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MEDLINE Abstracts: West Nile Virus
What's new concerning the epidemiology of West Nile Virus and its recent outbreaks? Find out in this easy-to-navigate collection of recent MEDLINE abstracts compiled by the editors at Medscape Neurology.
Update: West Nile-like Viral Encephalitis -- New York, 1999
Morb Mortal Wkly Rep 1999 Oct 8;48(39):890-2
The outbreak of human arboviral encephalitis attributable to a mosquito- transmitted West Nile-like virus (WNLV) continues to wane in the Northeast. As of October 5, the number of laboratory-positive cases had increased to 50 (27 confirmed and 23 probable), including five deaths. The increase in cases is mainly a result of completed retesting with West Nile virus antigen of specimens previously tested with the related St. Louis encephalitis virus antigen and to intensive retrospective case finding in the ongoing epidemiologic investigations.
Of the 50 case-patients, none had onset of illness after September 17. Thirty-eight resided within boroughs of New York City (NYC): 26 from Queens, nine from the Bronx, two from Manhattan, and one from Brooklyn. An additional 12 cases were reported from the adjacent counties of Westchester (eight) and Nassau (four). In NYC, the earliest laboratory-positive case occurred in a patient on August 4, followed by 11 cases in patients from Queens with onset dates ranging from August 5 to August 18.
The association of WNLV with deaths in crows and domestic and exotic birds was confirmed during September. As a result, CDC, state wildlife veterinarians, and an expanding group of federal agencies are using deaths in crows as sentinel events to define the current geographic distribution of mosquitoes and birds infected with WNLV (1). As of October 5, results from selected bird tissue samples tested indicate that WNLV has been identified from 41 avian tissue specimens collected in NYC; Nassau, Suffolk, Rockland, and Westchester counties in New York; Fairfield County, Connecticut; and Bergen, Union, Middlesex, and Essex counties in New Jersey. No human cases of encephalitis attributable to WNLV have been reported from either Connecticut or New Jersey. Pools of Culex mosquitoes collected in localized areas of Queens, Brooklyn, and the Bronx in mid-September and a pool of Culex pipiens collected from Nassau County in late September have been positive for WNLV by reverse transcriptase polymerase chain reaction testing. One pool of Culex pipiens and one pool of Aedes vexans mosquitoes collected from a single trap in Greenwich, Connecticut, on September 13 yielded isolates of WNLV.
Mosquito-Borne Viruses in Western Europe: A Review
Lundstrom JO
J Vector Ecol 1999 Jun;24(1):1-39
Several mosquito-borne arboviruses belonging to the genera Alphavirus, Flavivirus, and Bunyavirus have been reported to occur in mosquitoes and to infect humans and other vertebrates in western Europe. These zoonotic viruses circulate in nature either in an Aedes-mammal, Anopheles-mammal, or Culex-bird transmission cycle. Infected humans normally do not contribute to the virus circulation. West Nile virus (Flavivirus) caused an outbreak of fever, malaise, pain in eyes and muscles, and headache and encephalitis in southern France during 1962-1965, and an outbreak of encephalitis with a high case-fatality rate in Romania during 1996. West Nile virus has been isolated from birds, horses, and mosquitoes in Portugal, France, the former Czechoslovakia, and Romania. These data, together with reports of antibodies to West Nile virus in birds, domestic mammals, and humans in several other countries, show virus activity in southern and central Europe. Sindbis virus (Alphavirus) caused outbreaks of fever, rash, and arthralgia in northern Europe during 1981-1982, 1988, and 1995. Two California group viruses (Bunyavirus), Tahyna virus and Inkoo virus, have been identified in western Europe. Tahyna virus causes fever and respiratory symptoms and sometimes also central nervous system involvement. It occurs in most countries of central and southern Europe, and is most common in central Europe. Inkoo virus has not been associated with disease in humans in western Europe although Russian studies indicated that it can cause encephalitis. Inkoo virus occurs in northern Europe, especially in the far north. Batai virus of the Bunyamwera-group (Bunyavirus) occurs in southern, central, and northern Europe, most frequently in central Europe. The antibody prevalence in humans generally is very low, indicating that the potential of this virus as a human pathogen is probably low in Europe. The Lednice virus (Bunyavirus) has been reported only from the former Czechoslovakia and Romania, and apparently is not transmitted to humans. In addition to the six mosquito-borne viruses documented in western Europe, there is serological evidence of infection with a Semliki Forest complex virus (Alphavirus) in central and southern Europe. Although mosquito-borne viruses presently are not considered to be the cause of major health problems in western Europe, the morbidity caused by Sindbis virus, and the morbidity and mortality caused by West Nile virus, merit further studies on the ecology, epidemiology, and medical importance of these viruses. The California group of viruses and a virus of the Semliki Forest complex may be the cause of unrecognized health problems in western Europe. Specific sampling of potential vectors for virus isolation, detailed characterization of virus strains, and the use of fully characterized strains for serological diagnosis will help to elucidate the present and future potential of mosquito-borne viruses as human pathogens in Europe.
