Passage of yellow fever virus: its effect on infection and transmission rates in Aedes aegypti.

The effect of successive lytic passage of yellow fever virus on mosquito infection and transmission rates in the vector, Aedes aegypti, was determined. Three strains of yellow fever virus from Trinidad and Peru were passaged five times in suckling mouse brains and seven times in BHK-21 cells. Mosquitoes were fed meals containing passaged and unpassaged viruses and infection and transmission rates were compared. Rates were similar for all but one of the three virus strains grown in both substrates with the exception of virus strain 1899/81 (human isolate from Peru) passaged seven times in BHK-21 cells. Infection rates declined from 62% (109/177) to 35% (61/176), and transmission rates declined from 64% (60/94) to 45% (22/49). The oligonucleotide fingerprint of strain 1899/81 passaged seven times in BHK-21 cells shared 98% (45/46) of its large, T1-resistant oligonucleotides with the parent strain, indicating limited biochemical differences. The data suggest that uncloned yellow fever virus populations, passaged a limited number of times, and exhibiting some phenotypic changes, are representative of the original virus strain and can be used with a reasonable degree of confidence in vector competence studies.