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.

Malaria and its vectors in the Caribbean: the continuing challenge of the disease forty-five years after eradication from the Islands.

OBJECTIVES: Given the occurrence of autochthonous malaria in non-endemic island countries in the last 10 years, this study evaluates the risk factors for malaria transmission in the malaria "endemic and "non-endemic" countries of the Caribbean region. DESIGN: Data on imported and autochthonous malaria for the 27-year period (1980-2006) were gathered from surveillance units in the 21 Caribbean Epidemiology Centre (CAREC) Member Countries (CMCs) via the CAREC epidemiology unit. Anopheles mosquito data were also gathered from various sources. The vector and malaria data were correlated to determine the current risk of malaria transmission. RESULTS: Imported cases. For the 26-year period (1980-2005), there were 897 reported cases in the CMC islands. Jamaica (38.4%) > Trinidad and Tobago (19.5%) > Bahamas (15.8%) > Cayman Islands (12.5%) were mostly affected. Only the smallest CMCs eg Anguilla and British Virgin Islands reported no imported malaria. Indigenous malaria. Over the same time period, malaria was seen mainly in the three mainland countries of Guyana (514 386 cases) > Suriname (275 361) > Belize (85 313). However, for the period 1995-2005, Belize and Guyana reported reduction in case numbers of 84% and 54% respectively. At the same time, Suriname reported a cyclical pattern of reported cases resulting in 77% increase in cases between 1995 and 2005. "Non-endemic" CMCs such as Trinidad and Tobago, and Bahamas, did report autochthonous malaria. In 2006/7, Jamaica reported 340 P falciparum cases, coming just 1-2 years after a massive 505% increase in imported malaria in the region--88% in Jamaica. Anopheles spp: There was a rich diversity of Anopheles mosquitoes--29 spp. in CMCs. Mainland CMCs and nearby island countries had most spp. recorded. Smaller countries with limited ecological niches such as St Kitts, Anguilla, Turks and Caicos Islands (TCI) and Bermuda had little or no Anopheles spp. Two main Anopheles axes were identified--An albimanus in the northern CMCs and An aquasalis in the southern Caribbean. CONCLUSION: All the essential malaria transmission conditions--vector, imported malaria organism and susceptible human host--now exist in most CMCs. A call is now made for enhanced surveillance, vector control and anti-malaria skills to be established in CMCs, in particular in: Recognizing the possible impact of climate change on the spread of anopheles and malaria transmission. Improving vector control skills for anopheles in CMCs. Strengthening malaria surveillance skills. Upgrading malaria therapy and prophylaxis. Emphasizing malaria prevention and educationfor all community and professional sectors.

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.

Endocrine studies in a pregnancy complicated by ovarian theca lutein cysts and hyperreactio luteinalis.

Severe virilization developed in a pregnant woman in association with the occurrence of theca lutein cysts and hyperreactio luteinalis of the ovaries. At term, maternal serum levels of androstenedione (58 ng/mL) and testosterone (20 ng/mL) were elevated massively; estrone (24 ng/mL) and estradiol-17 beta (23 ng/mL) levels were increased moderately. Maternal serum levels of human chorionic gonadotropin (hCG) just before delivery, 22,276 mlU/mL, though twice the mean for normal women at term, were within the normal range. The levels of androstenedione (1.06 ng/mL) and testosterone (0.26 ng/mL) in umbilical cord serum of her normal newborn female infant were normal. The levels of androstenedione and testosterone in serum of this woman declined slowly, but progressively, during the first two months after delivery; the serum levels of androstenedione and testosterone increased substantially, however, after she was treated with hCG eight weeks postpartum. These results are suggestive that, for reasons unknown, markedly increased androgen production with theca lutein cysts and hyperreactio luteinalis in some pregnant women results ultimately because of increased ovarian sensitivity to hCG.

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.

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.

Current trends in screwworm myiasis in the Caribbean region.

