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.

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 / Un estudio de conocimientos, actitudes y prácticas (CAP) de los problemas del cambio climático/variabilidad de los impactos y salud pública en Trinidad y Tobago y St Kitts 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...

OBJETIVO: Determinar los niveles de comprensión de los problemas del cambio climático (CC)/ variabilidad (CV) y salud pública por parte de las poblaciones de St Kitts y Nevis (SKN) y Trinidad y Tobago (T&T), y averiguar si los encuestados estarían dispuestos a incorporar estos valores en las estrategias para la previsión de la fiebre del dengue (FD). DISEÑO Y MÉTODOS: Usando un sistema de muestreo por conglomerados, muestras representativas de las comunidades de SKN (227) y de T&T (650) fueron encuestadas mediante un cuestionario en el que se les pedía responder preguntas sobre el impacto de la variabilidad del clima sobre la salud, el ambiente físico, y la disposición de los encuestados a aprovechar las cuestiones del clima para predecir y adaptarse a la variabilidad climática a fin de prevenir la FD. Los datos fueron analizados mediante Epi Info. RESULTADOS: Sesenta y dos por ciento de los encuestados de SKN y el 55% de los de T&T, mostraron cierta comprensión del concepto de cambio climático (CC) y fueron capaces de diferenciarlo de la variabilidad climática (CV). En relación con las causas del CC, el 48% (SKN) y el 50% (T&T) atribuyó el CC a los gases de efecto invernadero, los agujeros en la capa de ozono, la quema de la vegetación, y los gases de escape de vehículos.

Climate, mosquito indices and the epidemiology of dengue fever in Trinidad (2002-2004).

Between January 2002 and December 2004, a population-based study on the effects of climate and mosquito indices on the incidences of dengue fever (DF) and dengue haemorrhagic fever (DHF) was conducted in Trinidad, West Indies. The incidence of DF was 5.05 cases/1000 population in 2002, largely as the result of a major outbreak, but declined to 0.49 case/1000 in 2004. The monthly Aedes aegypti (L.) Breteau indices (BI) did not decline over the 3-year study period, however, but increased from a mean of 29 in 2002 to one of 36 in 2004, with seasonal variations (BI of 30-46 and 20-34 were recorded in the wet and dry seasons, respectively). No significant correlations were observed between temperature and DF or DHF incidence but rainfall was found to be significantly correlated with DF incidence, with a clearly defined 'dengue season', between June and November, in two of the study years. The apparent decline in dengue transmission since 2002 appears to be largely attributable to the development of 'herd immunity' in the general population and not to the attempts at vector control. Since the introduction of new serotypes or the fading of the herd immunity could lead to an explosive epidemic of dengue in Trinidad, there is clearly a need for continued surveillance.

American cutaneous leishmaniasis in Guyana, South America.

The 185 patients who presented at the dermatology clinic of Georgetown Public Hospital, Guyana, between 1992 and 1998, with skin ulcers indicative of American cutaneous leishmaniasis (ACL) were retrospectively reviewed. The laboratory-confirmed cases of ACL were identified and the corresponding data were analysed for risk factors such as age, gender, areas of residence and of possible exposure to the causative agent (Leishmania braziliensis guyanensis), ethnic origin, longevity of the ulcers, and treatment regimes prior to the definitive diagnosis. Eighty-one (43%) of the 185 subjects were confirmed to be infected with Le. b. guyanensis. Although 53 (66%) of the cases lived in or close to the capital city, Georgetown, most of the cases had travelled to (and probably been infected in) region X in the interior of Guyana (32%) or regions VII (23%), VIII (23%), IX (11%), VI (5%), I (3%) or III (3%), usually because they were involved in the mining (41%) or lumber (21%) industries, the army or hunting. Almost all (95%) of the cases were male and most (58%) were aged 20-39 years. In general, the cases had had their skin lesions for many days before presenting for treatment: 46% for 1-5 weeks and 3% for > 6 months. Prior to presentation at the clinic, many of the cases had attempted to cure themselves, using local herbal remedies (37%), antibiotics and antifungal remedies (39%), other creams (5%), household chemicals (9%) or miscellaneous remedies such as lead salts (especially lead sulphate) and battery acid, all without success. Recommendations are made for an epidemiological study of active ACL among forest workers, eco-tourists and residents of high-risk areas. Diagnostic centres need to be sited in the regions most at-risk, particularly in or near environments in which the main vectors - sandflies such as Lutzomyia umbratilis, Lu. anduzei and Lu. whitmani - are known to be prevalent.

Lymphatic filariasis in the Caribbean region: the opportunity for its elimination and certification.

