West Nile encephalitis epidemic in southeastern Romania

Potential vectors of West Nile virus following an equine disease outbreak in Italy

In the late summer of 1998, an outbreak of equine encephalomyelitis due to West Nile virus (WNV) occurred in the Tuscany region of central Italy. The disease was detected in 14 race horses from nine localities in four Provinces: Firenze, Lucca, Pisa and Pistoia. The outbreak area included Fucecchio wetlands (1800 ha), the largest inland marsh in Italy, and the adjacent hilly Cerbaie woodlands with farms breeding horses. To detect potential vectors of WNV, entomological surveys of Fucecchio and Cerbaie were undertaken during 1999-2002 by collecting mosquito larvae from breeding sites and adult mosquitoes by several methods of sampling. Among 6023 mosquitoes (Diptera: Culicidae) collected, 11 species were identified: Aedes albopictus (Skuse), Ae. vexans (Meigen), Anopheles atroparvus Van Thiel, An. maculipennis Meigen s.s., An. plumbeus Stephens, Culex impudicus Ficalbi, Cx. pipiens L., Culiseta longiareolata Macquart), Ochlerotatus caspius (Pallas), Oc. detritus (Haliday) and Oc. geniculatus (Olivier). In Fucecchio marshes, Cx. impudicus predominated with seasonal peak densities in spring and autumn: its greatest abundance during early spring coincides with arrival of migratory birds from Africa. In Cerbaie hills, Cx. pipiens predominated with peak population density in late summer. No viruses were isolated from 665 mosquitoes processed. These findings, plus other data on Italian mosquito bionomics, suggest a possible mode of WNV transmission involving the most abundant Culex in the Fucecchio-Cerbaie areas. Culex impudicus, being partly ornithophilic, might transmit WNV from migratory to non-migratory birds during springtime; Cx. pipiens, having a broader host range, would be more likely to transmit WNV from birds to horses and, perhaps, to humans by late summer.

West Nile virus: an overview of its spread in Europe and the Mediterranean basin in contrast to its spread in the Americas

West Nile (WN) virus is a mosquito-transmitted flavivirus. It is widely distributed in Africa, the Middle East, Asia, and southern Europe and was recently introduced to North America. Birds are involved in the cycle of transmission as amplifying hosts. Humans and horses are considered accidental dead-end hosts. WN fever was initially considered a minor arbovirosis, usually inducing a nonsymptomatic or a mild flu-like illness in humans, but some cases of encephalitis associated with fatalities were reported in Israel in the 1950s. After two silent decades, several human and equine outbreaks of fatal encephalitis occurred from 1996 to 2000 in Romania, Morocco, Tunisia, Italy, Russia, Israel, and France. In Romania, a few cases of WN encephalitis in humans are noticed every year, and in France, recent WN infections have been detected in monitored sentinel birds in 2001 and 2002. Phylogenetic studies have shown two main lineages of WN strains. Strains from lineage I are present in Africa, India, and Australia and are responsible for the outbreaks in Europe and in the Mediterranean basin, and strains from lineage II have been reported only in sub-Saharan Africa. In 1998, a virulent WN strain from lineage I was identified in dying migrating storks and domestic geese showing clinical symptoms of encephalitis and paralysis in Israel. A nearly identical WN strain suddenly emerged in New York in 1999, killing thousands of native birds and causing fatal cases in humans. The virus is now well established in the New World, and it disseminates rapidly. New modes of transmission through blood donations, organ transplants, and the intrauterine route have been reported. In Europe, an enhanced surveillance of WN infection in humans, horses, birds, and vectors may reveal the presence of the virus in different locations. Nevertheless, outbreaks of WN virus remain unpredictable. Further coordinated studies are needed for a better understanding of the ecology and the pathogenicity of the WN virus.

An occipital lobe epileptogenic focus in a patient with West Nile encephalitis

Although most human cases of West Nile (WN) fever are benign, approximately 1% produce severe neurological illness. Meningitis and/or encephalitis comprise 75% of hospitalized cases with seizures in 10-15%. Occipital lobe seizures, often mimicking other primary seizure types due to extra-occipital spread, is uncommon in adults and especially so from an infectious origin. A case of WN encephalitis presenting with a simple partial seizure, focal motor, resulting from an occipital epileptogenic focus is reported. The atypical epileptogenic location of the case and the observed frequency of seizures in WN encephalitis suggest that this virus is particularly irritative to cortical neuronal networks. Thus when seizures especially with atypical EEG patterns present during an acute febrile illness in the warmer months, WN encephalitis should be considered.

