Modoc Viral Infections in the Deer Mouse Peromyscus maniculatus

The pathogenesis of Modoc virus and its mechanism of transmission were investigated in Peromyscus maniculatus gambeli (deer mouse) as a model to understand the natural history of this virus. Animals were readily infected by the intranasal or subcutaneous route of inoculation. Virus could be detected by direct isolation techniques in many organs and body fluids during the first 7 to 9 days after intranasal inoculation. Increases in viral titers were detectable first in lungs and then the spleen, salivary-submaxillary glands, and lymph nodes. Viremias were low titered and ephemeral. Virus was recovered from urine and throat swabs 4 to 6 days and 4 to 7 days after inoculation, respectively. Serum dilution neutralization, hemagglutination inhibition, or complement fixation antibodies were detected in sera of some animals 13 days after infection and in all animals after 20 days. Antibodies persisted for the 168-day period of observation. Persistent viral infection was demonstrable by in vitro culturing of lungs or pooled lungs, salivary glands, and kidneys from 14 of 69 mice that were sacrificed from 1 to 6 months after intranasal inoculation. Attempts to demonstrate horizontal or vertical transmission of Modoc virus among mice were generally unsuccessful. Female deer mice infected with virus before mating passed maternal antibodies to their young.     

Propagation of the Kakegawa strain of bovine coronavirus in suckling mice,rats and hamsters

Summary The Kakegawa strain of bovine coronavirus was easily propagated in suckling mice. Infected animals died with nervous symptoms, and serial passage was readily accomplished by intracerebral inoculation with brain emulsions. The 3rd passage viral material from infected mice evoked the same disease in suckling mice, rats and hamsters inoculated by the intracerebral or by the subcutaneous route. Viruses recovered from mice, rats and hamsters could be clearly differentiated from mouse hepatitis virus strain 2 by the neutralization test.With 1 Figure     

Characterization of Persistent Modoc Viral Infections in Syrian Hamsters

Adult Syrian hamsters were readily infected by intranasal inoculation with Modoc virus. Viremias were detected 2 to 6 days after infection and peak viremia titers (10^6.2 plaque-forming units/ml of blood) occurred 4 days postinoculation. All infected animals developed neutralizing and hemagglutination-inhibiting antibodies by 7 days, and complement-fixing antibodies by 14 days postinoculation. High titers of antibodies persisted for at least 4 months. Modoc virus was recovered from throat swabs at 7 days postinoculation, but not at 14 days or later. Urine samples were positive for virus throughout a 12-week observation period. Isolation of virus from lungs and kidneys of one and three animals, respectively, at 151 to 221 days after inoculation confirmed chronic infection. Viral isolations were made only when organs were cultivated in vitro and were unsuccessful by tests on 10% homogenates of the organs. Horizontal viral transmission of virus by infected hamsters that were viruric was demonstrated in only 1 of 27 normal hamsters that were cocaged for 4 weeks under crowded conditions. General failure to obtain horizontal viral transmission may relate to rapid inactivation of virus in excreted urine. Vertical viral transmission was not demonstrated from five chronically infected female hamsters to their 34 offspring. However, if primary infection occurred during pregnancy, the progeny were either stillborn or died shortly after birth, and thus appeared to represent transplacental viral transmission.     

Neurovirulence of H7N7 influenza A virus: Brain stem encephalitis accompanied with aspiration pneumonia in mice

Summary. A mouse-adapted influenza A virus, A/equine/London/1416/73-MA (H7N7) caused viral pneumonia, ganglionitis and encephalitis after intranasal inoculation in mice. Virological and pathological data suggested that this virus spreads to the brain by both hematogenous and transneuronal routes, and produces encephalitic lesions similar to those seen in mice infected with H5 highly pathogenic avian influenza A viruses by intranasal infection. Some mice infected with this strain were affected by aspiration pneumonia, which may be caused by neurogenic dysfunction of the pharyngeal/laryngeal reflex due to brain stem encephalitis.     

Further observations on subacute sclerosing encephalitis in adult hamsters: the effects of intranasal infections with Langat virus, measles virus and SSPE-measles virus.

