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Biomedical subjects

D R Roberts

Publications and source records attributed to D R Roberts.

At least 19 recordsLinked to original sources
PubMed1998

Characterization and detection of Anopheles vestitipennis and Anopheles punctimacula (Diptera: Culicidae) larval habitats in Belize with field survey and SPOT satellite imagery.

Surveys of larval habitats of Anopheles vestitipennis and Anopheles punctimacula were conducted in Belize, Central America. Habitat analysis and classification resulted in delineation of eight habitat types defined by dominant life forms and hydrology. Percent cover of tall dense macrophytes, shrubs, open water, and pH were significantly different between sites with and without An. vestitipennis. For An. punctimacula, percent cover of tall dense macrophytes, trees, detritus, open water, and water depth were significantly different between larvae positive and negative sites. The discriminant function for An. vestitipennis correctly predicted the presence of larvae in 65% of sites and correctly predicted the absence of larvae in 88% of sites. The discriminant function for An. punctimacula correctly predicted 81% of sites for the presence of larvae and 45% for the absence of larvae. Canonical discriminant analysis of the three groups of habitats (An. vestitipennis positive; An. punctimacula positive; all negative) confirmed that while larval habitats of An. punctimacula are clustered in the tree dominated area, larval habitats of An. vestitipennis were found in both tree dominated and tall dense macrophyte dominated environments. The forest larval habitats of An. vestitipennis and An. punctimacula seem to be randomly distributed among different forest types. Both species tend to occur in denser forests with more detritus, shallower water, and slightly higher pH. Classification of dry season (February) SPOT multispectral satellite imagery produced 10 land cover types with the swamp forest and tall dense marsh classes being of particular interest. The accuracy assessment showed that commission errors for the tall, dense marsh and swamp forest appeared to be minor; but omission errors were significant, especially for the swamp forest (perhaps because no swamp forests are flooded in February). This means that where the classification indicates there are An. vestitipennis breeding sites, they probably do exist; but breeding sites in many locations are not identified and could be more abundant than indicated.

Animals↗
PubMed1997

Multi-modality mapping of motor cortex: comparing echoplanar BOLD fMRI and transcranial magnetic stimulation. Short communication.

Multiple non-invasive methods of imaging brain function are now available for presurgical planning and neurobiological research. As these new methods become available, it is important to understand their relative advantages and liabilities, as well as how the information gained compares across different methods. A current and future trend in neurobiological studies as well as presurgical planning is to combine information from different imaging techniques. Multi-modal integration may perhaps give more powerful information than each modality alone, especially when one of the methods is transcranial magnetic stimulation (TMS), with its ability to non-invasively activate the brain. As an initial venture in cross comparing new imaging methods, we performed the following 2 studies, locating motor cortex with echoplanar BOLD fMRI and TMS. The two methods can be readily integrated, with concurring results, although each have important limitations.

Adult↗
PubMed1997

Comparison of functional magnetic resonance imaging for language localization and intracarotid speech amytal testing in presurgical evaluation for intractable epilepsy. Preliminary results.

A comparison is made between the results of standard intracarotid speech amytal testing and a new methodology, echoplanar blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD fMRI), in patients undergoing presurgical evaluation for intractable epilepsy. Of the 15 patients entered in the study, all had fMRIs while performing a verbal fluency task. Twelve of these patients also underwent standard intracarotid sodium amytal testing for speech and memory. Results of the fMRIs as compared to the intracarotid speech amytal testing are discussed, including agreement and disagreement between studies. Potential reasons for poor concordance are discussed, including complexity of the verbal fluency task, and motion and technical issues in MRI scan acquisition and data analysis.

Adolescent↗
PubMed1997

Assessment of a remote sensing-based model for predicting malaria transmission risk in villages of Chiapas, Mexico.

A blind test of two remote sensing-based models for predicting adult populations of Anopheles albimanus in villages, an indicator of malaria transmission risk, was conducted in southern Chiapas, Mexico. One model was developed using a discriminant analysis approach, while the other was based on regression analysis. The models were developed in 1992 for an area around Tapachula, Chiapas, using Landsat Thematic Mapper (TM) satellite data and geographic information system functions. Using two remotely sensed landscape elements, the discriminant model was able to successfully distinguish between villages with high and low An. albimanus abundance with an overall accuracy of 90%. To test the predictive capability of the models, multitemporal TM data were used to generate a landscape map of the Huixtla area, northwest of Tapachula, where the models were used to predict risk for 40 villages. The resulting predictions were not disclosed until the end of the test. Independently, An. albimanus abundance data were collected in the 40 randomly selected villages for which the predictions had been made. These data were subsequently used to assess the models' accuracies. The discriminant model accurately predicted 79% of the high-abundance villages and 50% of the low-abundance villages, for an overall accuracy of 70%. The regression model correctly identified seven of the 10 villages with the highest mosquito abundance. This test demonstrated that remote sensing-based models generated for one area can be used successfully in another, comparable area.

