The 1952 outbreak of encephalitis in California; epidemiologic aspects

For the most part, epidemiologic phenomena observed in the outbreak of encephalitis in 1952 accorded with patterns that had been apparent in previous years. Ninety-seven per cent of the 414 laboratory-confirmed cases of western equine and St. Louis encephalitis in humans occurred in the 20 Central Valley counties. The cases of western equine encephalomyelitis in horses were generally scattered over the state. In the Central Valley most of the cases in horses were in animals less than two years of age; elsewhere the incidence was higher in older horses.There were no laboratory-confirmed cases of western equine or St. Louis encephalitis in humans earlier than June or later than October. In 1952 there were far more cases of western equine than of St. Louis encephalitis-a departure from the pattern in the previous seven years when there were about as many of one as of the other. No known satisfactory index is available for the prediction of the extent or type of outbreaks in humans. Approximately one-third of the cases of western equine encephalitis were in patients less than one year of age, whereas there were no cases of the St. Louis disease in patients that young.The incidence of western equine encephalitis in persons under 5 years of age was about the same for girls as for boys. In higher age brackets, males with western equine encephalitis outnumbered females 2 to 1. The corresponding ratio for St. Louis encephalitis was only 1.2 to 1.     

The 1952 Outbreak of Encephalitis in California (A Symposium): EPIDEMIOLOGIC ASPECTS

For the most part, epidemiologic phenomena observed in the outbreak of encephalitis in 1952 accorded with patterns that had been apparent in previous years. Ninety-seven per cent of the 414 laboratory-confirmed cases of western equine and St. Louis encephalitis in humans occurred in the 20 Central Valley counties. The cases of western equine encephalomyelitis in horses were generally scattered over the state. In the Central Valley most of the cases in horses were in animals less than two years of age; elsewhere the incidence was higher in older horses.There were no laboratory-confirmed cases of western equine or St. Louis encephalitis in humans earlier than June or later than October.In 1952 there were far more cases of western equine than of St. Louis encephalitis—a departure from the pattern in the previous seven years when there were about as many of one as of the other. No known satisfactory index is available for the prediction of the extent or type of outbreaks in humans.Approximately one-third of the cases of western equine encephalitis were in patients less than one year of age, whereas there were no cases of the St. Louis disease in patients that young.The incidence of western equine encephalitis in persons under 5 years of age was about the same for girls as for boys. In higher age brackets, males with western equine encephalitis outnumbered females 2 to 1. The corresponding ratio for St. Louis encephalitis was only 1.2 to 1.     

Eastern equine encephalitis in the United States, 1971: Past and prologue

During 1971, surveillance for equine encephalitis in the United States was increased due to an epizootic of Venezuelan equine encephalomyelitis. Of 1,982 specimens from 1,551 equines, 76 isolates of eastern equine encephalitis (EEE) virus were recovered from 67 individuals. The virus was isolated from 50/176 brains, 8/74 spleens, 14/1,127 sera, and 4/147 whole bloods from infected equines in 12 of the 31 states bounded by or east of the Mississippi River and in Texas and Iowa; no specimens were received from 9 of these 31 states. Thus, EEE virus was isolated from equines in 12 of 22 of these states. Determinations of antibody to EEE and western equine encephalitis (WEE) viruses indicated a relatively high prevalence of infection with EEE virus in the eastern USA and similarly high prevalence of antibody to WEE virus in the western USA. These data indicate that equine infections with EEE virus in the eastern USA are considerably more common than previous surveillance data have suggested. Increased surveillance and submission of specimens to diagnostic laboratories for diagnosis of EEE virus infections in equines are suggested so that a greater proportion of the thousands of unspecified equine encephalitis cases occurring in the United States each year can be laboratory confirmed.     

Serologic survey for selected arboviruses and other potential pathogens in wildlife from Mexico.

