Impact of environmental temperatures on resistance to organophosphate insecticides in Aedes aegypti from Trinidad / Repercusión de las temperaturas ambientales sobre la resistencia de Aedes aegypti a los insecticidas organofosforados en Trinidad

OBJECTIVE: To examine the effects of increasing larval rearing temperatures on the resistance status of Trinidadian populations of Aedes aegypti to organophosphate (OP) insecticides. METHODS: In 2007-2008, bioassays and biochemical assays were conducted on A. aegypti larvae collected in 2006 from eight geographically distinct areas in Trinidad (Trinidad and Tobago). Larval populations were reared at four temperatures (28 ± 2ºC, 32ºC, 34ºC, and 36ºC) prior to bioassays with OP insecticides (fenthion, malathion, and temephos) and biochemical assays for esterase enzymes. RESULTS: Most larval populations reared at 28 ± 2ºC were susceptible to fenthion (>98% mortality) but resistant to malathion and temephos (< 80% mortality). A positive association was found between resistance to OP insecticides and increased activities of α- and β-esterases in larval populations reared at 28 ± 2ºC. Although larval populations reared at higher temperatures showed variations in resistance to OPs, there was a general increase in susceptibility. However, increases or decreases in activity levels of enzymes did not always correspond with an increase or decrease in the proportion of resistant individuals reared at higher temperatures. CONCLUSIONS: Although global warming may cause an increase in dengue transmission, based on the current results, the use of insecticides for dengue prevention and control may yet be effective if temperatures increase as projected.

OBJETIVO: Examinar los efectos del aumento de las temperaturas de desarrollo larvario sobre el estado de resistencia a los insecticidas organofosforados de las poblaciones de Aedes aegypti en Trinidad. MÉTODOS: En 2007 y 2008 se llevaron a cabo ensayos biológicos y bioquímicos en larvas de A. aegypti recogidas en el 2006 de ocho áreas geográficamente separadas en Trinidad (Trinidad y Tabago). Las poblaciones larvarias se desarrollaron en cuatro temperaturas (28 ± 2 ºC, 32 ºC, 34 ºC y 36 ºC) antes de los ensayos biológicos con insecticidas organofosforados (fentión, malatión y temefós) y los análisis bioquímicos para las enzimas de esterasa. RESULTADOS: La mayoría de las poblaciones larvarias que se desarrollaron a 28 ± 2 ºC fueron susceptibles al fentión (mortalidad > 98%) pero resistentes al malatión y al temefós (mortalidad < 80%). Se encontró una asociación positiva entre la resistencia a los insecticidas organofosforados y la mayor actividad de αy β-esterasas en las poblaciones larvarias que se desarrollaron a 28 ± 2 ºC. Aunque las poblaciones larvarias que se desarrollaron a temperaturas mayores mostraron variaciones en la resistencia a los organofosforados, hubo un aumento general de la sensibilidad. Sin embargo, los aumentos o las disminuciones en los niveles de actividad de las enzimas no siempre se correspondieron con un aumento o disminución en la proporción de individuos resistentes desarrollados a las temperaturas más altas. CONCLUSIONES: Aunque el recalentamiento del planeta puede causar un aumento de la transmisión del dengue, según los resultados de este estudio el uso de insecticidas para la prevención y el control del dengue todavía puede ser eficaz si las temperaturas aumentan según lo proyectado.

Short communication: concomitant malaria and filariasis infections in Georgetown, Guyana

Lymphatic filariasis and malaria are endemic in Guyana, South America. To determine the prevalence of concomitant infections, we conducted a 1-year survey of febrile patients attending the malaria (day) and filariasis (night) clinics in Georgetown. In all, 1278 thick blood smears were collected; 769 for filariasis, of which 103 were positive for Wucheria bancrofti, and three for both W. bancrofti and malaria parasites; and 509 for malaria, 21 of which tested positive for malaria and 17 for both malaria and filariasis. The age groups and sex of the infected persons with malaria and W. bancrofti are descibed. These results suggest that the incidence of concomitant infections in Guyana may be quite low but efforts should be made to reduce the disease burden in Georgetown, Guyana (AU)

