West Nile encephalitis epidemic in southeastern Romania

Outbreak of West Nile virus infection, Volgograd Region, Russia, 1999

From July 25 to October 1, 1999, 826 patients were admitted to Volgograd Region, Russia, hospitals with acute aseptic meningoencephalitis, meningitis, or fever consistent with arboviral infection. Of 84 cases of meningoencephalitis, 40 were fatal. Fourteen brain specimens were positive in reverse transcriptase-polymerase chain reaction assays, confirming the presence of West Nile/Kunjin virus.

Mosquito surveillance for West Nile virus in Connecticut, 2000: isolation from Culex pipiens, Cx. restuans, Cx. salinarius, and Culiseta melanura

Fourteen isolations of West Nile (WN) virus were obtained from four mosquito species (Culex pipiens [5], Cx. restuans [4], Cx. salinarius [2], and Culiseta melanura [3]) in statewide surveillance conducted from June through October 2000. Most isolates were obtained from mosquitoes collected in densely populated residential locales in Fairfield and New Haven counties, where the highest rates of dead crow sightings were reported and where WN virus was detected in 1999. Minimum field infection rates per 1,000 mosquitoes ranged from 0.5 to 1.8 (county based) and from 1.3 to 76.9 (site specific). Cx. restuans appears to be important in initiating WN virus transmission among birds in early summer; Cx. pipiens appears to play a greater role in amplifying virus later in the season. Cs. melanura could be important in the circulation of WN virus among birds in sylvan environments; Cx. salinarius is a suspected vector of WN virus to humans and horses.

West Nile virus infection in the golden hamster (Mesocricetus auratus): a model for West Nile encephalitis

This report describes a new hamster model for West Nile (WN) virus encephalitis. Following intraperitoneal inoculation of a New York isolate of WN virus, hamsters had moderate viremia of 5 to 6 days in duration, followed by the development of humoral antibodies. Encephalitic symptoms began 6 days after infection; about half the animals died between the seventh and 14th days. The appearance of viral antigen in the brain and neuronal degeneration also began on the sixth day. WN virus was cultured from the brains of convalescent hamsters up to 53 days after initial infection, suggesting that persistent virus infection occurs. Hamsters offer an inexpensive model for studying the pathogenesis and treatment of WN virus encephalitis.

West Nile outbreak in horses in southern France, 2000: the return after 35 years

On September 6, 2000, two cases of equine encephalitis caused by West Nile (WN) virus were reported in southern France (Hérault Province), near Camargue National Park, where a WN outbreak occurred in 1962. Through November 30, 76 cases were laboratory confirmed among 131 equines with neurologic disorders. The last confirmed case was on November 3, 2000. All but three cases were located in a region nicknamed "la petite Camargue," which has several large marshes, numerous colonies of migratory and resident birds, and large mosquito populations. No human case has been confirmed among clinically suspected patients, nor have abnormal deaths of birds been reported. A serosurvey has been undertaken in horses in the infected area, and other studies are in progress.

West Nile fever outbreak, Israel, 2000: epidemiologic aspects

From August 1 to October 31, 2000, 417 cases of West Nile (WN) fever were serologically confirmed throughout Israel; 326 (78%) were hospitalized patients. Cases were distributed throughout the country; the highest incidence was in central Israel, the most populated part. Men and women were equally affected, and their mean age was 54+/-23.8 years (range 6 months to 95 years). Incidence per 1,000 population increased from 0.01 in the 1st decade of life to 0.87 in the 9th decade. There were 35 deaths (case-fatality rate 8.4%), all in patients >50 years of age. Age-specific case-fatality rate increased with age. Central nervous system involvement occurred in 170 (73%) of 233 hospitalized patients. The countrywide spread, number of hospitalizations, severity of the disease, and high death rate contrast with previously reported outbreaks in Israel.