In a random sample of animal producers and animal health personnel, 33% of the respondents in Trinidad, 15% in Guyana, 11% in Suriname and 9% in Jamaica recalled at least one case of human myiasis due to Cochliomyia homivorax (Coquerel). During 1981, respondents in Surinam (88%), Jamaica (90%), Guyana (85%) and Trinidad and Tobago (82%) found at least one case of myiasis in their livestock, occurring mainly in cattle, pigs and dogs. Feral animals, e.g. jaguars, were also found to be infested. The initial wounds were mainly the umbilicus of neonates, and arbitrary wounds, and vampire bites were also affected. Fifty-three to 78% of all respondents examined their livestock daily for wounds and infestation by the screwworm. Annual estimates of losses (in U.S. dollars) due to surveillance and medication ranged from $4.82 to $10.71 per animal. Nationally, these losses amount to $0.30 million (Surinam), $1.02 million (Trinidad and Tobago), $4.33 million (Guyana) and $6.78 million (Jamaica). Figures for other losses, arising from failure to thrive, reduction in milk production and hide injury due to screwworm activity were not available. Most producers found that the greatest screwworm infestation occurred in the wet season, and most described it as second in importance to Boophilus spp. ticks as a pest of livestock, but of greater significance than biting flies, such as tabanids and stable flies. Eradication of the screwworm from the islands of Jamaica and Trinidad and Tobago can be recommended, but in Surinam and Guyana eradication seems feasible only on the 100-km wide coastal strips where most human and livestock populations exist.

Comparative organophosphorus insecticide susceptibility in Caribbean populations of Aedes aegypti and Toxorhynchites moctezuma.

Aedes aegypti larvae from Antigua, Jamaica, Puerto Rico, St. Lucia, Trinidad and Union Island and predatory larvae, Toxorhynchites moctezuma, from Trinidad were tested for susceptibility to temephos, malathion, fenthion, fenitrothion and chlorpyrifos. There was some organophosphorus resistance in all strains of Ae. aegypti, in the approximate order: Antigua greater than Jamaica greater than Puerto Rico greater than St. Lucia greater than Trinidad greater than Union Island. Toxorhynchites moctezuma was much less susceptible to temephos than the Ae. aegypti strain, indicating its possible usefulness in an integrated management program.

Resistance in some Caribbean populations of Aedes aegypti to several insecticides.

Thirty-four strains of Aedes aegypti larvae from 17 Caribbean countries were bioassayed for sensitivity to temephos, malathion, fenitrothion, fenthion, and chlorpyrifos. There were fairly high levels of resistance in Tortola (10-12-fold resistance) and Antigua (6-9-fold resistance) strains to temephos and to fenthion (Tortola, 7-10-fold; Antigua, 6-10-fold resistance). Most other strains showed some resistance to malathion, fenitrothion, and chlorpyrifos, but only moderate levels. Adult populations of Ae. aegypti--Aruba, Jamaica, Trinidad, Puerto Rico, St. Lucia, and Antigua strains--also showed moderate resistance to malathion. Mosquito control field data supported the laboratory findings. Doubling the diagnostic dosage of temephos for larval Ae. aegypti was only partially effective against a more resistant strain, and even so, the chemical lost its limited efficacy over a short period of time. Integrated strategies for Ae. aegypti control to mitigate the negative effects of insecticide resistance in the Caribbean strains are suggested.

Effects of single introduction of Toxorhynchites moctezuma upon Aedes aegypti on a Caribbean Island.

In March 1989, first instar Toxorhynchites moctezuma larvae were introduced into all potential Aedes aegypti oviposition sites (n = 214) that contained water in the village of Clifton on Union Island in St. Vincent and The Grenadines. One month after this introduction, the mean number of adult Ae. aegypti collected with a backpack aspirator in houses in Clifton dropped significantly. Sixty-four percent fewer males and 80% fewer females were collected after introduction of the predator. In the untreated village of Ashton, the overall drop was 24%, with males showing an increase of 27% and females a drop of 55%. The average wing length of females collected in Clifton increased slightly, whereas it remained the same in Ashton.

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%) was significantly more sensitive than the visual inspection system (10.1%). At the same time, the presence of the nuisance mosquito Culex quinquefasciatus was detected in 38.4% 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%) produced more Ae. aegypti than did lower middle class (LMC) areas (7.8-38.8%), which produced more than working class (WC) areas (3.9-29.9%). For Cx. quinquefasciatus, the order of production was reversed with WC areas (50.1%) > LMC areas (30.0%) > UMC areas (26.0%). Change in vector surveillance strategies incorporating some ovitrapping and stratified sampling are recommended for Caribbean countries.

Evaluation of Caribbean strains of Macrocyclops and Mesocyclops (Cyclopoida:Cyclopidae) as biological control tools for the dengue vector Aedes aegypti.