The Epidemiological Process of West Nile Viral Infection
Pitigoi D; Popa MI; Streinu-Cercel A
Bacteriol Virusol Parazitol Epidemiol 1998 Oct-Dec;43(4):281-8
An important number of arboviruses are known to produce clinical or subclinical infections in humans. Most of these viruses are maintained in zoonotic cycles and are transmitted by mosquitoes or ticks. Viruses believed to be associated with human disease are classified according to the type of vector, the main clinical sign and the geographic distribution. The arboviruses are classified in families and genera, of which Togaviridae, Flaviviridae and Bunyaviridae are the best known. West Nile virus is present in Egypt, Israel, India and is widespread in parts of Africa, the northern Mediterranean area and Western Asia. The first major West Nile fever epidemic in Europe occurred in Romania, in 1996, with a high rate of neurological infections. 393 patients with serologically confirmed or probable West Nile fever infection (352 had acute central-nervous-system infections) were identified. The number of mild cases could not be estimated. WN virus was recovered from Culex pipiens mosquitoes. The virus is not transmitted through direct human contact, probably the infected mosquitoes transmit the virus throughout their life. Viremia is essential for vector infection and occurs during early clinical illness in humans. Susceptibility appears to be general, in both males and females, throughout life. Inapparent infections and mild disease are common.
Risk Factors for West Nile Virus Infection and Meningoencephalitis, Romania, 1996
Han LL, Popovici F, Alexander Jr JP, et al.
J Infect Dis 1999 Jan;179(1):230-3
In 1996, an epidemic of 393 cases of laboratory-confirmed West Nile meningoencephalitis occurred in southeast Romania, with widespread subclinical human infection. Two case-control studies were performed to identify risk factors for acquiring infection and for developing clinical meningoencephalitis after infection. Mosquitoes in the home were associated with infection (reported by 37 [97%] of 38 asymptomatically seropositive persons compared with 36 [72%] of 50 seronegative controls, P<.01) and, among apartment dwellers, flooded basements were a risk factor (reported by 15 [63%] of 24 seropositive persons vs. 11 [30%] of 37 seronegative controls, P=.01). Meningoencephalitis was not associated with hypertension or other underlying medical conditions but was associated with spending more time outdoors (meningoencephalitis patients and asymptomatically seropositive persons spent 8.0 and 3.5 h [medians] outdoors daily, respectively, P<.01). Disease prevention efforts should focus on eliminating peridomestic mosquito breeding sites and reducing peridomestic mosquito exposure.
Clinical Manifestations in the West Nile Virus Outbreak
Ceausu E, Erscoiu S, Calistru P, et al.
Rom J Virol 1997 Jan-Dec;48(1-4):3-11
During the summer of 1996 an unusual clustering of meningoencephalitis cases was recorded in the Capital City, Bucharest, and in some areas from South-East Romania. After an initial suspicion of an enteroviral etiology was discarded, the West Nile etiology was confirmed by specific antibodies demonstration through hemagglutination-inhibition and ELISA tests. This study included 251 patients with the diagnoses of West Nile acute encephalitis (166 cases), acute meningitis (57 cases) and acute febrile disease (33 cases). The patients' ages ranged from 1 to 89 years (mean 51.1 years). The most frequent clinical manifestations were: fever (95.7% of cases), cephalalgia (92.6%), stiffness of the neck (89.1%), vomiting (62.5%), marked asthenia (46.5%), myalgia (28.9%). In addition, patients with encephalitis exhibited: alteration of consciousness (89.2% of cases), tremor of extremities (40.4%), ataxia (44%), paralysis (15.1%). The fatality rate was 15.1% in acute encephalitis, 1.8% in acute meningitis and 0% in the acute febrile disease.
West Nile Encephalitis Epidemic in Southeastern Romania
Tsai TF, Popovici F, Cernescu C, et al.
Lancet 1998 Sep 5;352(9130):767-71
Background: West Nile fever (WNF) is a mosquito-borne flavivirus infection endemic in Africa and Asia. In 1996, the first major WNF epidemic in Europe occurred in Romania, with a high rate of neurological infections. We investigated the epidemic to characterise transmission patterns in this novel setting and to determine its origin.
Methods: Hospital-based surveillance identified patients admitted with acute aseptic meningitis and encephalitis in 40 Romanian districts, including Bucharest. Infection was confirmed with IgM capture and indirect IgG ELISAs. In October, 1996, we surveyed outpatients in Bucharest and seven other districts to estimate seroprevalence and to detect infected patients not admitted to hospital. We also measured the rates of infection and seropositivity in mosquitoes and birds, respectively.
Results: Between July 15 and Oct 12, we identified 393 patients with serologically confirmed or probable WNF infection, of whom 352 had acute central-nervous-system infections. 17 patients older than 50 years died. Fatality/case ratio and disease incidence increased with age. The outbreak was confined to 14 districts in the lower Danube valley and Bucharest (attack rate 12.4/100000 people) with a seroprevalence of 4.1%. The number of mild cases could not be estimated. WN virus was recovered from Culex pipiens mosquitoes, the most likely vector, and antibodies to WN virus were found in 41% of domestic fowl.
Interpretation: The epidemic in Bucharest reflected increased regional WNF transmission in 1996. Epidemics of Cx pipiens- borne WNF could occur in other European cities with conditions conducive to transmission.
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