West Nile encephalitis epidemic in southeastern Romania

A rapid and quantitative assay for measuring antibody-mediated neutralization of West Nile virus infection

West Nile virus (WNV) is a neurotropic flavivirus within the Japanese encephalitis antigenic complex that is responsible for causing West Nile encephalitis in humans. The surface of WNV virions is covered by a highly ordered icosahedral array of envelope proteins that is responsible for mediating attachment and fusion with target cells. These envelope proteins are also primary targets for the generation of neutralizing antibodies in vivo. In this study, we describe a novel approach for measuring antibody-mediated neutralization of WNV infection using virus-like particles that measure infection as a function of reporter gene expression. These reporter virus particles (RVPs) are produced by complementation of a sub-genomic replicon with WNV structural proteins provided in trans using conventional DNA expression vectors. The precision and accuracy of this approach stem from an ability to measure the outcome of the interaction between antibody and viral antigens under conditions that satisfy the assumptions of the law of mass action as applied to virus neutralization. In addition to its quantitative strengths, this approach allows the production of WNV RVPs bearing the prM-E proteins of different WNV strains and mutants, offering considerable flexibility for the study of the humoral immune response to WNV in vitro. WNV RVPs are capable of only a single round of infection, can be used under BSL-2 conditions, and offer a rapid and quantitative approach for detecting virus entry and its inhibition by neutralizing antibody.

[West Nile fever/encephalitis as one of the arboviral infections]

West Nile virus maintains natural infection cycle between birds and mosquitoes. It has been known that about 200 species of birds are infected with West Nile virus and the virus is isolated from more than 40 species of mosquitoes. This suggests that West Nile virus has an ability to be transmitted by many species of mosquitoes and infect many kinds of animals. Approximately 20% of infected humans develop symptoms. West Nile fever, an acute febrile illness, is the main disease, and meningitis and encephalitis (meningoencephalitis) occasionally occur. Cases with flaccid paralysis or polyneuritis have been recently reported. Thus, West Nile virus causes multiple types of symptoms in humans. The endemic area has expanded in North America and Siberia. West Nile virus may enter Japan in the near future; therefore, we should keep paying attention to the endemic and epidemic situations in the world.

Viral zoonoses in Europe

A number of new virus infections have emerged or re-emerged during the past 15 years. Some viruses are spreading to new areas along with climate and environmental changes. The majority of these infections are transmitted from animals to humans, and thus called zoonoses. Zoonotic viruses are, as compared to human-only viruses, much more difficult to eradicate. Infections by several of these viruses may lead to high mortality and also attract attention because they are potential bio-weapons. This review will focus on zoonotic virus infections occurring in Europe.

Serial Electrodiagnostic Studies in West Nile Virus–Associated Acute Flaccid Paralysis

A man in his 70s presented for acute rehabilitation with severe acute flaccid asymmetric weakness in both lower limbs. Cerebrospinal fluid and serum immunoglobulin M titers were positive for West Nile virus. Electrodiagnostic studies demonstrated severe diffuse motor axonopathy consistent with an anterior myelitis. Electrodiagnostic and clinical improvements were monitored. Electrodiagnostic testing at 6 and 18 mos demonstrated continuing reinnervation; nascent voluntary motor unit action potentials were first noted proximally and, at 18 mos, distally in the left lower limb, including muscles in which motor unit potentials were not initially noted. Corresponding clinical improvements, though slow, were demonstrated even at 1(1/2) yrs after onset. Thus, motoric changes after West Nile virus-associated anterior myelitis need to be monitored over a prolonged time period to allow accurate assessment of prognosis for recovery in rehabilitation programs.

The epidemiology and early clinical features of West Nile virus infection

We studied early clinical features of the West Nile virus (WNV) infection. Case patients were Ohio residents who reported to the Ohio Department of Health from August 14 to December 31, 2002, with a positive serum or cerebrospinal fluid for anti-WNV IgM. Of 441 WNV cases, medical records of 224 (85.5%) hospitalized patients were available for review. Most frequent symptoms were fever at a temperature of 38.0 degrees C or higher (n = 155; 69.2%), headache (n = 114; 50.9%), and mental status changes (n = 113; 50.4%). At least one neurological symptom, one gastrointestinal symptom, and one respiratory symptom was present in 186 (83.0%), 119 (53.1%), and 46 (20.5%) patients, respectively. Using multivariate logistic regression and controlling for age, we found that the initial diagnosis of encephalitis (P = .001) or reporting abdominal pain (P < .001) was associated with death. Because initial symptoms of WNV infection are not specific, physicians should maintain a high index of suspicion during the epidemic season, particularly in elderly patients with compatible symptoms.