During 1988 and 1989, a serologic survey of wildlife was conducted in northeastern Mexico to determine the presence, prevalence, and distribution of arboviruses and other selected disease agents. Eighty mammal specimens were tested. Antibodies to vesicular stomatitis-Indiana, Venezuelan equine encephalitis-Mena II, Rio Grande virus, and vesicular stomatitis-New Jersey were detected predominantly in small mammals. Deer and mouflon (Ovis musimon) had antibodies to bluetongue and epizootic hemorrhagic disease. Two species had serologic evidence of recent exposure to Francisella tularensis. A white-tailed deer (Odocoileus virginianus) had antibodies to Anaplasma marginale. All specimens tested for antibodies against Yersinia pestis and Brucella abortus were negative. Sera from 315 birds were tested for antibody against five equine encephalitis viruses and six avian pathogens. During 1988, antibodies to Venezuelan equine encephalitis-Mena II, Venezuelan equine encephalitis-TC83, St. Louis encephalitis, eastern equine encephalitis, and western equine encephalitis were detected in birds of several species. Antibodies to Pasteurella multocida and Newcastle disease virus were also detected. Birds from five species presented antibodies to Mycoplasma meleagridis. Specimens tested for M. gallisepticum, M. synoviae, and Chlamydia psittaci were negative. To the best of our knowledge, this survey represents the first serologic evidence of bluetongue, Cache Valley virus, epizootic hemorrhagic disease, Jamestown Canyon virus, vesicular stomatitis-Indiana, vesicular stomatitis-New Jersey, Rio Grande virus, and tularemia reported among wildlife in Mexico.     

Focal neurologic signs in western equine encephalitis.

Focal neurologic signs developed in a 75-year-old woman who had presented with encephalitis. A diagnosis of western equine encephalitis was made from serologic findings. Although she was improving clinically the patient died from acute dissection of an aortic aneurysm 11 days after admission to hospital. The pathological findings--perivascular infiltrates and multifocal necrosis in the deep grey matter--were consistent with the diagnosis of western equine encephalitis. Similar findings in the basal ganglia and spinal cord corresponded to the focal clinical signs.     

Evaluation of the Epidemic Potential of Western Equine Encephalitis Virus in the Northeastern United States

The problem of evaluating the epidemic potential of western equine encephalitis in the northeastern United States is presented and possible reasons are discussed for the present lack of human and horse cases of this disease even though increased numbers of isolations of the virus have been obtained in the East during recent years. Epidemiologic factors of vector bionomics and virus strain variations are considered. It is concluded that while this virus strain can no longer be regarded as uncommon in the Northeast, the evidence indicates there is little potential for epidemic expression of this agent in the human and horse population. This appears to be due to differences in the bionomics of the mosquito Culiseta melanura, which serves as the primary enzootic vector in the northeastern United States and in the bionomics of Culex tarsalis that is the vector in the western region of the United States. Other limiting factors in the epidemic potential may be variations between virus strains located in the East and West.     

Labile Serum Factor and Its Effect on Arbovirus Neutralization

Enhancement of neutralization of Sindbis, Venezuelan equine encephalitis, Eastern equine encephalitis, Western equine encephalitis, and St. Louis encephalitis viruses by labile serum factor (LSF) in human serum and plasma was demonstrated. Human serum and plasma could be diluted 1:8 and 1:16 and still retain some LSF activity. Satisfactory storage temperatures for retention of LSF activity were −20 or −56 C. Repeated freeze-thaw cycles of serum did not alter LSF activity, but the activity was completely eliminated by heating at 56 C for 5 min. LSF of human serum equally enhanced neutralization by Sindbis immune mouse and rabbit sera; these results suggest a lack of species specificity. Rehydrated lyophilized gunea pig complement did not restore LSF activity to heated human plasma. Serum components responsible for LSF activity were not dialyzable. Discovery of fresh serum without LSF activity established the need to pretest all sera used as LSF sources.     

Experimental inoculation of three arboviruses in black-bellied whistling ducks (Dendrocygna autumnalis).

Wild-caught, immature black-bellied whistling ducks (Dendrocygna autumnalis) were inoculated with eastern equine encephalitis (EEE), St. Louis encephalitis (SLE), or western equine encephalitis (WEE) virus. Susceptibility, duration and titer of viremia, and antibody response to these arboviruses were determined. Birds from all inoculated groups became viremic. Higher virus titers occurred in the EEE group but overall mean titers were not significantly different among experimental groups. All birds inoculated with EEE and SLE viruses developed antibodies, and six of seven ducks receiving WEE virus were seropositive. All seropositive ducks had antibodies for at least 59 days, when the study was terminated. The EEE group had significantly more seropositive ducks during more days than the WEE and SLE groups. Geometric mean antibody titers were significantly smaller in the WEE group when compared to the EEE and SLE groups. Control ducks did not develop viremia or antibodies. Gross and histopathologic lesions compatible with viral encephalitis were absent in all of nine ducks necropsied. Black-bellied whistling ducks can develop low and short-term levels of viremia sufficient to infect mosquitoes, but probably cannot contribute significantly to the transmission of EEE and SLE. They may serve as good indicators of virus activity.     

