Jungle yellow fever mosquito studies in Trinidad: 1954

Eruption of a yellow fever epizootic/epidemic was signalled by the Trinidad Regional Virus Laboratory with the isolation of virus from the first human case in April 1954. Mosquito investigations were conducted in three major areas. Descriptions are provided of the forest environments, the mosquito collection techniques, transportation logistics, mosquito identification and isolation of viruses. An addendum briefly reviews subsequent yellow fever outbreaks in the island, addresses the question of origin and provides recommendations for the future.

Yellow fever: evolution of ideas concerned with demonstrating the natural occurrence of transovarial transmission of virus in mosquitoes

In November 1978, an outbreak of disease among wild simians of south Trinidad alerted officials to the presence of jungle yellow fever (YF). Learning of the epizootic and having recently been involved in studies establishing transovarial transmission (TOT) of YF virus, this laboratory urged Trinidad workers to undertake demonstration of the natural occurence of TOT in the forest environment. The idea as well as a suggested procedural protocol involving vector mosquitoes (Haemagogus spp.) was accepted and acted upon. Initial procedures called for undertaking studies in areas where sick or dead monkeys were observed, collecting larvae as well as adult female Haemagogus from which eggs were to be obtained, hatched, and the ensuing larvae reared to adults and tested for virus. As time passed, various problems were encountered necessitating changes in field procedures. The most important was the substitution of ovitraps for adult female collections as a source of eggs. By 1980, the epizootic/epidemic was waning. Funding for additional studies became available from Canadian sources and the author was invited to be a consultant. Field and laboratory procedures were again modified and streamlined. Described are: (1) choice of field sites, (2) choice of ovitraps, (3) siting of ovitraps, (4) frequency of collections, (5) laboratory procedures, (6) search for male Haemagogus and female ovipositing activity, and (7) duration of a TOT study and conclusions.

Yellow fever: evolution of ideas concerned with demonstrating the natural occurrence of transovarial transmission of virus in mosquitoes

In November 1978, an outbreak of disease among wild simians of south Trinidad alerted officials to the presence of jungle yellow fever (YF). Learning of the epizootic and having recently been involved in studies establishing transovarial transmission (TOT) of YF virus, this laboratory urged Trinidad workers to undertake demonstration of the natural occurence of TOT in the forest environment. The idea as well as a suggested procedural protocol involving vector mosquitoes (Haemagogus spp.) was accepted and acted upon. Initial procedures called for undertaking studies in areas where sick or dead monkeys were observed, collecting larvae as well as adult female Haemagogus from which eggs were to be obtained, hatched, and the ensuing larvae reared to adults and tested for virus. As time passed, various problems were encountered necessitating changes in field procedures. The most important was the substitution of ovitraps for adult female collections as a source of eggs. By 1980, the epizootic/epidemic was waning. Funding for additional studies became available from Canadian sources and the author was invited to be a consultant. Field and laboratory procedures were again modified and streamlined. Described are: (1) choice of field sites, (2) choice of ovitraps, (3) siting of ovitraps, (4) frequency of collections, (5) laboratory procedures, (6) search for male Haemagogus and female ovipositing activity, and (7) duration of a TOT study and conclusions (AU)

Jungle yellow fever mosquito studies in Trinidad: 1954

Eruption of a yellow fever epizootic/epidemic was signalled by the Trinidad Regional Virus Laboratory with the isolation of virus from the first human case in April 1954. Mosquito investigations were conducted in three major areas. Descriptions are provided of the forest environments, the mosquito collection techniques, transportation logistics, mosquito identification and isolation of viruses. An addendum briefly reviews subsequent yellow fever outbreaks in the island, addresses the question of origin and provides recommendations for the future (AU)

Oral infection of Aedes aegypti with yellow fever virus: geographic variation and genetic consideration

Twenty-eight populations representing a worldwide distribution of Aedes aegypti were tested for their ability to become orally infected with yellow fever virus (YFV). Populations had been analyzed for genetic variations at 11 isozyme loci and assigned to one of 8 genetic geographic groups of Ae. aegypti. Infection rates suggest that populations showing isozyme genetic relatedness also demonstrate similarity to oral infection rates with YFV. The findings support the hypothesis that genetic variation exists for oral susceptibility to YFV in Ae. aegypti.(AU)

Arbovirus studies in an evergreen seasonal marsh forest in Trinidad, West Indies

Studies carried out in Turure Forest, north-eastern Trinidad, from March, 1966, to March, 1969, resulted in the isolation of 462 arbovirus strains: 198 Venezuelan equine encephalitis (VEE), 42 eastern equine encephalitis (EEE), 75 group C, 136 Guama group, 2 Ilheus, 1 St. Louis encephalitis, 5 Wyeomyia, 1 Maguari, 1 Cocal, and 1 Aruac, Strains of VEE were recovered most frequently from sentinel mice (109) and Culex portesi (82), and the same was true for the group C and Guana group isolates. EEE strains came from sentinel mice (30), C. pedroi (11), and C. portesi (1). Forest rodents yielded only 9 isolates, all group C and Guana group and all from Proechimys guyannensis and Oryzomys capito; however, 21 percent of 639 rodent sera had haemagglutination-inhibiting (HI) antibodies to one or more viruses. VEE HI antibodies were more common in O. capito that in P. guya nnensis. In complement-fixation (CF) tests, 32 percent of O. capito and 8 percent of P. guyannensis reacted with a Guama group antigen. Birds yielded 3 isolates, 2 Iheus and 1 St. Louis, but 10 percent of 1,414 Manacus manacus sera reacted with EEE antigen in HI test. Three of 4 horses had CF antibodies to EEE, and 54 percent of 158 human sera wer HI-positive for one or more of 9 antigens used, including VEE and EEE (AU)

