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

Abstract

(Calisher et al. 1989). The genome of flaviviruses contains a single-stranded positive sense RNA, about 10,800 nucleotides long that encodes 10 distinct proteins in a single reading frame (Chambers et al. 1990). SLEV is the etiologic agent of St. Louis encephalitis, a disease of epidemiological importance in North America. This virus was first isolated in the United States of America (US) in 1933, during an outbreak, which occurred in St. Louis and Kansas City, Mo. (Muckenfuss et al. 1934). In the US intermittent and unpredictable epidemics have been occurring during the last decades. The majority of SLEV infections is sub clinical or result in mild illness. The severity of infections is strongly dependent on the age of a patient, and the case fatality rate during epidemics ranges from 2% in young adults to more than 22% in the elders (Monath & Heinz 1996). In spite of being endemic in Central and South America, causing sporadic illness, occurrence of SLEV outbreaks is unknown (Spence 1980, Monath & Heinz 1996.The biological cycle of SLEV in nature involves primarily wild birds and several mosquito species; humans and other mammals are considered to be incidental hosts (Monath & Heinz 1996). In the US, Culicinae mosquitoes and birds, Passeriformes and Columbiformes, are involved in the dynamics of SLEV transmission. The transmission Financial support: Fapesp (no. 2004/07819-6) and CNPq (no. 305339/2003-6) cycle varies regionally, depending on the biology of mosquito species, virulence of SLEV strains and susceptibility to infection of vertebrate hosts (Monath & Tsai 1987, Day 2001, Reisen 2003. In Central and South America SLEV transmission cycle is not well defined, but it may include mosquito species of the genera Culex, Mansonia, Haemagogus, and Sabethes. A variety of bird taxa, including herons, egrets, and cormorant may be virus reservoirs (Spence 1980, Monath & Heinz 1996, Reisen 2003.The occurrence of SLEV in Brazil was recorded in 1953, by the finding of antibodies to this virus in residents of the Amazon Valley (Causey & Theiller 1958). A pool of mosquito Sabethes belisarioi, captured along the Belém-Brasília highway, was the source for the first isolation of a SLEV strain (Causey et al. 1964). Later in 1970 and 1978 two strains were recovered from human blood in Amazon region. In both cases the patients developed a febrile illness with jaundice, neither of them presenting neurological involvement (Pinheiro et al. 1981, Vasconcelos et al. 1998. SLEV was also found in the Southeast region of Brazil where it was isolated from wild birds, rodents, and sentinel mice during a surveillance program on arbovirus activity carried out in the state of São Paulo from 1967 to 1969 (Lopes et al. 1979).In the summer of 2004, after more than two decades of the last human Brazilian report, a clinical case of infection by SLEV was detected in the state of São Paulo. Epidemiologic data about the SLEV case was fully detailed by Rocco et al. (2005). Briefly, a patient, suffering from severe uncharacterized febrile illnes...

Molecular characterization of viruses associated with encephalitis in São Paulo, Brazil

“…In Brazil, three strains of SLEV have been isolated from the blood of patients who did not display neurological symptoms. Two patients from Pará, in the North of the country, presented with fever and jaundice, and one from São Paulo had clinical symptoms consistent with dengue fever [27–29]. Non-human SLEV infections have also been found in southeastern Brazil, where the virus was isolated from wild birds, rodents and sentinel mice during a surveillance program of arbovirus activity carried out in the state of São Paulo from 1967 to 1969 [27–29].…”

Genetic variation of St. Louis encephalitis virus

“…Published SLEV sequences since 2001 include 12 isolates from the Coachella Valley in California (Reisen et al , 2002), two 2005 isolates from Argentina (Diaz et al , 2006) and one 2004 human isolate from Brazil (Santos et al , 2006). During our study, we have determined the E gene sequence of 25 isolates from Texas, one from Jamaica and two from California.…”

Culex nigripalpus Theobald (Diptera, Culicidae) feeding habit at the Parque Ecológico do Tietê, São Paulo, Brazil

“…These authors hypothesized that the strain of SLE virus at São Paulo State was not virulent for humans and circulated mainly in the forested areas. However, Rocco et al (2005) reported the first isolation of SLE virus from a febrile human case suspected to be dengue in São Pedro in 2004 andSantos et al (2006) indicated that this isolated SLE virus belongs to genotype III, being closely related to an Argentinean strain isolated in 1979 from Culex spp. mosquitoes (Kramer & Chandler 2001).…”