Abstract
We isolated and characterized St. Louis encephalitis virus (SLEV) from cloacal swabs of naturally exposed adult sentinel chickens in 2006. Phylogenetic analysis of SLEV strains isolated in Florida indicated that Brazilian SLEV circulated in 1972 and 2006; lineages were VA and VB.
Highlights
St. Louis encephalitis virus (SLEV) seroconversion rates declined after the 2001 introduction of West Nile virus (WNV) despite continued surveillance, and an increased number, of susceptible birds located in regions historically at risk for SLEV enzootic transmission
Experimental evidence suggests that WNV cross-protective immunity in wild bird species may limit subsequent SLEV infections (3)
Sequence analysis of reference strains and the 2006 SLEV isolates has shown the circulation of genotype V SLEV strains in Florida
Summary
We isolated and characterized St. Louis encephalitis virus (SLEV) from cloacal swabs of naturally exposed adult sentinel chickens in 2006. In central and south Florida, 5 partner agencies targeted a subset (n = 15) of sentinel chicken sites with recent confirmed arbovirus transmission activity for cloacal swab collection from 95 chickens. SLEV seroconversion rates declined after the 2001 introduction of WNV despite continued surveillance, and an increased number, of susceptible birds located in regions historically at risk for SLEV enzootic transmission. The phylogenetic tree places FL06-S569 and FL06S650 into genotype VA (online Appendix Figure, available from www.cdc.gov/EID/content/15/4/604-appF.htm) This analysis further supports classification of SLEV into 7 lineages and 13 clades (IA-IB, IIA-IIE, III, IV, VA-VB, VI, VII), as previously suggested (9). Envelope sequence analysis demonstrated that strains isolated during 1989 and 1990 shared 98% homology with USA (V 2380-42), Guatemala (78A28), Tennessee (TNM 4-711), or Texas strains (83V4953, PVI-2419, 98V3181)
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