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 Wucheria 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 Blanchisseusse, Trinidad, where mass treatment for LF elimination had been carried out in 1981. The prevalence of W. bancrofti circulating antigen found in the school children populations ranged from 1.7 percent to 33.2 percent in Guyana and were .22 percent overall in Suriname and 0.0 percent in Trinidad. Among adults in two Guyana communities the prevalences were 16.7 percent and 32.1 percent. 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 (AU)

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

Lymphatic filariasis in the Caribbean region: the opportunity for its elimination and certification / sivo para la eliminación de la FL. La prevalencia del antígeno circulante de Wuchereria bancrofti en los escolares osciló entre 1,7 y 33,2% en Guyana; en Suriname la prevalencia global fue de 0,22% y en Trinidad de 0,0%. En los adultos de dos comunidades de Guyana las cifras de prevalencia fueron de 16,7 y 32,1%. Los resultados de la prueba fueron negativos en los 211 adultos de comunidades del norte, centro y sur de Trinidad, así como en los 29 adultos de Suriname. Los resultados obtenidos indican que, al contrario de lo que afirman los informes de la Organización Mundial de la Salud (OMS) sobre la endemicidad de la FL, la enfermedad parece haber desaparecido en Trinidad y tener una prevalencia muy baja en Suriname. Trinidad y Tabago y otros países del Caribe en los que se demuestre la ausencia de la enfermedad podrían obtener un certificado de eliminación de la FL. En Suriname, la pequeña y localizada bolsa de personas infectadas que actuarían como reservorio podrían ser investigadas y tratadas con el fin de conseguir la eliminación de la enfermedad. Los países donde todavía hay FL, como Guyana, podrían acceder a los nuevos recursos internacionales como parte de los esfuerzos para la eliminación de la FL. Un programa de certificación adecuado ayudaría a identificar cuáles son los países que deberían buscar estos nuevos recursos para la eliminación de la LF. RESUMEN F

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

Con el fin de documentar la posibilidad de certificar la eliminación de la filariasis linfática (FL) en algunos países del Caribe, hemos comparado la prevalencia del antígeno circulante de Wuchereria bancrofti en comunidades de Guyana, de Suriname y de la isla de Trinidad. Para ello, utilizamos una nueva prueba inmunocromatográfica de FL en escolares de seis comunidades de Guyana, cinco de Suriname y tres de la isla de Trinidad. También estudiamos adultos de los tres países, centrándonos especialmente en Blanchisseuse, Trinidad, donde en 1981 se llevó a cabo un tratamiento masivo para la eliminación de la FL. La prevalencia del antígeno circulante de Wuchereria bancrofti en los escolares osciló entre 1,7 y 33,2% en Guyana; en Suriname la prevalencia global fue de 0,22% y en Trinidad de 0,0%. En los adultos de dos comunidades de Guyana las cifras de prevalencia fueron de 16,7 y 32,1%. Los resultados de la prueba fueron negativos en los 211 adultos de comunidades del norte, centro y sur de Trinidad, así como en los 29 adultos de Suriname. Los resultados obtenidos indican que, al contrario de lo que afirman los informes de la Organización Mundial de la Salud (OMS) sobre la endemicidad de la FL, la enfermedad parece haber desaparecido en Trinidad y tener una prevalencia muy baja en Suriname. Trinidad y Tabago y otros países del Caribe en los que se demuestre la ausencia de la enfermedad podrían obtener un certificado de eliminación de la FL. En Suriname, la pequeña y localizada bolsa de personas infectadas que actuarían como reservorio podrían ser investigadas y tratadas con el fin de conseguir la eliminación de la enfermedad. Los países donde todavía hay FL, como Guyana, podrían acceder a los nuevos recursos internacionales como parte de los esfuerzos para la eliminación de la FL. Un programa de certificación adecuado ayudaría a identificar cuáles son los países que deberían buscar estos nuevos recursos para la eliminación de la LF.

