Inhalation anesthetic-induced neuroinvasion by an attenuated strain of West Nile virus in mice

West Nile Virus Encephalitis in a Dog

In November 2002, a 2-year-old, spayed Maltese Terrier in central Mississippi was presented for an acute illness characterized by uncontrolled hyperactivity that rapidly progressed to generalized tremors, ataxia, and intermittent hyperthermia. Postmortem examination after a 2-week course revealed mild, multifocal, nonsuppurative meningo encephalitis, with focal necrosis in the medulla. Reverse transcriptase-nested-polymerase chain reaction for West Nile virus (WNV) was positive on brain and negative on other tissues. Immunohistochemistry was negative on all tissues. The clinical, postmortem, and laboratory findings are consistent with acute encephalitis due to WNV infection. WNV infection should be considered in dogs showing signs of encephalitis when and where WNV and mosquito vectors occur.

West Nile virus infection and postoperative neurological symptoms: a case report and review of the literature

The incidence of West Nile virus, which may cause a range of clinical presentations including subclinical infections, mild febrile illness, meningitis, or encephalitis, has increased over recent years. Rare complications, including optic neuritis, also have been reported. A patient who presented with preoperative asymptomatic West Nile virus developed fever, altered mental status and temporary vision loss after elective multilevel spine fusion surgery.

Duck Tembusu virus exhibits neurovirulence in BALB/c mice

Background

Duck Tembusu virus is a member of the Ntaya group in the genus Flavivirus. The virus has been responsible for severe duck egg-drop syndrome in China since 2010. Its emergence and rapid spread have caused great economic loss for the poultry industry. The epidemiology of the virus infection and the potential threat to public health is of great concern because of the infective and zoonotic nature of flaviviruses.

Results

In this study, the pathogenicity of duck Tembusu virus in BALB/c mice was investigated. Infected mice developed clinical signs, including loss of appetite, ruffled hair, weight loss, disorientation, blindness and paralysis of hind limbs from six days post- infection following intracerebral inoculation. Morbidity was 100%, with mortality ranging from 20 to 80% in three- to eight-week-old mice. High virus titers were recovered from the brain, and the virus was distributed in several organs. Histologically, there was widespread non-suppurative encephalitis in the brain. Lymphocyte depletion in the spleen was observed, along with fatty degeneration in the liver and kidney.

Conclusions

Our results demonstrate, for the first time, that duck Tembusu virus is highly neurovirulent in BALB/c mice. The mouse model used in this work was able to produce Tembusu virus infection and could be useful for elucidating some of the aspects of the pathophysiology of other flavivirus infections.

West Nile 25A virus infection of B-cell-deficient ((micro)MT) mice: characterization of neuroinvasiveness and pseudoreversion of the viral envelope protein

The attenuated West Nile virus 25A strain (WN25A) was investigated for its neuroinvasive properties in B-cell-deficient (microMT) mice. After peripheral inoculation, WN25A caused fatal encephalitis in the majority of 6-8-week-old mice, characterized by a systemic infection with viraemia, moderate virus burdens in peripheral tissues and a high titre of brain-associated virus. Mice generally succumbed to infection within a few weeks of infection. However, others survived for as long as 10 weeks, and some for even longer. Normal age-matched C57BL/6 mice showed no signs of illness after inoculation with WN25A virus. Nucleotide sequencing of WN25A viruses recovered from the brains of B-cell-deficient mice revealed that the conserved N-linked glycosylation site in the viral envelope protein was abolished by substitution of a serine residue at position 155. This was found to be a pseudoreversion relative to the wild-type WN-Israel strain, based on virulence testing of one such brain-associated virus in both B-cell-deficient and normal C57BL/6 mice. This study provides further characterization of the mouse virulence properties of the attenuated WN25A virus in the context of B-cell deficiency. Replication in these mice does not involve rapid neuroadaptation or reversion of WN25A virus to a neuroinvasive phenotype. Molecular modelling studies suggest a difference in local structure of the E protein associated with either an asparagine or serine residue at position 155 compared with the tyrosine found in the virulent parental WN-Israel virus.

