The role of viral strain in a congenital brain infection

Lymphocytic Choriomeningitis Virus (LCMV) is a common arenavirus and natural murine pathogen that causes congenital neurodevelopmental disease in humans. Exposure to the virus in utero often results in severe and permanent damage the fetal brain and eyes. While usually severe, symptoms vary from case to case. Little is known about the pathological mechanism of congenital LCMV disease. Animal models of congenital LCMV infections suggest that timing of infection during gestation may influence disease outcomes; however, time alone cannot explain all of the variation observed in humans. Another possibility is that individuals are infected with different strains of LCMV.

The LCMV genome is composed of four highly conserved genes, yet even single amino acid mutations can cause the virus to exhibit very different properties in animal models. However, the role of viral strain in the context of neurodevelopment remains relatively unexplored. Here, using a rat model of congenital LCMV infection, we demonstrate that three related strains of LCMV produce different patterns of infection and disease states.

Infection with the highly neurotropic E350 strain induces a disease comparable to that observed in many confirmed cases of human congenital LCMV infection. While most of these animals survive to adulthood, they suffer permanent motor and behavioral abnormalities. Postmortem analyses of infected brains suggest that this strain has a proclivity for infecting mitotically active regions of the brain, including the cerebellum, olfactory bulb, hippocampus and subventricular region. E350 is not known to induce immunosuppression and viral clearance is likely mediated by a robust T-cell response. Indeed, we find high numbers of inflammatory cells in the brains of E350 animals and elevated pro-inflammatory cytokines and chemokines. The immune response, though responsible for the clearance of the virus from the brain, is also implicated in severe and sometimes permanent brain damage.

The Clone 13 strain, a strain typically associated with lymphatic tissue, readily infects the brains of developing rats. Many of these animals do not live to adulthood. Those that survive exhibit extreme stunted growth, but relatively normal neurodevelopment and little discernable neurological disease. By adulthood, the brains of these animals are comparable in size and structure to controls, despite reduced body mass. The Clone 13 infects the same brain regions as the E350, but is not cleared and remained at high titers for the duration of the study. Chronic infection is likely a consequence of the immunosuppressive effects of Clone 13 on the host immune system.

The WE2.2 causes a severe disease with both neurological and systemic symptoms. These animals exhibit persistent seizure like discharges during peak infection and significant motor deficits. They all fail to thrive, losing weight shortly after infection and die invariably 9-11 days post-inoculation. The brains of WE2.2 animals exhibit widespread infection of neurons in the cerebellum, hippocampus, olfactory bulbs, and cortex. WE2.2 does not cause immunosuppression and high levels of inflammatory cells are observed in the brain. Cytokine and chemokine expression is complex, without discernible trends and variable by brain region.

Finally, we looked at alpha-dystroglycan (α-DG) expression in the brain and compared it with infectivity among the strains. Alpha-dystroglycan is recognized as the principle receptor for LCMV and due to mutations in the viral glycoprotein, certain strains are more dependent on α-DG for infection. Several associations between α-DG expression and viral infectivity were observed; however α-DG expression alone could not explain all the differences in infection patterns.