Seroprevalence of arboviruses in Ecuador: Implications for improved surveillance

Introduction:Arthropod-borne viruses (arboviruses) cause morbidity and mortality in humans and domestic animals worldwide. The percentage of population immunity or susceptibility to these viruses in Ecuador is unknown.Objectives:To investigate the proportion of Ecuadorian populations with IgG antibodies (Abs) (past exposure/immunity) and IgM Abs (current exposure) against flaviviruses and alphaviruses and to study the activity of these viruses in Ecuador.Materials and methods:During 2009-2011, we conducted a serosurvey for selected arboviruses in humans (n=1,842), equines (n=149), and sentinel hamsters (n=84) at two coastal locations and one in the Amazon basin (Eastern Ecuador) using enzyme-linked immunosorbent assay and hemagglutination inhibition test.Results:From 20.63% to 63.61% of humans showed IgG-antibodies for the flaviviruses: Dengue virus (DENV), yellow fever virus (YFV) Saint Louis encephalitis virus, and West Nile virus (WNV); from 4.67% to 8.63% showed IgG-Abs for the alphaviruses: Venezuelanequine encephalitis virus, eastern equine encephalitis virus, and western equine encephalitis virus. IgM-Abs were found for DENV and WNV. Equines and hamsters showed antibodies to alphaviruses in all locations; two hamsters seroconverted to YFV in the Amazonia.Conclusions:The results show a YFV vaccination history and suggest the activity of arboviruses not included in the current surveillance scheme. Enhanced arbovirus and mosquito surveillance, as well as continued YFV vaccination and evaluation of its coverage/ effectiveness, are recommended.     

A serologic survey of mule deer and elk in Utah.

Sera from mule deer (Odocoileus hemionus) and elk (Cervus canadensis) in central and northern Utah were tested for the prevalence of antibodies to 11 diseases communicable to man or domestic livestock. Antibodies to Francisella tularensis (at 1:20) were found in 47 of 88 (53.4%) elk and 1 of 89 (1.1%) deer. A screening slide agglutination test for titers to Brucella (at 1:20) showed two reactors in elk but none in deer sera. No positive antibody titers were obtained in tests for anaplasmosis, Colorado tick fever, Rocky Mountain spotted fever, Q-fever, psittacosis, Powassan, western equine encephalitis, St. Louis encephalitis and California encephalitis.     

Purification of the envelope glycoproteins of western equine encephalitis virus by glass wool column chromatography.

Glass wool column chromatography was used for separation of the two glycoproteins of western equine encephalitis virus. Cross-contamination of each protein separated was confirmed to be negligible by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.     

Arbovirus-related encephalitis.

Arthropod-borne virus encephalitis in the U.S.A. includes LaCrosse, St Louis, western equine, eastern equine, Venezuelan equine, and Powassan in that order of frequency. Diagnosis can be aided by the history of seasonal occurrence, climate, geographic location, exposure to vectors, and age of the patient. The definitive diagnosis is usually made by serological tests such as neutralization, complement-fixation, hemagglutination-inhibition, and immunofluorescence, the radioimmune assay and the enzyme-linked immunosorbent assay show promise of future utility. These diseases are prevented by vector control. It is unlikely that vaccines or anti-viral agents will have application in the near future.     

Prevalence of selected zoonotic diseases in vertebrates from Haiti, 1972.

Vertebrate animals collected in Haiti in 1972 were tested for selected zoonotic diseases. No rabies virus or neutralizing (N) antibody was detected in bats (Artibeus jamaicensis). However, N antibody against St. Louis encephalitis, Western equine encephalitis (WEE), and Eastern equine encephalitis were detected in resident species of birds and WEE antibody in bats. No N antibody against Venezuelan equine encephalitis was found. The possible introduction by migratory birds and local transmission of these arboviruses is discussed.     

Identification of Hotspots in the European Union for the Introduction of Four Zoonotic Arboviroses by Live Animal Trade

Live animal trade is considered a major mode of introduction of viruses from enzootic foci into disease-free areas. Due to societal and behavioural changes, some wild animal species may nowadays be considered as pet species. The species diversity of animals involved in international trade is thus increasing. This could benefit pathogens that have a broad host range such as arboviruses. The objective of this study was to analyze the risk posed by live animal imports for the introduction, in the European Union (EU), of four arboviruses that affect human and horses: Eastern and Western equine encephalomyelitis, Venezuelan equine encephalitis and Japanese encephalitis. Importation data for a five-years period (2005-2009, extracted from the EU TRACES database), environmental data (used as a proxy for the presence of vectors) and horses and human population density data (impacting the occurrence of clinical cases) were combined to derive spatially explicit risk indicators for virus introduction and for the potential consequences of such introductions. Results showed the existence of hotspots where the introduction risk was the highest in Belgium, in the Netherlands and in the north of Italy. This risk was higher for Eastern equine encephalomyelitis (EEE) than for the three other diseases. It was mainly attributed to exotic pet species such as rodents, reptiles or cage birds, imported in small-sized containments from a wide variety of geographic origins. The increasing species and origin diversity of these animals may have in the future a strong impact on the risk of introduction of arboviruses in the EU.     

