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.

Cutaneous human myiasis due to Dermatobia hominis / La miasis cutánea humana debido a Dermatobia Hominis

This is a case report of cutaneous myiasis due to Dermatobia hominis in a female physician who had travelled to Belize. Cutaneous myiasis is endemic in Central and South America but is seldom reported from the Caribbean islands.

Éste es un reporte de caso de miasis cutánea debido a Dermatobia hominis en una mujer médico que había viajado a la Belice. La miasis cutánea es endémica en América Central y América del Sur, pero rara vez se reporta en las islas del Caribe.

Cutaneous human myiasis due to Dermatobia hominis.

This is a case report of cutaneous myiasis due to Dermatobia hominis in a female physician who had travelled to Belize. Cutaneous myiasis is endemic in Central and South America but is seldom reported from the Caribbean islands.

Induced lactation in prepubertal Holstein heifers.

Lactation was hormonally induced in six prepuberal Holstein heifers by seven daily injections of estrogen and progesterone and three injections of dexamethasone on d 18, 19, and 20, followed by twice daily hand milking beginning on d 21. Heifers were about 6 mo old and weighed 162 kg at the beginning of the experiment. Secretions were obtained from five of six of heifers, and twice daily milking continued for 75 d in three of five heifers. The volume of milk obtained on d 7 ranged from 32 to 500 ml and averaged 4.7, 4.1, and 3.7% lactose, protein, and fat, respectively. In the first natural lactation, milk yield and composition were nearly identical for controls and induced heifers. Serum alpha-lactalbumin was increased in induced heifers after treatment with dexamethasone and was highest on d 10 after onset of milking. Our data suggest that sufficient secretions for extensive biochemical testing can be obtained following hormonal induction of lactation in a majority of prepubertal heifers. Moreover, hormonal induction of lactation had no apparent effect on reproduction or first natural lactation. While it is unlikely that hormonal induction of lactation in prepubertal heifers is practical from a dairy production viewpoint, the advent of biotechnology for production of therapeutic recombinant proteins in the mammary gland of transgenic livestock has made early detection of these transgenic proteins very desirable. We conclude that induction of lactation in prepubertal heifers is a viable technique for testing the expression of mammary-linked gene constructs in transgenic cattle.

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)

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)