Acute flaccid paralysis and West Nile virus infection

Emerging flaviviruses: the spread and resurgence of Japanese encephalitis, West Nile and dengue viruses

Mosquito-borne flaviviruses provide some of the most important examples of emerging and resurging diseases of global significance. Here, we describe three of them: the resurgence of dengue in tropical and subtropical areas of the world, and the spread and establishment of Japanese encephalitis and West Nile viruses in new habitats and environments. These three examples also illustrate the complexity of the various factors that contribute to their emergence, resurgence and spread. Whereas some of these factors are natural, such as bird migration, most are due to human activities, such as changes in land use, water impoundments and transportation, which result in changed epidemiological patterns. The three examples also show the ease with which mosquito-borne viruses can spread to and colonize new areas, and the need for continued international surveillance and improved public health infrastructure to meet future emerging disease threats.

Neuromuscular Manifestations of Human West Nile Virus Infection

Physicians in areas with active West Nile virus (WNV) transmission should be aware that WNV infection can present as a polio-like syndrome and that the spectrum of neuromuscular signs and symptoms may range from acute flaccid paralysis in the absence of fever or meningoencephalitis to subjective weakness and disabling fatigue. This awareness will help to avoid less tenable diagnoses and the morbidity associated with inappropriate treatment. Although anterior horns are the major site of spinal cord pathology, inflammatory changes also may involve spinal sympathetic neurons and ganglia, providing an explanation for the autonomic instability seen in some patients with WNV infection. However, the role that autonomic dysfunction plays in the morbidity and mortality of human WNV infection has to be elucidated. Another unresolved issue with important neuromuscular implications is whether WNV infection may lead to autoimmune disease. Support for this contention arises from reports of WNV patients presenting with various neuromuscular diseases that have a presumed autoimmune mechanism, including Guillain-Barre syndrome, other demyelinating neuropathies, myasthenia gravis, brachial plexopathies, and stiff-person syndrome. Although there is no specific treatment or vaccine currently approved for WNV infection in humans, and the standard is supportive care only, several drugs that can alter the cascade of immunobiochemical events leading to neuronal death may be potentially useful. Among these agents, minocycline (a semisynthetic derivative of tetracycline), interferon alpha, and high-dose corticosteroids are candidate therapies, although human experience is limited. In addition, passive immunization with intravenous immune globulin containing WNV-specific antibodies seems promising, based on anecdotal human reports.

West Nile virus—an old virus learning new tricks?

West Nile virus (WNV) has spread across the United States causing annual outbreaks since its emergence in 1999. Although severe disease develops only in about 1% of infections, WNV has claimed a total of 564 lives in the 5 years from 1999 to 2003. Observation of flaccid paralysis due to WNV infection at a higher incidence than previously documented and the devastating mortality recorded in infected American bird species triggered concerns about a potentially enhanced virulence of this virus. Here we summarize recent observations made during the American outbreaks regarding host range and transmission modes of WNV, and discuss epidemiological aspects of the emergence of this pathogen in the new habitat.

West Nile Virus: a case report with flaccid paralysis and cervical spinal cord: MR imaging findings

We present a case of serologically proved West Nile virus (WNV) flaccid paralysis of the right upper extremity. Radiologic correlation revealed striking T2 hyperintensities in the anterior horns of the cervical spinal cord, similar to those seen in cases of poliomyelitis. Recognition of the MR imaging findings in cases of WNV flaccid paralysis can provide early evidence of infection.

Differential diagnosis of West Nile encephalitis

PURPOSE OF REVIEW

This article reviews recent developments in West Nile encephalitis. Because of the large number of individuals infected in the United States, an expanded spectrum of the disease has been recognized. Flaccid paralysis presenting as poliomyelitis-like syndrome is being increasingly recognized.

RECENT FINDINGS

Since 1999, West Nile encephalitis in the United States has involved thousands of patients providing an opportunity to observe the protean manifestations of the virus. Recently, ophthalmological manifestations have been described that appear to be common and specific for the virus. Clinicians in endemic areas should be careful to distinguish between West Nile encephalitis and its mimics. The virus may occur in patients with underlying disorders that have encephalopathy as a clinical feature, and clinicians should test for the virus during the mosquito season, even in patients that appear to have an explanation for their encephalopathy. West Nile encephalitis may present as viral aseptic meningitis, meningoencephalitis, or encephalitis. Muscle weakness may or may not accompany any of these clinical variants. This virus may be transmitted via blood transfusion.

SUMMARY

Clinical manifestations of West Nile encephalitis continue to expand following each year's outbreaks. New neurologic and ophthalmologic manifestations continue to be described. Because of the protean manifestations, testing should be carried out during mosquito season, even in patients that have another explanation for their encephalopathy. There is no effective therapy. Flaccid paralysis may be prolonged/permanent. Prognosis may be related to the degree of relative lymphopenia on presentation, the degree of elevation of serum ferritin levels and advanced age. The course of West Nile encephalitis and its clinical manifestations are the same in normal and compromised hosts.