In order to support the case for a certification of elimination of lymphatic filariasis (LF) in some Caribbean countries, we compared the prevalence of circulating Wuchereria bancrofti antigen in communities in Guyana, Suriname, and Trinidad. For the study, we assayed school children in six communities in Guyana, five communities in Suriname, and three communities in Trinidad for the prevalence of circulating W. bancrofti antigen, using a new immunochromatographic test for LF. We also assayed adults in these three countries, with a special focus on Blanchisseuse, Trinidad, where mass treatment for LF elimination had been carried out in 1981. The prevalences of W. bancrofti circulating antigen found in the school children populations ranged from 1.7% to 33.2% in Guyana and were 0.22% overall in Suriname and 0.0% in Trinidad. Among adults in two Guyana communities the prevalences were 16.7% and 32.1%. The results were all negative from 211 adults in communities in the north, center, and south of Trinidad, as well as from 29 adults in Suriname. The data suggest that contrary to reports of LF endemicity from the World Health Organization, LF may no longer be present in Trinidad and may be of very low prevalence in Suriname. Trinidad and Tobago and other Caribbean nations proven negative could seek to be awarded a certificate of LF elimination. In Suriname the small localized pocket of infected persons who may serve as a reservoir of LF infection could be tested and appropriately treated to achieve LF elimination. Such LF-positive countries as Guyana should access new international resources being made available for LF elimination efforts. An adequate certification program would help identify which countries should seek the new LF elimination resources.

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.

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.

Spatial distribution of insecticide resistance in Caribbean populations of Aedes aegypti and its significance.

To monitor resistance to insecticides, bioassays were performed on 102 strains of the dengue vector Aedes aegypti (L.) from 16 countries ranging from Suriname in South America and through the chain of Caribbean Islands to the Bahamas, where the larvicide temephos and the adulticide malathion have been in use for 15 to 30 years. There was wide variation in the sensitivity to the larvicide in mosquito populations within and among countries. Mosquito strains in some countries such as Antigua, St. Lucia, and Tortola had consistently high resistance ratios (RR) to temephos, ranging from 5.3 to 17.7. In another group of countries--e.g., Anguilla and Curaçao--mosquitoes had mixed levels of resistance to temephos (RR = 2.5-10.6), and in a third group of countries, including St. Kitts, Barbados, Jamaica, and Suriname, mosquitoes had consistently low levels of resistance to temephos (RR = 1-4.6) (P < 0.05). On occasion significantly different levels of resistance were recorded from neighboring A. aegypti communities, which suggests there is little genetic exchange among populations. The impact of larval resistance expressed itself as reduced efficacy of temephos to kill mosquitoes when strains were treated in the laboratory or in the field in large container environments with recommended dosages. Although a sensitive strain continued to be completely controlled for up to 7 weeks, the most resistant strains had 24% survival after the first week. By week 6, 60% to 75% of all resistant strains of larvae were surviving the larval period. Responses to malathion in adult A. aegypti varied from a sensitive population in Suriname (RR = 1.3) to resistant strains in St. Vincent (RR = 4.4), Dominica (RR = 4.2), and Trinidad (RR = 4.0); however, resistance was generally not on the scale of that observed to temephos in the larval stages and had increased only slightly when compared to the levels that existed 3 to 4 years ago. Suggestions are made for a pesticide usage policy for the Caribbean region, with modifications for individual countries. This would be formulated based on each country's insecticide-resistance profile. Use of physical and biological control strategies would play a more critical role than the use of insecticides.

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.

Pulmonary pathogens in induced sputum in persons with Human Immunodeficiency Virus (HIV) in Trinidad

A study was undertaken to identify the common micro-organisms occuring in induced sputum specimens from HIV-infected/non-infected individuals with pulmonary manifestations in Trinidad. Only 13 percent of HIV seropositive patients with pneumonia were found to be positive for P. carinii. This low yield may have been due to low prevalence of the P. carinii in Trinidad or to prior antibiotic therapy. Active mycobacterial infection was demonstrated in only 13 percent HIV seropositive patients with pneumonia, though 43 percent HIV patients had a clinical diagnosis of tuberculosis. This may have been due to the low sensitivity of the acid-fast technique. The most common microbial pathogen is identified in HIV patients with pneumonia was Candida sp. Followed by gram negative bacteria. A listing is made of the various organisms occuring singly or mixed in HIV seropositive and HIV seronegative patients (AU)

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.

"New protozoal parasites" Causing diarrhoeal syndrome in humans

This article will serve as a medium to sensitize laboratory and medical personnel that these parasites do exist and that several diagnostic methods are presently available (at CAREC) for their detection(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% 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.