Diel activity patterns of male Aedes albopictus in the laboratory.

This study was conducted to investigate the flight and dispersal behavior of male Aedes albopictus under laboratory conditions. Two different methods, the Observer and Ethovision software devices, were used to determine the total duration, the mean and maximum flight speed, and the distance covered by these mosquitoes. During 24 h, mosquitoes were more active from 0800 to 1200 h and from 1700 to 2100 h than during the rest of the day. Male Ae. albopictus displayed different activities at different times. The flight activity was 47 min and 57 sec over 24 h. During this period, sugar-fed males flew an average distance of 236.20 m at an average speed of 8.5 cm/sec. The unfed males flew significantly faster than recently fed males, with maximum flight speeds of 44.9 cm/sec and 33.6 cm/sec, respectively. The time used for resting (22 h 2 min +/- 13 min) was significantly higher (P < 0.0001) than walking and flying times (68 min +/- 10 sec and 49 min +/- 5 min, respectively). Overall, both methods allowed observations on flight activity, and the camera recordings allowed these activities to be quantified.

Characterisation of DDT and pyrethroid resistance in Trinidad and Tobago populations of Aedes aegypti.

Insecticide resistance is an important factor in the effectiveness of Aedes aegypti control and the related spread of dengue. The objectives of this study were to investigate the status of the organochlorine dichlorodiphenyltrichloroethane (DDT) and pyrethroid (permethrin and deltamethrin) resistance in Trinidad and Tobago populations of Ae. aegypti and the underlying biochemical mechanisms. Nine populations of Ae. aegypti larvae from Trinidad and Tobago were assayed to DDT and PYs using the Centers for Disease Control and Prevention (CDC) time-mortality-based bioassay method. A diagnostic dosage (DD) was established for each insecticide using the CAREC reference susceptible Ae. aegypti strain and a resistance threshold (RT), time in which 98-100% mortality was observed in the CAREC strain, was calculated for each insecticide. Mosquitoes which survived the DD and RT were considered as resistant, and the resistance status of each population was categorised based on the WHO criteria with mortality <80% indicative of resistance. Biochemical assays were conducted to determine the activities of α and ß esterases, mixed function oxidases (MFO) and glutathione-S-transferases (GST) enzymes which are involved in resistance of mosquitoes to DDT and PYs. Enzymatic activity levels in each population were compared with those obtained for the CAREC susceptible strain, and significant differences were determined by Kruskal-Wallis and Tukey's non-parametric tests (P<0.05). The established DDs were 0.01 mg l(-1), 0.2 mg l(-1) and 1.0 mg l(-1) for deltamethrin, permethrin and DDT, respectively; and the RTs for deltamethrin, permethrin and DDT were 30, 75 and 120 min, respectively. All Ae. aegypti populations were resistant to DDT (<80% mortality); two strains were incipiently resistant to deltamethrin and three to permethrin (80-98% mortality). Biochemical assays revealed elevated levels of α-esterase and MFO enzymes in all Ae. aegypti populations. All, except three populations, showed increased levels of ß-esterases; and all populations, except Curepe, demonstrated elevated GST levels.Metabolic detoxification of enzymes is correlated with the manifestation of DDT and PY resistance in Trinidad and Tobago populations of Ae. aegypti. The presence of this resistance also suggests that knock down (kdr)-type resistance may be involved, hence the need for further investigations. This information can contribute to the development of an insecticide resistance surveillance programme and improvement of resistance management strategies aimed at combatting the spread of dengue in Trinidad and Tobago.

The diel oviposition periodicity of Aedes aegypti (L.) (Diptera: Culicidae) in Trinidad, West Indies: effects of forced egg retention.

The diel oviposition periodicity of two groups of Aedes aegypti females (Trinidad strain), (i) thoses allowed access to oviposition sites and (ii) females forced to retain-eggs for four days, were studied under laboratory conditions using one female per cage and monitoring by changing substrates every two hours. The individual females which were allowed access to oviposition sites showed peak oviposition between 16.00-18.00 h (50% of eggs), whereas individuals forced to retain eggs for four days showed a similar pattern but with a significantly (P<0.001) larger peak oviposition between 16.00-18.00 h (94% of eggs). However, females forced to retain eggs laid most or all of their eggs in one container (84%), while females given access to oviposition sites distributed their eggs among 2-4 containers. The results of this study are discussed in the context of the strength of the circadian rhythms, oviposition strategies and its impact on vector control activities.