Focal neurological injury caused by West Nile virus infection may occur independent of patient age and premorbid health

INTRODUCTION

Limited evidence suggests that focal neurological injury (e.g., acute flaccid paralysis) caused by infection with the West Nile virus (WNV) is more common in older patients. We re-evaluate this association in a series of patients who were infected with the WNV during the 2002 epidemic.

METHODS

We performed a retrospective chart review of 34 patients who were hospitalized for treatment of serologically confirmed WNV infection. Measurements included the patient's demographic characteristics, baseline medical diagnoses, the occurrence of symptoms and exam findings, the results of various diagnostic tests, and the patient's clinical outcome.

RESULTS

Patients infected with the WNV who developed focal neurological injury were found to be comparable to patients who did not develop focal neurological injury both in terms of patient age and the number of medical conditions the patient had prior to infection. This is in contrast to WNV-infected patients who developed an encephalitis-like clinical course, or who died or were institutionalized after their hospitalization; such patients tended to be older and-in cases with a poor outcome-have more medical conditions prior to WNV infection.

CONCLUSIONS

In our patient group, focal neurological injury caused by WNV infection was not related to advanced patient age or to the number of medical conditions the patient had prior to infection. Our findings bring into question commonly held views about the development of focal neurological injury caused by WNV infection, and they raise concerns about the management of future WNV epidemics and the testing and use of potential antiviral treatments against this infection.

Mosquito vectors of the 1998-1999 outbreak of Rift Valley Fever and other arboviruses (Bagaza, Sanar, Wesselsbron and West Nile) in Mauritania and Senegal

Following an outbreak of Rift Valley fever (RVF) in south-eastern Mauritania during 1998, entomological investigations were conducted for 2 years in the affected parts of Senegal and Mauritania, spanning the Sénégal River basin. A total of 92 787 mosquitoes (Diptera: Culicidae), belonging to 10 genera and 41 species, were captured in light traps. In Senegal, Culex poicilipes (41%) and Mansonia uniformis (39%) were the most abundant species caught, whereas Aedes vexans (77%) and Cx. poicilipes (15%) predominated in Mauritania. RVF virus was isolated from 63 pools of Cx. poicilipes: 36 from Senegal in 1998 and 27 from Mauritania in 1999. These results are the first field evidence of Cx. poicilipes naturally infected with RVFV, and the first isolations of this virus from mosquitoes in Mauritania - the main West African epidemic and epizootic area. Additional arbovirus isolates comprised 25 strains of Bagaza (BAG) from Aedes fowleri, Culex neavei and Cx. poicilipes; 67 Sanar (ArD 66707) from Cx. poicilipes; 51 Wesselsbron (WSL) from Ae. vexans and 30 strains of West Nile (WN) from Ma. uniformis, showing differential specific virus-vector associations in the circulation activity of these five arboviruses.

Balance and gait abnormalities of a child with West Nile virus infection

We describe a case of a previously healthy 2-year-old female patient with rash, fever and vomiting for 10 days who presented for medical attention with acute profound balance and gait disturbances and intentional movement dysmetria. West Nile virus-specific IgM and IgG antibodies were detected in the patient's cerebrospinal fluid.

Molecular typing of West Nile Virus, Dengue, and St. Louis encephalitis using multiplex sequencing

We report the development of an assay to simultaneously identify three of the clinically important flaviviruses (West Nile Virus, Dengue, and St. Louis encephalitis). This assay is based on the nucleotide sequence variations within a 266-bp region of the non-structural protein 5. Further, based on the nucleotide variations in the same region of the non-structural protein 5, four of the present Dengue serotypes were identified. To identify some of the subtypes of WNV we have developed a second assay using multiplex sequencing technology. The format of the result of this assay is an electropherogram of two genomic segments of the WNV genome: a 48-nucleotide sequence from the anchored core protein C and a 45-nucleotide sequence coding for the non-structural proteins (proteinase and putative helicase genes).