Community-acquired West Nile virus infection in solid-organ transplant recipients

BACKGROUND

West Nile virus (WNV) is rapidly spreading through North America. In the general population, the majority of WNV infections are asymptomatic. During 2002, an outbreak of WNV occurred in Toronto, Canada. We observed four cases of severe symptomatic community-acquired WNV infection in our organ-transplant population.

METHODS

Patient data were obtained from chart review. WNV was diagnosed by acute and convalescent serology. Incidence was compared with data obtained from a population-based surveillance program.

RESULTS

Four transplant patients had WNV encephalitis (n=3) or meningitis (n=1). Mean age was 44.5 (range 26-58) years and transplant type included kidney (n=2), liver (n=1), and heart (n=1). The mean time posttransplant was 3.8 years (range 2 months-8 years). The presenting symptoms were fever (4/4), confusion (3/4), headache (4/4), and weakness (2/4). Cerebrospinal fluid showed a pleocytosis in all patients and elevated protein in three of four. All patients had identifiable occupational or recreational risk factors. There was no evidence that the infection was acquired by transfusion or the transplanted organ. Outcomes were full recovery (2/4), lower limb paralysis (1/4), and death (1/4). On the basis of active population surveillance data, the rate of WNV meningoencephalitis in the general population in the Toronto area was approximately 5 per 100,000. This compares to four cases in a transplant population of 2,000 patients (rate 200 per 100,000) (P<0.001).

CONCLUSIONS

Transplant patients are likely at greater risk of severe neurologic disease caused by community-acquired WNV compared with the general population. Prevention of transmission and patient education may be more important in this population.

Antibody prophylaxis and therapy against West Nile virus infection in wild-type and immunodeficient mice

West Nile virus (WNV) is a mosquito-borne Flavivirus that causes encephalitis in a subset of susceptible humans. Current treatment for WNV infections is supportive, and no specific therapy or vaccine is available. In this study, we directly tested the prophylactic and therapeutic efficacy of polyclonal antibodies against WNV. Passive administration of human gamma globulin or mouse serum prior to WNV infection protected congenic wild-type, B-cell-deficient ( micro MT), and T- and B-cell-deficient (RAG1) C57BL/6J mice. Notably, no increased mortality due to immune enhancement was observed. Although immune antibody completely prevented morbidity and mortality in wild-type mice, its effect was not durable in immunocompromised mice: many micro MT and RAG1 mice eventually succumbed to infection. Thus, antibody by itself did not completely eliminate viral reservoirs in host tissues, consistent with an intact cellular immune response being required for viral clearance. In therapeutic postexposure studies, human gamma globulin partially protected against WNV-induced mortality. In micro MT mice, therapy had to be initiated within 2 days of infection to gain a survival benefit, whereas in the wild-type mice, therapy even 5 days after infection reduced mortality. This time point is significant because between days 4 and 5, WNV was detected in the brains of infected mice. Thus, passive transfer of immune antibody improves clinical outcome even after WNV has disseminated into the central nervous system.

Innate and adaptive immune responses determine protection against disseminated infection by West Nile encephalitis virus

WNV continues to spread throughout the Western Hemisphere as virus activity in insects and animals has been reported in the United States, Canada, Mexico, and the Caribbean islands. West Nile virus (WNV) infects the central nervous system and causes severe disease primarily in humans who are immunocompromised or elderly. In this review, we discuss the mechanisms by which the immune system limits dissemination of WNV infection. Recent experimental studies in animals suggest important roles for both the innate and the adaptive immune responses in controlling WNV infection. Interferons, antibody, complement components and CD8+ T cells coordinate protection against severe infection and disease. These findings are analyzed in the context of recent approaches to vaccine development and immunotherapy against WNV.

Neurovirulence and host factors in flavivirus encephalitis--evidence from clinical epidemiology

Japanese encephalitis virus (JEV) and West Nile virus (WNV) provide some of the most important examples of emerging zoonotic viral encephalitides. For these flaviviruses, only a small proportion of those infected develop clinical features, and these may range from a non-specific flu-like illness to a severe fatal meningoencephalitis, often with Parkinsonian features, or a poliomyelitis-like flaccid paralysis. The factors governing the clinical presentations, and outcome of flavivirus infections are poorly understood, but studies have looked at viral virulence determinants and the host immune response. Previous studies on JEV have suggested that the distribution of the four genotypes across Asia may relate to the differing clinical epidemiology (epidemic disease in the north, endemic disease in the south). However, new data based on the complete nucleotide sequence of a virus representing one of the oldest lineages, and phylogenetic analyses of all JEV strains for which genetic data are available, suggest that the distribution is best explained in terms of the virus' origin in the Indonesia-Malaysia region (where all genotypes have been found), and the spread of the more recent genotypes to new geographical areas. Clinical studies have shown that innate immunity, as manifested by interferon alpha levels, is important in JEV and other flaviviruses, but treatment with interferon alpha did not improve the outcome. A failure of the humoral immune response, is associated with death from encephalitis caused by JEV and WNV. Cellular immunity has been less well characterized, but CD8+ and CD4+ T cells are thought to be important.