Aedes aegypti in Jamaica, West Indies: container productivity profiles to inform control strategies.

OBJECTIVE: To describe the Aedes aegypti container profile in the three parishes of Portland, St. Anns and St. Catherine, Jamaica. METHOD: Traditional stegomyia and pupae per person indices. RESULTS: A total of 8855 containers were inspected. A. aegypti were breeding in 19.2% of the 4728 containers in Portland, in 6.7% of the 2639 containers in St. Ann, and in 27.2% of the 1488 containers in Tryhall Heights, St. Catherine. Container types differed between Portland (P > 0.02) on one hand and St. Ann and Tryhall Heights, St. Catherine on the other hand: there were with no vases or potted plants with water saucers in St. Ann and St. Catherine. A. aegypti were breeding in more containers in St. Catherine (38%) (38% in wet season and 21% in the dry season) than in Portland (19%) or St. Ann (6%), both of which had more containers but A. aegypti breeding in fewer: 17.7% and 11.2% in the wet and 20.4% and 3.5% in the dry seasons respectively. The daily production of adult mosquitoes in the three study sites was 1.51, 1.29 and 0.66 adult female mosquitoes per person in Portland, St. Ann and St. Catherine during the dry season and 1.12, 0.23 and 1.04 female mosquitoes per person in the wet season respectively. CONCLUSION: All three communities are at risk for dengue outbreaks and vector control should concentrate on reducing the mosquito populations from the most productive containers before a new dengue virus serotype is introduced into Jamaica.

The elderly in Trinidad: health, social and economic status and issues of loneliness.

OBJECTIVES: To determine the general health and social status of elderly persons surveyed in Trinidad and to explore issues of loneliness. METHOD: An island-wide survey of persons aged 65 years and older was conducted in early 2002 in Trinidad Eight hundred and forty-five (845) elderly persons were chosen using systematic random sampling. The main survey instrument for data collection was a questionnaire that included structured as well as open-ended questions. The subjects were chosen in a house-to-house survey conducted in all eight counties in Trinidad. Elderly people who were unable to comprehend the questions were excluded from the survey. RESULTS: Those selected ranged in age from 65-102 years and represented all the ethnic groups in Trinidad. These elderly persons lived in a wide range of housing situations. The majority lived in the homes of family members (57%) and 16% lived on their own. A large proportion (80%) had at least one chronic medical problem, although 44% reported their health as "fairly good" or "good". More than a half of the males (53%) and 67% of the females were taking at least one prescribed medicine. The main sources of income were old age pension (85%) and National Insurance (15%). Thirty-three per cent reported feelings of loneliness. This figure includes 28% of those who did not live alone. CONCLUSION: The data revealed that across all ethnic groups more than one-third of the sample reported themselves to be in fair to good health. Many of these elders were lonely because their relatives were quite occupied with their own affairs.

Seroprevalence of dengue in Trinidad using rapid test kits: a cord blood survey.

A cross-sectional sero-epidemiological study was conducted to determine the prevalence of dengue in Trinidad. Two commercial rapid test kits, PanBio Dengue Duo IgM and IgG Rapid Strip Test and the Bio-Check Plus Dengue G/M Cassette Test (Brittney) were used. The immunosorbent assay (ELISA) (FOCUS Technologies, California) was used as the control. One hundred and twenty five cord blood samples were collected (46 from Mt. Hope Women's Hospital (MH) and 79 from the San Fernando General Hospital (SF)). All blood samples were tested in accordance with the two rapid kits and ELISA assay manufacturer's instructions. From 125 cord blood samples, the IgG FOCUS ELISA results showed 93.5 and 95% infections at MH and SF, respectively. Whereas the Brittney and PanBio kits showed 10.9 and 5.1%, and 26.1 and 50.6% for MH and SF, respectively. Based on the FOCUS ELISA (control) assays, the combined seroprevalence rate from north and south Trinidad was 94.4%. IgG and IgM sensitivity and specificity levels were higher in the PanBio than Brittney test kits. The high seroprevalence rates observed in Trinidad are discussed to stimulate more research to explain this phenomenon and to prevent the Southeast Asian scenario from developing in the Americas.

A knowledge, attitude and practices study of the issues of climate change/variability impacts and public health in Trinidad and Tobago, and St Kitts and Nevis.