West Nile Virus: the buzz on Ottawa residents' awareness, attitudes and practices

BACKGROUND

In 2002, the City of Ottawa was interested in the public perception of West Nile Virus (WNV) and mosquito control. Their objectives were to assess: awareness of WNV, practices to reduce mosquito sources, personal protective measures, and attitudes towards community-based insecticide programs.

METHODS

In July 2002, we administered a telephone survey to a random, stratified sample of urban, suburban and rural Ottawa households.

RESULTS

Surveys were completed for 491 households. Most (77.2%) respondents reported they had heard of WNV, and of these, 58.3% reported WNV was an important health issue. Mosquito repellent was the most common personal protective measure, reported among 72.5% of respondents, of whom 76.9% used DEET products. Multivariate regression analyses showed that age was a significant predictor of repellent use, with respondents aged less than 51 years more likely to use repellent than older respondents (ORadj =2.0; 95% CI: 1.2-2.3). This age group was also more likely to use at least one personal protective behaviour (ORadj = 2.5; 95% CI: 1.4-4.5). Of 315 people selecting a justified time to larvicide, 4.8% chose "larvicides should never be used in Ottawa"; 33.4% stated that larviciding would be appropriate "when WNV was detected in birds or mosquitoes"; one third "needed more information" on the health and environmental effects of insecticides, prior to selecting a response.

CONCLUSIONS

Our findings highlight the need for public education reinforcing WNV importance, emphasizing the health and environmental effects of insecticides as well as appropriate personal protective behaviours. Such messages should target older and urban residents.

Shifting epidemiology of Flaviviridae

The dengue, West Nile, Japanese encephalitis and yellow fever viruses are important mosquito-borne viruses whose epidemiology is shifting in response to changing societal factors, such as increasing commerce, urbanization of rural areas, and population growth. All four viruses are expanding geographically, as exemplified by the emergence of West Nile virus in the Americas and Japanese encephalitis virus in Australasia. The large, recent global outbreaks of severe neurological disease caused by West Nile virus, the increasing frequency of dengue hemorrhagic fever outbreaks in the Americas, and the emergence of yellow fever virus vaccination-associated viscerotropic disease, are new clinical epidemiologic trends. These worrisome epidemiologic trends will probably continue in coming decades, as a reversal of their societal and biological drivers is not in sight. Nevertheless, the substantial reductions in Japanese encephalitis virus incidence resulting from vaccination programs and economic development in some Asian countries provide some encouragement within this overall guarded outlook.

An infectious West Nile Virus that expresses a GFP reporter gene

West Nile virus is a mosquito-borne, neurotropic flavivirus that causes encephalitis in humans and animals. Since being introduced into the Western hemisphere in 1999, WNV has spread rapidly across North America, identifying this virus as an important emerging pathogen. In this study, we developed a DNA-launched infectious molecular clone of WNV that encodes a GFP reporter gene. Transfection of cells with the plasmid encoding this recombinant virus (pWNII-GFP) resulted in the production of infectious WNV capable of expressing GFP at high levels shortly after infection of a variety of cell types, including primary neurons and dendritic cells. Infection of cells with WNII-GFP virus was productive, and could be inhibited with both monoclonal antibodies and interferon-beta, highlighting the potential of this system in the development and characterization of novel inhibitors and therapeutics for WNV infection. As expected, insertion of the reporter gene into the viral genome was associated with a reduced rate of viral replication, providing the selective pressure for the development of variants that no longer encoded the full-length reporter gene cassette. We anticipate this DNA-based, infectious WNV reporter virus will allow novel approaches for the study of WNV infection and its inhibition both in vitro and in vivo.

