SOME ECOLOGICAL ASPECTS OF THE PROBLEM OF ARTHROPOD-BORNE ANIMAL VIRUSES IN THE WESTERN PACIFIC AND SOUTH-EAST ASIA REGIONS.
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In recent years there has been an increasing awareness of the importance of arthropod-borne viruses in the Western Pacific region and in South-East Asia. This realization of the importance of these viruses as causes of human morbidity and mortality and of economic loss due to infection of domestic animals has led to studies attempting to elucidate the basic ecology of some of these viruses. The author reviews the extent of knowledge of the ecology of Japanese and Murray Valley encephalitis viruses and indicates possible mechanisms for the overwintering of the viruses based on experiments in which other viruses were mainly used. He discusses the limited available knowledge on the ecology of dengue and emphasizes the necessity of research on the possibility that this disease is a zoonosis. A brief discussion is also given of the haemorrhagic diseases which are found in these regions and a brief description of the state of knowledge on the ecology of Kyasanur Forest disease and epidemic nephroso-nephritis. A brief discussion is also included on the ecology of the tick-borne Russian spring-summer encephalitis. (+info)
STUDIES OF ARBOVIRUSES IN WESTERN AUSTRALIA. SEROLOGICAL EPIDEMIOLOGY.
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In order to obtain information on the occurrence of arboviruses in Western Australia, sera from white persons and Australian aborigines and from animals were subjected to antibody estimations with selected viruses as a prelude to virus isolations. The serological evidence shows the presence of group A and group B arboviruses but significant differences in antibody distribution between the two groups. Antibodies to group A viruses, particularly to the Malayan mosquito virus AMM 2354, are present in both the aboriginal and the white populations over the entire territory. Neutralizing antibody to another group A virus, AMM 2021, isolated in Malaya, is found in much lower prevalence, while antibodies to the newly isolated Queensland group A virus, MRM 39, are found only in the Kimberley area. No avian group A antibodies were detected. The prevalence of group B antibodies is high in the northern part of the State and almost non-existent in the central areas. The results indicate the presence of more than one group B virus and the absence of dengue neutralizing antibody in the Australian aborigine. A unique situation exists in central Australia, where all aboriginal sera have group A antibody but none has group B antibody. (+info)
DENGUE-TYPE VIRUSES ISOLATED IN SINGAPORE.
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A dengue-like illness with marked haemorrhagic manifestations appeared in Singapore in 1960. Its similarity in many respects to the haemorrhagic fevers of Thailand and the Philippines led to its being described as "Singapore haemorrhagic fever".This paper describes the isolation and identification of dengue-type viruses from patients in Singapore between 1960 and 1962. In addition to the conventional complement-fixation and neutralization tests, a new test, called the "sensitized erythrocyte agglutination test", was employed; this test method is described.Altogether 21 dengue-type viruses were isolated, including dengue types 1, 2 and 4. Chikungunya virus, prominent in the Thailand disease, was not detected.The author suggests that study of the epidemiology of haemorrhagic fevers in South-East Asia would cast further light on the transmission of arboviruses. (+info)
VIRUS BIOGRAPHIES. I. GROWTH OF WEST NILE AND GUAROA VIRUSES IN TISSUE CULTURE.
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Southam, Chester M. (Sloan-Kettering Institute for Cancer Research, New York, N.Y.), Frederick H. Shipkey, Virginia I. Babcock Roller Bailey, and Robert A. Erlandson. Virus biographies. I. Growth of West Nile and Guaroa viruses in tissue culture. J. Bacteriol. 88:187-199. 1964.-Monolayer tissue cultures of HEp 2 cells (human epidermoid carcinoma) were inoculated with Guaroa or West Nile viruses. At daily intervals for 4 days thereafter, these cultures were studied by (i) light microscopy of living cultures and stained cultures, (ii) intracerebral inoculation of mice to titrate infectivity, (iii) acridine orange stain to observe nucleic acid changes, (iv) fluorescein-labeled antibody technique to observe specific viral antigen, and (v) electron microscopy to observe virus particles. Guaroa virus infectivity increased progressively over the 4-day period, and caused definite cytolysis by day 3. Cytoplasmic ribonucleic acid (RNA) staining was increased by 24 hr, and by 48 hr the RNA formed globular masses, particularly in degenerating cells. Viral antigen was occasionally seen on day 1, and increased progressively thereafter, forming numerous sharply outlined particles in cytoplasm concentrated at the cell membrane. Virus particles were ellipsoids with a dense nucleoid and a single membrane approximately 70 by 90 mmu, which appeared to form at the cell membrane just before being discharged. West Nile virus infectivity increased sharply between 1 and 2 days, but caused little cytolysis even by 4 days. Cytoplasmic RNA staining increased progressively for the 4 days, usually forming a large juxtanuclear mass in each affected cell. Viral antigen was not detected on day 1, but increased progressively thereafter, forming a crescent or a single diffuse mass adjacent to the nucleus. Virus particles were spheres approximately 30 mmu in diameter, with a dense nucleoid and a single membrane. They appeared to form in granular foci in the cytoplasm and then to fill the channels of the endoplasmic reticulum. No significant nuclear changes were observed with either virus by any of these techniques. (+info)
PLAQUE ASSAY PROCEDURE FOR COLORADO TICK FEVER VIRUS.