OBJECTIVE: To determine the level of understanding of the issues of climate change (CC)/variability (CV) and public health by populations of St Kitts and Nevis (SKN) and Trinidad and Tobago (T&T) and to find whether respondents would be willing to incorporate these values into strategies for dengue fever (DF) prevention. DESIGN AND METHODS: Using a cluster sampling system, representative samples of the communities of SKN (227) and T&T (650) were surveyed for responses to a questionnaire document with questions on the impact of climate variability on health, the physical environment, respondents' willingness to utilize climate issues to predict and adapt to climate variability for DF prevention. Data were analyzed by Epi Info. RESULTS: Sixty-two per cent SKN and 55% T&T of respondents showed some understanding of the concept of climate change (CC) and distinguished this from climate variability (CV). With regard to causes of CC, 48% SKN and 50% T&T attributed CC to all of green houses gases, holes in the ozone layer burning of vegetation and vehicular exhaust gases. However some 39.3% SKN and 31% (T&T) did not answer this question. In response to ranking issues of life affected by CC/CV in both countries, respondents ranked them: health > water resources > agriculture > biodiversity > coastal degradation. The major health issues identified for SKN and T&T respondents were: food-borne diseases > water-borne diseases > heat stresses; vector-borne diseases were only ranked 4th and 5th for SKN and T&T respondents respectively. There was in both countries a significant proportion of respondents (p < 0.001) who reported wet season-related increase of DF cases as a CC/CV link. Respondents identified use of environmental sanitation (ES) at appropriate times as a method of choice of using CC/CV to prevent DF outbreaks. More than 82% in both countries saw the use of the CC/CV information for DF prevention by prediction and control as strategic but only 50-51% were inclined to become personally involved. Currently, only 50% SKN and 45% T&T respondents claimed current involvement in DF vector surveillance and control in the last two days. CONCLUSION: Despite the fact that knowledge and attitudes did not always coincide with practices of using ES for DF prevention, in both countries, even with CC/CV tools of prediction being available, it seems that respondents could be persuaded to use such strategies. There is a need for demonstration of the efficacy of CC/CV information and promotion of its usefulness for community involvement in DF and possibly other disease prevention.

Evidence for genetic hitchhiking effect associated with insecticide resistance in Aedes aegypti.

Information on genetic variation within and between populations is critical for understanding the evolutionary history of mosquito populations and disease epidemiology. Previous studies with Drosophila suggest that genetic variation of selectively neutral loci in a large fraction of genome may be constrained by fixation of advantageous mutations associated with hitchhiking effect. This study examined restriction fragment length polymorphisms of four natural Aedes aegypti mosquito populations from Trinidad and Tobago, at 16 loci. These populations have been subjected to organophosphate (OP) insecticide treatments for more than two decades, while dichlor-diphenyltrichlor (DDT) was the insecticide of choice prior to this period. We predicted that genes closely linked to the OP target loci would exhibit reduced genetic variation as a result of the hitchhiking effect associated with intensive OP insecticide selection. We also predicted that genetic variability of the genes conferring resistance to DDT and loci near the target site would be similar to other unlinked loci. As predicted, reduced genetic variation was found for loci in the general chromosomal region of a putative OP target site, and these loci generally exhibited larger F(ST) values than other random loci. In contrast, the gene conferring resistance to DDT and its linked loci show polymorphisms and genetic differentiation similar to other random loci. The reduced genetic variability and apparent gene deletion in some regions of chromosome 1 likely reflect the hitchhiking effect associated with OP insecticide selection.

Seroepidemiology of selected alphaviruses and flaviviruses in bats in Trinidad.