Emergence and virulence of encephalitogenic arboviruses

Each arbovirus that causes encephalitis is geographically restricted by the availability of appropriate vectors and reservoir hosts. These viruses evolve regionally by recombination, reassortment and point mutation and can "emerge" as causes of human encephalitis through extension to new geographic regions or by selection of more virulent or more efficiently transmitted virus variants. The properties of arboviruses that result in encephalitis involve efficient replication in peripheral tissues after initiation of infection, production of a viremia, entry into the central nervous system and efficient replication in neurons with spread to additional populations of neurons. Many of these steps are determined by properties of the envelope glycoproteins responsible for cellular attachment, but changes in noncoding regions of the genome, as well as in other structural and nonstructural proteins, also contribute to neurovirulence.

Infectious causes of acute flaccid paralysis

PURPOSE OF REVIEW

Although acute flaccid paralysis (AFP) is more frequently seen in the tropics than in temperate regions, recent outbreaks of West Nile virus (WNV) in North America have drawn attention to this important presentation. Starting with anatomical and neurophysiological considerations, this article examines data on AFP caused by WNV, and considers recent data on paralysis caused by enteroviruses, and Guillain-Barré syndrome (GBS).

RECENT FINDINGS

Neurophysiological, radiological and pathological studies suggest WNV causes AFP by damaging anterior horn cells in the spinal cord. The clinical presentation is probably best described as a 'poliomyelitis-like illness', and the disease as 'WNV myelitis'. Other findings during the recent outbreaks include increasing recognition of a Parkinson's-disease like presentation, and descriptions of virus transmission in blood transfusions and transplanted organs. GBS is now recognized as several disorders characterized by immune-mediated attack on peripheral nerves: in acute inflammatory demyelinating polyneuropathy the myelin sheath and Schwann cell of sensory and motor nerves are targeted; acute motor axonal and acute motor and sensory axonal neuropathy often follow Campylobacter jejuni enteritis and are associated with antibodies against the ganglioside component of the nerve axolemmal membrane. In Asia-Pacific, enterovirus 71 has caused outbreaks of neurological diseases with AFP and encephalitis, but no single genogroup of virus appears responsible for severe disease.

SUMMARY

Despite the near eradication of poliomyelitis, AFP caused by viruses remains an important clinical presentation. Distinguishing direct viral causes from GBS is important for public health reasons, and to avoid inappropriate therapies.

A critical role for induced IgM in the protection against West Nile virus infection

In humans, the elderly and immunocompromised are at greatest risk for disseminated West Nile virus (WNV) infection, yet the immunologic basis for this remains unclear. We demonstrated previously that B cells and IgG contributed to the defense against disseminated WNV infection (Diamond, M.S., B. Shrestha, A. Marri, D. Mahan, and M. Engle. 2003. J. Virol. 77:2578–2586). In this paper, we addressed the function of IgM in controlling WNV infection. C57BL/6J mice (sIgM^−/−) that were deficient in the production of secreted IgM but capable of expressing surface IgM and secreting other immunoglobulin isotypes were vulnerable to lethal infection, even after inoculation with low doses of WNV. Within 96 h, markedly higher levels of infectious virus were detected in the serum of sIgM^−/− mice compared with wild-type mice. The enhanced viremia correlated with higher WNV burdens in the central nervous system, and was also associated with a blunted anti-WNV IgG response. Passive transfer of polyclonal anti-WNV IgM or IgG protected sIgM^−/− mice against mortality, although administration of comparable amounts of a nonneutralizing monoclonal anti-WNV IgM provided no protection. In a prospective analysis, a low titer of anti-WNV IgM antibodies at day 4 uniformly predicted mortality in wild-type mice. Thus, the induction of a specific, neutralizing IgM response early in the course of WNV infection limits viremia and dissemination into the central nervous system, and protects against lethal infection.

