Virulence variation among epidemic and non-epidemic strains of Saint Louis encephalitis virus circulating in Argentina

Abstract

Saint Louis encephalitis virus caused an outbreak of febrile illness and encephalitis cases in Córdoba, Argentina, in 2005. During this outbreak, the strain CbaAr-4005 was isolated from Culex quinquefasciatus mosquitoes. We hypothesised that this epidemic variant would be more virulent in a mouse model than two other non-epidemic strains (78V-6507 and CorAn-9275) isolated under different epidemiological conditions. To test this hypothesis, we performed a biological characterisation in a murine model, including mortality, morbidity and infection percentages and lethal infection indices using the three strains. Mice were separated into age groups (7, 10 and 21-day-old mice) and analysed after infection. The strain CbaAr-4005 was the most infective and lethal of the three variants, whereas the other two strains exhibited a decreasing mortality percentage with increasing animal age. The strain CbaAr-4005 produced the highest morbidity percentages and no significant differences among age groups were observed. The epidemic strain caused signs of illness in all inoculated animals and showed narrower ranges from the onset of symptoms than the other strains. CbaAr-4005 was the most virulent for Swiss albino mice. Our results highlight the importance of performing biological characterisations of arbovirus strains likely to be responsible for emerging or reemerging human diseases.

Exploring Genomic, Geographic and Virulence Interactions among Epidemic and Non-Epidemic St. Louis Encephalitis Virus (Flavivirus) Strains

“…In our study comparing the coding region of Ep and NEp SLEV strains, we detected 17 amino acid changes of which 59% were non-conservative ( Fig 1 ). Some of these mutations are responsible for differences in biological behavior observed between Ep and NEp SLEV strains in animal models[ 12 , 23 – 25 ].…”

“… ± Viremia observed in subcutaneously inoculated birds (house sparrows/chicks). A [ 23 ]; B [ 24 ]; C [ 12 ]; D [ 25 ]. n.d.: No data available.…”

“…We used bibliographic data available in order to determine biological features associated with all studied viral strains including: source of isolation (mosquito, bird, mammals), viremia in birds, and virulence in mice[ 12 , 23 – 25 ]. SLEV strains were classified as high virema (HV) or low viremia (LV), and high pathogenicity (HP) or low pathogenicity (LP) ( Table 1 ).…”

Neuronal Degeneration in Mice Induced by an Epidemic Strain of Saint Louis Encephalitis Virus Isolated in Argentina

“…Most likely due to the few reports of SLEV infection during the decades preceding the reemergence, little is known about the neurological alterations induced by this virus. To address this fundamental gap in knowledge, we previously demonstrated that CbaAr-4005 strain of SLEV was more virulent (infective and lethal) than another strain isolated from a non-epidemic scenario ( Rivarola et al, 2014 ). The CbaAr-4005 strain of SLEV was capable of generating high viremia levels, invading peripheral organs such as spleen and lungs, causing severe histopathological damage.…”

SEROSURVEY OF SELECTED ARBOVIRAL PATHOGENS IN FREE-RANGING, TWO-TOED SLOTHS (CHOLOEPUS HOFFMANNI) AND THREE-TOED SLOTHS (BRADYPUS VARIEGATUS) IN COSTA RICA, 2005–07

“…Among flaviviruses, we investigated exposure to WNV, ILHV, and SLEV, all vectored by mosquitoes (Pauvolid-Correa et al 2013; Rivarola et al 2014). Saint Louis encephalitis virus infects a variety of vertebrate hosts, among which sloths, primates, birds, marsupials, and armadillos are considered reservoirs (Seymour et al 1983a; Figueiredo 2007).…”