The online version of this article (doi:10.1186/s12974-017-0837-2) contains supplementary material, which is available to authorized users.
Flaviviruses are a genre of closely related viral pathogens which emerged in the last decades in Brazil and in the world. Saint (St.) Louis encephalitis virus (SLEV) is a neglected flavivirus that can cause a severe neurological disease that may lead to death or sequelae. St. Louis encephalitis pathogenesis is poorly understood, which hinders the development of specific treatment or vaccine.
To address this problem, we developed a model of SLEV infection in mice to study mechanisms involved in the pathogenesis of severe disease. The model consists in the intracranial inoculation of the SLEV strain BeH 355964, a strain isolated from a symptomatic human patient in Brazil, in adult immunocompetent mice.
Inoculated mice presented SLEV replication in the brain, accompanied by tissue damage, disease signs, and mortality approximately 7 days post infection. Infection was characterized by the production of proinflammatory cytokines and interferons and by leukocyte recruitment to the brain, composed mainly by neutrophils and lymphocytes. In vitro experiments indicated that SLEV is able to replicate in both neurons and glia and caused neuronal death and cytokine production, respectively.
Altogether, intracranial SLEV infection leads to meningoencephalitis in mice, recapitulating several aspects of St. Louis encephalitis in humans. Our study indicates that the central nervous system (CNS) inflammation is a major component of SLEV-induced disease. This model may be useful to identify mechanisms of disease pathogenesis or resistance to SLEV infection.
Additional file 1: Figure S1. Adult immunocompetent mice are resistant to SLEV when inoculated through peripheral routes. Eight- to 12-week-old female C57BL/6 mice were inoculated with 103 PFU of SLEV BeH 355964 through different routes (intraperitoneal, intraplantar, subcutaneous, and intracranial) and observed for 14 days post infection. Results are expressed as percentage of survival in each group and is representative of one experiment. N = 5 mice. (TIF 40 kb)12974_2017_837_MOESM1_ESM.tif
Additional file 2: Figure S2. Experimental SLEV infection does not change platelet counts or the hematocrit index. Adult female C57BL/6 mice were inoculated i.c. with 1 LD100 of SLEV and euthanized at days 3, 5, and 7 p.i. for blood collection. Platelet counts (A) and the hematocrit index (B) were quantified in heparinized samples. Results are expressed as mean plus SEM and are representative of one experiment (N = 3–8). Mock = injected with saline. (TIFF 120 kb)12974_2017_837_MOESM2_ESM.tiff
Additional file 3: Figure S3. Intracranial SLEV infection does not affect the spleen or causes systemic inflammation. Adult female C57BL/6 mice were inoculated i.c. with 1 LD100 of SLEV and euthanized at days 3, 5, and 7 p.i. for collection of spleens and sera. Spleen samples were processed and assessed for SLEV load (A) by plaque assay and enzymatic activity of MPO (B) and NAG (C). Levels of the cytokines CCL5, TNFα, and IFNγ were measured in spleen (D, E, F) and serum samples (G, H, I). Results are expressed as dot plot or mean plus SEM and are representative of two experiments (N = 6–12). Mock = injected with saline. ND = not detectable. (TIFF 360 kb)12974_2017_837_MOESM3_ESM.tiff
Additional file 4: Figure S4. Histopathological alterations in SLEV-infected mice are quantifiable in the meninges, brain, hippocampus, and brainstem. Adult female C57BL/6 mice were inoculated i.c. with 1 LD100 of SLEV and euthanized at days 3, 5, and 7 p.i. for collection of brains for a histological semi-quantitative analysis. Slides were scored on up to four points, with four corresponding to maximum tissue damage. Scores were set based on the histological aspect of samples from the mock-infected group. Brain regions analyzed included the meninges (A), the cerebrum (B), the hippocampus (C) and the brainstem (D). Results are expressed as dot-plot and the median for each experiment group. *P < 0.05, **P < 0.01 compared to the respective day 3 p.i. group. Mock = injected with saline. (TIFF 122 kb)12974_2017_837_MOESM4_ESM.tiff
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- Development of a model of Saint Louis encephalitis infection and disease in mice
Rafael Elias Marques
Juliana L. Del Sarto
Rebeca P. F. Rocha
Giovanni F. Gomes
Milene A. Rachid
Danielle G. Souza
Maurício L. Nogueira
Mauro M. Teixeira
- BioMed Central