Use of Interferon- in Patients with West Nile Encephalitis: Report of 2 Cases

We describe 2 patients with West Nile virus (WNV) encephalitis who were treated experimentally with interferon (IFN)-alpha. Both patients demonstrated substantial improvement in mentation and speech on the second day of experimental therapy, and neither required endotracheal intubation or admission to the intensive care unit during hospitalization. Moreover, during the 9-month follow-up period, one patient achieved complete recovery, and the other nearly achieved complete resolution of sequelae. To our knowledge, this is the first published report of the use of IFN-alpha to treat WNV encephalitis. Clinical trials are underway to further define the role of this therapy in persons with WNV encephalitis.

[West Nile virus, an emerging arbovirus]

The West Nile virus (family Flaviviridae, genus Flavivirus), first isolated in 1937 in Africa, is an arthropod-borne virus transmitted through Culex mosquitoes bite. Its natural cycle includes a vector (Culex mosquitoes), a reservoir (birds of various species) and humans and large mammals are epidemiological dead-ends. PROGRESSIVE DISSEMINATION: This virus recently drew attention after several epidemics and epizooties were identified in France, Russia, Romania, and Israel. However, the most striking fact is its introduction in 1999 into the north-eastern United States, a country previously West Nile virus-free, and its progressive spread according to North-South and West-East gradients to finally cover the near-totality of the north American territory (USA, Canada and Mexico), in 2002. The year 2002 has been particularly prone to disseminating West Nile virus in the Unites States: more than 4,000 human cases have been recorded and resulted in the death of almost 300. In 2003, around 10,000 cases were recorded. From January to October 2004, around 2,000 human cases have been recorded in the USA. Among infected patients, few develop a symptomatic form, and only a small proportion of the latter will develop a neurological form. REGARDING DIAGNOSIS AND SURVEILLANCE: Although virus isolation remains the technique of reference, routine diagnosis basically relies on serology (detection of increased levels of specific antibodies on two blood tests at 21 days interval, detection of IgM on a single test) and on molecular techniques (detection of the viral genome); the latter have been developed in quantitative and real-time formats that provide results within 24 hours. We describe the situation in France following the equine epizooty that occurred in 2000, and the surveillance modalities initiated at that time.

Neurologic aspects of infections in international travelers

BACKGROUND

As international travel for business and pleasure becomes part of contemporary lifestyle, the clinician today is confronted with an increasing number of travelers returning ill with unfamiliar syndromes. The physician will encounter a myriad of patients with exotic infections, emerging infectious diseases, or resurgent Old-World infections.

REVIEW SUMMARY

This review article will discuss salient points of important infectious diseases associated with overseas travel, provide a syndromic approach to the traveler who returns with neurologic manifestations, and list resources for additional diagnostic, therapeutic, and preventive information.

CONCLUSIONS

As many of infections acquired in other countries can directly or indirectly affect the nervous system, the care of the ill traveler often falls into the hands of neurologists. The contemporary neurologist should therefore be knowledgeable of the clinical manifestations, potential complications, and appropriate management of region-specific infections.

Systemic and intraocular manifestations of West Nile virus infection

Since the introduction of West Nile virus in the Western Hemisphere in 1999, the incidence of human infection has increased dramatically. As this virus spreads westward across the United States, ophthalmologists should be aware of this presently uncommon but important condition. Systemic features of West Nile virus infection are well characterized; however, the ophthalmic presentations are not widely known. Intraocular involvement with West Nile virus infection was first described in February 2003, and a variety of ophthalmic manifestations have since been recognized. A complete survey of the systemic and intraocular manifestations of West Nile virus infection relevant to the ophthalmologist is presented.

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.

West Nile virus encephalitis: an emerging disease in renal transplant recipients

West Nile virus (WNV) has emerged as an important cause of several outbreaks of febrile illness and encephalitis in North America over the past few years. The most common manifestation in symptomatic patients is a transient febrile illness. Neuroinvasive disease, that can be fatal, occurs most often in elderly and immunocompromised hosts. The role of this virus as a cause of meninoencephalitis in organ transplant recipients is becoming better recognized. We describe herein the clinical course of two renal allograft recipients who developed WNV encephalitis. One patient developed status epilepticus and eventually died, while the other had a full recovery. In both cases, the diagnosis was confirmed by detection of WNV-specific IgM in CSF or serum, with a delayed antibody response in one patient. This viral infection should be considered in all renal transplant recipients who present with a febrile illness associated with neurological symptoms.