Clinical characteristics of the West Nile fever outbreak, Israel, 2000

West Nile (WN) virus is endemic in Israel. The last reported outbreak had occurred in 1981. From August to October 2000, a large-scale epidemic of WN fever occurred in Israel; 417 cases were confirmed, with 326 hospitalizations. The main clinical presentations were encephalitis (57.9%), febrile disease (24.4%), and meningitis (15.9%). Within the study group, 33 (14.1%) hospitalized patients died. Mortality was higher among patients >70 years (29.3%). On multivariate regressional analysis, independent predictors of death were age >70 years (odds ratio [OR] 7.7), change in level of consciousness (OR 9.0), and anemia (OR 2.7). In contrast to prior reports, WN fever appears to be a severe illness with high rate of central nervous system involvement and a particularly grim outcome in the elderly.

Clinical findings of West Nile virus infection in hospitalized patients, New York and New Jersey, 2000

Outbreaks of West Nile (WN) virus occurred in the New York metropolitan area in 1999 and 2000. Nineteen patients diagnosed with WN infection were hospitalized in New York and New Jersey in 2000 and were included in this review. Eleven patients had encephalitis or meningoencephalitis, and eight had meningitis alone. Ages of patients ranged from 36 to 87 years (median 63 years). Fever and neurologic and gastrointestinal symptoms predominated. Severe muscle weakness on neurologic examination was found in three patients. Age was associated with disease severity. Hospitalized cases and deaths were lower in 2000 than in 1999, although the case-fatality rate was unchanged. Clinicians in the Northeast should maintain a high level of suspicion during the summer when evaluating older patients with febrile illnesses and neurologic symptoms, especially if associated with gastrointestinal complaints or muscle weakness.

West Nile virus surveillance in Connecticut in 2000: an intense epizootic without high risk for severe human disease

In 1999, Connecticut was one of three states in which West Nile (WN) virus actively circulated prior to its recognition. In 2000, prospective surveillance was established, including monitoring bird deaths, testing dead crows, trapping and testing mosquitoes, testing horses and hospitalized humans with neurologic illness, and conducting a human seroprevalence survey. WN virus was first detected in a dead crow found on July 5 in Fairfield County. Ultimately, 1,095 dead crows, 14 mosquito pools, 7 horses, and one mildly symptomatic person were documented with WN virus infection. None of 86 hospitalized persons with neurologic illness (meningitis, encephalitis, Guillain-Barré-like syndrome) and no person in the seroprevalence survey were infected. Spraying in response to positive surveillance findings was minimal. An intense epizootic of WN virus can occur without having an outbreak of severe human disease in the absence of emergency adult mosquito management.

Advanced age a risk factor for illness temporally associated with yellow fever vaccination

In 1998, the Centers for Disease Control and Prevention was notified of severe illnesses and one death, temporally associated with yellow fever (YF) vaccination, in two elderly U.S. residents. Because the cases were unusual and adverse events following YF vaccination had not been studied, we estimated age-related reporting rates for systemic illness following YF vaccination. We found that the rate of reported adverse events among elderly vaccinees was higher than among vaccinees 25 to 44 years of age. We also found two additional deaths among elderly YF vaccinees. These data signal a potential problem but are not sufficient to reliably estimate incidence rates or to understand potential underlying mechanisms; therefore, enhanced surveillance is needed. YF remains an important cause of severe illness and death, and travel to disease-endemic regions is increasing. For elderly travelers, the risk for severe illness and death due to YF infection should be balanced against the risk for systemic illness due to YF vaccine.

West Nile encephalitis

WNV encephalitis in horses, previously reported in Africa, Asia, and Europe, occurred for the first time in the Western Hemisphere in 1999. The causative agent, WNV, is a flavivirus maintained in nature by a bird-mosquito cycle. The disease in horses is manifested primarily by ataxia of variable severity. Outbreaks of encephalitis may have a case fatality rate in excess of 40%, although this virus infection is inapparent in some horses. Early evidence indicates that WNV has overwintered in the northeastern United States and poses a threat for future disease occurrences in horses. No vaccine is available to protect against WNV infection in horses; disease control is predicated on mosquito abatement.

