Venezuelan Encephalitis Research Articles

The involvement of dogs in endemic cycles of Venezuelan encephalitis virus.

The involvement of dogs in endemic cycles of Venezuelan encephalitis virus.

Growth curves and clearance rates of virulent and benign Venezuelan encephalitis viruses in hamsters.

Four virulent strains of Venezuelan encephalitis virus attained higher concentrations of infectious virus in bloods of adult hamsters than two benign strains when given subcutaneously. One benign virus, the attenuated TC83 vaccine strain, reached higher concentrations in bone marrow and Peyer's patches than virulent subtype I strains, and another benign virus, subtype IV, grew to lower levels. When inoculated intracranially, the two benign viruses attained high concentrations in brain, but did not significantly alter in lethality although morbidity was increased. Intracardiac inoculation failed to increase virus concentrations of two benign viruses in blood or hematopoietic tissues above those found after subcutaneous inoculation, nor did it increase lethalities to those of virulent virus. Three benign virus strains were cleared more rapidly from hamster plasmas than six virulent strains. Differences in clearance rates were apparently not due to destruction of benign viruses by blood or tissue components. Thus viral concentrations in blood correlated directly and clearance rates inversely with hamster virulence, whereas the rate and extent of growth of a VE virus in hematopoietic or brain tissues did not correlate with ability to kill hamsters.

Homogeneity of Venezuelan Encephalitis Virion Populations of Hamster-Virulent and Benign Strains, Including the Attenuated TC83 Vaccine

A hamster-virulent strain of Venezuelan encephalitis virus (BeAn8, subtype III) and a benign strain (BeAr35645, subtype IV) each yielded 100 clones with virulence properties like those of the parental virion population. Another hamster-virulent strain (63U2, subtype I, variety E) was heterogeneous since 2 out of 100 clones were less virulent for hamsters than the other 98 clones or the parental virus population. The attenuated TC83 vaccine strain, (a derivative of subtype I, variety A), although over 99% homogeneous with respect to hamster virulence, was unstable since virulent virions could be selected from the parental population by passage through hamsters.

Ecological Profile of Culex (Melanoconion) aikenii (Diptera: Culicidae), Vector of Endemic Venezuelan Encephalitis in Panama1

Preliminary notes are presented on the ecology of Culex aikenii (Aiken & Rowland), vector of Venezuelan encephalitis (VE) in the middle Chagres river basin of Panama. C. aikenii probably represents a complex of at least 2 closely related species with similar habits and both are involved in the natural transmission of VE virus. However, until taxonomic work now in progress is completed the name in its present broad sense will be used. Immature stages of the species are almost always found closely associated with the aquatic floating plant water-lettuce, Pistia stratiotes . Eggs arc laid singly on the leaves. Larvae and pupae remain motionless for hours attached to airpockets under the Pistia leaves. When Pistia plants are dislodged from their anchorage by flooding, larvae and pupae move down with them and may seed new areas where the plants become tangled and proliferate. These movements of Pistia seem to serve the double effect of restricting growth of local populations of C. aikenii and of serving as one method for dispersal of the species. Females have a broad spectrum of hosts both homeothermic and poikilothermic. They have a slight predilection for mammals over birds. Among the latter, herons are the preferred hosts. The species bites a variety of mammals, but seems to prefer rodents, except where there are large concentrations of domestic mammals, such as cattle. They feed on blood between dusk and dawn with peaks of activity occurring irregularly throughout the night. Females feed preferably on the ground, seldom going up to the canopy of trees in search of hosts. Man is usually bitten very low on the legs, so that people wearing shoes and long pants arc seldom fed on.

Growth of Venezuelan encephalitis virus in embryonic cell cultures of wild birds.

Primary embryonic cell cultures made from nine species of wild and domestic birds were infected with Venezuelan encephalitis virus and reproduced each strain to moderately high levels.

Observations of equines, humans and domestic and wild vertebrates during the 1969 equine epizootic and epidemic of Venezuelan encephalitis in Guatemala.

Observations of equines, humans and domestic and wild vertebrates during the 1969 equine epizootic and epidemic of Venezuelan encephalitis in Guatemala.

Ecologic studies of Venezuelan encephalitis virus in southeastern Mexico. 8. Correlations and conclusions.

Ecologic studies of Venezuelan encephalitis virus in southeastern Mexico. 8. Correlations and conclusions.

Ecologic studies of Venezuelan encephalitis virus in southeastern Mexico. VI. Infection of wild birds.

Ecologic studies of Venezuelan encephalitis virus in southeastern Mexico. VI. Infection of wild birds.