Viral encephalitis: neuropsychiatric and neurobehavioral aspects

Viral encephalitis, a condition in which a virus infects the brain and produces an inflammatory response, affects approximately 20,000 individuals per year in the United States. The viral encephalidities include sporadic and epidemic acute viral encephalidities and subacute and chronic/progressive viral encephalitis or encephalomyelitis. In people who survive these conditions, postencephalitic impairments of elemental neurologic, cognitive, emotional, and behavioral function are common. This article will provide a brief overview of the diagnosis and acute management of acute viral infections of the central nervous system. The neurologic and neuropsychiatric features, neuropathologies, and treatments of two of the more common types of acute viral encephalitis in North America--herpes simplex encephalitis and West Nile encephalitis--will be reviewed. The current and future role of psychiatrists and neuropsychiatrists in the care and study of individuals with these conditions will be discussed.

Performance of immunoglobulin G (IgG) and IgM enzyme-linked immunosorbent assays using a West Nile virus recombinant antigen (preM/E) for detection of West Nile virus- and other flavivirus-specific antibodies

Focus Technologies developed an indirect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) and a mu-capture IgM ELISA for the detection of West Nile virus (WNV)-specific antibodies based on a WNV preM/E protein recombinant antigen. Normal and disease state serum panels were used to assess the performance characteristics of the two WNV ELISA kits. Totals of 807 and 1,423 sera were used to assess the IgG ELISA and IgM ELISA kits, respectively. The Focus Technologies IgG ELISA had a sensitivity of 97.6% and a specificity of 92.1% (excluding non-WNV flavivirus sera). The comparative method for WNV IgG may lack sensitivity in detecting IgG in early WNV infection, so the specificity of the Focus IgG ELISA may be higher than 92.1%. When sera from patients either infected with or vaccinated against other flaviviruses were tested on the WNV IgG assay, 35% of the sera reacted as positive for WNV IgG. Yellow fever and Japanese encephalitis vaccinees were less reactive in the IgG ELISA than St. Louis and dengue fever patients. The Focus Technologies IgM ELISA had a sensitivity and a specificity of 99.3% (excluding the non-WNV flavivirus sera). The overall cross-reactivity for the IgM ELISA to flavivirus sera was 12%, with 31% of St. Louis encephalitis patients found to be WNV IgM positive and no yellow fever vaccinees found to be WNV IgM positive. In a selected population of 706 sera, 15 false-positive WNV IgM sera were identified. The use of a background subtraction method for the IgM ELISA eliminated all 15 false-positive results, giving a specificity of 100% for the Focus IgM ELISA.

West Nile virus: where are we now?

Since the publication of a comprehensive review on West Nile virus (WNV) in 2002, there has been substantial progress in understanding of transmission, epidemiology, and geographic distribution of the virus and manifestations of disease produced by the infection. There have also been advances in development of diagnostic and therapeutic agents and vaccines. Nevertheless, many questions about the epidemic remain unanswered, and several new issues have arisen--for example: whether the epidemic will increase as the virus spreads to the Pacific coast of North America; whether arthropods other than mosquitoes will act as vectors for the infection; whether WNV will spread to South America and cause an epidemic there; whether the distribution of WNV in Asia and Europe will increase; and whether adaptation of WNV to new ecosystems will produce viruses with altered genetic and phenotypic properties. This review aims to provide an update on knowledge of WNV biology that can be used to highlight the advances in the field during the past 2 years and help to define the questions that academic, industrial, and public-health communities must address in development of measures to control WNV disease.

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.

Spinal cord neuropathology in human West Nile virus infection

CONTEXT

During the 1999 New York City West Nile virus (WNV) outbreak, 4 patients with profound muscle weakness, attributed to Guillain-Barré syndrome, were autopsied. These cases were the first deaths caused by WNV, a flavivirus, to be reported in the United States. The patients' brains had signs of mild viral encephalitis; spinal cords were not examined. During the 2002 national epidemic, several patients in Mississippi had acute flaccid paralysis. Electrophysiologic studies localized the lesions to the anterior horn cells in the spinal gray matter. Four of 193 infected patients in Mississippi died and were autopsied. All 4 experienced muscular weakness and respiratory failure that required intubation. Postmortem examinations focused on the spinal cord.

OBJECTIVE

To emphasize apparent tropism of WNV for the ventral gray matter of the spinal cord.

DESIGN

Cerebral hemispheres, basal ganglia, diencephalon, brainstem, cerebellum, and spinal cord sections were stained with hematoxylin-eosin and incubated with antibodies to T cells, B cells, and macrophages/microglial cells.

RESULTS

We identified neuronophagia, neuronal disappearance, perivascular chronic inflammation, and microglial proliferation in the ventral horns of the spinal cord, especially in the cervical and lumbar segments. Loss of ganglionic neurons, nodules of Nageotte, and perivascular lymphocyte aggregates were found in dorsal root and sympathetic ganglia. Severity of cellular reaction was proportional to the interval length between patient presentation and death.

