Results: the strains isolated at the end of the epidemic differed from those of the beginning showing increased neurovirulence in newborn mice and higher viral titers and greater cytopathogenic effect in HT C6/36 cells. On the other hand, the virus and the cell union was favored by acid pH when testing strains from the beginning of the epidemic, whereas this union was favored by the basic PH in the strains isolated at the end of the epidemic

Conclusions: the present study managed to show that in addition to the previously observed genotypical changes, there were phenotypical differences among the strains isolated at different points of time in the epidemic; all these aspects may be associated with differences in the viral fitness and/or in the virulent potential of these strains.