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)

Hepatitis B in Trinidad

Sera from various categories of persons in Port-of-Spain, Trinidad, were examined for the prevalence of antigens and antibodies to the Hepatitis B virus. The results of this preliminary report indicate a low carrier state of the Hepatitis B virus in the Trinidadian population (AU)

Leptospirosis in Trinidad: further studies resulting in recognition of two new serotypes

Investigations on leptospirosis in Trinidad during the period 1962-1967, and characteristic of previously isolated leptospires are reported. Leptospires in the serogroups hebdomadis icterohaemorrhagiae, canicola, grippotyphosa and ballum were recognized to be present on the island. Two of the serotypes in the hebdomadis group, for which the names Trinidad and Tabaquite are proposed, were shown to be previously undescribed serotypes. The complement fixation test proven to be useful in recognizing leptospiral infection in humans. (AU)

Studies on poliomyelitis in Trinidad and Tobago

Investigations on the epidemiology of poliomyelitis in Trinidad and Tobago were carried out during the anti-poliomtelitis immunization campaign in Trinidad during the first quater of 1963. Poliovirus types 1, 2 and 3 were isolated from children prior to immunization. Only 37.6 percent of 514 children tested were found to have antibodies to all three types of poliovirus. The response of two doses of oral trivalent vaccine was best for the type 2 virus and worst for the type 1 virus. Some recommendations are made for control of poliomyelitis in the Caribbean (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)

An outbreak of acute respiratory disease in Trinidad associated with para-influenza viruses

An outbreak of acute respiratory disease occurred among infants and pre-school-age children in nothern Trinidad during the last quater of 1967. There were 556 admissions to Port-of-Spain General Hospital during this period. Half of the children admitted were under 2 years of age, and 84 percent were under 5. A broad spectrum of clinical illness was observed, ranging from upper respiratory tract infection to bronchiolitis and pnuemonia. Para-influenza viruses were isolated from 12.3 percent of hospitalised children and were the only respiratory pathogens recovered in significant numbers. Para-influenza type 1, very rarely isolated during previous years, was the predominant serotype. Of 161 household contacts on whom paired sera were available, 14.3 percent had serologic evidence of recent para-influenza infection. Although age-specific prevalence rates among household contacts were similiar, respiratory illness more frequently ensued in younger individuals. Previous studies by the Trinidad Regional Virus Laboratory had shown para-influenza to be a cause of sparadic respiratory infections in Trinidadian children and respiratory syncytial virus to be associated with rainy season outbreaks of variable magnitude. This large-scale rainy season epidemic associated with para-influenza virus represents an epidemiologic pattern not previously recognized in Trinidad (Summary)

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)

Rubella in Trinidad: sero-epidemiologic studies of an institutional outbreak

An epidemic of rubella occurred in a home for the mentally retarded in Trinidad during 1967. Forty per cent of resident patients and staff members developed rubella with rash, as did 15 percent of non-resident students and staff. Sero-epidemiologic studies were carried out among 66 residents of the female in-patient wing. Only 8 (12 percent) appeared to have been immune prior to the outbreak. Twenty-three (35 percent) developed rubella with rash, while 34 (51 percent) had non-rash infection, as demonstrated by a 4-fold or greater rise in serum rubella hemagglutination-inhibition antibody titer. The overall ratio of rash to non-rash illness was 1:1.5. However, the proportion of infections with rash was higher for children within the first decade of life. Only 1 of 58 susceptibles escaped infection during the epidemic. These results indicate that, in a closed, largely susceptible population, rubella is a highly infectious disease. The true extent of spread is masked by the high proportion of infections unaccompanied by rash. (AU)

Respiratory syncytial virus associated with acute respiratory infections in Trinidadian patients

During 1964-1966, 94 cases of acute respiratory infection in Trinidad were found to be associated with respiratory syncytial virus infection. The clinical picture ranged from mild upper respiratory tract infection to severe infection of the lower respiratry tract. Seventy-nine of the patients were less than three years of age; 70 were diagnosed clinically as having bronchiolitis or pneumonia. Outbreaks of respiratory syncytial virus infection occurred annually during the rainy season in the second half of each year. The pattern was similar to that of temperate climates where outbreakes have occurred annually in the late fall and early winter or late winter and early spring. Although respiratory syncytial virus is reported to be relatively unstable, 18 strains of the virus were recovered from pharyngeal swabs that had been stored frozen at -56 C for 6-9 months. No antigenic relationships between respiratory syncytial virus and other myxoviruses were demonstrated by complement fixation tests on paired sera from three clinical cases of respiratory syncytial virus infection. The studies demonstrate the importance of respiratory pathogen on a tropical island. (AU)

Virological investigations in Guyana, 1956-1966

During the course of virological investigations in Guyana over a ten-year period, 1956-1966, several viruses were isolated. Eastern equine encephalitis, western equine encephalitis, Cache Valley, and rabies viruses were recovered from equines; poliovirus types 1 and 3, Coxsackie Group B type 3, Coxsackie Group A type 4, and rabies were recovered from humans. In addition, serlological evidence was obtained for the past occurrence of infection with Mayaro, Ilheus, and yellow fever viruses in the Amerindians of the Rupununi, and with Ilheus, St. Louis encephalitis, and dengue in residents of the coastal area. Outbreaks of illness in equines due to viruses occurred on the coast in 1953, 1958, 1962, and 1966 and on the Rupununi Savannahs in 1959. An outbreak of poliomyelitis due to poliovirus type 1 occurred on the coast in 1962. Three members of one family from the north-west district died from rabies, presumably bat transmitted, in 1960 (AU)

An epidemic of para-influenza infection in Trinidad - abstract

An outbreak of acute respiratory disease occurred among infants and children in northern Trinidad during the last quarter of 1967. Between October 1 and December 31, six hundred children were admitted to Port-of-Spain General Hospital. Approximately one half of these patients were less than two years of age. Clinical syndromes ranged from severe acute upper respiratory infections to bronchitis and pneumonia. Profuse muco-purulent upper respiratory secretions and severe bronchospasm were prominent clinical manifestations. There were six deaths. Hemabsorbing agents were isolated from 60 patients. To date, 31 have been identified as para-influenza I, eight as para-influenza III and one as para-influenza II. Although para-influenza viruses have been implicated as the cause of sporadic respiratory illnesses in Trinidad in the past, the occurrence of a large outbreak due to these agents is an epidemiologic pattern not previously recognized in the Eastern Caribbean(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)