Aedes aegypti strain fitness for yellow fever virus transmission

Three geographical strains of Aedes aegypti from Thailand (Amphur), East Africa (Kampala), and the West Indies (Santo Domingo) were compared for susceptibility to infection with low-passage yellow fever virus (French viscerotropic) as well as for ability to transmit virus by bite at varying extrinsic incubation periods. Santo Domingo strain appeared the most competent and Kampala the least when mosquitoes were exposed to a low level virus-infecting blood meal; at higher virus levels, a similar trend was noted but differences were less evident and in no case were the differences statistically significant. All three strains were infected with and transmitted yellow fever virus (AU)

Hughes virus from Trinidadian ticks and terns

Fifteen strains of Hughes virus were isolated from Soldado Rock, Trinidad, between 1962 and 1965. Seven isolates came from ticks of the Ornithodoros capensis complex and 8 from nestling birds, Sterna fuscata.(AU)

Epidemiological investigations relating to a case of Eastern Equine Encephalitis in a Trinidadian horse

The first equine death in Trinidad known to be due to eastern equine encephalitis (EEE) is reported. Diagnosis was by serologic means only. In related epidemiologic investigations, EEE virus was not isolated from over 5,000 arthropods and the organs of 99 birds, but the serum of five of the birds had neutralizing antibodies to the virus. A strain of Wyeomyia virus and a Turlock-like virus were isolated from the mosquitoes tested (AU)

Arbovirus studies in Bush Bush Forest, Trinidad, W.I., September 1959-December 1964. VI. Rodent-associated viruses (VEE and agents of groups C and Guama): isolations and further studies

Details are given on isolations of seven virus types from material collected in Bush Bush Forest during the study period: 262 of Venezuelan equine encephalitis (VEE), 71 of Caraparu-like, three of Oriboca, two of Restan, 63 of Bimiti, 56 of Catu, and 87 of Guama. Data from experimental-infection studies are presented, as well as results of serologic studies with hemagglutinating antigens of VEE and Caraparu-like viruses and some 1,200 sera of Bush Bush rodents. It was found that the natural transmission cycles of five of these virus types in Bush Bush are similar and include a period of multiplication and viremia in forest-floor rodents and a period of multiplication in mosquitoes among which Culex (Melanoconion) protesi, at least, is capable of subsequent transmission. Similar cycles are inferred for the remaining two virus types, Oriboca and Restan. In 1964 a severe reduction of the rodent population took place, Culex portesi continued abundant, and only Bimiti of the seven virus types was isolated. It is concluded that an alternate host population of sufficient size was not then available to these viruses in Bush Bush. Very little evidence was found to implicate mosquito species other than C.portesi as essential vectors during epizootic or inter-epizootic periods. (AU)

Arbovirus studies in Bush Bush Forest, Trinidad, W. I., September 1959-December 1964. IV. Vertebrate populations

An introduction has been given to the principal vertebrates of Bush Bush Forest, which include 59 species of mammal (32 of bat), 171 species of bird , 27 species of reptile, 7 species of amphibian, and an undetermined number of fish. Special attention was paid to the population dynamics, longevity, and range of small forest rodents. During the study years the populations of small rodents declined almost to the point of disappearence. (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)

Arbovirus studies in Bush Bush Forest, Trinidad, W.I., September 1959-December 1964. III. Entomologic studies

Bush Bush Forest entomologic investigations were concered mainly with mosquitoes, the most conspicuous element of the bloodsucking arthropod fauna. More than 92 species were demonstrated, but only about two dozen were common. Mosquitoes were studied in relation to thier physical environment, seasonal activity, diel activity, horizontal stratifaction in the forest, food preferences, and larval habitats. Large numbers were collected for virus studies. Other groups investigated were phlebotomine flies (10 species), Culicoides flies (10 species), horseflies (18 species), Cuterebridae (one species), sucking lice (four species), fleas (one species), ticks (nine species), and various mites including 15 species of trombiculid. (AU)

Arbovirus studies in Bush Bush Forest, Trinidad, W.I., September 1959-December 1964. II. Field program and techniques

The field program of the Trinidad Regional Virus Laboratory in Bush Bush Forest included studies in which arboviruses (their prevalence and epidemiology) were the chief interest and also studies on the biology of the arthropods and vertebrates possibly associated with arbovirus cycles. The techniques used included the exposure of sentinel animals, trapping and bleeding of small mammals and reptiles, netting and bleeding of birds, collection of bloodsucking arthropods, and observations on the diel- and seasonal-activity patterns, food sources, and habitat preferences of the more abundant species of mosquitoes.(AU)

Arbovirus studies in Bush Bush Forest, Trinidad, W.I., September 1959-December 1964. I. Description of the study area

Bush Bush Island and the surrounding Nariva Swamp, eastern Trinidad, are described in terms of their topography, flora, and fauna as an introduction to a series of papers reporting the results of 5 years of arbovirus studies in this area. (AU)