Western equine encephalitis in infants; a report on three cases with sequelae

Approximately one-third of the laboratory-confirmed cases of Western equine encephalitis occur in children under the age of 10. The present paper describes three instances of Western equine encephalomyelitis virus infection in infants under one year of age, together with the resultant sequelae. The difficulties associated with diagnosis of central nervous system disturbances in very young children are discussed, and it is pointed out that in view of the frequent occurrence of clinical infections with the arthropod-borne encephalitis viruses these agents should be given serious consideration as a cause of acute central nervous system infection in childhood and as the possible etiology for obscure, severe neurological disturbances in the pediatric age groups.     

Neutralising antibodies for Mayaro virus in Pantanal, Brazil

The Pantanal hosts diverse wildlife species and therefore is a hotspot for arbovirus studies in South America. A serosurvey for Mayaro virus (MAYV), eastern (EEEV), western (WEEV) and Venezuelan (VEEV) equine encephalitis viruses was conducted with 237 sheep, 87 free-ranging caimans and 748 equids, including 37 collected from a ranch where a neurologic disorder outbreak had been recently reported. Sera were tested for specific viral antibodies using plaque-reduction neutralisation test. From a total of 748 equids, of which 264 were immunised with vaccine composed of EEEV and WEEV and 484 had no history of immunisation, 10 (1.3%) were seropositive for MAYV and two (0.3%) for VEEV using criteria of a ≥ 4-fold antibody titre difference. Among the 484 equids without history of immunisation, 48 (9.9%) were seropositive for EEEV and four (0.8%) for WEEV using the same criteria. Among the sheep, five were sero- positive for equine encephalitis alphaviruses, with one (0.4%) for EEEV, one (0.4%) for WEEV and three (1.3%) for VEEV. Regarding free-ranging caimans, one (1.1%) and three (3.4%), respectively, had low titres for neutralising antibodies to VEEV and undetermined alphaviruses. The neurological disorder outbreak could not be linked to the alphaviruses tested. Our findings represent strong evidence that MAYV and all equine encephalitis alphaviruses circulated in the Pantanal.     

Functional pseudotyping of human immunodeficiency virus type 1 vectors by Western equine encephalitis virus envelope glycoprotein

We investigated the ability of western equine encephalitis virus envelope glycoproteins (WEEV GP) to pseudotype lentiviral vectors. The titers of WEEV GP-pseudotyped human immunodeficiency virus type 1 (HIV) ranged as high as 8.0 × 10⁴ IU/ml on permissive cells. Sera from WEEV-infected mice specifically neutralized these pseudotypes; cell transduction was also sensitive to changes in pH. The host range of the pseudotyped particles in vitro was somewhat limited, which is atypical for most alphaviruses. HIV vectors pseudotyped by WEEV GP may be a useful tool for characterizing WEEV cell binding and entry and screening for small-molecule inhibitors.     

Inhibition by Agaricus blazei Murill fractions of cytopathic effect induced by western equine encephalitis (WEE) virus on VERO cells in vitro

Anti-viral activities of Agaricus blazei Murill were investigated. The water extracts of the cultured mycelia and fruiting bodies were fractionated with different concentrations of ethanol. To several viruses which have cytopathic effects (CPE) on VERO cells, inhibition of these effects by the ethanol fractions was tested. Strong inhibition of CPE induced by western equine encephalitis (WEE) virus was observed in the mycelial fractions but not those of fruiting bodies.     

WESTERN EQUINE ENCEPHALITIS IN INFANTS—A Report on Three Cases with Sequelae

Approximately one-third of the laboratory-confirmed cases of Western equine encephalitis occur in children under the age of 10. The present paper describes three instances of Western equine encephalomyelitis virus infection in infants under one year of age, together with the resultant sequelae. The difficulties associated with diagnosis of central nervous system disturbances in very young children are discussed, and it is pointed out that in view of the frequent occurrence of clinical infections with the arthropod-borne encephalitis viruses these agents should be given serious consideration as a cause of acute central nervous system infection in childhood and as the possible etiology for obscure, severe neurological disturbances in the pediatric age groups.