Electroencephalography Findings in Adult Patients with West Nile Virus--Associated Meningitis and Meningoencephalitis

Eighteen adult patients with serologically confirmed West Nile virus (WNV)-associated meningitis or meningoencephalitis were admitted to our hospital during the 2000 West Nile fever outbreak in Israel. Thirteen of the patients had a more severe and prolonged clinical course, and an electroencephalogram (EEG) was, therefore, requested. A specific EEG pattern was seen in 8 patients, consisting of generalized slowing, which was more prominent over the anterior regions. Generalized slowing that was prominent over the temporal area was seen in 2 patients, and intermittent slowing over the temporal region was seen in 1 patient. Two patients had normal EEG findings. We suggest that WNV meningoencephalitis should be considered in the differential diagnosis of meningitis or meningoencephalitis with a prolonged clinical course and anteriorly predominant slowing on an EEG.

Aseptic meningitis epidemic during a West Nile virus avian epizootic

While enteroviruses have been the most commonly identified cause of aseptic meningitis in the United States, the role of the emerging, neurotropic West Nile virus (WNV) is not clear. In summer 2001, an aseptic meningitis epidemic occurring in an area of a WNV epizootic in Baltimore, Maryland, was investigated to determine the relative contributions of WNV and enteroviruses. A total of 113 aseptic meningitis cases with onsets from June 1 to September 30, 2001, were identified at six hospitals. WNV immunoglobulin M tests were negative for 69 patients with available specimens; however, 43 (61%) of 70 patients tested enterovirus-positive by viral culture or polymerase chain reaction. Most (76%) of the serotyped enteroviruses were echoviruses 13 and 18. Enteroviruses, including previously rarely detected echoviruses, likely caused most aseptic meningitis cases in this epidemic. No WNV meningitis cases were identified. Even in areas of WNV epizootics, enteroviruses continue to be important causative agents of aseptic meningitis.

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.

West Nile virus encephalitis causing fatal CNS toxicity after hematopoietic stem cell transplantation

We describe here a patient who died of progressive CNS deterioration following allogeneic stem cell transplant with West Nile virus as the sole pathogen on the cerebrospinal fluid and brain tissue analysis. A 50-year-old male with Philadelphia chromosome-positive acute lymphocytic leukemia (ALL) underwent allogeneic PBSCT from his HLA identical sister. After engraftment, the patient developed fever with progressive and ultimately fatal neurological deterioration. Imaging studies of the brain including CT and MRI scans were remarkable for mild low attenuation lesions of the white matter. CSF analysis was negative for neoplastic cells, bacteria, AFB, CMV, HSV, fungal infections and leukemic relapse. However, serological analysis of both the serum and CSF was positive for West Nile virus-specific IgM antibodies. At autopsy, West Nile virus PCR and cultures were positive in the mid-brain tissue. Electron micrographs showed evidence of viral particles. Given the recent increase in the spread of West Nile virus infections and the increased susceptibility of BMT patients to infectious complications, West Nile virus encephalitis should be considered in patients undergoing transplantation.

West Nile Encephalitis in 2 Hematopoietic Stem Cell Transplant Recipients: Case Series and Literature Review

Most human cases of West Nile virus infection are acquired via bites from an infected mosquito. In some cases, infection may also be transmitted by infected blood products or transplanted organs. There have been recent publications suggesting that chemotherapy and immunosuppression may increase a person's risks of developing central nervous system disease if the person is infected with the West Nile virus. Because patients undergoing hematopoietic stem cell transplantation not only are immunocompromised, but also receive multiple blood products, they are at a particularly high risk for acquiring symptomatic disease if exposed to the West Nile Virus. We describe here 2 patients who underwent hematopoietic transplantation at our institution and subsequently developed fatal West Nile virus infections.

Usutu virus activity in Austria, 2001–2002

Usutu virus (USUV), a member of the mosquito-borne clade within the Flaviviridae family, was responsible for avian mortality in Austria in 2001. In 2002, the virus continued to kill birds, predominantly blackbirds. High numbers of avian deaths were recorded within the city of Vienna and in surrounding districts of the federal state of Lower Austria, while single die-offs were noticed in the federal states of Styria and Burgenland. A total of 72 birds were submitted for laboratory examination, 30 of which tested positive for USUV by immunohistochemistry and/or polymerase chain reaction. Laboratory-confirmed cases of USUV infection originated from the federal states of Vienna and Lower Austria only. The data show that (i) USUV has managed to overwinter and has been able to establish a transmission cycle in Austria, (ii) the virus seems to have become a resident pathogen of Austria with a tendency to spread to other geographic areas, and (iii) the surveillance of dead blackbirds is a useful sentinel system for monitoring USUV activity.