Nonrecurring transient cortical blindness after coronary angiography: A role for hypoventilation and hypercarbia?

A 73-year-old morbidly obese patient suffered cortical blindness following coronary angiography. Symptoms rapidly resolved and did not recur following a repeated procedure. Hypoventilation due to narcotics with subsequent hypercarbia and blood-brain barrier breaching may be implicated in the pathogenesis of this complication.

Modeling hamsters for evaluating West Nile virus therapies

A hamster model infected with a New York crow brain isolate of West Nile virus (WNV) was characterized for evaluating potential antiviral therapies. Older hamsters (7-11 weeks old) had a lower mortality of approximately 50% and more apparent disease signs as compared to >90% mortality in younger hamsters and mice. Disease signs such as limb strength, lacrimation, front limb tremors, somnolence, and deficiencies in neurological responses were noted at different times after viral injection. Weight loss was a marker for WNV disease signs, whereas, the ability to climb up an inclined ramp was associated with whether the animals survived the disease or died. Infectious WNV assays performed on tissues from hamsters during development of the infection indicated that viral titers peaked first in plasma, but that titers were eventually highest in kidney tissue. Viral titers achieved maximal levels in brain tissue on 6 dpi, which was 1-2 days before strong neurological signs and death started to occur. Maximal spleen and plasma titers were achieved sooner in young hamsters as compared with older hamsters, which correlated with increased susceptibility. To test the hypothesis that older hamsters would be more sensitive for identifying antiviral effects, Infergen, a consensus human interferon-alpha highly active against WNV in cell culture, was administered subcutaneously to older and younger hamsters beginning on 2 dpi. The effects of Infergen on weight change, survival, and climbing ability of infected animals were more apparent in older hamsters than in younger hamsters. The use of older hamsters is another WNV-infectious model, in addition to mice, for evaluating potential antiviral therapies.

Vaccines and animal models for arboviral encephalitides

Arthropod-borne viruses ("arboviruses") cause significant human illness ranging from mild, asymptomatic infection to fatal encephalitis or hemorrhagic fever. The most significant arboviruses causing human illness belong to genera in three viral families, Togaviridae, Flaviviridae, and Bunyaviridae. These viruses represent a significant public health threat to many parts of the world, and, as evidenced by the recent introduction of the West Nile virus (WNV) to the Western Hemisphere, they can no longer be considered specific to any one country or region of the world. Like most viral diseases, there are no specific therapies for the arboviral encephalitides; therefore, effective vaccines remain the front line of defense for these diseases. With this in mind, the development of new, more effective vaccines and the appropriate animal models in which to test them become paramount. In fact, for many important arboviruses (e.g. California serogroup and St. Louis encephalitis viruses), there are currently no approved vaccines available for human use. For others, such as the alphaviruses, human vaccines are available only as Investigational New Drugs, and thus are not in widespread use. On the other hand, safe and effective vaccines against tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JEV) have been in use for decades. New challenges in vaccine development have been met with new technologies in vaccine research. Many of the newer vaccines are now being developed by recombinant DNA technology. For example, chimeric virus vaccines have been developed using infectious clone technology for many of the arboviruses including, WNV, JEV, and TBEV. Other successful approaches have involved the use of naked DNA encoding and subsequently expressing the desired protective epitopes. Naked DNA vaccines have been used for TBEV and JEV and are currently under development for use against WNV. The development of less expensive, more authentic animal models to evaluate new vaccines against arboviral diseases will become increasingly important as these new approaches in vaccine research are realized. This article reviews the current status of vaccines, both approved for use and those in developmental stages, against the major arboviral encephalitides causing human disease. In addition, research on animal models, both past and present, for these diseases are discussed.