Enhancement of virulence of Naegleria fowleri by growth in Vero-cell cultures.

The virulence of Naegleria fowleri for mice decreases with prolonged maintenance in axenic culture. Would the virulence be affected if amebas were grown in African green-monkey kidney (Vero)-cell cultures rather than in axenic culture? The weakly virulent LEE strain of N. fowleri was cultivated with Vero cells for 6 mo and tested in mice for changes in virulence. We found that continuous growth in Vero-cell cultures enhanced the virulence of the LEE strain and we propose that, as an alternative to serial passage in mice, the virulence of weakly virulent strains of N. fowleri may be enhanced by maintenance in Vero-cell cultures.