Passage by i.c. inoculations of suckling hamsters enhanced the virulence for adult hamsters of Langat virus (TP21), neurotropic strain of measles virus (HNT) and SSPE-measles virus (HBS), not only for i.c. infections but also for intranasal instillations. The various viral strains passaged in hamsters showed a great similarity of behaviour including the ability of producing in a proportion of apparently unaffected survivors a subacute sclerosing encephalitis, leading to atrophy of parts of the brain especially the rhinencephalon. When large groups of animals were used for transmission experiments it became obvious that within one week after intranasal exposure, all the hamsters either died or became clinically affected, or did not show signs of disease but developed acute inflammatory brain lessions. tlater on, between 2-6 weeks following inoculations only 90% of hamsters were affected with either overt signs of disease or subacute brain lesions, suggesting that in about 10% of hamsters the initial infection did not progress further and that in these animals the early brain lesions disappeared. Passage levels, irrespective of the virus used, did not influence the total numbers of infected hamsters but showed a significant effect on the mortality in TP21 and HNT infections where the number of dead and clinically affected increased in the higher passes. In these higher passes the number of survivors with subacute brain lesions decreased. In SSPE-measles virus the number of clinically affected hamsters and those surviving but developing brain lesions remained constant throughout. Vacuolated neurons were present in the brains of hamsters that survived one of the above 3 viral infections. They were seen beginning from 6 weeks after infection only in animals that developed subacute sclerosing lesions and were most commonly found in the amygdaloid nuclei and in the pyriform cortex. There was a dramatic increase in the number of brains with vacuolated neurons in hamsters infected with the high viral passes; however, in the 36th hamster passage of TP21 no vacuolated neurons were present but the total number of survivors was small, the majority had no brain lesions and none had subacute sclerosing changes.     

Perspectives for the treatment of infections with Flaviviridae

The family Flaviviridae contains three genera: Hepacivirus, Flavivirus, and Pestivirus. Worldwide, more than 170 million people are chronically infected with Hepatitis C virus and are at risk of developing cirrhosis and/or liver cancer. In addition, infections with arthropod-borne flaviviruses (such as dengue fever, Japanese encephalitis, tick-borne encephalitis, St. Louis encephalitis, Murray Valley encephalitis, West Nile, and yellow fever viruses) are emerging throughout the world. The pestiviruses have a serious impact on livestock. Unfortunately, no specific antiviral therapy is available for the treatment or the prevention of infections with members of the Flaviviridae. Ongoing research has identified possible targets for inhibition, including binding of the virus to the cell, uptake of the virus into the cell, the internal ribosome entry site of hepaciviruses and pestiviruses, the capping mechanism of flaviviruses, the viral proteases, the viral RNA-dependent RNA polymerase, and the viral helicase. In light of recent developments, the prevalence of infections caused by these viruses, the disease spectrum, and the impact of infections, different strategies that could be pursued to specifically inhibit viral targets and animal models that are available to study the pathogenesis and antiviral strategies are reviewed.     

Acute encephalitis,a poliomyelitis-like syndrome and neurological sequelae in a hamster model for flavivirus infections

Infection of hamsters with the murine flavivirus Modoc results in (meningo)encephalitis, which is, during the acute phase, frequently associated with flaccid paralysis, as also observed in patients with West Nile virus encephalitis. Twenty percent of the hamsters that recover from the acute encephalitis develop life-long neurological sequelae, reminiscent of those observed, for example, in survivors of Japanese encephalitis. Magnetic resonance imaging and histology revealed severe lesions predominantly located in the olfactory-limbic system, both in hamsters with acute encephalitis as in survivors. Prominent pathology was also detected in the spinal cord of hamsters with paralysis. Modoc virus infections in hamsters provide a unique model for the study of encephalitis, a poliomyelitis-like syndrome and neurological sequelae following flavivirus infection.     

The occurrence of vacuolated neurons in the brains of hamsters affected with subacute sclerosing encephalitis following measles or Langat virus infection.

