St. Louis encephalitis vírus: first isolation from a human in São Paulo state, Brasil

Abstract

This paper reports the isolation of St. Louis encephalitis virus (SLEV) from a febrile human case suspected to be dengue, in São Pedro, São Paulo State. A MAC-ELISA done on the patient's acute and convalescent sera was inconclusive and hemagglutination inhibition test detected IgG antibody for flaviviruses. An indirect immunofluorescent assay done on the C6/36 cell culture inoculated with the acute serum was positive for flaviviruses but negative when tested with dengue monoclonal antibodies. RNA extracted from the infected cell culture supernatant was amplified by RT-PCR in the presence of NS5 universal flavivirus primers and directly sequenced. Results of BLAST search indicated that this sequence shares 93% nucleotide similarity with the sequence of SLEV (strain-MSI.7), confirmed by RT-PCR performed with SLEV specific primers. Since SLEV was identified as the cause of human disease, it is necessary to improve surveillance in order to achieve early detection of this agent in the state of São Paulo and in Brazil. This finding is also an alert to health professionals about the need for more complete clinical and epidemiological investigations of febrile illnesses as in the reported case. SLEV infections can be unrecognized or confused with other ones caused by an arbovirus, such as dengue.

Genetic characterization of St. Louis encephalitis virus isolated from human in São Paulo, Brazil

“…Furthermore, monkeys, armadillos, and marsupials may be vertebrate amplifying hosts (Vasconcelos et al 1998). Regarding to the dynamics of the transmission of SPH 253157 strain isolated in São Paulo, it remains unclear because no virus was isolated either from birds or mosquitoes during the eco-epidemiological studies carried out in that region where the patient was probably infected (Rocco et al 2005).…”

“…Viruses -The SLEV SPH 253157 strain was isolated from acute phase-serum specimen of a patient in monolayer cultures of clone C6/36 cells of Aedes albopictus (Rocco et al 2005). Viral strains, locations, years of isolation, and GenBank accession numbers of the E sequences utilized in the phylogenetic analyses are listed in Table I.…”

“…Epidemiologic data about the SLEV case was fully detailed by Rocco et al (2005). Briefly, a patient, suffering from severe uncharacterized febrile illness without neurological involvement, was hospitalized as a probable case of dengue fever.…”

“…Serological tests detected antibodies to flavivirus but were negative in tests specific for Dengue virus (DENV). The virus was isolated in cells culture inoculated with patient acute phase serum and identified by reverse-transcription-polymerase chain reaction (RT- PCR) and sequencing (Rocco et al 2005). SPH 253157 is the first strain of SLEV isolated from human reported in the state of São Paulo and the third one in Brazil.…”

Management of acute viral encephalitis in Brazil

“…The complete genomic characterization of this virus isolated from a fatal case was recently published [34]. Three cases of Saint Louis encephalitis were also described in Brazil [35][36][37].…”