Factors influencing the international spread of equine diseases

In an era of increasing globalization, the risk of spread of infectious diseases in humans and animals, including equids, has never been greater. International movement of equids and trade in semen are the most important factors responsible for the dissemination of various equine pathogens. Other factors that can or do have the potential to influence the global distribution of equine infectious diseases include: multinational trade agreements, emergent diseases, mutation of pathogens, climate related phenomena, migration of amplifying/reservoir hosts or vectors, availability of new vectors, vaccine contamination and agroterrorism. The relative importance of each of these factors is considered in relation to the spread of equine diseases.

Rapid detection of west nile virus from human clinical specimens, field-collected mosquitoes, and avian samples by a TaqMan reverse transcriptase-PCR assay

The authors report on the development and application of a rapid TaqMan assay for the detection of West Nile (WN) virus in a variety of human clinical specimens and field-collected specimens. Oligonucleotide primers and FAM- and TAMRA-labeled WN virus-specific probes were designed by using the nucleotide sequence of the New York 1999 WN virus isolate. The TaqMan assay was compared to a traditional reverse transcriptase (RT)-PCR assay and to virus isolation in Vero cells with a large number ( approximately 500) of specimens obtained from humans (serum, cerebrospinal fluid, and brain tissue), field-collected mosquitoes, and avian tissue samples. The TaqMan assay was specific for WN virus and demonstrated a greater sensitivity than the traditional RT-PCR method and correctly identified WN virus in 100% of the culture-positive mosquito pools and 98% of the culture-positive avian tissue samples. The assay should be of utility in the diagnostic laboratory to complement existing human diagnostic testing and as a tool to conduct WN virus surveillance in the United States.

Guillain-Barré syndrome: An unusual presentation of West Nile virus infection

West Nile fever is a mosquito-borne febrile illness seen in Africa, Asia, and Europe, but reported in North America only once. The recent outbreak in New York City represents the first time this virus has been detected in North America. West Nile virus usually causes mild symptoms, though rarely it can cause neurologic diseases, with a fatal outcome or permanent neurologic sequelae. We describe an elderly patient with West Nile virus infection who presented with Guillain-Barré syndrome.

Evaluation of immunoglobulin M (IgM) and IgG enzyme immunoassays in serologic diagnosis of West Nile Virus infection

A unique urban encephalitis epidemic in Romania signaled the emergence of neurological infection due to West Nile (WN) virus as a novel public health threat in Eastern Europe and provided an opportunity to evaluate patterns of immunoglobulin G (IgG) and IgM reactivity in IgM capture and IgG enzyme-linked immunosorbent assays (ELISAs). WN virus infection was diagnosed serologically in 236 of 290 patients from whom acute serum or cerebrospinal fluid (CSF) samples were available. In 37% of serum samples and in 25% of CSF samples collected in the first week of illness, anti-WN virus IgM antibody was detected in the absence of virus-specific IgG. The switch to an IgG antibody response occurred after 4 to 5 days of illness and earlier in CSF than in serum. A specific humoral immune response was detected in the CSF before the serum in some patients for whom paired CSF and serum samples from the same day were available. IgM antibody in convalescent serum samples persisted beyond 2 months after the onset of illness in more than 50% of patients. ELISA optical density values and antibody concentrations were well correlated for both IgM and IgG immunoassays. Anti-WN virus IgM antibody in acute-phase samples did not cross-react significantly with flaviviruses in other antigenic groups.

