A comparison of surveillance systems for the dengue vector Aedes aegypti in Port of Spain, Trinidad

When the currently used larval surveillance system (visual inspection) for the dengue vector Aedes aegypti was compared with the surveillance for the presence of eggs by ovitrapping in Port of Spain, Trinidad, it was found that the latter (39.1 percent) was significantly more sensitive than the visual inspection system (10.1 percent). At the same time, the presence of the nuisance mosquito Culex quinquefasciatus was detected in 38.4 percent of the households. Both Ae. aegypti and Cx. quinquefasciatus showed preference for ovipositional attractants in ovitraps: hay infusion > yeast suspension > plain tap water. Although all the socioeconomic and geographic areas produced both mosquito species in 1996, upper middle class (UMC) areas (8.6-43.4 percent), produced more Ae. aegypti than did lower middle class (LMC) area 7.8-38.8 percent), which produced more than working class (WC) areas (3.9-29.9 percent). For Cx. quinquefasciatus, the order of production was reversed with WC areas (50.1 percent) > LMC areas (30.0 percent) > UMC areas (26.0 percent). Change in vector surveillance strategies incorporating some ovitrapping and stratified sampling are recommended for Caribbean countries(AU)

Duplication of the Ace.1 locus in Culex pipiens mosquito from the Caribbean

In Culex pipiens mosquitoes, AChE1 encoded by the locus Ace.1 is the target of organophosphorous and carbamate insecticides. In several resistant strains hompzygous for Ace.1RR, insensitive AChE1 is exclusively found. An unusual situation occurs in two Caribbean resistant strains where each mosquito, at each generation, displays a mixture of sensitive and insensitive AChE1. These mosquitoes are not heterozygotes, Ace.1RS, as preimaginal mortalities cannot account for the lethality of both homozygous classes. This situation is best explained by the existence of two Ace.1 loci, coding, respectively, a sensitive and insensitive AChE1. Thus, we suggest that in the Caribbean a duplication of the Ace.1 locus occurred before the appearance of insecticide resistance at one of the two copies.(AU)

Control of Culex quinquefasciatus in pit latrines, using shredded, waste polystyrene

As an alternative to the use of commercially available, expanded-polystyrene beads, a study was made of the effectiveness of shredded, waste polystyrene (SWAP) for the control of Culex quinquefasciatus. The relevant physical properties of the SWAP were first investigated in the laboratory. Then, under field conditions in wet pit latrines, mosquito emergence rates were measured before and after application of the material. In the laboratory, when compared with the commercial product, the irregular shape of the SWAP particles greatly reduced their capacity to spread over the water surface and the interstitial air spaces also permitted respiration and development of mosquito larvae. Nevertheless, under field conditions, with careful application of the SWAP over the water surfaces in wet pit latrines, almost complete control of mosquito breeding was observed within a few days. This was sustained for 60 days, at which time observation were discontinued. SWAP appears to offer an effective, cheap and readily available alternative to the commercial product for the control of C. quinquefasciatus. The practicality of using it in community-based, mosquito-control programmes warrants further study.(AU)

Community participation in dengue prevention and control: a survey of knowledge, attitudes, and practice in Trinidad and Tobago

The priorities of public health planners are often at variance with the community's own environmental sanitation priorities and perspectives. Public opinion about individual, collective, and governmental responsibilities in addressing these issues and priorities is of particular importance when designing community-based programs. In a study conducted in Trinidad and Tobago on knowledge, attitudes, and practice regarding dengue, its prevention and control, a high level of awareness about dengue and its etiology was evident, but there was poor understanding of the symptoms and hence little concern about the health risks associated with it. The most important household pest problem identified by the respondents was related to mosquito nuisance, particularly from night-biting mosquitoes. Rodents were also a major concern perceived as being responsible for economic losses, ruined food, and a health hazard. Unreliable water supply, a factor associated with Aedes aegypti abundance, was an environmental sanitation issue of major importance to householders in rural areas. No correlation was found between knowledge of dengue and levels of Ae.aegypti abundance as measured by larval surveys of the respondents' premises. The study gave a clear indication of the need for broad-based environmental sanitation strategies when planning community-based vector control initiatives for the prevention and control of dengue in Trinidad and Tobago (AU)

Mass chemotherapy with diethylcarbamazine for the control of Bancroftian Filariasis: a twelve-year follow-up in Northern Trinidad, including observations on Mansonella Ozzardi