CONCLUSION

West Nile virus caused poliomyelitis. Injury to spinal and sympathetic ganglia mirrored the damage to the spinal gray matter. The disappearance of sympathetic neurons could lead to the autonomic instability observed in some WNV patients, including labile vital signs, hypotension, and potentially lethal cardiac arrhythmias.

New insights on the neuropathology of West Nile virus

West Nile virus (WNV) is a mosquito-borne disease that emerged in North America where it caused in 2002 te largest arboviral meningoencephalitis outbreak ever recorded in this area. The viral variant responsible for this outbreak has been found to share 99.7% identity over the entire genome with the viral variant that caused the epizootic in Israel in 1998 and has been referred as "Isr98/NY99". It has been shown to exhibit an increased neurovirulence in humans, as well as in experimental infections in different animal models. Mouse model has allowed to demonstrate the preferential infection of neurons within the central nervous system and to point out the genetic determinism of host susceptibility to WNV. In murine neural cell cultures, the selective infection of neurons was accompanied by physiopathological changes and a cytopathic effect, showing the direct effect of infection of neurons as one of the causes of WNV neuropathogenicity.

West Nile encephalitis and myelitis

PURPOSE OF REVIEW

This article will review the recent experience with West Nile virus encephalitis and myelitis.

RECENT FINDINGS

In the summer of 2003, the majority of cases of West Nile virus infection in the United States were reported from the western states. The transmission of West Nile virus through blood transfusion and organ transplantation was recognized and blood collection agencies implemented West Nile virus nucleic acid-amplification tests to identify infected donors. Intrauterine transmission of West Nile virus infection was reported. The identification of West Nile virus immunoglobulin M in cerebrospinal fluid is the recommended test to document central nervous system infection, but this test may not be positive in spinal fluid collected less than 8 days after the onset of symptoms. Serial samples of cerebrospinal fluid may be required to identify the antibodies. A clinical trial got underway to evaluate the efficacy of human immunoglobulin with high titers of antibodies to West Nile virus in the therapy of West Nile virus encephalitis and myelitis.

SUMMARY

In the summer of 2003, the majority of cases of West Nile virus infection in the United States were reported from states west of the Mississippi river. The identification of West Nile virus IgM in CSF is the recommended test to document CNS infection. A single serum antibody titer is an unreliable test of recent infection.

West Nile virus infection: a pediatric perspective

West Nile virus (WNV) infection recently became a major public health concern in the western hemisphere. This article describes recent information regarding previously unrecognized mechanisms of WNV transmission and reviews clinical manifestations of WNV infection, diagnostic tests, and prevention strategies from a pediatric perspective. WNV is transmitted to humans primarily through the bite of infected mosquitoes, but during the epidemic that spread across North America in 2002, transmission of WNV through blood transfusions and organ transplantation was described for the first time. Individual case reports indicate that WNV can be transmitted also in utero and probably through breast milk. Although most WNV infections are asymptomatic, the virus causes a broad range of manifestations from uncomplicated febrile illness to meningitis, neuropathies, paralysis, and encephalitis. Severe manifestations of WNV infection are far more common in adults than in children, but 105 cases of neuroinvasive WNV disease were reported among children in the United States in 2002. The distribution of the virus in North America continues to spread. WNV infection can be diagnosed by detecting WNV-specific antibody in cerebrospinal fluid or serum, or by detecting the virus or viral nucleic acid in cerebrospinal fluid, blood, or tissues. Cornerstones of prevention include personal protection against mosquitoes, including wearing insect repellent, reducing populations of vector mosquitoes, and screening the blood supply for WNV-contaminated blood donations.

Alexander the Great and West Nile virus encephalitis

Alexander the Great died in Babylon in 323 BC. His death at age 32 followed a 2-week febrile illness. Speculated causes of death have included poisoning, assassination, and a number of infectious diseases. One incident, mentioned by Plutarch but not considered by previous investigators, may shed light on the cause of Alexander’s death. The incident, which occurred as he entered Babylon, involved a flock of ravens exhibiting unusual behavior and subsequently dying at his feet. The inexplicable behavior of ravens is reminiscent of avian illness and death weeks before the first human cases of West Nile virus infection were identified in the United States. We posit that Alexander may have died of West Nile encephalitis.

West Nile virus: epidemiology, clinical presentation, diagnosis, and prevention

West Nile virus was recognized in the United States for the first time in 1999, when it caused an epidemic of encephalitis and meningitis in New York City, NY. Since then, the disease has been steadily moving westward, and human cases were recognized in 39 states and the District of Columbia in 2002. The infection is caused by a flavivirus that is transmitted from birds to humans through the bite of culicine mosquitoes. Most infections are mild, with symptoms primarily being fever, headache, and myalgias. People older than 50 years are at highest risk of severe disease, which may include encephalomyelitis. In 2002, 5 new modes of transmission were recognized: blood product transfusion, organ transplantation, breast-feeding, transplacental transmission, and occupational exposure in laboratory workers. The transmission season was long, with cases occurring into December in some parts of the United States. Currently, there is no specific drug treatment or vaccine against the infection, and avoiding mosquito bites is the best way to protect against the disease.