Acute flaccid paralysis associated with West Nile virus: Motor and functional improvement in 4 patients

OBJECTIVE

To describe motor and functional recovery in 4 patients with acute flaccid paralysis associated with West Nile virus (WNV) infection.

DESIGN

A case series describing patient clinical features at admission to rehabilitation through 6-month follow-up.

SETTING

Academic acute free-standing inpatient rehabilitation hospital.

PARTICIPANTS

The patients (3 men, 1 woman; age range, 29-72 y) with central nervous system WNV infection presented on rehabilitation admission, 18 to 112 days after onset of symptoms, with severe flaccid asymmetric weakness without sensory loss, and decreased functional independence. Electrodiagnostic studies demonstrated a severe diffuse motor axonopathy consistent with an anterior myelitis.

INTERVENTION

Acute inpatient rehabilitation program over a period of 35 to 106 days.

MAIN OUTCOME MEASURES

Motor and FIM instrument scores at admission to rehabilitation, discharge, and 6-month follow-up.

RESULTS

All patients showed modest improvements in strength and function; no patient made full recovery of strength or became ambulatory by 6-month follow-up.

CONCLUSIONS

Little is known about recovery in patients with WNV-associated anterior myelitis. It will be important to document any further improvements in strength and function in such patients over a longer follow-up period.

A seroprevalence study of west nile virus infection in solid organ transplant recipients

West Nile virus (WNV) causes severe neurological disease in less than 1% of infections. However, meningoencephalitis may be more common in immunosuppressed transplant patients. In 2002, a WNV outbreak occurred in our region. To determine the spectrum of disease of community acquired WNV infection and assess public health behavior patterns in transplant recipients, we carried out a seroprevalence study. Patients were enrolled from outpatient transplant clinics in October 2002 and sera were screened for WNV. Questionnaires about WNV were provided to patients. Eight hundred sixteen organ transplant patients were enrolled. The seroprevalence of WNV IgM was 2/816 (0.25%; 95% CI 0.03-0.88%). By extrapolation to our entire transplant population of 2360 patients, and using data from hospital-based surveillance, the risk of meningoencephalitis in a transplant patient infected with WNV is estimated to be 40% (95% CI 16-80%). With regards to knowledge and behavior, 56% patients knew of and 47% used at least one protective measure against WNV. Only 33% used insect repellent. The risk of meningoencephalitis in transplant recipients is much higher than in the general population. There is incomplete knowledge and poor rates of compliance amongst patients with regards to WNV prevention.

West Nile: worldwide current situation in animals and humans

West Nile (WN) virus is a mosquito-borne flavivirus that is native to Africa, Europe, and Western Asia. It mainly circulates among birds, but can infect many species of mammals, as well as amphibians and reptiles. Epidemics can occur in rural as well as urban areas. Transmission of WN virus, sometimes involving significant mortality in humans and horses, has been documented at erratic intervals in many countries, but never in the New World until it appeared in New York City in 1999. During the next four summers it spread with incredible speed to large portions of 46 US states, and to Canada, Mexico, Central America and the Caribbean. In many respects, WN virus is an outstanding example of a zoonotic pathogen that has leaped geographical barriers and can cause severe disease in human and equine. In Europe, in the past two decades there have been a number of significant outbreaks in several countries. However, very little is known of the ecology and natural history of WN virus transmission in Europe and most WN outbreaks in humans and animals remain unpredictable and difficult to control.

Epidemic West Nile virus encephalitis in Tunisia

West Nile fever (WNF) is a mosquito-borne flavivirus infection. It is epidemic in Africa and Asia. In autumn 1997, a WNF epidemic occurred in the Sfax area (southeastern Tunisia). Fifty-seven patients were hospitalized with aseptic meningitis and/or encephalitis. Search for specific anti-West Nile virus (WNV) antibodies in serum and cerebrospinal fluid (CSF) was performed using an ELISA test. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the WNV genome in CSF and brain specimens. Recent central nervous system (CNS) infection by WNV was confirmed in 30 patients, probable infection in 17 and it was excluded in 10. In the confirmed subgroup, patients with encephalitis were older than those with meningitis. CSF showed pleocytosis, high protein (47%) and normal glucose levels. Brain computed tomography-scan (CT-scan) and magnetic resonance imaging (MRI) were normal. RT-PCR disclosed WNV genome in the CSF in two cases and in a brain specimen in one. Three patients died rapidly, the remaining cases had favorable prognosis. Autopsy was performed in two cases and showed nonspecific lesions of encephalitis. No viral inclusions were seen with light microscopy. Seropositivity rate in patients' proxies for WNV was 23.4%. Prognosis of CNS involvement during WNF seemed to be poor in older patients. This is the first WNV encephalitis epidemic report in the Sfax area of Tunisia.