Emerging infectious diseases in the 21st century

The emergence of novel infectious diseases, and the re-emergence of others, is not new. The global ecosystem is constantly changing, influencing the micro- and macroenvironments in which humans and their microbial companions reside and interact. Sometimes the environmental circumstances favour the pathogen and there is an unexpected increase in disease activity or emergence of a new infection. Alternatively, pathogenicity factors are acquired by the microbe, allowing new diseases to emerge or old diseases to increase in importance. The forces that drive the emergence, submergence and re-emergence of infectious diseases are varied, but the influence that humans have on the global ecosystem is often of central importance. This review considers infections that are of particular emerging importance.

Pathology of fatal West Nile virus infections in native and exotic birds during the 1999 outbreak in New York City, New York

West Nile fever caused fatal disease in humans, horses, and birds in the northeastern United States during 1999. We studied birds from two wildlife facilities in New York City, New York, that died or were euthanatized and were suspected to have West Nile virus infections. Using standard histologic and ultrastructural methods, virus isolation, immunohistochemistry, in situ hybridization and reverse-transcriptase polymerase chain reaction, we identified West Nile virus as the cause of clinical disease, severe pathologic changes, and death in 27 birds representing eight orders and 14 species. Virus was detected in 23/26 brains (88%), 24/ 25 hearts (96%), 15/18 spleens (83%), 14/20 livers (70%), 20/20 kidneys (100%), 10/13 adrenals (77%), 13/ 14 intestines (93%), 10/12 pancreata (83%), 5/12 lungs (42%), and 4/8 ovaries (50%) by one or more methods. Cellular targets included neurons and glial cells in the brain, spinal cord, and peripheral ganglia; myocardial fibers; macrophages and blood monocytes; renal tubular epithelium; adrenal cortical cells; pancreatic acinar cells and islet cells; intestinal crypt epithelium; oocytes; and fibroblasts and smooth muscle cells. Purkinje cells were especially targeted, except in crows and magpies. Gross hemorrhage of the brain, splenomegaly, meningoencephalitis, and myocarditis were the most prominent lesions. Immunohistochemistry was an efficient and reliable method for identifying infected cases, but the polyclonal antibody cross-reacted with St. Louis encephalitis virus and other flaviviruses. In contrast, the in situ hybridization probe pWNV-E (WN-USAMRIID99) reacted only with West Nile virus. These methods should aid diagnosticians faced with the emergence of West Nile virus in the United States.

The West Nile Virus outbreak of 1999 in New York: the Flushing Hospital experience

West Nile Virus (WNV) is a mosquito-borne flavivirus, which has been known to cause human infection in Africa, the Middle East, and southwestern Asia. It has also been isolated in Australia and sporadically in Europe but never in the Americas. Clinical features include acute fever, severe myalgias, headache, conjunctivitis, lymphadenopathy, and a roseolar rash. Rarely is encephalitis or meningitis seen. During the month of August 1999, a cluster of 5 patients with fever, confusion, and weakness were admitted to the intensive care unit of the same hospital in New York City. Ultimately 4 of the 5 developed flaccid paralysis and required ventilatory support. Three patients with less-severe cases presented shortly thereafter. With the assistance of the New York City and New York State health departments and the Centers for Disease Control and Prevention, these were documented as the first cases of WNV infection on this continent.

Perspectives for the treatment of infections with Flaviviridae

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

Perspectives for the treatment of infections with Flaviviridae

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

Clinical and neuropathological features of West Nile virus equine encephalomyelitis in Italy

West Nile (WN) virus infection is a mosquito-borne flavivirosis endemic in Africa and Asia. Clinical disease is usually rare and mild and only in a few cases the infection causes encephalomyelitis in horses, fever and meningoencephalitis in man. We report here the clinical and pathological findings in an epidemic of the disease involving 14 horses from Tuscany, Italy. All cases were observed from August to October 1998. Affected horses showed ataxia, weakness paresis of the hindlimbs and, in 6 cases, there was paraparesis progressing to tetraplegia and recumbency within 2 to 9 days. Eight animals recovered without any important consequences. Serological investigations revealed positivity to WN virus in all the 14 horses and the agent was isolated from the cerebellum and spinal cord of an affected horse. Postmortem examination was carried out on 6 horses. The neuropathological pattern was that of a mild to moderate, nonsuppurative polioencephalomyelitis with constant involvement of the ventral horns of the thoracic and lumbar spinal cord, where focal gliosis and haemorrhage were also apparent in some cases. Differential diagnoses with other equine viral encephalomyelitides are discussed. Climatological and environmental characteristics of the geographic area in which the outbreaks occurred suggest the existence of suitable conditions for the development of the disease. This is the first report of WN virus equine encephalomyelitis in Italy.

