Recovery of dengue-2 and dengue-3 viruses from man in Jamaica

Dengue-like illness has been reported in Jamaica since 1824, although the viruses concerned were never isolated. The emphasis of this work was isolating and typing the etiologic agents involved; 679 cases were reported to the Microbiology Department, University of the West Indies, during 1968 and 1969. Primary serum samples were tested; 112 of 175 indicated recent arbovirus group B infections. Primary infections and reinfections with dengue viruses were indicated by hemagglutination-inhibition and complement-fixation tests. Challenge-virus resistance technique was used to isolate eight agents from human serum. Six of these strains have been typed as dengue-3 and two as dengue-2 viruses.(AU)

A comparitive study of virulences, plaque morphologies and antigenic characteristics of Venezuelan encephalitis virus strains

Virulences of VE virus strains from tropical regions of the North and South American continents were studied in adult Syrian hamsters, Swiss albino mice and cotton rats. Virulence profiles were based on frequency and time of illness and death following subcutaneous inoculation of small doses of virus as collected in nature or after only a few passages in laboratory hosts. Forty-one strains from Mexico, USA-Florida, Panama, Colombia, and Venezuela uniformity killed hamsters inoculated s.c. with 4-1000 PFU; incubation periods were usually 3-6 days, but some Panamanian and USA-Florida strains had incubation periods 1-2 days longer than strains from other countries. All of 37 strains from these countries regularly produced illness in adult mice, but killed only 71-82 percent; in adult cotton rats, signs of illness were not recognized, but death occurred in 18-30 percent. Variations in virulence profiles for mice and cotton rats among 28 Mexican strains were ogten as great as those seen among 9 strains from USA-Florida, Panama, Colombia and Venezuela. Virus strains from the Bush Bush areas of Trinidad, however, had distinctive virulence profiles. All 5 of these strains killed hamsters only after prolonged incubation periods of more than 5 days, and killed only 1 of 25 mice; neither of two strains killed cotton rats. Young and Johnson reported (Amer. J. Epid., 1969, 89 286-307) that these Trinidad strains should antigenically be classified as Mucambo rather than VE virus. The TC 83 attenuated strain of VE virus in a dose of 500 PFU given s.c. killed no hamsters, mice or cotton rats, but in some experiments employing larger doses, up to 20 percent hamsters became ill and 5-10 percent died without apparent relationship to dose. Plaque sizes and morophologies of 19 VE and 5 Trinidad Mucambo virus strains in primary chicken embryonic cell cultures did not correlate with virulence for hamsters, mice, cotton rats or man, nor with geographic, host or tissue source or year of collection. In sera of cotton rats and mice 3-4 weeks after s.c. inoculation, titers of VE virus HI antibody measured with hemagglutinin from a Mexican virus strain were similar for strains from Mexico, Colombia and Venezuela. However they were lower with USA-Florida and TC 83 virus strains and with Trinidad Mucambo virus strains, suggesting that these viruses differ antigenically from Mexican, Colombian and Venezuelan strains. Nevertheless the attenuated TC 83 vaccine virus protected adult mice against s.c. challenge by 28 Mexican and 8 other VE virus strains from USA-Florida, Panama, Colombia and Venezuela, suggesting that immunologically distinct types of VE virus based on cross-protection do not exist in these countries. (AU)

Laboratory studies with wild rodents and viruses native to Trinidad. III. Studies with three Guama-group viruses

Data obtained at the Bush Bush Forest field station in the Nariva Swamp, eastern Trinidad, indicated the continuous presence there of three Guama-group agents - Bimiti, Catu, and Gauma - all apparently dependent on the same rodent host and vector populations. This suggested the possibility that the antigenic relation of these viruses might influence their epidemiology. The question was investigated by examining the effect of cross-immunity on circuling-virus levels in captive-reared Oryzomys laticeps and zygodontomys brevicauda, two species of rodent that are natural hosts for these viruses. Bimiti virus was circulated at lower levels in nonimmune Zygodontomys than were the other two viruses, and in cross-immunized zygodontomys, Bimiti-virus levels were still lower and occasionaly undetectable. Catu viremia reached high titers in both nonimmune Oryzomys and Zygodontomys, and even in cross-immunized rodents, titers often reached 2.4 to 3.3 log LD50. Guama viremia in nonimmune Oryzomys and Zygodontomys was of the same order as that of Catu virus, but in cross-immunized rodents it was often completely suppressed. These data suggest that when hosts are scarce Catu virus would be affected least and Guama virus most. The experimental findings are compared with field observation. (AU)

Arbovirus studies in Bush Bush Forest, Trinidad, W.I., September 1959-December 1964. V. Virus isolations

Virus isolates totaling 593 and representing 19 different virus types were recovered from sentinel animals, small mammals, and arthropods during studies carried out in Bush Bush Forest, Trinidad, over a 5-year period. The laboratory techniques used are described, and details are given regarding 49 isolates belonging to 12 virus types: Una, St. Louis encephalitis, Ilheus, Bush-bush, TRVL 57896 (Moriche), Wyeomyia, Cache Valley, Cocal, Oropouche, Aruac, Nariva, and TVRL 39316-1-5 type (Pacui). The remaining 544 isolates were identified as Venezuelan equine encephalitis virus or members of serologic groups C and Guama, and are discussed elsewhere (AU)

Respiratory viruses in Jamaica: a virologic and serologic study. 1. Virus isolations and serological studies on clinical specimens

A survey of respiratory viruses and their antibodies in the Caribbean island of Jamaica has revealed that infleunza A, B and C viruses, parainfleunza type 1 and 3 viruses, respiratory syncytial virus and several types of adenovirus are causing respiratory infections in the Jamaican population. Respiratory virus infections were detected in Jamaica more frequently in the cooler months of the year, October through March, than in the warmer months. Adenoviruses were observed to be causing infections at all times of the year, but some evidence that parainfleunza type 1 infections are occurring at intervals only was obtained. Almost all infections by respiratory syncytial virus were obtained in infants and young children with severe lower respiratory tract disease.(Summary)