Spatial analysis of West Nile virus: rapid risk assessment of an introduced vector-borne zoonosis

The distribution of human risk for West Nile virus was determined by spatial analysis of the initial case distribution for the New York City area in 1999 using remote sensing and geographic information system technologies. Cluster analysis revealed the presence of a statistically significant grouping of cases, which also indicates the area of probable virus introduction. Within the cluster, habitat suitability for potentially infective adult mosquitoes was measured by the amount of vegetation cover using satellite imagery. Logistic regression analysis revealed satellite-derived vegetation abundance to be significantly and positively associated with the presence of human cases. The logistic model was used to estimate the spatial distribution of human risk for West Nile virus throughout New York City. Accuracy of the resulting risk map was cross-validated using virus-positive mosquito sample sites. These new epidemiological methods aid in rapid entry point identification and spatial prediction of human risk of infection for introduced vector-borne pathogens.

Transmission of West Nile virus through blood transfusion in the United States in 2002

BACKGROUND

During the 2002 West Nile virus epidemic in the United States, patients were identified whose West Nile virus illness was temporally associated with the receipt of transfused blood and blood components.

METHODS

Patients with laboratory evidence of recent West Nile virus infection within four weeks after receipt of a blood component from a donor with viremia were considered to have a confirmed transfusion-related infection. We interviewed the donors of these components, asking them whether they had had symptoms compatible with the presence of a viral illness before or after their donation; blood specimens retained from the time of donation and collected at follow-up were tested for West Nile virus.

RESULTS

Twenty-three patients were confirmed to have acquired West Nile virus through transfused leukoreduced and nonleukoreduced red cells, platelets, or fresh-frozen plasma. Of the 23 recipients, 10 (43 percent) were immunocompromised owing to transplantation or cancer and 8 (35 percent) were at least 70 years of age. Immunocompromised recipients tended to have longer incubation periods than nonimmunocompromised recipients and infected persons in mosquito-borne community outbreaks. Sixteen donors with evidence of viremia at donation were linked to the 23 infected recipients; of these donors, 9 reported viral symptoms before or after donation, 5 were asymptomatic, and 2 were lost to follow-up. Fever, new rash, and painful eyes were independently associated with being an implicated donor with viremia rather than a donor without viremia. All 16 donors were negative for West Nile virus-specific IgM antibody at donation.

CONCLUSIONS

Transfused red cells, platelets, and fresh-frozen plasma can transmit West Nile virus. Screening of potential donors with the use of nucleic acid-based assays for West Nile virus may reduce this risk.

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.

West Nile virus infection transmitted by blood transfusion

BACKGROUND

A patient with transfusion-transmitted West Nile virus (WNV) infection confirmed by viral culture of a blood component is described. A 24-year-old female with severe postpartum hemorrhage developed fever, chills, headache, and generalized malaise after transfusion of 18 units of blood components; a serum sample and the cerebrospinal fluid tested positive for the presence of WNV IgM antibodies. An investigation was initiated to determine a possible association between transfusion and WNV infection.

STUDY DESIGN AND METHODS

Blood donors were assessed for recent infection through questionnaires and WNV testing of serum samples. Whole-blood retention segments and untransfused blood components were sent to the CDC to test for the presence of WNV through PCR (TaqMan, Applied Biosystems), IgM ELISA, plaque reduction neutralization testing, and viral culture.

RESULTS

Three of 15 available donor retention segments were WNV PCR-positive. WNV was recovered from one associated blood component. The implicated donor was symptomatic near the time of donation; serology confirmed WNV IgM seroconversion.

CONCLUSION

Seroconversion of a symptomatic donor, the presence of viral genetic material in an associated whole-blood retention segment, and recovery of WNV from an associated component provides compelling evidence for transfusion-acquired infection. This report has important implications for blood safety.

West Nile virus infection. What you need to know about this emerging threat

The most important aspects to remember about West Nile virus infection are summed up in the following points: West Nile virus is transmitted by bites from infected Culex species mosquitoes. Most infections do not result in serious illness. Encephalitis and serious morbidity and mortality are more likely to occur in elderly persons than in any other age-group. No effective antiviral treatment is available. Avoiding contact with mosquitoes is the key preventive measure.