A case control study of dengue fever cases in Trinidad in 1997 - Poster abstract

OBJECTIVE: To determine whether or not persons who have been directly affected by dengue fever (DF) in Trinidad in 1997, were made more aware of the disease and developed behaviour patterns that prevented vector production. DESIGN AND METHODS: The study was a matched case control investigation. Cases were persons who were clinically diagnosed with DF and were matched with the cases on residence. A knowledge, attitude, practice and behaviour (KAPB) survey was done using a questionnaire. An entomological survey was done and oviposition traps placed on each premise to detect the presence of gravid Ae aegypti mosquitoes. The study was carried at the beginning of the wet season between June and July 1998. RESULTS: Knowledge of dengue symptoms was higher in the case than the control group. CONCLUSION: Awareness of the disease was higher in cases than controls but this knowledge did not translate into preventive action or significant expected behaviour change. There was therefore no significant differences in attitudes, practices and behaviour between persons who were directly affected by DF and those who were not.(AU)

A pilot evaluation of impact of school children's anti-dengue/Aedes aegypti environmental Sanitation Competitions on mosquito production in home communities - Poster abstract

OBJECTIVE: To determine if children's knowledge, attitude and practices (KAP) with respect to dengue prevention and control in the school environment had any impact on the prevention of mosquito production practices at home. DESIGN AND METHODS: A case-control study was designed to compare the mosquito production behaviour of two school populations, the Mt Lambert Roman Catholic (RC) and the Barataria Anglican (AC) schools. The former successful in the environmental sanitation (ES) competitions while the latter, the control school, was never a part of the competitions. Thirty students, aged 7-13 years, were randomly selected from each school and interviewed to assess their KAP in relation to dengue fever (DF). A visit was made to 50 percent of the children's homes where the parents were also interviewed. In addition, a survey was conducted to identify potential and actual Ae aegypti habitats and enhanced oviposition traps placed at each home. RESULTS: Awareness of DF and its vector was high among both sets of children. All students at Mt. Lambert RC school reported practising source reduction in their homes. A positive change in behaviour was noticed by 87 percent of them in their family members. Knowledge among parents was also very high. No parent from Mt Lambert admitted to receiving DF control information from their children, whereas 33 percent from Barataria said otherwise. Inspection of premises yielded 612 containers in Mt. Lambert and 275 in Barataria. Ovitraps were positive in 33 percent of Mt Lambert and 40 percent of Barataria homes. CONCLUSION: Mt Lambert students although sensitized by the ES competitions did not have a distinct advantage over the non-sensitized Barataria students. High knowledge levels in parents could not be attributed to their children. Knowledge had little or no impact on practices as indicated by the potentially large number of Ae aegypti breeding habitats.(AU)

Seroprevalence of Toxocara infections in children in Trinidad: effects of infection on cognitive skills

OBJECTIVE: To determine the seroprevalence of Toxocara infections and their effects on cognitive skills in children. DESIGN AND METHODS: Serum specimens from 1009 students from 27 primary schools in Trinidad were tested by the ELISA method for the presence of antibodies to Toxocara using an excretory-secretory antigen. Students having a titre of > or = 1:800 as well as matched controls were administered with the school achievement test to measure cognitive skills. Relationships between seroloprevalence and host factors were explored using information obtained via a questionnaire. RESULTS: Overall seroprevalence was 62.3 percent while prevalence indicative of current or recent infection (> or = 1:800) was 27.2 percent. There was no significant relationship between age and the presence of infection. Males were significantly more commonly infected than females as were attendees of rural schools. Pet ownership and the absence of pipe-borne water in the house were significantly associated with positive serology (P<0.05). Measurement of cognitive skills by the school achievement test showed that children with positive serology had lower scores (P<0.001) than age- and sex-matched controls with negative serology. CONCLUSION: The high level of infection indicated by earlier though limited studies in Trinidad was confirmed. It is recommended that the public should be educated on the transmission of disease and all dogs and cats should be periodically dewormed and environmental sanitation measures should include children away from contaminated areas.(AU)

