Ecological and immunological interactions in antigenically related flavivirus: St. Louis Encephalitis and West Nile

LUIS ADRIÁN DIAZ

Buenos Aires

Simposio; III International Clinical Virology Symposium and Advances in Vaccine; 2010

Centro de Educación Médica e Investigaciones Clínicas

St. Louis encephalitis virus (SLEV, Flavivirus, Flaviviridae) is a re-emerging mosquito-borne pathogen in South America, with human encephalitis cases reported in Argentina and Brazil. In Argentina, this virus is mainly maintained in central area by transmission cycles between Culexquinquefasciatusmosquito and doves species (Columbina picui -Picui Ground Dove- and Zenaida auriculata -Eared Dove-). West Nile virus (WNV; genus Flavivirus; family Flaviviridae) has been rapidly dispersing through the Americas since its introduction in 1999 in New York. In South America it has been detected in Argentina, Colombia, Trinidad and Venezuela. Its eco-epidemiological characteristics are still unknown since its recently introduction in the subcontinent. In a seroepidemiological study carried out in free ranging birds collected in 3 sites (Mar Chiquita -Córdoba Province, Monte Alto -Chaco Province and San Miguel de Tucumán -Tucumán Province) shows the authoctonous activity for both SLEV and WNV, even more they overlaped spatio-temporal patterns. Several bird species belonging to families Cardinalidae, Columbidae, Dendrocolaptidae, Emberizidae, Furnariidae, Icteridae, Troglodytidae and Turdidae were detected infected with both viruses.Experimental studies indicate that Picui Ground Doves developed higher viremias enough to infected Culex quinquefasciatus mosquitoes, indicating their possible role as amplifying host for both SLEV and WNV. However, Bay-winged and Shiny Cowbirds are not able to amplify those viruses.House sparrows infected with the SLEV epidemic strain (CbaAr-4005) when pre-existing flavivirus-reactive antibodies were present developed higher viremias than other with no pre-existing flavivirus-reactive antibodies (mean peak titer was ≥ 107.1 PFU/mL vs. 105.3 PFU/mL). This preliminary results suggests antibody-dependent enhancement may increase the risk of avian-amplified transmission of SLEV in the presence of previous antigenically related flavivirus (i.e. WNV). The appearance of WNV in central Argentina shortly before an unprecedented encephalitis epidemic caused by SLEV may be no coincidence, but potentially the consequence of the same antibody-dependent enhancement that were observed in this study.<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } -->