Mode of spread to and within the central nervous system after oral infection of neonatal mice with the DA strain of Theiler's murine encephalomyelitis virus

Diverse picornaviruses are prevalent among free-living and laboratory rats (Rattus norvegicus) in Hungary and can cause disseminated infections

In this study, the full length genomes of three phylogenetically distant picornaviruses (family Picornaviridae) belonging to the genus Rosavirus (rat08/rRoB/HUN, MN116648), Kobuvirus (rat08/rAiA/HUN, MN116647), and Cardiovirus (rat08/rCaB/HUN, MN116646) were obtained from a single faecal sample of a free-living Norway rat (Rattus norvegicus) in Hungary using viral metagenomics and RT-PCR/Sanger sequencing. The acquired complete genomes were in silico analyzed in detail revealing the presence of a second minor open reading frame encoding an alternative Leader peptide (L*) in rat08/rCaB/HUN and a ca. 222 nt-long sequence repeat with compact secondary RNA structure in the 3' UTR of rat08/rRoB/HUN. The studied rat picornaviruses were frequently detectable by RT-PCR with relatively high viral loads ranged between 8.99E+02 and 1.29E+06 copies/ml in rat faecal samples collected from five geographically distant locations throughout Hungary. The VP1 sequence-based phylogenetic analyses show the presence of multiple, mostly location-specific lineages for all three picornaviruses. Rat rosavirus and rat cardiovirus were identified in spleen while rat cardiovirus was also detected in liver, muscle and kidney samples with variable copy numbers (6.42E+01-1.90E+05 copies/μg total RNA) suggesting extra-intestinal dissemination. Both viruses were also prevalent (70.0% and 18.2%) among two populations of laboratory rats ("Wistar-type" and "hooded-type") held in different, isolated laboratory animal units.

Efficacy of Intracerebral Immunization against Pseudorabies Virus in Mice

To evaluate the efficacy of intracerebral (IC) immunization, mice were immunized with formalin-inactivated pseudorabies virus (PRV) by either subcutaneous (SC) or IC injection, and then 10(6) plaque-forming units of PRV were introduced into the hindleg of the immunized or non-immunized mice by intramuscular injection. The antibody titer in serum was elevated and boosted by additional immunization via both the SC and IC routes, but was higher after IC immunization. Intracerebrally immunized mice were completely protected from mortality and neurological signs, whereas all the non-immunized and 80% of the subcutaneously immunized mice died after developing neurological signs. In mouse models, IC immunization is more effective at inducing a protective immune response against the transneural spread of PRV than SC immunization.

Neuropathogenesis of a highly pathogenic avian influenza virus (H7N1) in experimentally infected chickens

In order to understand the mechanism of neuroinvasion of a highly pathogenic avian influenza virus (HPAIV) into the central nervous system (CNS) of chickens, specific pathogen free chickens were inoculated with a H7N1 HPAIV. Blood, cerebrospinal fluid (CSF), nasal cavity and brain tissue samples were obtained from 1 to 4 days post-inoculation (dpi) of infected and control chickens. Viral antigen topographical distribution, presence of influenza A virus receptors in the brain, as well as, the role of the olfactory route in virus CNS invasion were studied using different immunohistochemistry techniques. Besides, viral RNA load in CSF and blood was quantified by means of a quantitative real-time reverse transcription-polymerase chain reaction. Viral antigen was observed widely distributed in the CNS, showing bilateral and symmetrical distribution in the nuclei of the diencephalon, mesencephalon and rhombencephalon. Viral RNA was detected in blood and CSF at one dpi, indicating that the virus crosses the blood-CSF-barrier early during infection. This early dissemination is possibly favoured by the presence of Siaα2,3 Gal and Siaα2,6 Gal receptors in brain vascular endothelial cells, and Siaα2,3 Gal receptors in ependymal and choroid plexus cells. No viral antigen was observed in olfactory sensory neurons, while the olfactory bulb showed only weak staining, suggesting that the virus did not use this pathway to enter into the brain. The sequence of virus appearance and the topographical distribution of this H7N1 HPAIV indicate that the viral entry occurs via the haematogenous route, with early and generalized spreading through the CSF.

In vivo tropisms and kinetics of rat theilovirus infection in immunocompetent and immunodeficient rats

Rat theilovirus (RTV) is a cardiovirus related to Theiler's murine encephalomyelitis virus. While RTV is a prevalent viral pathogen of rats used in biomedical research, the pathogenesis and characterization of RTV infections is not well understood. In the studies reported herein, we used immunohistochemistry to identify viral antigens in enterocytes of the small intestines of Sprague-Dawley (SD) rats. Fecal viral shedding in immunocompromised and immunocompetent rats following oral gavage with RTV1 was high for the first 2 weeks of infection with persistent shedding of high viral loads being observed in immunocompromised nude rats but not in immunocompetent rats. RTV was also detected in mesenteric lymph nodes and spleen of immunocompromised rats but not immunocompetent rats. In addition, the magnitude of serum antibody responses differed between immunocompetent rat strains with Brown Norway and SD rats having a significantly higher antibody response than CD or Fischer 344 rats. These data suggest that RTV1 has a tropism for the epithelial cells of the small intestine, immunocompetent rats have differing serum antibody responses to RTV infection, and sustained fecal shedding and extraintestinal dissemination of RTV1 occurs in rats deficient in T cell-dependent adaptive immunity. RTV infection in immunocompromised and immunocompetent rats has merit as a model for further studies of theilovirus pathogenesis following oral viral exposure.

Central neuroinvasion and demyelination by inflammatory macrophages after peripheral virus infection is controlled by SHP-1

SHP-1 is a protein tyrosine phosphatase that negatively regulates cytokine signaling and inflammatory gene expression. Mice genetically lacking SHP-1 (me/me) display severe inflammatory demyelinating disease following intracranial inoculation with the BeAn strain of Theiler's murine encephalomyelitis virus (TMEV) compared to infected wild-type mice. Furthermore, SHP-1-deficient mice show a profound and predominant infiltration of blood-derived macrophages into the CNS following intracerebral injection of TMEV, and these macrophages are concentrated in areas of demyelination in brain and spinal cord. In the present study we investigated the role of SHP-1 in controlling CNS inflammatory demyelination following a peripheral instead of an intracerebral inoculation of TMEV. Surprisingly, we found that while wild-type mice were entirely refractory to intraperitoneal (IP) infection by TMEV, in agreement with previous studies, all SHP-1-deficient mice displayed profound macrophage neuroinvasion and macrophage-mediated inflammatory demyelination. Moreover, SHP-1 deficiency led to increased expression of inflammatory molecules in macrophages, serum, and CNS following IP infection with TMEV. Importantly, pharmacological depletion of peripheral macrophages significantly decreased both paralysis and CNS viral loads in SHP-1-deficient mice. In addition, peripheral MCP-1 neutralization attenuated disease severity, decreased macrophage infiltration into the CNS, and decreased monocyte numbers in the blood of SHP-1-deficient mice, implicating MCP-1 as an important mediator of monocyte migration between multiple tissues. These results demonstrate that peripheral TMEV infection results in a unique evolution of macrophage-mediated demyelination in SHP-1-deficient mice, implicating SHP-1 in the control of neuroinvasion of inflammatory macrophages and neurotropic viruses into the CNS.

Effective prevention against rabies by intracerebral immunization in mice

To evaluate the efficacy of intracerebral (IC) immunization, mice were immunized with a rabies vaccine by the subcutaneous (SC), intramuscular (IM) or IC route, and 10-fold the 50% lethal dose of rabies virus was inoculated into the hindleg of the immunized or non-immunized mice. The antibody titer in serum was elevated and boosted by additional immunization via all routes, but highest after the IC immunization followed by the IM and SC routes, in this order. Intracerebrally immunized mice were completely protected from death and the neurological signs of infection, whereas the IM or SC immunization only partly protected the mice. In mouse models, IC immunization is more effective at inducing a protective immune response against the transneural spread of rabies virus than IM or SC immunization.

Identification of cardioviruses related to Theiler's murine encephalomyelitis virus in human infections

Cardioviruses comprise a genus of picornaviruses that cause severe illnesses in rodents, but little is known about the prevalence, diversity, or spectrum of disease of such agents among humans. A single cardiovirus isolate, Saffold virus, was cultured in 1981 in stool from an infant with fever. Here, we describe the identification of a group of human cardioviruses that have been cloned directly from patient specimens, the first of which was detected using a pan-viral microarray in respiratory secretions from a child with influenza-like illness. Phylogenetic analysis of the nearly complete viral genome (7961 bp) revealed that this virus belongs to the Theiler's murine encephalomyelitis virus (TMEV) subgroup of cardioviruses and is most closely related to Saffold virus. Subsequent screening by RT-PCR of 719 additional respiratory specimens [637 (89%) from patients with acute respiratory illness] and 400 cerebrospinal fluid specimens from patients with neurological disease (aseptic meningitis, encephalitis, and multiple sclerosis) revealed no evidence of cardiovirus infection. However, screening of 751 stool specimens from 498 individuals in a gastroenteritis cohort resulted in the detection of 6 additional cardioviruses (1.2%). Although all 8 human cardioviruses (including Saffold virus) clustered together by phylogenetic analysis, significant sequence diversity was observed in the VP1 gene (66.9%-100% pairwise amino acid identities). These findings suggest that there exists a diverse group of novel human Theiler's murine encephalomyelitis virus-like cardioviruses that hitherto have gone largely undetected, are found primarily in the gastrointestinal tract, can be shed asymptomatically, and have potential links to enteric and extraintestinal disease.

Comparison of antibody titers in rabbits following immunization with inactivated influenza virus via subarachnoidal or subcutaneous route

Rabbits were immunized with inactivated influenza virus via the subarachnoidal (SA) or subcutaneous (SC) route, and the antibody titers in cerebrospinal fluid (CSF) and serum were assayed. There were no nervous signs or morphological lesions related to SA immunization. In the SC group, the antibody titer was elevated in serum, but not elevated in CSF. In the SA group, the antibody titer was significantly elevated in serum and even in CSF, and their antibody titers were much greater than in the SC group. The present results suggest that intrathecal immunization is more effective than SC immunization at inducing a protective immune response against the transneural spread of viruses.

Restraint stress facilitates systemic dissemination of Theiler's virus and alters its pathogenecity

Theiler's murine encephalomyelitis virus (TMEV), a Picornavirus used as a viral model for multiple sclerosis (MS), causes an acute encephalomyelitis and chronic demyelination. The failure to clear the virus, which can result from stress, is a prerequisite for development of the later disease. Similarly, stressful life events have been associated with the development of MS. In the present study, a restraint stress (RS) model was used to investigate the effect of stress on the systemic dissemination of TMEV during the early stage of disease. Experimental data demonstrated that repeated RS remarkably facilitated the spread of virus from the CNS to such systemic organs as the spleen, lymph nodes, thymus, lungs and heart and compromised the ability of viral clearance within those tissues. RS also altered the pathogenecity of TMEV, enabling it to become cardiotropic, resulting in higher myocardial infectivity. These results demonstrate the profound impact that RS has upon both the tissue and organ dissemination of the virus, and the organ tropism of TMEV. An additional finding associated with stress was hepatic necrosis in the restrained animals, regardless of whether or not they were infected.

A comparison of the neurotropism of Theiler's virus and poliovirus in CBA mice

Theiler's murine encephalomyelitis virus (TMEV) and poliovirus infect the central nervous system (CNS) and cause neurological damage. The exact route by which TMEV and polioviruses enter the CNS remains, for the most part, unknown, although the neural and/or the hematogenous pathway have both been postulated. To explore these hypotheses, this research focuses on both the site of entry and the pathway used to invade the CNS. Following different inoculation sites of the GDVII strain of Theiler's virus or Lansing Type 2 poliovirus in CBA mice, the incidence of paralysis and/or encephalitis was evaluated on the basis of clinical signs and histopathology. The forms of paralysis displayed corresponded to the site of viral inoculation. Following intramuscular (i.m.), intraperitoneal (i.p.), and footpad routes of injection, bilateral and or contralateral paralyses were observed for both TMEV and poliovirus. In mice injected intratongue and in the hypoglossal nerve, tongue paralysis or paralysis of the forelimb, which progressed to bilateral forelimb paralysis, was observed, additionally the penis of most infected males was protruded. Intracranial (i.c.) injections with type II poliovirus strain resulted in forelimb paralysis. Intravenous (i.v.), injections with TMEV also resulted in forelimb paralysis. Thus Lansing Type II poliovirus and TMEV infections of CBA mice, result in similar incidence of paralysis and histopathological findings.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

The infection of mouse by Theiler's virus: from genetics to immunology

Theiler's virus is a picornavirus of mouse which causes an acute encephalomyelitis followed by a persistent infection of the white matter of the spinal cord with chronic inflammation and demyelination. This late disease is studied as a model for multiple sclerosis. Inbred strains of mice differ in their susceptibility to persistent infection and demyelination. Resistant strains clear the infection after the acute encephalomyelitis. This observation is the basis of genetic studies which we used as a thread for this review. The H-2D locus has a major effect on susceptibility. The H-2Db gene is involved in a fast and intense CTL response which confers resistance. The Tcrb locus is also implicated, although there is no proof that the susceptibility gene in this region codes for the T-cell receptor. A complete screen of the genome uncovered the role of the Ifng locus and led to the demonstration that IFN-gamma limits viral spread in the white matter. The roles of NK cells and B cells in limiting the infection are discussed. CD4+ T cells participate both in protection against the infection and in demyelination. Finally, the effect of non-immune factors in resistance is illustrated by mice with mutations in the MBP or PLP gene.

Timed appearance of lymphocytic choriomeningitis virus after gastric inoculation of mice

Arenaviruses present an emerging health threat in agrarian areas of Africa and South America; however, the natural routes of arenaviral infections are not clearly understood. Our previous studies with lymphocytic choriomeningitis virus (LCMV), the prototype arenavirus, implicate oral and intragastric routes as natural routes of infection. Our studies raised many questions about the primary site of infection and the route of dissemination after gastric infection. In this report, we use in situ hybridization to detect LCMV in various organs at different time points (0 to 96 hours). After gastric inoculation, the gastric mucosa is the initial site of viral infection, followed by infection of the spleen and liver, then ileum and last, lung, kidney, brain, and esophagus. Furthermore, our observations suggest that virus is disseminated lymphatically rather than by a hematogenous route. Infectious center assays using mononuclear cells from stomach, blood, and spleen of mice infected by the gastric route confirmed active infection with LCMV and the presence of mononuclear cells producing infectious virus in these tissues. This is the first identification of gastric epithelia as a primary site of virus infection.