Hamsters infected by the intranasal route with either hamster adapted Langat virus passaged at least 10 times in hamsters and the HNT strain of measles virus passaged 149 times in hamsters, developed subacute sclerotic lesions in the pyriform cortex, and beginning from 2 months after infection, were accompanied by neuronal vacuolation with ballooning of the cytoplasm, especially in parts of the brain in close proximity of the sclerotic lesions. The vacuolated neurons resembled those seen in scrapie, especially of sheep and goats, suggesting a similarity between the effects of slow and subacute viral infections.     

Comparison of intranasal and aerosol infection of mice in assessment of immunity to influenza virus infection.

A comparison was made of intranasal and aerosol routes of infection with X-31 influenza A virus in Balb/c mice. Mice were first infected with 100 MID50 by either route then challenged 42 days later with the same virus given by the same or alternative route. Three days following each infection, pulmonary virus was measured by inoculation of chick embryos. Mice initially infected under ether anesthesia by intranasal inoculation experienced higher initial mortality but proved most resistant to subsequent challenge by either method. In contrast, mice first infected by aerosol were least resistant to intranasal challenge, as indicated by increased rate of infection and pulmonary virus titers, but, like mice previously infected intranasally, were not reinfected by the aerosol route. Thus, intranasal infection appears to be more effective both in inducing and challenging immunity from infection. These results should be considered in the design of experiments utilizing influenza virus infection of mice as a model system.     

Pathogenicity and immunogenicity for mice of temperature-sensitive mutants of vesicular stomatitis virus

Temperature-sensitive (ts) mutants of vesicular stomatitis (VS) virus were tested for their pathogenicity and immunogenicity in weanling mice. Compared with the wild-type virus (ts(+)), ts mutants representing genetic complementation groups I, II, and IV were considerably less pathogenic for mice infected by the intracerebral route and caused few deaths after intranasal inoculation. Mice were completely resistant to ts(+) and ts mutants by the intraperitoneal route. Resistance to intracerebral challenge with ts(+) VS virus was only minimal in mice vaccinated intraperitoneally with ts(+) or ts mutants and only moderate in mice vaccinated intranasally with three ts mutants. Intranasal vaccination, particularly with group IV mutants, resulted in solid immunity within 3 days to intranasal challenge with ts(+) virus. VS viral neutralizing antibody was present in the bronchial secretions of mice by 12 h after intranasal inoculation of mutant ts IV44; the bronchial antibody titers declined to undetectable levels between 3 and 7 days after vaccination. Neutralizing antibody was detected in the serum of mice by the third day after intranasal vaccination with ts IV44 and persisted at high level for at least 11 days. Certain classes of ts mutants would appear to be promising candidates for use as attenuated, live virus vaccines.     

小鼠巨细胞病毒开放阅读框M43突变株体内效应研究

小鼠巨细胞病毒RvM4 3突变株的M4 3开放阅读框中插入Tn -gpt序列。突变株和野生型RqM4 3分别通过唾液腺注射感染免疫缺陷型小鼠CM17SCID ,在感染后不同的时间内分别取出小鼠的唾液腺 ,脾 ,肝 ,肺和肾脏 ,测定M4 3突变株的滴度。实验显示RvM4 3在唾液腺 ,脾 ,和肝中的滴度与野生型无显著性差异 ,但在感染 2 1天后 ,肾脏和肺中的病毒滴度有显著性差异。突变型和野生型感染后影响的死亡时间也存在着显著性差异。结果证实M4 3突变不影响体外细胞的复制 ,但对体内不同器官病毒的生长有不同的影响 ,同时有较弱的降低毒性的作用。研究为探索巨细胞病毒的致病机制提供了新的资料。     

Effect of exogenous interferon and an interferon inducer on western equine encephalitis virus disease in a hamster model

Mice are used as models for western equine encephalitis virus (WEEV) infection, but high mortality is generally only seen with intracranial or intranasal challenge, while peripheral inoculation results in approximately 50% mortality and is not dose-dependent. Hamsters were therefore studied as a model for WEEV infection. Hamsters were highly sensitive to intraperitoneal (i.p.) infection with WEEV. Disease progression was rapid, and virus titers in serum, brain, liver, and kidney of infected hamsters peaked between 2 and 4 days post-virus inoculation (dpi). Foci of virus infection were detected in neurons of the cerebral cortex and midbrain. Pre-treatment i.p. with either interferon alfacon-1 (5 microg/kg/day) or with Ampligen (3.2 mg/kg/day) resulted in complete survival, reduced brain titers, and improved weight gain. This model of WEEV infection in hamsters appears to serve as a suitable model for the evaluation of potential therapeutic agents for the treatment of WEE disease.     