A serosurvey of antibodies against selected flaviviruses and alphaviruses in 384 bats (representing 10 genera and 14 species) was conducted in the Caribbean island of Trinidad. Sera were analysed using epitope-blocking enzyme-linked immunosorbent assays (ELISAs) specific for antibodies against West Nile virus (WNV), Venezuelan equine encephalitis virus (VEEV) and eastern equine encephalitis virus (EEEV), all of which are zoonotic viruses of public health significance in the region. Overall, the ELISAs resulted in the detection of VEEV-specific antibodies in 11 (2.9%) of 384 bats. Antibodies to WNV and EEEV were not detected in any sera. Of the 384 sera, 308 were also screened using hemagglutination inhibition assay (HIA) for antibodies to the aforementioned viruses as well as St. Louis encephalitis virus (SLEV; which also causes epidemic disease in humans), Rio Bravo virus (RBV), Tamana bat virus (TABV) and western equine encephalitis virus (WEEV). Using this approach, antibodies to TABV and RBV were detected in 47 (15.3%) and 3 (1.0%) bats, respectively. HIA results also suggest the presence of antibodies to an undetermined flavivirus(es) in 8 (2.6%) bats. Seropositivity for TABV was significantly (P<0.05; χ2) associated with bat species, location and feeding preference, and for VEEV with roost type and location. Differences in prevalence rates between urban and rural locations were statistically significant (P<0.05; χ2) for TABV only. None of the aforementioned factors was significantly associated with RBV seropositivity rates.

Pupal survey: an epidemiologically significant surveillance method for Aedes aegypti: an example using data from Trinidad.

This report documents the results of a country-wide pupal survey of Aedes aegypti (L.) conducted in Trinidad. The survey was designed to identify the important Ae. aegypti-producing containers, importance being a function of a container's abundance and its productivity. Results are summarized on a country-wide basis and by county: urban versus rural comparisons are also made. Numerically, the most common water-filled containers positive for the larvae or pupae of Ae. aegypti (foci) were outdoor drums, water storage tanks and buckets, laundry tubs, discarded tires, and small miscellaneous containers such as drink bottles and cans. The island-wide average number of foci per hectare was 287 and ranged between 65 and 499. The average standing crop per container of Ae. aegypti pupae was 9.5 and ranged 12-fold, the most and least productive being the flower pot (> 30) and the small indoor vase (< 3), respectively. In terms of production by type of container, four of the 11 types, outdoor drums, tubs, buckets, and small containers, accounted for > 90% of all Ae. aegypti pupae: the remaining seven types were responsible for < 10%. If targeted source reduction programs were directed by how important various container types were in the production of Ae. aegypti, environmental sanitation efforts designed to actually eliminate the ubiquitous small receptacle and tires would reduce mosquito densities by 43%; the provision of an adequate water supply system precluding the need for water storage in drums and buckets would have the potential to eliminate an additional 38%. Combined, these two measures have the potential to reduce the sources responsible for > 80% of Ae. aegypti production in the country. In our survey, the traditional Stegomyia indices used to document the density of Ae. aegypti and predict the threat of dengue transmission, the House, Container, and Breteau indices, were seen to have virtually no correspondence with the actual number of pupae per hectare or per person. We conclude that pupal survey is more appropriate for assessing risk and directing control operations.

Spatial and temporal patterns of imported malaria cases and local transmission in Trinidad.

Over a 30-year period (1968-1997) 213 malaria cases in Trinidad were investigated by the Trinidad and Tobago Ministry of Health. Using a global positional system and a geographic information system, we mapped the precise location of all reported malaria cases, and associated them with breeding habitats of anopheline vectors. The majority of the cases (138, 63%) were individual imported cases around the big port cities. Plasmodium falciparum was the most common parasite, and Africa the most common source of imported cases. Two clusters of cases occurred: an introduced P. vivax outbreak associated with Anopheles aquasalis in 1990-1991, and an autochtonous focus of P. malariae associated with An. bellator and An. homunculus in 1994-1995. Application of a space-time statistic showed a significant clustering of P. malariae cases, and, to a lesser extent of P. vivax cases, but not of P. falciparum cases. Based on potential for occurrence of local transmission, we are developing risk maps to determine surveillance priorities, outbreak potential, and necessary degree and spatial range of control activities following case detections.

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% 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 reexamined 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%) than females (20.9%) being microfilaremic. The combined results showed similar prevalence rates for M. ozzardi from 23.3% to 21.6% in 1980 and 1992. Nuclepore 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.

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.

Sylvatic yellow fever activity in Trinidad, 1988-1989.

Of a total of 18,068 mosquitoes (361 pools) collected in south-eastern Trinidad forests from December 1988 to May 1989, 47 species belonging to 14 genera were identified. Five yellow fever virus isolates were made from Haemagogus janthinomys and one from Sabethes chloropterus. All the other pools of mosquitoes examined were negative for the virus. The mosquito isolates were made in December and January. In addition, in late February and early March, 2 infected howler monkeys (Alouatta sp.) were detected. Since March, despite continued surveillance, no yellow fever virus has been detected in mosquitoes or monkeys. There has been no reported human infection.