Concomitant malaria and filariasis infections in Georgetown, Guyana

OBJECTIVE: To determine the prevalence of concomitant malaria and bancroftian filariasis among febrile patients in Georgetown, Guyana, South America. METHODOLOGY: From January to December 1997, all patients visiting the Georgetown Malaria and Filariasis Clinics were enrolled in the study. At the Filariasis Clinic, nocturnal thick blood smears prepared from blood taken between 8:00 pm and 12:00 midnight were dried and stored overnight. At the Malaria Clinic, thick blood smears were taken during the period 8:30 am to 4:00 pm, representing the diurnal study. All slides were stained using the standard Giemsa protocol and microscopically examined for the presence of filariasis and malaria. RESULTS: Of 1,267 persons, 83 percent were of African descent, 10 percent were of East Indian descent, and 7 percent were mixed or of other ethnic origins. Sixty-one per cent (769/1267) of smears were prepared from nocturnal blood samples whereas 509/1267 (40 percent) were diurnal samples from the Malaria Clinic. One hundred and three of 769 nocturnal blood smears were positive for only W bancrofti and 3 smears contained mixed infections, W bancrofti and malaria parasites. Only 21/509 diurnal blood smears had malaria parasites while 17 persons had both malaria and microfilaria parasites. CONCLUSION: The 20 cases of concomitant infection of malaria and bancroftian filariasis in this study may represent the first report of the occurrence of this phenomenon in Guyana.(AU)

A baseline of organophosphate susceptibility/resistance in Trinidad and Tobago strains of the dengue fever vector Aedes aegypti (Linnaeus)

OBJECTIVE: To establish a baseline of organophosphate susceptibility/resistance in Trinidad and Tobago strains of 4th instar Aedes aegypti. DESIGN AND METHODS: Twenty-one strains of Aedes aegypti (Linneaus) were collected throughout Trinidad and Tobago and 4th instar larvae were bioassayed for sensitivity to five organophosphate insecticides, temephos, malathion, fenthion, fenitrothion and bromophos. The data were computer probit analyzed, resistance ratios [RR] were calculated and statistical analysis was done to determine any incidence of cross-resistance. RESULTS: Low to moderate levels of larval resistance to tenephos [RR 0.8-6.3], malathion [RR 0.8-3.8], fenthion [RR 0.7-6.7], fenitrothion [RR 0.7-3.] and bromophos [RR 0.9-6.4] were observed. Significant levels of cross-resistance were found between pairs of insecticides as follows: temephos/fenthion [rsq = 0.6219]; temephos/fenitrothion [rsq = 0.6117]; fenthion/malathion [rsq = 0.5751]; fenthion/bromophos. [rsq = 0.7255] and fenthion/fenitrothion [rsq = 0.6111]. CONCLUSIONS: The generally low levels of organophosphate insecticide resistance shown in this study indicate that these chemicals can continue to be used in the fight against Ae aegypti and dengue, while we continue to monitor trends in changing resistance patterns.(AU)

Comparative impact of intra- and extra extra-domiciliary malathion adulticidal sprays on the dengue vector and other mosquitoes in Trinidad

OBJECTIVE: To measure the short- and long-term impact of intra- and extra-domiciliary malathion sprays on adult Aedes aegypti and other mosquitoes. DESIGN AND METHODS: Caged populations of Ae aegypti and Culex quinquefasciatus were exposed within and outside homes to malathion sprays from hand-held and vehicle-mounted equipment. Short-term impact was determined by mortality of caged mosquitoes and long-term impact by the reduced oviposition by wild gravid mosquitoes. RESULTS: There was an immediate 100 percent mortality in both species of caged mosquitoes in and around homes and a reduction of oviposition by wild gravid mosquitoes twenty-four hours after exposure to malathion dispensed from hand-held equipment. Thereafter, there were significant immigration of gravid females from adjacent areas. Vehicle-mounted spraying from the streets killed 94 percent - 100 percent Cx quinquefascitus in the interior areas where mosquitoes may rest. There was little delayed effect from vehicle-mounted treatment since by day 5 wild mosquitoes had quadrupled their oviposition. CONCLUSIONS: Hand-held insecticide spraying by the householder has a short-lived impact but repeated, sustained treatments could effectively break the transmission cycle of dengue. Vehicle-mounted sprays are less effective both in the short- and long-term impact. In emergencies, there is a need for integrated physical and chemical methods for immediate and sustained vector management.(Au)

