Favipiravir treatment prolongs the survival in a lethal mouse model intracerebrally inoculated with Jamestown Canyon virus.

BACKGROUND: Jamestown Canyon virus (JCV) is a mosquito-borne orthobunyavirus that causes acute febrile illness, meningitis, and meningoencephalitis, primarily in North American adults. Currently, there are no available vaccines or specific treatments against JCV infections. METHODOLOGY/PRINCIPAL FINDINGS: The antiviral efficacy of favipiravir (FPV) against JCV infection was evaluated in vitro and in vivo in comparison with that of ribavirin (RBV) and 2'-fluoro-2'-deoxycytidine (2'-FdC). The in vitro inhibitory effect of these drugs on JCV replication was evaluated in Vero and Neuro-2a (N2A) cells. The efficacy of FPV in the treatment of JCV infection in vivo was evaluated in C57BL/6J mice inoculated intracerebrally with JCV, as per the survival, viral titers in the brain, and viral RNA load in the blood. The 90% inhibitory concentrations (IC90) of FPV, RBV, and 2'-FdC were 41.0, 61.8, and 13.6 µM in Vero cells and 20.7, 25.8, and 8.8 µM in N2A cells, respectively. All mice infected with 1.0×104 TCID50 died or were sacrificed within 10 days post-infection (dpi) without treatment. However, mice treated with FPV for 5 days [initiated either 2 days prior to infection (-2 dpi-2 dpi) or on the day of infection (0 dpi-4 dpi)] survived significantly longer than control mice, administered with PBS (p = 0.025 and 0.011, respectively). Moreover, at 1 and 3 dpi, the virus titers in the brain were significantly lower in FPV-treated mice (0 dpi-4 dpi) versus PBS-treated mice (p = 0.002 for both 1 and 3 dpi). CONCLUSIONS/SIGNIFICANCE: Although the intracerebral inoculation route is thought to be a challenging way to evaluate drug efficacy, FPV inhibits the in vitro replication of JCV and prolongs the survival of mice intracerebrally inoculated with JCV. These results will enable the development of a specific antiviral treatment against JCV infections and establishment of an effective animal model.

Age-dependent myeloid dendritic cell responses mediate resistance to la crosse virus-induced neurological disease.

UNLABELLED: La Crosse virus (LACV) is the major cause of pediatric viral encephalitis in the United States; however, the mechanisms responsible for age-related susceptibility in the pediatric population are not well understood. Our current studies in a mouse model of LACV infection indicated that differences in myeloid dendritic cell (mDC) responses between weanling and adult mice accounted for susceptibility to LACV-induced neurological disease. We found that type I interferon (IFN) responses were significantly stronger in adult than in weanling mice. Production of these IFNs required both endosomal Toll-like receptors (TLRs) and cytoplasmic RIG-I-like receptors (RLRs). Surprisingly, IFN expression was not dependent on plasmacytoid DCs (pDCs) but rather was dependent on mDCs, which were found in greater number and induced stronger IFN responses in adults than in weanlings. Inhibition of these IFN responses in adults resulted in susceptibility to LACV-induced neurological disease, whereas postinfection treatment with type I IFN provided protection in young mice. These studies provide a definitive mechanism for age-related susceptibility to LACV encephalitis, where mDCs in young mice are insufficiently activated to control peripheral virus replication, thereby allowing virus to persist and eventually cause central nervous system (CNS) disease. IMPORTANCE: La Crosse virus (LACV) is the primary cause of pediatric viral encephalitis in the United States. Although the virus infects both adults and children, over 80% of the reported neurological disease cases are in children. To understand why LACV causes neurological disease primarily in young animals, we used a mouse model where weanling mice, but not adult mice, develop neurological disease following virus infection. We found that an early immune response cell type, myeloid dendritic cells, was critical for protection in adult animals and that these cells were reduced in young animals. Activation of these cells during virus infection or after treatment with type I interferon in young animals provided protection from LACV. Thus, this study demonstrates a reason for susceptibility to LACV infection in young animals and shows that early therapeutic treatment in young animals can prevent neurological disease.

Evidence that fatal human infections with La Crosse virus may be associated with a narrow range of genotypes.

La Crosse (LAC) virus belongs to the California (CAL) serogroup of the genus Bunyavirus, family Bunyaviridae. It is considered one of the most important mosquito-borne pathogens in North America, especially in the upper Mid-West, where it is associated with encephalitis during the time of year when mosquitoes are active. Infections occur most frequently in children and young adults and, while most cases are resolved after a period of intense illness, a small fraction (< 1%) are fatal. At present there have only been three isolates of LAC virus from humans all made from brain tissue postmortem. The cases yielding viruses are separated chronologically by 33 years and geographically from Minnesota/Wisconsin (1960, 1978) to Missouri (1993). The M RNA sequence of the first two isolates was previously reported. The present study extends the observations to the isolate from the 1993 case and includes several mosquito isolates as well. A comparison of the M RNAs of these viruses shows that for the human isolates both nucleotide sequence and the deduced amino-acid sequence of the encoded proteins are highly conserved, showing a maximum variation of only 0.91% and 0.69%, respectively. This high degree of conservation over time and space leads to the hypothesis that human infections with this particular genotype of LAC virus are those most likely to have a fatal outcome. It is also shown that a virus with this genotype could be found circulating in mosquitoes in an area more or less intermediate between the locations of the first and second fatal cases.

Effects of La Crosse virus infection on pregnant domestic rabbits and mongolian gerbils.

The transplacental transmission of La Crosse virus (LACV) was evaluated in domestic rabbits (Oryctolagus cuniculus) and Mongolian gerbils (Meriones unguiculatis) as a potential mechanism for the maintenance of the virus. Rabbits were infected with LACV at different times of gestation by injection of viral suspensions or by exposure to LACV transovarially (TO) infected Aedes triseriatus. Pregnant gerbils were exposed between 16-24 days of gestation to LACV TO- infected Ae. triseriatus. Our results indicate that LACV can infect gerbils in utero. The LACV was isolated from the brain of suckling gerbils that died 3-5 days after birth from LACV-exposed mothers, representing the first evidence of LACV transplacental transmission. Microgliosis was found histologically in the cerebral cortex. In addition, LACV infection of both pregnant gerbils and rabbits resulted in in utero and neonatal mortality. La Crosse virus was not detected in surviving young of infected rabbits even after immunosuppression by administration of cyclophosphamide. Thus, there was no evidence of persistent infection of rabbits following in utero exposure. Surprisingly, some of the infected pregnant gerbils developed progressive paralysis 9-14-days postexposure, and LACV was isolated from the brains of these animals. Histopathologic studies of these tissue samples showed acute meningoencephalitis. The effects of natural LACV infection should be studied in pregnant amplifying hosts, such as chipmunks and squirrels, and in pregnant women.