Detection of neurotropic viruses circulating in Tuscany: the incisive role of Toscana virus

Acute meningitis is perhaps the most frequent among central nervous system infections. We report a study considering 277 cases of meningitis hospitalized in the southern Tuscany area (Italy) during the period from 1995 to 1998 investigated by tissue culture and polymerase chain reaction (PCR) methods. The cytochemical analysis of the cerebrospinal fluid samples suggested the diagnosis of aseptic meningitis, recognized as viral meningitis in 104 cases by detection of viral DNA or RNA. The results collected by tissue culture technique, available for 95 clinical samples, reported a positive isolation for only 12 cases. The viruses identified in the neurological infection were Toscana virus (81%), enterovirus (12%), mumps virus (3%), measles virus (1%), and herpes virus type 1 (3%). These data demonstrate the incisive role of the RNA viruses as the cause of meningitis, and overall the relevance of Toscana virus.

Isolation of West Nile virus from mosquitoes, crows, and a Cooper's hawk in Connecticut

West Nile (WN) virus, a mosquito-transmitted virus native to Africa, Asia, and Europe, was isolated from two species of mosquitoes, Culex pipiens and Aedes vexans, and from brain tissues of 28 American crows, Corvus brachyrhynchos, and one Cooper's hawk, Accipiter cooperii, in Connecticut. A portion of the genome of virus isolates from four different hosts was sequenced and analyzed by comparative phylogenetic analysis. Our isolates from Connecticut were similar to one another and most closely related to two WN isolates from Romania (2.8 and 3.6 percent difference). If established in North America, WN virus will likely have severe effects on human health and on the health of populations of birds.

Origin of the West Nile virus responsible for an outbreak of encephalitis in the northeastern United States

In late summer 1999, an outbreak of human encephalitis occurred in the northeastern United States that was concurrent with extensive mortality in crows (Corvus species) as well as the deaths of several exotic birds at a zoological park in the same area. Complete genome sequencing of a flavivirus isolated from the brain of a dead Chilean flamingo (Phoenicopterus chilensis), together with partial sequence analysis of envelope glycoprotein (E-glycoprotein) genes amplified from several other species including mosquitoes and two fatal human cases, revealed that West Nile (WN) virus circulated in natural transmission cycles and was responsible for the human disease. Antigenic mapping with E-glycoprotein-specific monoclonal antibodies and E-glycoprotein phylogenetic analysis confirmed these viruses as WN. This North American WN virus was most closely related to a WN virus isolated from a dead goose in Israel in 1998.

Identification of a Kunjin/West Nile-like flavivirus in brains of patients with New York encephalitis

Molecular analysis of brains from patients of the recent New York City encephalitis outbreak reveals the presence of a flavivirus not previously described in the Americas.

West Nile fever--a reemerging mosquito-borne viral disease in Europe

West Nile virus causes sporadic cases and outbreaks of human and equine disease in Europe (western Mediterranean and southern Russia in 1962-64, Belarus and Ukraine in the 1970s and 1980s, Romania in 1996-97, Czechland in 1997, and Italy in 1998). Environmental factors, including human activities, that enhance population densities of vector mosquitoes (heavy rains followed by floods, irrigation, higher than usual temperature, or formation of ecologic niches that enable mass breeding of mosquitoes) could increase the incidence of West Nile fever.