Fifteen Caribbean strains of copepods were assessed for their predation ability against mosquito larvae. Macrocyclops albidus from Nariva. Mesocyclops aspericornis from Oropouche, and Mesocyclops longisetus from E1 Socorro, Trinidad, were most effective against Aedes aegypti but not against Culex quinquefasciatus. Mesocyclops longisetus and Me. aspericornis prevented any mosquito survival over 25 wk of observation despite weekly challenges with Ae. aegypti. The copepods were tolerant to dosages of the insecticide temephos that are usually toxic to mosquito larvae. This indicated that copepods could be incorporated into an integrated control system. To determine whether pathogenic microbes might be introduced with copepods into drinking water, microbial studies were done on the copepods. These showed the presence of only Aeromonas sobria, Pseudomonas sp., Alcalignes sp., and gram-positive bacilli. Although none of these are highly pathogenic to humans, the application of these copepods has not yet been recommended for use in drinking water.

Ivermectin treatment of mansonellosis in Trinidad.

This study was conducted to determine the efficacy and long-term effects of an intervention programme based on a single dose of Ivermectin (6 mg) administered during a double-blind placebo study of 40 persons with Mansonella ozzardi infections in Blanchisseuse, Trinidad. After four years, ivermectin reduced microfilariae levels by 82.2%. Short- and long-term effectiveness of the drug is contingent upon the initial microfilariae levels of the patient. We conclude that a single dose of ivermectin reduces microfilariae densities and provides both short- and long-term reductions in M ozzardi microfilaraemia.

Microscopical and serological diagnosis of Wuchereria bancrofti.

Venous blood from 292 patients attending a Filaria Clinic in Georgetown, Guyana, was assayed by ELISA for IgG and IgM antibodies and by Indirect Haemagglutination Antibody Assay (IHA) against filaria parasites. They were also assayed by microscopic methods before and after concentration procedures for microfilaraemia. Of the 41 blood samples microscopically positive for Wuchereria bancrofti microfilariae, 87.8% (ELISA IgG), 65.9% (ELISA IgM) and 73.2% (IHA) occurred in samples with sub-diagnostic serological threshold titres of < 1:32 (IgG and IgM) and < 1:128 (IHA). But indicators of value based on the standards of the presence of chronic and acute symptoms, the IgG and IgM diagnostic data gave 79.9% sensitivity, 96.4% specificity, 97.1% positive predictable value and 44.3% negative predictive value. A membrane filtration system (92.7%) was slightly better than a centrifugation technique (90.2%), but more efficient than a thick smear preparation (75.6%) for the detection of microfilariae. The filtration system was vastly superior for yields of microfilariae. However, the Knott's concentration (sedimentation) was the most economical in terms of technician time and materials. Most microscopically confirmed filaria cases were in the 20-29-year age group (25%), followed by the broad 30-69-year age groups (10-12%). Males were significantly more commonly affected by the ratio 24.2:6.0. It is recommended that skills and materials for concentration of microfilariae from peripheral blood be maintained in all Caribbean countries. In known filaria endemic countries, it is recommended that the serological tool be used as an aid in diagnosis for patients with acute and chronic symptoms.

Evaluation of methods for the laboratory diagnosis of malaria in Guyana.

When 297 blood samples taken from patients attending a fever clinic in Georgetown Public Hospital were examined microscopically, after thick and thin blood films had been stained with Giemsa, one hundred and forty-two (47.8%) were microscopically positive for malaria. After processing the patient's serum, samples by the Indirect Fluorescent Antibody (IFA) technique, specific IgG and IgM antibodies were detected in 239 (81.3%) and 179 (60.1%), respectively, of the sera. Based on the microscopical findings, the IFAT gave positive predictive and negative values of 54.4% and 81.8% (IgG), and 57.5% and 67.8% (IgM), suggesting that the IgM would be more useful than the IgG in the diagnosis of current malaria. An odds ratio analysis showed that the presence of symptoms, IgG or IgM antibodies, as well as visits to endemic regions, could be good indicators of current malaria. Age and occupation were not. The microscopical method will continue to be the gold standard-the best available criterion for the validation of our tests-for diagnosis of acute malaria.

Significant changes in gastrointestinal tract parasitic infections in children of St. Kitts over the 9-year period 1982-1991.

When 239 (1982) and 361 (1991) five- and nine-year-old children in St. Kitts were assessed for the presence of parasitic infections, there were significant reductions in the prevalence of trichuriasis from 83% to 58%, of ascariasis from 24% to 8.6% and of giardiasis from 15% to 9.4%. Anthelminthic use, which appeared to be the most important responsible intervention tool, remained roughly at the same level at 59-51%. However, the types of anthelminthics used changed over the period. Piperazine citrate, which was used by 66% in 1982, only had 35% usage in 1991. Albendazole which was not used at all in 1982 was taken by 32% of the children in 1991 and at the same time use of laevo-tetramisole increased by 20% from 14%. Suggestions are made for an island-wide mass intervention programme to manage parasitic infections.