A microfilaria survey was conducted in Trinidad in 1992, 12 years after mass treatment with spaced doses of diethylcarbamazine citrate (DEC-C) for the control of Bancroftian filariasis; 348 persons were examined using thick blood smears and a membrane filtration technique. They included 104 who had participated in the mass chemotherapy campaign in 1980. No Wuchereria bancrofti microfilariae were detected among 66 percent of the population examined. In 1980, 86 of 592 persons examined were found to be infected with W. bancrofti, 140 with Mansonella ozzardi and 44 with mixed infections, while in 1992, only M. ozzardi infections persisted despite treatment with DEC-C. Of the 104 persons re-examined 12 years later, 46 had M. ozzardi, of which five were new cases, but none had W. bancrofti. During both the 1980 and 1992 surveys, low microfilariae rates for M. ozzardi were observed among those 19 years of age or younger. Of the 302 persons newly examined in 1992, 29 were infected with significantly (P<0.001) more males (79.3 percent) than females (20.9 percent) being microfilaremic. The combined results showed similiar prevalence rates for M. ozzardi from 23.3 percent to 21.6 percent in 1980 and 1992. Nucleopore membrane filtration and thick blood films were very efficient in demonstrating the presence of microfilariae. The usefulness of these methods and spaced treatment using DEC-C are also discussed (AU)

The life table characteristics of a laboratory population of Culex Quinquefasciatus say, the vector of Bancroftian Filariasis

The fate of 1,092 eggs representing 10 Culex quinquefasciatus was studied to determine life table characteristics under laboratory conditions. Real developmental mortality was high (24.9 percent) with death during the larval instars accounting for 77.4 percent or 10.4 percent of all mortality. The length of the life cycle was 9.5 days, with a larval duration of 7.5 days. The mean observed fecundity of Cx. quinquefasciatus under laboratory conditions was 109.6 +/- 23.29 eggs. The implications for vector control programs are discussed (AU)

Diel biting activity of Culex (Melanoconion) caudelli in Trinidad, West Indies

The diel biting periodicity of the arbovirus vector Culex (Melanoconion) caudelli Dyar and Knab (Diptera; Culicidae) in the Aripo-Wallerfield forest, Trinidad, was studied by collecting mosquitoes attracted to mouse-baited traps at 2-hourly intervals during eight 24 h periods. Biting females of Cx. caudelli were collected during all night-time hours, 18.00-06.00 hours, within overall unimodal pattern, i.e. one well-defined peak between 22.00 and 04.00 hours. This contrasts with previous reports that Cx. caudelli is diurnally active. During the four moon phases, the period of peak biting activity varied from 22.00 to 24.00 hours at fullmoon, from 22.00 to 04.00 hours at first quarter, and from 24.00 to 02.00 hours at new moon and last quarter phases, the highest (152/24 h) being collected in the first lunar quarter and the lowest (71/24 h) in the last lunar quarter. Cloud cover and rainfall had no significant effect on the diel biting periodicity of Cx. caudelli.(AU)

Laboratory observations on the life history of Culex (Melanoconion) caudelli Dyar and Knab in Trinidad, West Indies

Culex (Melanoconion) caudelli has been reared in the laboratory for the first time. The average life-cycle takes approximately 24ñ5.9 days. Observations on the egg, larval and pupal stages were also made. (AU)

Bancroftian filariasis in coastal north Trinidad, West Indies: intensity of transmission by Culex quinquefasciatus

The intensity of transmission of Wuchereria bancrofti was measured in a coastal community in north Trinidad where 15 percent of the residents were microfilaraemic. The only significant vector Culex quinquefasciatus, was studied in detail to determine seasonal abundance, longevity, infection and infectivity rates. Only 2.1 percent of the indoor biting population and 7.0 percent of the indoor resting population were infected. The daily mortality rate of the vector increased with age from 27 percent at 4 days to 44 to 47 percent at 12 days and is considered to be an important factor contributing to the low infectivity rate (0.1 percent). The mean number of C. quinquefasciatus bites received by a resident of the village during the year of observation was estimated to be 17,948 of which 14 were from mosquitoes harbouring infective larvae of W. bancrofti. The results from similar studies elsewhere are outlined, but the need for standardisation of procedures is emphasised before more reliable comparisons can be made (Summary)