Acute flaccid paralysis and West Nile virus infection

Acute weakness associated with West Nile virus (WNV) infection has previously been attributed to a peripheral demyelinating process (Guillain-Barré syndrome); however, the exact etiology of this acute flaccid paralysis has not been systematically assessed. To thoroughly describe the clinical, laboratory, and electrodiagnostic features of this paralysis syndrome, we evaluated acute flaccid paralysis that developed in seven patients in the setting of acute WNV infection, consecutively identified in four hospitals in St. Tammany Parish and New Orleans, Louisiana, and Jackson, Mississippi. All patients had acute onset of asymmetric weakness and areflexia but no sensory abnormalities. Clinical and electrodiagnostic data suggested the involvement of spinal anterior horn cells, resulting in a poliomyelitis-like syndrome. In areas in which transmission is occurring, WNV infection should be considered in patients with acute flaccid paralysis. Recognition that such weakness may be of spinal origin may prevent inappropriate treatment and diagnostic testing.

West Nile virus infection presenting as cerebellar ataxia and fever: case report

Evidence of West Nile encephalitis virus infection has been documented in most states of the continental United States within a short period of its first introduction in 1999. Health care providers are mostly aware of the usual presentations of this disease, eg, aseptic meningitis, encephalitis and Guillain-Barré syndrome. We present a patient whose only manifestations were cerebellar ataxia and fever.

Transmission of West Nile virus from an organ donor to four transplant recipients

BACKGROUND

In August 2002, fever and mental-status changes developed in recipients of organs from a common donor. Transmission of West Nile virus through organ transplantation was suspected.

METHODS

We reviewed medical records, conducted interviews, and collected blood and tissue samples for testing with a variety of assays. Persons who donated blood to the organ donor and associated blood components were identified and tested for West Nile virus.

RESULTS

We identified West Nile virus infection in the organ donor and in all four organ recipients. Encephalitis developed in three of the organ recipients, and febrile illness developed in one. Three recipients became seropositive for West Nile virus IgM antibody; the fourth recipient had brain tissue that was positive for West Nile virus by isolation and nucleic acid and antigen assays. Serum specimens obtained from the organ donor before and immediately after blood transfusions showed no evidence of West Nile virus; however, serum and plasma samples obtained at the time of organ recovery were positive on viral nucleic acid testing and viral culture. The organ donor had received blood transfusions from 63 donors. A review of blood donors and follow-up testing identified one donor who had viremia at the time of donation and who became seropositive for West Nile virus IgM antibodies during the next two months.

CONCLUSIONS

Our investigation of this cluster documents the transmission of West Nile virus by organ transplantation. Organ recipients receiving immunosuppressive drugs may be at high risk for severe disease after West Nile virus infection. Blood transfusion was the probable source of the West Nile virus viremia in the organ donor.

Molecular detection of West Nile virus RNA

West Nile virus is a mosquito-borne flavivirus that is primarily maintained in nature in a mosquito-bird-mosquito transmission cycle. Mammals, including humans and horses, are incidentally infected through biting by mosquitoes infected with West Nile virus. Since 1994, West Nile virus outbreaks have occurred with a high incidence of severe disease in humans and horses. In the USA, West Nile virus was first detected in 1999 in New York City and has since spread to 39 states in humans. The virus has resulted in over 4161 known human cases and at least 277 human deaths. Surveillance techniques employing nucleic acid-based assays have played an essential role in monitoring the spread of West Nile virus and are displacing the former gold standard cell culture-based assays. In this article we review the current techniques for diagnosis of West Nile virus, focusing on RNA detection, and suggest a number of new directions for genetic diagnosis of West Nile virus.

West Nile virus infection and its neurological manifestations

The West Nile virus caused an epidemic of meningoencephalitis in Midwest North America during 2002. The peak incidence coincided with the highest activity period of mosquito vectors in affected states. This epidemic followed recent established trends, not only of increased central nervous system involvement by the virus, but also increased incidence of dramatic neuromuscular impairment. Two cases are presented which illustrate the most concerning types of neuromuscular sequelae, diffuse weakness leading to respiratory insufficiency, and the development of focal weakness similar to poliomyelitis. The epidemiology and clinical characteristics of West Nile virus infection are also reviewed. Concern is expressed regarding the possibility of epidemics in other Midwestern states during future seasons of increased mosquito activity.

Emerging viral infections of the nervous system

New viral infections of the nervous system have been appearing with great regularity. Some result from the evolution of new agents and others from the entry of viruses into new hosts or environments. The emergence of neurovirulent enteroviruses causing a paralytic poliomyelitis syndrome and rhomboencephalitis represent the evolution of new human viruses. Most emerging viral infections represent movement of an agent into new geographic areas or across species barriers. The transport of neurovirulent strains of West Nile virus into the Western Hemisphere and the penetration of Nipah virus, a newly recognized paramyxovirus, across species barriers from bat to pig to man are examples that are highlighted in this review. The burgeoning human population and the speed and frequency of travel favor the evolution, preservation, and spread of new viral agents.