Animals↗
PubMed1997

Methods of testing and analyzing excito-repellency responses of malaria vectors to insecticides.

A new test system that includes an excito-repellency test box, test procedures, and statistical treatment of data is described. The method consists of enclosing 25 mosquitoes in an exposure chamber lined with insecticide-treated or untreated (control) test papers. Each chamber has a single portal for mosquitoes to escape to a receiving cage, and numbers escaping are manually recorded at 1-min intervals. The exposure chamber accommodates a screened, 2nd chamber that, when placed in the exposure chamber, prevents the mosquitoes from making physical contact with test papers. A full assay utilized one exposure chamber that permits physical contact with insecticide-treated papers, one chamber that permits physical contact with control papers, one chamber that prevents physical contact with insecticide-treated papers, and a 4th chamber that prevents contact with control papers. After insecticide exposure, test populations are held for observations on 24-h mortalities. A survival analysis approach is described for estimating mosquito escape rates and for comparing differences in mosquito escape rates, with or without physical contact with insecticide, among populations, insecticides, and doses of insecticide.

Animals↗
PubMed1997

Use of generalized regression tree models to characterize vegetation favoring Anopheles albimanus breeding.

We propose the use of generalized tree models (GTMs) to analyze data from entomological field studies. Generalized tree models can be used to characterize environments with different mosquito breeding capacity. A GTM simultaneously analyzes a set of predictor variables (e.g., vegetation coverage) in relation to a response variable (e.g., counts of Anopheles albimanus larvae), and how it varies with respect to a set of criterion variables (e.g., presence of predators). The algorithm produces a treelike graphical display with its root at the top and 2 branches stemming down from each node. At each node, conditions on the value of predictors partition the observations into subgroups (environments) in which the relation between response and criterion variables is most homogeneous.

Animals↗
PubMed1997

Pesticide avoidance behavior in Anopheles albimanus, a malaria vector in the Americas.

The behavioral responses of 4 populations of Anopheles albimanus females to DDT, permethrin, and deltamethrin were characterized in excito-repellency tests. One test population (ST) from El Salvador has been maintained as a colony for 20 years. A second population (ES) from Guatemala was colonized in 1992. Third and fourth populations consisted of field-caught specimens from Toledo District (TO) of southern Belize in 1994 and Corozal District (CO) of northern Belize, respectively. Females of ES, TO, and CO populations rapidly escaped from direct contact with treated surfaces for each of the 3 insecticides. Similarities in escape responses of insecticide-resistant (ES) versus insecticide-susceptible populations (TO, CO) suggest that there is no relationship between physiological and behavioral responses of An. albimanus populations to DDT, permethrin, and deltamethrin. Females from all but the ST colony escaped in greater numbers from chambers without direct contact with treated surfaces than from control chambers (P < 0.05). Few females from the ST colony escaped from test chambers, regardless of which insecticide was used or whether contact was allowed, indicating that the ST colony has lost its capability to respond to insecticides. Repellent responses were significant; but they were not pronounced in 30-min exposures, and they were very pronounced in 4-h exposures. We conclude that irritant and repellent responses of malaria vectors to insecticides are important components of malaria control operations.

Americas↗
PubMed1997

A comparison of two collection methods for estimating abundance and parity of Anopheles albimanus in breeding sites and villages of southern Mexico.