Influence of type 2 T cell responses on the severity of encephalitis associated with influenza virus infection

The role of type 2 T cell responses on the severity of post-infectious encephalitis was investigated in a mouse model of influenza virus infection. When mice were infected intracerebrally with 3.0 LD(50) of A/NWS33 strain of influenza virus, they all showed clinical signs of encephalitis, and 90% of them died within 10 days of the infection. However, the post-infectious encephalitis was not demonstrated in mice exposed to 0.5 LD50 of the same virus. The mortality rates of mice infected with 0.5 LD(50) of the virus were increased to levels observed in mice exposed to 3.0 LD(50) of influenza virus infection, after the administration of a mixture of interleukin (IL)-4 and IL-10 (2 ng/mouse each; immediately, 1 and 2 days after the infection). In contrast, mortality rates of mice exposed to 3.0 LD(50) of influenza virus were substantially decreased when these mice were treated with a mixture of monoclonal antibodies directed against IL-4 and IL-10. A predominance of type 2 T cell responses was demonstrated in splenic T cells of mice infected with 3.0 LD(50) of influenza virus, although these responses were minimal in mice infected with 0.5 LD(50) of the virus. After the treatment with the mixture of type 2 cytokines, an increase in the type 2 T cell responses in mice exposed to 0.5 LD(50) of the virus was shown. These results indicate that type 2 T cell responses associated with the viral infection play an important role in the severity of post-infectious encephalitis induced in mice by the intracerebral infection of influenza A virus.     

Distribution of mouse cytomegalovirus in organs of white mice experimentally infected by natural route

One, 10, 21-day-old and adult mice were inoculated by peroral and/or intranasal routes with mouse cytomegalovirus (MCMV). In animals surviving generalized infection, the virus could be demonstrated in salivary glands up to 123 days postinfection (p.i.). In mouse females which had eaten their infected and diseased offspring, the virus was detectable in salivary glands up to day 121, p.i. On day 16 p.i., the virus was present in salivary glands, lungs and kidneys of mice of different age groups, but no virus was recovered from their Gasserian ganglia. These results were compared with those obtained after infection with murine alpha herpesvirus.     

Arbovirus growth inAedes aegypti mosquitoes throughout their viable temperature range

After intrathoracic inoculation of laboratory-bred Aedes aegypti mosquitoes with 3 Yukon isolates of California encephalitis (CE) virus (showshoe hare subtype), Northway (NOR) and Murray Valley encephalitis (MVE) viruses, viral replication was observed following incubation at 13, 21, 35 and 39 degrees C, which constituted the full temperature range of viability of A. aegypti. Rates of viral replication were reduced at low temperatures and accelerated at high temperatures. Virus-specific immunoperoxidase staining of mosquito salivary glands occurred regularly after thoraces attained maximum infectivity levels. At 13 and 21 degrees C, mosquitoes were infected by 10 to 100 times less CE and MVE viruses than mice, but about 10 times more NOR virus was required to infect mosquitoes than mice.     