West Nile virus surveillance and diagnostics: A Canadian perspective

A surveillance program has been in place since 2000 to detect the presence of West Nile virus (WNV) in Canada. Serological assays are most appropriate when monitoring for human disease and undertaking case investigations. Genomic amplification procedures are more commonly used for testing animal and mosquito specimens collected as part of ongoing surveillance efforts. The incursion of WNV into this country was documented for the first time in 2001 when WNV was demonstrated in 12 Ontario health units during the late summer and fall. In 2002 WNV activity was documented by avian surveillance in Ontario by mid-May with subsequent expansion of the virus throughout Ontario and into Quebec, Manitoba, Saskatchewan and Nova Scotia. Human cases were recorded in both Ontario and Quebec in 2002 with approximately 800 to 1000 probable, confirmed and suspect cases detected. The possible recurrence and further spread of WNV to other parts of Canada in 2003 must be anticipated with potential risk to public health. The continued surveillance and monitoring for WNV-associated human illness is necessary and appropriate disease prevention measures need to be in place in 2003.

Origin and evolution of Japanese encephalitis virus in southeast Asia

Since it emerged in Japan in the 1870s, Japanese encephalitis has spread across Asia and has become the most important cause of epidemic encephalitis worldwide. Four genotypes of Japanese encephalitis virus (JEV) are presently recognized (representatives of genotypes I to III have been fully sequenced), but its origin is not known. We have determined the complete nucleotide and amino acid sequence of a genotype IV Indonesian isolate (JKT6468) which represents the oldest lineage, compared it with other fully sequenced genomes, and examined the geographical distribution of all known isolates. JKT6468 was the least similar, with nucleotide divergence ranging from 17.4 to 19.6% and amino acid divergence ranging from 4.7 to 6.5%. It included an unusual series of amino acids at the carboxy terminus of the core protein unlike that seen in other JEV strains. Three signature amino acids in the envelope protein (including E327 Leu-->Thr/Ser on the exposed lateral surface of the putative receptor binding domain) distinguished genotype IV strains from more recent genotypes. Analysis of all 290 JEV isolates for which sequence data are available showed that the Indonesia-Malaysia region has all genotypes of JEV circulating, whereas only more recent genotypes circulate in other areas (P < 0.0001). These results suggest that JEV originated from its ancestral virus in the Indonesia-Malaysia region and evolved there into the different genotypes which then spread across Asia. Our data, together with recent evidence on the origins of other emerging viruses, including dengue virus and Nipah virus, imply that tropical southeast Asia may be an important zone for emerging pathogens.

B cells and antibody play critical roles in the immediate defense of disseminated infection by West Nile encephalitis virus

West Nile virus (WNV) causes severe central nervous system (CNS) infection primarily in humans who are immunocompromised or elderly. In this study, we addressed the mechanism by which the immune system limits dissemination of WNV infection by infecting wild-type and immunodeficient inbred C57BL/6J mice with a low-passage WNV isolate from the recent epidemic in New York state. Wild-type mice replicated virus extraneuronally in the draining lymph nodes and spleen during the first 4 days of infection. Subsequently, virus spread to the spinal cord and the brain at virtually the same time. Congenic mice that were genetically deficient in B cells and antibody (microMT mice) developed increased CNS viral burdens and were vulnerable to lethal infection at low doses of virus. Notably, an approximately 500-fold difference in serum viral load was detected in micro MT mice as early as 4 days after infection, a point in the infection when low levels of neutralizing immunoglobulin M antibody were detected in wild-type mice. Passive transfer of heat-inactivated serum from infected and immune wild-type mice protected micro MT mice against morbidity and mortality. We conclude that antibodies and B cells play a critical early role in the defense against disseminated infection by WNV.

West Nile virus epidemic in horses, Tuscany region, Italy

During the late summer of 1998, veterinary authorities in Tuscany, Italy, received reports of cases of neurologic disease among horses residing in a large wetland area located in the provinces of Florence and Pistoia. West Nile virus was isolated from two of the six horses that died or were euthanized. A retrospective epidemiologic study identified 14 clinical neurologic cases that occurred from August 20 to October 6 (attack rate of 2.8%). A serologic survey conducted over a 700-km2 area in stables with and without apparent clinical cases confirmed a wider spread of the infection, with an overall seroprevalence rate of 38% in the affected area. No significant differences in age-specific prevalence were observed, suggesting that the horses residing in the area had not been exposed previously to West Nile virus and supporting the hypothesis of its introduction in the wetland area during the first half of 1998.