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Deig, E. Frank (University of California, Berkeley), and H. M. S. Watkins. Plaque assay procedure for Colorado tick fever virus. J. Bacteriol. 88:42-47. 1964.-A reproducible plaque assay procedure is described for the quantitation of Colorado tick fever virus in a cell line established from embryonic hamster tissue. Under the best conditions, plaques approximately 4 mm in diameter were formed after incubation at 37 C of 4 to 6 days. Several environmental variables in the procedure were studied. Efficiency was increased markedly by combining the virus during adsorption with serum proteins, and by carrying out this step at 25 C rather than at 37 C. The overlay medium used contained metabolites which promoted cell viability for periods greater than 1 week, and allowed plaques to develop. Plaque formation was relatively insensitive to a variation in pH between 7.1 and 8.1 (with optimal concentrations of bicarbonate). However, plaque development was inhibited with medium containing greater than 0.22% bicarbonate (at optimal pH), or when the initial pH was less than 7.0. (+info)
COLORADO TICK FEVER VIRUS IN CELL CULTURE. I. CELL-TYPE SUSCEPTIBILITY AND INTERACTION WITH L CELLS.
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Trent, Dennis W. (University of Oklahoma School of Medicine, Oklahoma City) and L. Vernon Scott. Colorado tick fever virus in cell culture. I. Cell-type susceptibility and interaction with L cells. J. Bacteriol. 88:702-708. 1964.-Colorado tick fever (CTF) virus was serially propagated in monolayer cultures of L and FL cells. Early passages of virus in FL cells yielded viral titers 10(4)-fold greater than did the corresponding L-cell passages. During L-cell passage number 4, there was a 10(3)-fold increase in the amount of infectious virus produced as compared with virus cultured earlier in this cell line. Viruses from L-cell passages 8 and 12 were identified with specific immune serum to be CTF viruses which were antigenically similar, if not identical, to the mouse-adapted virus. Parallel titrations of mouse-, L cell-, and FL cell-adapted viruses were performed in mice and replicate monolayers of L, FL, HeLa, KB, chick embryo, and cotton rat kidney cells. Cytopathic effects and viral replication were noted in all cultures except HeLa and cotton rat kidney. Cultures of L, FL, and chick embryo cells were as sensitive to infection as were suckling or weanling mice. KB cells were the least susceptible of those cell types examined. In L-cell cultures, 90% of the input virus was adsorbed to the cells during the first 30 min of incubation. The latent period lasted 10 to 12 hr, and was followed by rapid viral synthesis for the next 10 to 24 hr, depending upon the multiplicity of infection. Curves describing exponential increase in cell-associated and cell-released virus were separated by 4 hr. When the maximal total virus titers were reached, 80 to 90% of the virus was released from the cell. (+info)
FURTHER STUDIES ON ANTIGENIC RELATIONSHIPS AMONG THE VIRUSES OF THE GROUP B TICK-BORNE COMPLEX.
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This paper is a report on further studies of the antigenic relationships among viruses of the Group B tick-borne complex, carried out by the haemagglutination-inhibition (HI), complement-fixation, absorption-HI and diffusion-in-gel techniques. Earlier work has been extended to include Powassan and Negishi viruses.Comparisons of a number of strains of tick-borne viruses have revealed inter-strain variation only in the case of Omsk haemorrhagic fever virus, where two subtypes are distinguishable.This recognition of subtypes of Omsk virus has led the author to review the concept that Central European encephalitis and Russian spring-summer encephalitis viruses are distinct entities. On the basis of their close relationship, as well as new information on vectors and geographical range, she suggests that they be considered variant subtypes of one virus, designated Group B tick-borne encephalitis virus. (+info)
TWELVE ISOLATIONS OF ZIKA VIRUS FROM AEDES (STEGOMYIA) AFRICANUS (THEOBALD) TAKEN IN AND ABOVE A UGANDA FOREST.
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In continuation of a series of studies of arboreal mosquitos as virus vectors in Uganda, 12 strains of Zika virus and one strain of another Group B arbovirus were isolated between November 1961 and June 1963 from pools of Aedes (Stegomyia) africanus caught on a 120-foot (36.5-m) tower in Zika forest. For five strains it is known at what height the mosquitos were caught: one was from mosquitos taken at ground level, and the other four were from mosquitos taken in or above the upper canopy after sunset. No small mammal trapped in the forest either on the ground or in the trees showed serum antibody for Zika virus.These findings suggest that in Zika forest, A. (S.) africanus becomes infected from a virus reservoir that is probably not among the small animals tested and that infected mosquitos are liable to be spread widely beyond the forest by convection currents above the tree-tops in the first two or three hours after sunset. (+info)