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)

The epizootiology of the vesicular stomatitis viruses: a reappraisal

The pattern of epizootics caused by vesicular stomatitis viruses is examined, together with relevant laboratory evidence. The hypothesis that these viruses are arthropod-borne is examined and found wanting. The hypothesis is advanced that the pasture is the basic epizootiologic unit. The virus source is thought to be passive in or on the soil or vegetation and present in the pasture before outbreaks. Neither livestock nor rodents are regarded as essential for the life cycle of VS viruses (AU)

The study of small mammal ecology in Turure Forest, Trinidad, with associated virological and parasitology problems

The main arbovirus part of the field programme was conducted with the object of following the epidemiology of rodent-associated viruses by isolation and serological conversions. Parasitology studies were added to this programme in August 1968, and the results can be summarized as follows: From a total of 590 sera or organs processed from 15 species, nine strains of viruses were isolated. Of these, four Guama gp. strains came from Oryzomys laticeps, while two Groups C strain s and three Guama gp. strains came from Proechimys guyannensis. Of 618 sera tested in H I, 115 (18.6 percent) were positive to one or more of the following antigens: VEE, Caraparu, Restan, Oriboca. All were negative to EEE, Una, IIheus and St. Louis antigens. Oryzomys appear to be more commonly infected with Group C agents than with VEE (group A), while with Proechimys the order is reversed. The C.F. tests showed that only Marmosa mitis (1/8), Oryzomys (39/106) and Proechimys (11/134) were found to have been infected with Guama group viruses. Only one serum (Oryzomys laticeps) reacted with Pacui antigen, and none reacted with Cocal. However, in mouse neutralization tests 42 sera, out of 184, were positive for Cocal virus. In the parasitological studies 179 animals have been processed; these have yielded possibly three species of trypanosomes and two species of filariae. In addition, Leishmania has been recovered from three species of small mammals (AU)

Mongoose rabies in Grenada

From June, 1965, to March, 1968, the Trinidad Regional Virus Laboratory carried out examinations for rabies on 655 mongoose and domestic animal specimens from Grenada by fluorescent antibody techniques and mouse inoculation. Rabies virus was isolated from 29 of 600 routinely trapped mongooses, from 25 to 35 domestic animals. There was incomplete agreement in diagnosis between flourescent antibody assay and mouse inoculation technique, the latter detecting more positives. (AU)

Dengue type 3 virus isolated from an Antiguan patient during the 1963-64 Caribbean epidemic

A strain of dengue type 3 virus was isolated from the blood of an Antiguan patient in cell cultures of African green-monkey kidney during studies on a dengue outbreak that occured in the Caribbean region in 1963 and 1964. The virus was adapted to mice by blind intracerebral passage. Illness appeared in mice at the 11th mouse-brain passage. Four other agents, presumed to be dengue type 3 strains, were isolated from Antiguan patients. Serologic studies on serum from patients of five Caribbean territories showed that the outbreak was due to a group B arbovirus. (AU)

Eastern equine encephalitis virus activity in Trinidad: a threat or a challenge? - abstract

The presence of EEE virus in Trinidad was first noted through serology in 1954 in a native donkey. Subsequently, the virus was isolated twice from Culex taeniopus and once from Culex nigripalpus in 1959. When it was shown that EEE virus caused the death of a horse at Los Hermanas Estate in East Central Trinidad in 1963 a surveillance programme for this virus was initiated by TRVL. From this programme 2,295 bird sera (or organs) were tested without recovering the virus. However, of the 2,817 sera studied in neutralization test 161 (5.7 percent) were positive for EEE virus. Only one isolation of the virus was made from the 25,473 mosquitoes tested. From 1966 through 1968 some 225,000 mosquitoes were processed for virus isolation from Turure Forest. Twelve isolations were made, 11 of which came from Culex taeniopus. The twelfth came from C. portesi. It would appear, therefore, that taeniopus may be the vector of EEE virus in Trinidad. Sera from humans living around Turure Forest were mainly negative to EEE antigen in HI tests, while 3 of 4 equine sera were positive for this antigen in CF tests. The Trinidadian strain of EEE virus is antigenically different from the North American strain. There might also be other differences between the two strains. For example, it is not uncommon to isolate the virus from birds in the U.S., while we have yet to do so in Trinidad. Once infected with the virus, the fatality rate seems to be high in humans and equines in the U.S. Again this has not been our experience in Trinidad. It would appear that we have a strain that might be suitable for the production of a good vaccine after further attenuation, and that this virus may no indeed pose a threat to the community(AU)