West Nile virus encephalitis in the United States

West Nile virus appeared in New York City in 1999 and has subsequently spread over the eastern United States. The mode of transport across the Atlantic Ocean is unknown. During the past decade, encephalitis has been a more prominent feature of West Nile virus infection in Europe, the Middle East, and the United States, suggesting the emergence of more neurovirulent strains. The rapid spread of the virus and more serious disease caused by the virus have spurred vaccine development.

West Nile virus

West Nile (WN) virus is a mosquito-borne flavivirus and human, equine, and avian neuropathogen. The virus is indigenous to Africa, Asia, Europe, and Australia, and has recently caused large epidemics in Romania, Russia, and Israel. Birds are the natural reservoir (amplifying) hosts, and WN virus is maintained in nature in a mosquito-bird-mosquito transmission cycle primarily involving Culex sp mosquitoes. WN virus was recently introduced to North America, where it was first detected in 1999 during an epidemic of meningoencephalitis in New York City. During 1999-2002, the virus extended its range throughout much of the eastern parts of the USA, and its range within the western hemisphere is expected to continue to expand. During 1999-2001, 142 cases of neuroinvasive WN viral disease of the central nervous system (including 18 fatalities), and seven cases of uncomplicated WN fever were reported in the USA. Most human WN viral infections are subclinical but clinical infections can range in severity from uncomplicated WN fever to fatal meningoencephalitis; the incidence of severe neuroinvasive disease and death increase with age. Serology remains the mainstay of laboratory diagnosis. No WN virus-specific treatment or vaccine is available. Prevention depends on organised, sustained vector mosquito control, and public education.

Possible benefit of intravenous immunoglobulin therapy in a lung transplant recipient with West Nile virus encephalitis

During the summer of 2000, a countrywide epidemic of West Nile fever (WNF) occurred in Israel, with 417 confirmed cases and 35 deaths. Immunosuppressed patients had a 31% case-fatality rate, which was significantly higher compared to non-immunosuppressed patients (13%). We describe a 42-year-old male lung-transplant recipient with serologically confirmed West Nile virus (WNV) encephalitis and deteriorating level of consciousness. He was treated with 0.4 g/kg intravenous immunoglobulin preparation from Israeli donors that contained a high titer of anti-WNV antibodies (1 : 1600). The patient showed rapid improvement within 24 h and complete disappearance of signs and symptoms within 48 h. This is the second case of an immunosuppressed patient responding to the same preparation of intravenous immunoglobulins. Larger studies are required in order to establish the therapeutic role of immunoglobulins in patients with WNF.

West Nile virus activity in the United States, 2001

West Nile virus (WNV) first appeared in the naive environment of the Western Hemisphere in 1999 in New York. Genetic analysis determined that the virus was introduced into the United States from the Mediterranean Basin. This review discusses the spread of the virus in 2001 from the initial focus in Queens, New York, to widespread activity in the eastern and midwestern United States. It concentrates on viral ecology, epizootiology, pathology, prediction, and prevention. Research questions to further our understanding of the transmission cycle of WNV are discussed, including host-preference studies, molecular confirmation of implicated mosquito vectors, and survival of WNV in the temperate environment of the United States. Comparisons are drawn with two other arboviruses enzootic in the United States, eastern equine encephalitis, and St. Louis encephalitis viruses. Although not recently introduced, these two viruses also demonstrated increased activity in the United States in 2001.

Neurological features of West Nile virus infection during the 2000 outbreak in a regional hospital in Israel

During the summer of 2000, 35 patients with West Nile Virus Fever were admitted to our hospital. Of these, the 26 (21 adults, mean age 56 (19-86) and 5 children (aged 9-15)) presented have neurological involvement, 33% with meningitis, 52% with meningoencephalitis, 10% with encephalitis and 5% with acute polyneuropathy. Presenting clinical features were fever in 95% of cases, headache in 90%, nausea/vomiting in 52%, confusion in 48%, somnolence in 38%, neck stiffness in 33%, a skin rash in 19%, diarrhea in 14%, cervical pain in 14%, seizure in 9%, photophobia in 9% and limb weakness in 4%. Leucopenia was not found. Two patients diagnosed with meningoencephalitis died. Three patients had signs of an acute polyneuropathy, this being the only complaint of one patient. The EEG was abnormal in all cases of meningitis or meningoencephalitis, except in three cases. Outbreaks of West Nile Virus Fever are emerging as a worldwide disease with high rates of neurological involvement and death. It should be considered in cases presenting with aseptic meningoencephalitis, meningitis and acute polyneuropathy, especially during the summer months and in areas along bird migration pathways.