Outbreak of West Nile virus causing severe neurological involvement in children, Nuba Mountains, Sudan, 2002

An atypical outbreak of West Nile virus (WNV) occurred in Ngorban County, South Kordophan, Sudan, from May to August 2002. We investigated the epidemic and conducted a case-control study in the village of Limon. Blood samples were obtained for cases and controls. Patients with obvious sequelae underwent cerebrospinal fluid (CSF) sampling as well. We used enzyme-linked immunosorbent assay (ELISA) and neutralization tests for laboratory diagnosis and identified 31 cases with encephalitis, four of whom died. Median age was 36 months. Bivariate analysis did not reveal any significant association with the risk factors investigated. Laboratory analysis confirmed presence of IgM antibodies caused by WNV in eight of 13 cases, indicative of recent viral infection. The unique aspects of the WNW outbreak in Sudan, i.e. disease occurrence solely among children and the clinical domination of encephalitis, involving severe neurological sequelae, demonstrate the continuing evolution of WNV virulence. The spread of such a virus to other countries or continents cannot be excluded.

Enhancing West Nile virus surveillance, United States

We provide a method for constructing a county-level West Nile virus risk map to serve as an early warning system for human cases. We also demonstrate that mosquito surveillance is a more accurate predictor of human risk than monitoring dead and infected wild birds.

Role of CD8+ T cells in control of West Nile virus infection

Infection with West Nile virus (WNV) causes fatal encephalitis more frequently in immunocompromised humans than in those with a healthy immune system. Although a complete understanding of this increased risk remains unclear, experiments with mice have begun to define how different components of the adaptive and innate immune response function to limit infection. Previously, we demonstrated that components of humoral immunity, particularly immunoglobulin M (IgM) and IgG, have critical roles in preventing dissemination of WNV infection to the central nervous system. In this study, we addressed the function of CD8(+) T cells in controlling WNV infection. Mice that lacked CD8(+) T cells or classical class Ia major histocompatibility complex (MHC) antigens had higher central nervous system viral burdens and increased mortality rates after infection with a low-passage-number WNV isolate. In contrast, an absence of CD8(+) T cells had no effect on the qualitative or quantitative antibody response and did not alter the kinetics or magnitude of viremia. In the subset of CD8(+)-T-cell-deficient mice that survived initial WNV challenge, infectious virus was recovered from central nervous system compartments for several weeks. Primary or memory CD8(+) T cells that were generated in vivo efficiently killed target cells that displayed WNV antigens in a class I MHC-restricted manner. Collectively, our experiments suggest that, while specific antibody is responsible for terminating viremia, CD8(+) T cells have an important function in clearing infection from tissues and preventing viral persistence.