Indoor and outdoor host-seeking rhythms of Anopheles albitarsis (Diptera: Culicidae) in Trinidad, West Indies.

The diel host-seeking periodicity of Anopheles (Nyssorhynchus) albitarsis Lynch-Arribalzaga (sensu latu) was monitored on humans during a period of 6 mo in Frederick Settlement, County Caroni, Trinidad, West Indies. Similar abundances and periodicities were recorded at indoor and outdoor sites, with peak host-seeking occurring at 1900 hours. Only 78 An. albitarsis females were collected resting indoors, indicating that most females rest outdoors and, therefore, may escape contact with residual insecticides applied on wall surfaces.

Seasonal abundance and diel landing periodicity of Sabethes chloropterus (Diptera: Culicidae) in Trinidad, West Indies.

The seasonal occurrence and diel landing periodicity of Sabethes chloropterus (Humboldt) was studied weekly for 1 yr using the human bait catch in the Pt. Gourde Forest, Trinidad, W.I. Population abundance remained low throughout the dry season (16%) but increased after the onset of the rains in May and peaked by the middle of the rainy season (July-October). The diurnal periodicity of landing was unimodal during the wet season with a major peak between 1200-1600 hours and bimodal during the dry season with peaks at 0800-1000 and 1200-1400 hours. This study documents for the first time the periodicity of landing by Sa. chloropterus at ground level and suggests reasons for failure to detect the yellow fever virus at this level.

Fine structure of the eggs of Haemagogus equinus and Hg. janthinomys (Diptera: Culicidae).

The eggs of Haemagogus equinus Theobald and Hg. janthinomys Dyar, the first of this genus to be examined with a scanning electron microscope, are described from material collected in Trinidad, West Indies. All surfaces of the eggs are described, including both dorsal and ventral surfaces at the anterior and posterior ends as well as the micropyle and associated apparatus. The dorsal surface, normally attached to the substrate, consists of a dense, hairlike mat of filaments formed from numerous, greatly elongated outer chorionic tubercles. These filaments possibly serve to improve anchorage of the egg as a protection against flushing by rain water or physical removal by predators. The outer chorionic cells on the ventral (upper) surfaces are extremely similar to those of two species of the subgenus Finlaya of Aedes, Ae. albolateralis (Theobald) and Ae. melanopterus (Giles), both collected in Taiwan.

Diel rhythms of oviposition and fecundity of Anopheles aquasalis (Diptera:Culicidae) under laboratory conditions.

The oviposition patterns of Anopheles aquasalis Curry collected from a grass swamp in Gloudon, Caroni Swamp, Trinidad, were studied in the laboratory by recording the egg-laying performance of 30 individuals and a group of 150 females at 2-h intervals. Oviposition was nocturnal, with a peak between 2400 and 0400 hours when 72% of the eggs were laid. Wild-caught females engorged on human blood matured 89.8 +/- 21.3 follicles (range, 50-118). These findings provide vector control workers with the opportunity to maximize the effect of adulticides on An. aquasalis populations by restricting their operations to the time of peak flight activity.

Seasonal incidence and vertical distribution patterns of oviposition by Aedes aegypti in an urban environment in Trinidad, W. I.

The oviposition patterns of Aedes aegypti were investigated using modified ovitraps placed along 4 vertical transects and monitored weekly for 52 wk in St. Augustine, Trinidad, W.I. From the 832 ovitraps exposed at ground level, 1.2, 3.0 and 4.6-m elevations, 43% (361) were found containing 20,114 Ae. aegypti eggs. During the wet season, 52.7% of the eggs were collected whereas during the dry season only 47.3% were collected. Egg populations were highest at the 1.2-m elevation. The implications of these results are discussed.

Aedes aegypti surveillance in Tobago, West Indies (1983-88).

During 1983-88 Aedes aegypti were collected using larval surveys and ovitraps in Tobago, W.I. The main artificial containers used by Ae. aegypti were drums (35.4%) and small miscellaneous containers (23.4%). From a total of 15,600 ovitraps exposed, 183 ovitraps (1.3%) were positive, with 25 containing Ae. aegypti eggs and 158 with Haemagogus equinus eggs. No Aedes albopictus eggs were detected in Tobago during this study.