RESUMEN
BACKGROUND: Dengue is an acute arboviral disease responsible for most of the illness and death in tropical and subtropical regions. Over the last 25 years there has been increase epidemic activity of the disease in the Caribbean, with the co-circulation of multiple serotypes. An understanding of the space and time dynamics of dengue could provide health agencies with important clues for reducing its impact. METHODS: Dengue Haemorrhagic Fever (DHF) cases observed for the period 1998-2004 were georeferenced using Geographic Information System software. Spatial clustering was calculated for individual years and for the entire study period using the Nearest Neighbor Index. Space and time interaction between DHF cases was determined using the Knox Test while the Nearest Neighbor Hierarchical method was used to extract DHF hot spots. All space and time distances calculated were validated using the Pearson r significance test. RESULTS: Results shows that (1) a decrease in mean distance between DHF cases correlates with activity leading up to an outbreak, (2) a decrease in temporal distance between DHF cases leads to increased geographic spread of the disease, with an outbreak occurrence about every 2 years, and (3) a general pattern in the movement of dengue incidents from more rural to urban settings leading up to an outbreak with hotspot areas associated with transportation hubs in Trinidad. CONCLUSION: Considering only the spatial dimension of the disease, results suggest that DHF cases become more concentrated leading up to an outbreak. However, with the additional consideration of time, results suggest that when an outbreak occurs incidents occur more rapidly in time leading to a parallel increase in the rate of distribution of the disease across space. The results of this study can be used by public health officers to help visualize and understand the spatial and temporal patterns of dengue, and to prepare warnings for the public. Dengue space-time patterns and hotspot detection will provide useful information to support public health officers in their efforts to control and predict dengue spread over critical hotspots allowing better allocation of resources.
Asunto(s)
Dengue/epidemiología , Viaje , Análisis por Conglomerados , Dengue/transmisión , Humanos , Incidencia , Estudios Retrospectivos , Factores de Tiempo , Trinidad y Tobago/epidemiologíaRESUMEN
The acute salinity tolerance of three tropical freshwater cladoceran species, M. macleayi, C. rigaudii and D. brachyurum was determined. The existence of these species represented new records for Trinidad and Tobago, a tropical Caribbean island. It has a large oil based industry, in which, the primary effluent (saline produced water) is discharged directly into many freshwater systems. Cladoceran species are used routinely in temperate regions, to assess the impacts of chemicals and effluents in freshwater systems. However, relatively few studies have assessed the salinity tolerance of these organisms. Test organisms were assayed using seven salinity treatments (0, 1, 3, 5, 10, 15, 20, 25 per thousand) prepared by volumetrically mixing natural filtered seawater with dilution water. C. rigaudii had a 48 h LC50 of 1.6 per thousand, M. macleayi 1.5 per thousand and D. brachyurum <1 per thousand. The CSmax (critical salinity maximum) for C. rigaudii and M. macleayi was 3 per thousand after 48 h, compared to 1 per thousand for D. brachyurum. There was no salinity value at which there was 100% survival. The resulting salinity response curve was a straight line which indicated that each species was intolerant of salt. Consequently, any of these can be considered as a representative freshwater organism for toxicity testing in Trinidad and Tobago.
Asunto(s)
Cladóceros , Agua Dulce/análisis , Ríos , Cloruro de Sodio/análisis , Animales , Brasil , Ríos/química , Especificidad de la EspecieRESUMEN
The toxicities of six chemicals (cadmium chloride, potassium dichromate, sodium dodecyl sulfate, potassium chloride, Tritox X-100 and copper (II) sulphate) was determined for three tropical freshwater cladoceran, Moinodaphnia macleayi, Ceriodaphnia rigaudii and Diaphanosoma brachyurum. The data was subsequently used to compare the relative sensitivity of the three species. Relative sensitivities were determined by comparing the 48-hour LC50 values using an independent t-test and interspecies correlation. Potassium dichromate was the most toxic compound tested, while potassium chloride was the least toxic to all three species. The 48 h LC50 values for D. brachyurum ranged from 0.003 mg/L to 30.4 mg/L; M. macleayi LC50 values ranged from 0.003 mg/L to 30.1 mg/L whereas for C. rigaudii the values ranging between 0.002 mg/L to 21.1 mg/L. The LC50 values for C. rigaudii was significantly less (P < 0.05) than M. macleayi for five of the compounds tested, whereas for D. brachyurum it was significantly (P < 0.05) less than four of the compounds tested. The interspecies correlation also suggested that C. rigaudii and M. macleayi were more similar in sensitivity (R2 = 0.96) to each other than D. brachyurum (R2 = 0.91 with M. macleayi, and R2 = 0.87 with C. rigaudii).
Asunto(s)
Cladóceros/efectos de los fármacos , Contaminantes Químicos del Agua/toxicidad , Animales , Cloruro de Cadmio/toxicidad , Sulfato de Cobre/toxicidad , Dosificación Letal Mediana , Octoxinol/toxicidad , Cloruro de Potasio/toxicidad , Dicromato de Potasio/toxicidad , Dodecil Sulfato de Sodio/toxicidadRESUMEN
Toxicity identification evaluations (TIEs) were performed on seven produced water (PW) effluents from inland discharge facilities operated in Trinidad and Tobago, a Caribbean tropical country with one of the oldest commercial oil industries in the world. The research was performed to determine the presence and magnitude of toxicity and characterize which toxicants are responsible for observed effects. Marine effluent toxicity characterizations with Metamysidopsis insularis revealed high whole acute toxic-unit response for produced water ranged from 8.1 to > 17.0 acute toxic-unit (initial toxicity test) and 5.7 to 1,111 acute toxic-unit (baseline toxicity test). Toxicity test results for all sites except one, which had the highest toxicity, are comparative with similar studies on produced water. The toxicological causality of this complex mixture differed for each PW with nonpolar organics being consistently toxic in all samples. Other potential toxicants contributing to overall toxicity to a much lesser extent were metals, ammonia, and volatile organic compounds. With the use of sodium thiosulfate and filtration manipulations for only PW6 sample, there was very slight reduction in toxicity; therefore, oxidants and filterable materials were not a great contributing factor. Whole effluent toxicity also can be attributed to ionic imbalance and the very stable oil-in-water emulsion that consists of fine oil droplets (less than 0.1-10 microm with an average diameter of 2.5 microm). This investigation is the first of its type in Trinidad and demonstrates clearly the applicability of this test method and local test species for evaluating complex effluents in tropical environments.