Characteristics of dengue fever in the Caribbean region II: the vector and its management

OBJECTIVE: To analyze plans and execution practices in 23 of 30 Caribbean countries for the control of dengue fever through the management of the vector Aedes aegypti during the period 1997-1998. DESIGN AND METHODS: A questionnaire was sent to all public health authorities in 30 Caribbean countries soliciting information on the present status of their national dengue/vector control (VC) programmes. RESULTS: Ae aegypti was reported from 22/23 countries. The percentage of homes found to be positive for Ae aegypti production (House Index), ranged from 0 percent to 62 percent. In 19 (83 percent) countries, environmental sanitation was a key component of the programme while 61 percent routinely used community participation as a support for the official VC programme. Mass media have been used systematically to promote community participation in VC activities in 16 (70 percent) countries and biological control tools used in 50 percent of countries but evaluated in only 35 percent. Personnel employed for VC management varied from a low of 0.025 men/1,000 capita (Jamaica) to 0.44 men/1,000 capita (Trinidad). Quality of staff was also important. In the Cayman Islands, the only country successful in eliminating Ae aegypti, 3 entomologists were employed. Total programme expenditures for dengue prevention ranged from a per capita sum of US$12.89 (Bermuda) to $0.03 (Guyana). CONCLUSIONS: Selection of the best strategies for future strengthening of the various vector management programmes for dengue prevention must be informed by evaluations of current VC programmes.(Au)

Characteristics of dengue fever in the Caribbean region 1: the epidemiology of the disease

OBJECTIVE: To collect and analyze data on the epidemiology of dengue in 3 Caribbean countries during 1997 and 1998. DESIGN AND METHODS: A questionnaire was sent to all public health authorities in the region soliciting information on the incidence of dengue and dengue haemorrhagic fever (DHF) for 1997 and 1998 surveillance systems in place for dengue and mortality data which were analyzed. RESULTS: In 1998, there was a two-fold increase in dengue cases over the 1997 figures. Incidence rates for 1997 ranged from 748/10,000 (Martinique) through 201/10,000 (Puerto Rico), down to no cases detected in countries such as the Cayman Islands. Encouragingly, some countries showed reduced numbers of cases in 1998; 6 countries reported types 2 and 3, 7 countries, type 1 and two countries, type 4. In 1997, there were 30 deaths attributed to DHF in the region, while in 1998 there were only 20. Only 8 countries (35 percent) reported the use of a stratified surveillance system for the early detection of dengue. Sentinel posts were used in only 10 (43 percent) countries. There was a marked seasonal occurrence of dengue cases with the wetter periods of the year. CONCLUSIONS: These data will help to improve surveillance and enhance management programmes aimed at the elimination of disease transmission.(Au)

Ivermectin treatment of mansonelliasis 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 percent. Short-and long-term effectiveness of the drug is contingent upon the initial microfilariae levels of patients. We conclude that a single dose of ivermectin reduces microfilariae densities and provides both short and long term reductions in M ozzardi microfilaremia.(AU)

Absence of impact of aerial malathion treatment on Aedes aegypti during a dengue outbreak in Kingston, Jamaica

During an outbreak of dengue fever in Jamaica from October to December 1995, a study was carried out to determine the impact of aerial ultra-low volume malathion treatment on adult Aedes aegypti. This was done by monitoring oviposition rates of the vector in three urban communities in Kingston and by exposing caged mosquitoes both directly and indirectly to the aerial malathion treatment. The insecticide was delivered at a rate of 219 mL/ha between 7:10 a.m. and 8:45 a.m. The results of the study clearly showed that the insecticide application was ineffective in interfering with Aedes aegypti oviposition, and adult mosquitoes held in cages inside dwellings were largely unaffected. Consequently, this type of intervention seemed to have little significant impact in arresting or abating dengue transmission (Au)