Attraction of Culex portesi Senevet and Abonnenc and Culex taeniopus Dyar and Knab (Dipterea: Culicidae) to 20 animal species exposed in a Trinidad forest. I. baits ranked by numbers of mosquitoes caught and engorged

n an attempt to define the favoured hosts of Culex portesi Senevet & Abonnec and C. teaniopus D. & K., one bat, ten rodents, four marsupials, two birds and one crustacean, one amphibian and one reptile were exposed in groups of six in suction traps located in a forest in Trinidad. Each group of six baits included two white mice as a standard. The numbers of mosquitoes caught at each bait on three or six replicate exposures were analysed by an analysis of variance to separate population and site variations. Baits were then compared for `attractiveness' by ranking according to an adjusted mean catch for each mosquito species. The proportion of each mosquito species that engorged on individual baits was also determined. In some cases, attraction and engorgement varied widely, and this was attributed to defensive action on the part of the bait animal. It was concluded that C. taeniopus was particularly attracted by tho opossum Didelphis, which was superior to all indigenous mammals, while C. portei=si was attracted by the cold-blooded animals. Both mosquitoes engorged well on the relatively insensitive marsupials with long bare tails, Didelphis, Marmosa and Caluromys, and also on the well-furred but diurnal squirrel. Of the mainly nocturnal remainder, Culex portesi showed higher engorgement rates than C. teaniopus, suggesting a more aggressive of persistent feeding behaviour

Predation on peridomestic mosquitoes by hylid tadpoles on Grand Bahamas Island

In order to determine whether tadpoles of Hyla septentrionalis are effective predators of larval peridomestic mosquitoes, larvae were exposed to tadpoles and the association between larvae and tadpoles in nature was recorded. Tadpoles were cannibalistic, eating egg masses of their own species, as well as a variety of material of both plant and animal origin. Tadpoles captured and ate more than 13 larval Culex pipiens per day. In natural breeding sites on Grand Bahamas Island, larval C. papiens were never abundant in sites that contained tadpoles and when tadpoles were introduced into vessels that contained mosquitoes, these containers soon became free of mosquitoes. The habitat of H. septentrionlis tadpoles in the study area seemed identical to that of larval C. papiens and more than half of apparently suitable sites contained tadpoles. Thus, the presence of these frogs appeared to limit the abundance of C. papiens.(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)

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. 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)

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)

Observations on the habits and control of Culex pipiens fatigans in Guyana

Investigations in Guyana in 1961-63 showed that Wuchereria bancrofti was the only filarial parasite causing elephantiasis and that Culex pipiens fatigans was the primary vector. Mansonia titillans and Anopheles aquasalis were found to be secondary vectors. C. p. fatigans bred primarily in pit latrines and secondarily in the clean, confined water of drums and barrels near latrines. No breeding occurred in the relatively clean open water of trenches, ditches and drains. Of 21,016 mosquitos collected from houses, 39.9 percent were found resting on walls, 34.9 percent on clothing and other hanging objects, and 23.4 percent on or under furniture. Of 15,622 female mosquitos caught, 9.6 percent contained W. bancrofti parasites and 0.5 percent contained infective larvae. The flight range was found to be about half a mile (0.8 km). Control was achieved by a combination of antimosquito (spraying with gas-oil) and antiparasitic (chemotherapy with diethylcarbamazine) measures, which reduced the average infection rates in the Buxton control area from 17.7 percent to 2.2 percent. Over the same period, breeding in drums dropped from 14 percent-25 percent to 4.7 percent, even though the drums were not treated or covered.(AU)

Nepuyo virus, a new group C agent isolated in Trinidad and Brazil. II. Serological studies

Nepuyo virus, represented by one strain from Trinidad and five from Brazil, reacts by hemagglution-inhibition (HI), neutralization and complement-fixation (CF) testing with previously described group C types but is distinct from them. By HI and neutralization testing Nepuyo is most closely related to Murutucu virus, and by CF testing to Apeu and Marituba viruses. (AU)

Cocal virus Epizootiology in Bush Bush Forest and the Nariva Swamp, Trinidad, W. I.: further studies

Three additional strains of Cocal virus were isolated in Trinidad, 1 each from a Heteromys rodent, a pool of Culex mosquitoes, and a sentinel baby mouse. Complement-fixation and neutralisation tests on 842 rodent serums provided evidence of Cocal virus infection of rodents in Bush Bush forest during the rainy seasons of 1961 and 1962. The 1961 epizootic was explosive in character and involved about 65 percent of the forest floor rodent population. Failure to isolate Cocal virus more than once each from mosquitoes and sentinel mice suggests that mosquitoes probably were not the principal agents responsible for Cocal virus transfer during epizootic periods. The single isolation from Gigantolaelaps in Trinidad is not adequate to confirm these as principal vectors. A parallel is drawn between the characteristics of the 1961 Cocal virus epizootic in small rodents and those of the livestock epizootics caused by the vesicular stomatitis viruses. (Summary)