The epidemic of West Nile virus in the United States, 2002

Since 1999, health officials have documented the spread of West Nile virus across the eastern and southern states and into the central United States. In 2002, a large, multi-state, epidemic of neuroinvasive West Nile illness occurred. Using standardized guidelines, health departments conducted surveillance for West Nile virus illness in humans, and West Nile virus infection and illness in non-human species. Illnesses were reported to the Centers for Disease Control and Prevention (CDC) through the ArboNET system. In 2002, 39 states and the District of Columbia reported 4,156 human West Nile virus illness cases. Of these, 2,942 (71%) were neuroinvasive illnesses (i.e., meningitis, encephalitis, or meningoencephalitis) with onset dates from May 19 through December 14; 1,157 (28%) were uncomplicated West Nile fever cases, and 47 (1%) were clinically unspecified. Over 80% of neuroinvasive illnesses occurred in the central United States. Among meningitis cases, median age was 46 years (range, 3 months to 91 years), and the fatality-to-case ratio was 2%; for encephalitis cases (with or without meningitis), median age was 64 years (range, 1 month to 99 years) and the fatality-to-case ratio was 12%. Neuroinvasive illness incidence and mortality, respectively, were significantly associated with advanced age (p = 0.02; p = 0.01) and being male (p < 0.001; p = 0.002). In 89% of counties reporting neuroinvasive human illnesses, West Nile virus infections were first noted in non-human species, but no human illnesses were reported from 77% of counties in which non-human infections were detected. In 2002, West Nile virus caused the largest recognized epidemic of neuroinvasive arboviral illness in the Western Hemisphere and the largest epidemic of neuroinvasive West Nile virus ever recorded. It is unknown why males appeared to have higher risk of severe illness and death, but possibilities include higher prevalence of co-morbid conditions or behavioral factors leading to increased infection rates. Several observations, including major, multi-state West Nile virus epidemics in 2002 and 2003, suggest that major epidemics may annually reoccur in the United States. Non-human surveillance can warn of early West Nile virus activity and needs continued emphasis, along with control of Culex mosquitoes.

Clinical and neuroradiologic features of 39 consecutive cases of West Nile Virus meningoencephalitis

BACKGROUND

West Nile Virus (WNV) is a flavivirus WNV that has spread westwards across North America in recent years. It can cause a febrile illness and infection of the central nervous system, which is associated with poor outcome.

METHODS

We retrospectively studied the clinical and neuroradiologic features of 39 consecutive patients admitted during summer of 2002 that had IgM in the cerebrospinal fluid positive for WNV.

RESULTS

Fever, headache and altered mentation were predominant clinical features. Clinically significant involvement of lower motor neurons was seen in few cases. Magnetic resonance imaging (MRI) of the brain did not show changes attributable to meningitis or encephalitis except for one case of subcortical signal abnormalities. Unfavorable prognostic factors are old age, decreased level of alertness and elevated serum creatinine.

CONCLUSIONS

Encephalopathic presentations, with or without additional neurological focality, dominated this series. Fever and meningitic signs are often absent. Involvement of lower motor neurons was uncommon. Given the paucity of positive findings, the value of MRI to support the diagnosis of WNV-meningoencephalitis is limited.

Molecular determinants of virulence of West Nile virus in North America

West Nile virus (WNV) is a mosquito-borne flavivirus that until very recently had not been found in the Americas. In 1999, there was an outbreak of West Nile encephalitis in New York and surrounding areas, involving 62 human cases, including 7 fatalities. The virus has subsequently become established in the United States of America (U.S.) with 4156 human cases, including 284 deaths, in 2002. The WNV strains found in the U.S. are members of "lineage I", a genetic grouping that includes viruses from Europe, Asia and Africa. Molecular epidemiologic studies indicate that two genetic variants of WNV emerged in 2002. The major genetic variant is found in most parts of the U.S., while the minor genetic variant has been identified only on the southeast coast of Texas. Investigation of WNV in mouse and hamster models demonstrated that strains from the U.S. are highly neurovirulent and neuroinvasive in these laboratory rodents. Other strains, such as Ethiopia 76a from lineage I, are not neuroinvasive and represent important viruses which can be used to elucidate the molecular basis of virulence and attenuation of WNV. To identify putative molecular determinants of virulence and attenuation, we have undertaken comparative nucleotide sequencing of Ethiopia 76a and strains from the U.S. The results show that the two viruses differ by 5 amino acids in the envelope (E) protein, including loss of the glycosylation site. Comparison of our panel of 27 WNV strains suggests that E protein glycosylation is a major determinant of the mouse neuroinvasive phenotype.

West Nile virus: a growing concern?

West Nile virus was first detected in North America in 1999 and has subsequently spread throughout the United States and Canada and into Mexico and the Caribbean. This review describes the epidemiology and ecology of West Nile virus in North America and the prospects for effective treatments and vaccines.

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.