Dengue fever in the Caribbean 1968-1969 - abstract

At the end of July 1968 paired serum specimens were received at TRVL from Dominica with the information that dengue-like fever was frequently seen at that time. Subsequent inquiry revealed that a similar illness was active on the islands of Barbados, St. Vincent, St. Lucia, St. Kitts, Montserrat, Jamaica and Curacao. Dengue type 2 virus was isolated from acute serum specimens received from Montserrat, St. Lucia and Curacao. Antibody development consistent with dengue virus infection was found on St. Kitts. The 1963 dengue fever epidemic in the Caribbean was due to dengue type 3 virus. The shift from type 3 in 1963 to type 2 in 1968 cannot be explained at present. This epidemic once again demonstrates that dengue epidemics may be expected in the Caribbean as long as Aedes aegypti mosquitoes are abundantly available. The possibility of much more serious epidemics caused by yellow fever virus or Chikungunya virus form a constant threat (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)

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)

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)

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)

Arbovirus infections in Dutch military personnel stationed in Surinam: further studies

Serum specimens of Dutch military personnel were taken immediately after arrival in Surinam and again, one year later, just prior to departure. A total of 500 paired serum specimens covering the period February 1962-1964 were received at the Trinidad Regional Virus Laboratory. Screening HIV tests were done with 5 group A antigens, 1 group B antigen, 4 group C antigens and 1 Bunyamwera group antigen (Cache Valley). A total of 34 converters were found with antigens prepared from Trinidadian and Surinamese Venezuelan equine encephalitis strains. With Mayaro antigen 7 converters were found. Sera positive to Una and Paramaribo virus antigens were positive to Mayaro also with the highest titer to the latter antigen. With Caraparu antigens 14 converters were found, with Restan antigen 17 and with antigen of a Surinamese Oriboca strain 8. No conversions were discovered with an antigen prepared with a Trinidadian Oriboca strain. An additional five serum pairs showed conversions with more than one of the group C antigens. With St. Louis encephalitis antigen not more than 5 serum pairs showed conversion. With Cache Valley antigen conversion was found in only one serum pair. The data indicate that infections with VEE, Mayaro and the group C agents tended to occur in small epidemics (AU)

Restan virus, a new group C arbovirus from Trinidad and Surinam

Restan virus is a new serotype of arbovirus group C that has been isolated seven times in Trinidad and Surinam during 1963 and 1964. Three strains were recovered from Culex spp. and four from acutely ill human beings. The new agent is related most closely to Marituba and Murutucu viruses, from which it is distinguishable only in hemagglutination-inhibitation test. It circulates to high titer in laboratory-colonized rodents of the species Zygodontomys b. brevicauda and Oryzomys laticeps velutinus. In the laboratory it has been transmitted by Aedes aegypti. Results of serum surveys are reported. (AU)

Arthropod-borne encephalitis viruses in the West Indies area. Part VIII: A serological survey of Montserrat

Two hundred and fourteen sera collected in 1963 from human residents of Monserrat were studied for the presence of antibodies to arboviruses in hemagglutination-inhibition (HI) and neutralization tests. Only 19 sera were positive for group B viruses in HI tests. Dengue virus may be solely responsible for these reactions, but yellow fever and St. Louis viruses cannot be dismissed as possibilities. No evidence was found for the presence of the following viruses: Eastern, Western and Venezuelan equine encephalitis, Mayaro and Una in Group A; Caraparu-like (TRVL 34053-1), Oriboca and TRVL 51144 (Restan) in Group C; Cache Valley in the Bunyamwera group; and Manzanilla in the Simbu group (AU)