TABLE 1.

Phenotypic properties of mutant viruses derived from the WNV NY99ic

Virusa	Plaque sizeb	Temp sensitivity (log10 no. of PFU/ml)			Mouse neuroinvasiveness
		37.0°C	41.0°C	Δc	i.p. LD50 (PFU)	AST ± SDd
NY99 (wt virus)	lp	8.1	7.6	0.5	0.8	8.0 ± 1.2
NY99ic	lp	7.0	7.3	0.3	1.0	7.2 ± 0.6
Bird 1153 (wt virus)	sp	7.7	4.8	2.9†	>10,000e	NA
NS4B-E249G mutant	lp	6.2	6.0	0.2	1.2	7.5 ± 0.4
prM-V156I mutant	lp	5.9	6.1	0.2	0.7	8.6 ± 1.4
NS5-A804V mutant	mp	6.3	5.5	0.8	5	8.0 ± 0.5
3′UTRB mutant	lp	6.4	5.0	1.4*	0.6	8.8 ± 2.0
prM-V156I + NS4B-E249G mutant	lp	7.0	7.2	0.2	1.4	8.8 ± 1.5
prM-V156I + 3′UTRB mutant	lp	6.6	5.1	1.5*	4.2	9.0 ± 1.0
NS4B-E249G + 3′UTRB mutant	sp	6.7	3.9	2.8†	>10,000e	NA
NS4B-E249G + NS5-A804V mutant	sp	6.2	6.4	0.2	2,000e	9.2 ± 1.2
NS5-A804V + 3′UTRB mutant	mp	5.4	4.2	1.2*	>10,000e	NA

^aThe wt NY99 and Bird 1153 WNV isolates are indicated. The remaining mutant-virus designations indicate each Bird 1153 virus-specific locus incorporated into the NY99ic viral background.

^bPlaque sizes were as follows: sp were <1.0 mm, lp were >3.0 mm, and mp were 1 to 3 mm in Vero cells.

^cΔ indicates the difference between average virus titers at 37.0°C and 41.0°C (triplicate experiments) at 72 h postinfection in Vero cells. † indicates a P of <0.001 in a comparison of the viral titer at 41.0°C versus that at 37.0°C, with experiments performed in triplicate. * indicates a P of <0.05 in a comparison of the viral titer at 41.0°C versus that at 37.0°C, with experiments performed in triplicate.

^dAST, average survival time ± standard deviation following intraperitoneal inoculation of virus. NA, not applicable, as no mice died following inoculation.

^eAttenuated for mouse neuroinvasiveness.