Ecologic Studies of Venezuelan Encephalitis Virus in Southeastern Mexico

Hemagglutination-inhibiting (HI) antibody to VE virus was found in 0.26 to 0.32 of sera from persons residing at endemic sites in southeastern Mexico (Sontecomapan and Minatitlan, Veracruz). Prevalences of HI antibody were low (0.02) at Lake Catemaco villages (near Sontecomapan but at higher altitude) and on the Pacific side of the Isthmus of Tehuantepec opposite Minatitlan. Many sera (0.65) with HI antibody (titers ≧10) had detectable complement-fixing antibody (titers ≧4), and most sera (0.87) without detectable HI antibody had no detectable neutralizing (N) antibody to VE virus with heated serum diluted 1:4, although in undiluted, unheated serum, N substances suggesting falsely positive results were found in 0.70. Four cases of disease were identified as being caused by Mexican strains of VE virus, three naturally-acquired (two moderately severe and one encephalitic and fatal) and one acquired by aerosol exposure in the laboratory. All but the fatal case were diagnosed by isolation of virus from blood (and a throat swab of one case) and by rises in titers of VE virus antibodies in serum. Although the two moderately severe, naturally-acquired cases occurred in field workers at Sontecomapan and Minatitlan, nine other susceptible field workers did not become infected, presumably at least in part due to exposure only to daytime-biting mosquitoes, and use of protective clothing and repellants.

Ecologic studies of Venezuelan encephalitis virus in southeastern México. V. Infection of domestic animals other than equines.

In southeastern México, sera from cattle and pigs, but not the sera of chickens, were frequently positive with Venezuelan encephalitis (VE) virus in hemagglutination-inhibition and neutralization tests. This evidence of natural infection of cattle and swine suggested that they may be involved in cycling virus between vector mosquitoes and vertebrates that amplify it. The geographical distribution of positive cattle and pig sera on the Gulf coast conformed with that of VE virus from other studies, and the low prevalence of antibodies in the arid, irrigated region on the Pacific side of the Isthmus of Tehuantepec corresponded with the inability of other studies to detect much virus activity there. Positive antibody tests of swine sera from the Pacific coast in Chiapas suggested that VE virus was also active there.

Ecologic studies of Venezuelan encephalitis virus in southeastern México. I. Introduction and study sites.

Abstract Hemagglutination-inhibiting (HI) antibody to VE virus was found in 0.26 to 0.32 of sera from persons residing at endemic sites in southeastern Mexico (Sontecomapan and Minatitlan, Veracruz). Prevalences of HI antibody were low (0.02) at Lake Catemaco villages (near Sontecomapan but at higher altitude) and on the Pacific side of the Isthmus of Tehuantepec opposite Minatitlan. Many sera (0.65) with HI antibody (titers ≧10) had detectable complement-fixing antibody (titers ≧4), and most sera (0.87) without detectable HI antibody had no detectable neutralizing (N) antibody to VE virus with heated serum diluted 1:4, although in undiluted, unheated serum, N substances suggesting falsely positive results were found in 0.70. Four cases of disease were identified as being caused by Mexican strains of VE virus, three naturally-acquired (two moderately severe and one encephalitic and fatal) and one acquired by aerosol exposure in the laboratory. All but the fatal case were diagnosed by isolation of virus from blood (and a throat swab of one case) and by rises in titers of VE virus antibodies in serum. Although the two moderately severe, naturally-acquired cases occurred in field workers at Sontecomapan and Minatitlan, nine other susceptible field workers did not become infected, presumably at least in part due to exposure only to daytime-biting mosquitoes, and use of protective clothing and repellants.

An Outbreak of Venezuelan Encephalitis in Man in the Panamá Canal Zone

Abstract An outbreak of Venezuelan equine encephalomyelitis (VEE) virus infection occurred in seven of a 24-man unit of U.S. soldiers engaged in jungle survival training in the Canal Zone. The illness was characterized by sudden onset of fever, intense headache, generalized muscular and joint pains, and leukopenia. Transient signs of encephalitis occurred in only one man. VEE virus was isolated from the serum of each of the affected men, and all developed specific, neutralizing antibodies during convalescence. Epidemiologic evidence strongly suggested that the disease was acquired at a single campsite, with a high incidence of infection among men bivouacked in a small area of that site. VEE virus was isolated from two of five sentinel hamsters exposed in the camp 1 month later, suggesting that the outbreak resulted from contact with a localized area of endemic virus activity.

Discovery and geographic distribution of Venezuelan encephalitis virus in Guatemala, Honduras, and British Honduras during 1965-68, and its possible movement to Central America and México.

"Discovery and Geographic Distribution of Venezuelan Encephalitis Virus in Guatemala, Honduras, and British Honduras During 1965–68, and its Possible Movement to Central America and México" published on Jul 1970 by The American Society of Tropical Medicine and Hygiene.

Infectivity of nucleic acid and adsorptive properties of Venezuelan encephalitis virions inactivated by lipid solvents.

SummaryVenezuelan encephalitis (VE) virions, inactivated by 0.1% sodium deoxycholate (SDC), 50% diethyl ether, or 50% chloroform yielded infectious ribonucleic acid (IRNA) upon hot or cold phenol treatment, but they could not be shown to adsorb to cultured chicken embryonic cells as measured by hemagglutinin in cultural fluid or by interference with homologous virus. These lipid solvents in the above concentrations did not inactivate phenol-extracted IRNA nor did they release IRNA from purified VE virions, although it was found after treatment of crude suspensions of virus which apparently contained incomplete, unstable virions. Therefore, it is postulated that SDC, diethyl ether, or chloroform inactivate VE virus by altering viral surface properties related to adsorption to susceptible cells rather than by disruption of the capsid with release of IRNA or by destruction of IRNA within the virus.