Experimental rabies in skunks and foxes. Pathogenesis of the spongiform lesions

The pathogenesis of rabies spongiform lesions in striped skunks (Mephitis mephitis) and red foxes (Vulpes vulpes) was studied by light and electron microscopy and peroxidase-antiperoxidase immunocytochemistry. Studies in skunks included use of several street virus variants (different antigenic profiles as tested by monoclonal antibodies) different routes of inoculation (intranasal, intracerebral and intramuscular), immunosuppression of infected skunks, different preparations of virus (brain and salivary gland suspensions and infective tissue culture fluids), and sequential development of the lesions. Foxes (Vulpes vulpes) were infected intramuscularly with a street virus isolate. Except for the group of immunosuppressed skunks, all animals that developed clinical signs of rabies had encephalitis characterized by varying degrees of mononuclear perivascular cuffing, focal gliosis, and Negri bodies. Spongiform change occurred in the neuropil of the grey matter (especially thalamus and cerebral cortex) in rabid animals from all groups, but not in controls or exposed animals that did not develop rabies. Rabies antigen (detected by peroxidase-antiperoxidase immunocytochemistry) occurred only in small amounts in many thalami; some vacuolated areas were devoid of antigen. Ultrastructurally, there was a gradation in lesions from small to large membrane-bound vacuoles in cellular processes (mainly dendrites, less frequently axons) and to large tissue spaces containing granular and/or membranous material. These studies indicate that rabies spongiform change occurs in skunks given street virus of several different antigenic profiles and challenge virus standard rabies virus and that the distribution of the lesions has remarkable similarities to those of the traditional spongiform encephalopathies. The occurrence of the lesion is not affected by the immune response, the route of inoculation of virus, the preparation (suspension of salivary gland or brain, or tissue culture fluid), or the incubation period. The paucity of antigen in many thalami suggests that incorporation of viral components into vacuolar membranes is not necessary for development of the spongiform change. The development of the lesions includes formation of small membrane-bound vacuoles in cellular processes, rapid enlargement (less than 3 days) with compression of adjacent neural tissue, and rupture resulting in the large tissue spaces readily visible by light microscopy.     

The pathogenesis of spinal cord involvement in the encephalomyelitis of mice caused by neuroadapted Sindbis virus infection

Weanling mice develop an acute encephalomyelitis with high mortality after intracerebral inoculation of neuroadapted Sindbis virus. The mice develop kyphoscoliosis and hindlimb paralysis. Immunohistochemical and in situ hybridization studies have demonstrated virus in the gray matter of the brain and spinal cord. Ventral horn cells are prominently infected, providing an anatomical basis for the clinical poliomyelitis. A novel route of spread of inoculated virus within the central nervous system has been found. The virus enters the ventricular system, and then travels caudally in the central canal of the spinal cord where ependymal cells are infected. The virus subsequently spreads into the gray matter. The distribution of virus in the spinal cord is likely dependent both on variations in the susceptibility of neural cells and on this route of entry and subsequent spread.     

Avian influenza virus intranasally inoculated infects the central nervous system of mice through the general visceral afferent nerve

Summary.  To define the route of influenza virus invasion into the central nervous system (CNS), an avian influenza A (H5N3) virus was inoculated into mice intranasally or intravenously. Only the intranasal infection group mice showed depression and retention of gas in the digestive system. Pathological findings in the animals were bronchointerstitial pneumonia and non-suppurative encephalitis restricted to the brain stem. The nerve nucleus primarily affected was the nucleus of solitary tract. Prior to the development of the CNS lesions, viral antigen was detected in vagal and trigeminal ganglia. These results suggest that the primarily replicated virus in the respiratory mucosa ascended to the CNS via sensory nerve routes, inducing lesions in the brain stem, and then spread trans-synaptically in the CNS. Received June 4, 1999/Accepted August 3, 1999     

Puumala virus infection in Syrian hamsters (Mesocricetus auratus) resembling hantavirus infection in natural rodent hosts

The mechanism of hantavirus persistent infection in natural hosts is poorly understood due to a lack of laboratory animal models. Herein, we report that Syrian hamsters (Mesocricetus auratus) infected with Puumala virus (PUUV) at 4 weeks old show persistent infection without clinical symptoms for more than 2 months. IgG and IgM antibodies against the viral nucleocapsid protein and neutralizing antibody were first detectable at 14 days postinoculation (dpi) and maintained through 70 dpi. Viral RNA was first detected from 3 dpi in lungs and blood clots, and was detected in all tissues tested at 7 dpi. The viral RNA persisted for at least 70 days in the lungs, kidney, spleen, heart, and brain. The highest level of RNA copies was observed at 14 dpi in the lungs. Slight inflammatory reactions were observed in the lungs, adrenal glands, and brain. Immunohistochemical analysis revealed that PUUV antigen persisted until 56 dpi in the kidneys and adrenal glands. Infected hamsters showed no body weight loss or clinical signs. These results indicate that PUUV infection in hamsters is quite similar to the hantavirus infection of natural host rodents.