West Nile virus-associated encephalitis in recipients of renal and pancreas transplants: case series and literature review

Although West Nile fever is mild in the vast majority of infected persons, there is growing evidence that the disease may be more severe in the immunocompromised population. We describe 3 recipients of kidney or pancreas transplants who developed West Nile fever, 2 of whom had meningoencephalitis. As is the norm when treating serious infections in transplant recipients, a reduction of immunosuppression was pursued for these patients. Despite the severe nature of the disease in 2 patients, all recovered from the disease. The time course of neurologic recovery in the 2 patients with meningoencephalitis is highlighted. We also review the literature on West Nile fever in organ transplant recipients. In areas where West Nile virus is endemic, one must have a high index of suspicion for the illness when dealing with fever in transplant recipients.

The potential for West Nile virus to establish outside of its natural range: a consideration of potential mosquito vectors in the United Kingdom

Outbreaks of West Nile virus (WNV) infection have occurred sporadically in Europe, apparently due to the migration of infected birds and the subsequent establishment of a transmission cycle involving culicine and anopheline mosquitoes. Both human and equine species become infected, but are considered as dead end hosts since they play an insignificant role in the maintenance of the cycle. Following the introduction of WNV into the United States in 1999 it is increasingly apparent that the virus has an extraordinary ability to infect a very broad range of arthropod species. Here we consider the potential for British mosquitoes to transmit WNV in the event that it is introduced into the UK.

Electrodiagnostic features of acute paralytic poliomyelitis associated with West Nile virus infection

West Nile virus (WNV) infection is a potentially fatal disease, with meningoencephalitis being its most common neurological manifestation. Guillain-Barré syndrome (GBS) has also been described, but acute paralytic poliomyelitis has only recently been recognized. We report the clinical and electrodiagnostic findings of five patients with WNV infection, who presented with acute paralytic poliomyelitis. Three patients manifested focal asymmetrical weakness, and two had rapid ascending quadriplegia mimicking GBS. Electrodiagnostic studies during the acute illness showed normal sensory nerve action potentials, compound motor action potentials of normal or reduced amplitude, and no slowing of nerve conduction velocities. Depending on the timing of the examination, fibrillation potentials were widespread, including in those with focal weakness. Cervical magnetic resonance imaging in one patient showed abnormal T2-weighted signals in the spinal cord gray matter. On follow-up, signs of clinical improvement were seen in one patient, whereas two remained quadriplegic and ventilator-dependent 5 months after the onset. This report highlights the value of the electrodiagnostic studies in the diagnosis and prognosis of focal or generalized weakness due to acute paralytic poliomyelitis associated with WNV infection.

Melatonin and viral infections

The therapeutic effects of melatonin against viral infections, with emphasis on the Venezuelan equine encephalomyelitis (VEE), are reviewed. Melatonin has been shown to prevent paralysis and death in mice infected with the encephalomyocarditis virus and to decrease viremia. Melatonin also postpones the onset of the disease produced by Semliki Forest virus inoculation and reduces the mortality of West Nile virus-infected mice stressed by either isolation or dexamethasone injection. An increase in the host resistance to the virus via a peripheral immunostimulatory activity is considered responsible for these effects. It has also been demonstrated that melatonin protects some strains of mink against Aleutian disease, and prevents the reduction of B- and T-cells as well as Th1 cytokine secretion in mice infected with leukemia retrovirus. In VEE-infected mice, melatonin postpones the onset of the disease and death for several days and reduces the mortality rate. This protective effect seems to be due to the increase in the production of interleukin-1beta (IL-1beta), as 100% of the infected mice treated with melatonin die when IL-1beta is blocked with antimurine IL-1beta antibodies. Although melatonin administration raises serum levels of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), the mortality observed in neutralization experiments with the corresponding anticytokine antibodies, suggests that neither TNF-alpha nor IFN-gamma are essential for the protective effect of melatonin on murine VEE virus infection. Melatonin treatment also enhances the efficiency of immunization against the VEE virus. Reactive oxygen species have been implicated in the dissemination of this virus, and their deleterious effects may be diminished by melatonin. This indole inhibits nitric oxide synthetase activity and it is a potent scavenger of nitric oxide, which also plays an important role in the spread of the VEE virus. In conclusion, the immunomodulatory, antioxidant, and neuroprotective effects of melatonin suggest that this indole must be considered as an additional therapeutic alternative to fight viral diseases.

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.