Different effects of deoxycholate, ether, chloroform, hydrocarbons, and alcohols on Venezuelan encephalitis viral infection, hemagglutination, and complement-fixation.

SummaryVenezuelan encephalitis virus suspensions were affected differently by various lipid solvents. Infectivity titers of both crude virus suspensions from mouse brain or primary chicken embryonic cell cultures and density gradient-purified virus from cultures were reduced more and faster by sodium deoxycholate (SDC), diethyl ether, or chloroform than by pentane or hexane. Benzene failed to affect infectivity titers of even density gradient-purified virus. Hemagglutinin (HA) titers decreased after 2–6 hr of treatment of virus with diethyl ether or chloroform, but remained unchanged for 24 hr with SDC, pentane, hexane, or benzene. Complement-fixing antigen titers of crude virus suspensions were unchanged by these lipid solvents. Alcohols rapidly destroyed all three viral properties, although water was essential for alcohol inactivation since lyophilized virus was unaffected by absolute ethanol. Evidently hydrophilic hydroxyl groups are important in viral inactivation by these chemicals since pentanol and...

SEROLOGIC EVIDENCE OF ARBOVIRUS INFECTIONS IN WILD RUMINANTS1

Trainer, D. O. and R. P. Hanson (Dept. Veterinary Science, University of Wisconsin, Madison, Wis. 53706). Serologic evidence of arbovirus infections in wild ruminants. Amer. J. Epid., 1969, 90: 354–358.—Almost 1,500 sera from wild ruminants of North America, including bighorn sheep, prong horn antelope and whilte-tailed deer, were tested for neutralizing antibodies to 7 viruses: eastern, western, St. Louis, Venezuelan and California encephalitis, vesicular stomatitis and encephalomyocarditis. Among the bighorn sheep sampled, neutralizing antibodies were detected for western encephalitis virus (12%) and California encephalitis virus (12%); among prong horn antelope 16% were positive for California encephalitis. In white-tailed deer, serologic evidence of Venezuelan encephalitis was restricted to deer from Texas, while deer from Nebraska and Texas had antibodies to western encephalitis virus, and deer from Wisconsin and Texas had antibody to St. Louis encephalitis virus. California encephalitis antibodies were detected in almost every species and geographic site examined, and the largest number of reactors occurred in deer from Wisconsin (26%) and Texas (50%). Approximately 8% of the Texas deer sera were serologically positive for vesicular stomatitis and 4% for encephalomyocarditis. Results of this study suggest that wild ruminants and white-tailed deer in particular could serve as a valuable indicator for the activity of arboviruses—a “natural” sentinel system.

Venezuelan encephalitis antibody studies in certain Florida wildlife.

Between November, 1966 and November, 1968 serum samples from 725 wild vertebrates from south Florida were examined for antibody to Venezuelan encephalitis virus by the hemagglutination-inhibition test. Antibodies to Venezuelan encephalitis were found in 29 sera from the cotton mouse, Peromyscus gossypinus, the cotton rat, Sigmodon hispidus, the rice rat, Oryzomys palustris, the black rat, Rattus rattus, and the white-tailed deer, Odocoileus virginianus. Recent circulation of Venezuelan encephalitis virus in habitats other than documented enzootic foci warrants extensive ecological studies in areas adjacent to the Everglades National Park.

Serologic study of some infectious diseases of Canada geese.

A serologic study was conducted to investigate the exposure of captive and free-flying Canada geese (Branta canadensis) to five arboviruses, chlamydiae and Mycoplasma gallisepticum. Of more than 1200 serums screened in the metabolic-inhibition test (MIT), no serums neutralized eastern encephalitis virus (EEV), less than 1% neutralized western (WEV) or Venezuelan (VEV) encephalitis viruses, 2% neutralized St. Louis encephalitis virus (SLEV), and 29% neutralized California encephalitis virus (CEV). Supplementary serologic procedures indicated that a nonspecific inhibitor probably caused inhibition of CEV in the MIT. Fifty-six per cent of 197 serums had hemagglutination-inhibition titers of 1:80 or higher against M. gallisepticum and were considered “positive”. Two hundred and eight serums were negative for complement-fixing antibody against chlamydiae.

Venezuelan encephalitis viremia in hamsters and its relation to virus feedback from sentinel hamsters to mosquitoes in nature.

"Venezuelan Encephalitis Viremia in Hamsters and its Relation to Virus Feedback from Sentinel Hamsters to Mosquitoes in Nature" published on Sep 1968 by The American Society of Tropical Medicine and Hygiene.

Comparison of starch, agarose, and agar for plaquing Venezuelan encephalitis virus.

Comparison of starch, agarose, and agar for plaquing Venezuelan encephalitis virus.