The abundance and age structure of Anopheles albimanus populations were estimated by UV updraft light traps and human landing catches within villages and in nearby breeding sites of southern México. Four villages and 5 breeding sites were selected for the study. Light trap and human landing catches were simultaneously carried out in each breeding site and each village. Anopheles albimanus was the most abundant malaria vector caught in breeding sites and in villages. Significant differences in overall An. albimanus abundance among villages and among breeding sites were detected only by human landing catches. In both villages and breeding sites, more mosquitoes were captured by 1 human bait (34.3 +/- 6.3 and 14.6 +/- 2.9, respectively) than by one light trap (15.9 +/- 3.3 and 2.4 +/- 0.3 respectively) collection. After pooling, no significant differences were detected in the abundance estimated by each method in breeding sites and villages. A significant correlation of numbers of specimens between methods was detected. Age structure was different between samples from breeding sites and villages, with more gravid females collected in breeding sites, whereas more nulipars were collected in villages. By collection method, age structure was also different both in breeding sites and in villages. In breeding sites, the percentage of parous females was significantly higher in human landing catches, whereas the percentage of gravid females was significantly higher in light traps. In villages, only the percentage of gravid females was significantly higher in light traps. Our results suggests that UV light traps could be used to measure several entomological parameters of An. albimanus populations because both abundance variations and parity rates were similarly detected by both methods.

Animals↗
PubMed1996

Monitoring of aromatic amine exposures in workers at a chemical plant with a known bladder cancer excess.

BACKGROUND: In April 1991, an excess of bladder cancer cases among workers employed at a chemical manufacturing facility in Niagara Falls, NY, was reported. This excess was primarily confined to 708 workers who had ever been employed in the rubber chemicals manufacturing area of the plant, where the aromatic amines aniline and o-toluidine have historically been used. PURPOSE: An environmental and biological monitoring survey was conducted to evaluate current exposures to aniline and o-toluidine in the rubber chemicals department. METHODS: Personal air sampling for aniline and o-toluidine was conducted with the use of a modified Occupational Safety and Health Administration (OSHA) 73 method. Urine samples were collected before and after work (i.e., pre-shift and post-shift, respectively) and stored at -70 degrees C. Base hydrolysis was used to convert acetanilide and N-acetyl-o-toluidine, metabolites of aniline and o-toluidine present in the urine, to the parent compounds. The parent compounds were extracted from the alkaline urine into butyl chloride and then back-extracted from the butyl chloride into aqueous hydrochloric acid. An aliquot of each acidic extract was subjected to ion-interaction reversed-phase liquid chromatography with coulometric electrochemical detection. Hemoglobin (Hb) was extracted from blood and stored at -70 degrees C. For the measurement of adducts of aniline, o-toluidine, and 4-aminobiphenyl (4-ABP), precipitated Hb was dissolved in 0.1 M sodium hydroxide in the presence of recovery standards, and the hydrolysate was extracted with hexane, derivatized with pentafluoropropionic anhydride, and analyzed by gas chromatography-mass spectrometry with negative chemical ionization. RESULTS: A total of 73 workers, including 46 of 64 exposed workers who were employed in the rubber chemicals department and had the potential for exposure to aniline and o-toluidine and 27 of 52 unexposed workers employed in other departments where aniline and o-toluidine were not used or produced, had data available for both aniline and o-toluidine and Hb adducts; 28 of the workers in the former group also had personal air-sampling data. Personal air sample measurements showed that airborne concentrations of aniline and o-toluidine were well within the limits allowed in the workplace by OSHA. Urinary aniline and o-toluidine levels, however, were substantially higher among exposed workers than among unexposed control subjects. The most striking differential was for post-shift urinary o-toluidine levels, which averaged (+/- standard deviation) 2.8 micrograms/L (+/- 1.4 micrograms/L) in unexposed subjects and 98.7 micrograms/L (+/- 119.4 micrograms/L) in exposed subjects (P = .0001). Average aniline-Hb and o-toluidine-Hb adduct levels were also significantly higher (P = .0001) among exposed workers than among unexposed control subjects. Average levels of adducts to 4-ABP, a potential contaminant of process chemicals, were not significantly different (P = .48), although three exposed workers had 4-ABP levels above the range in unexposed workers. CONCLUSIONS: The adduct data suggest that, among current workers, o-toluidine exposure substantially exceeds aniline exposure and that 4-ABP exposure, if it occurs at all, is not widespread. These data support the conclusion that occupational exposure to o-toluidine is the most likely causal agent of the bladder cancer excess observed among workers in the rubber chemicals department of the plant under study, although exposures to aniline and 4-ABP cannot be ruled out.

Air↗
PubMed1996

Landscape surrounding human settlements and Anopheles albimanus (Diptera: Culicidae) abundance in Southern Chiapas, Mexico.

Landscape characteristics that may influence important components of the Anopheles albimanus Wiedemann life cycle, including potential breeding sites, suitable diurnal resting sites, and possible sources of blood meals, were analyzed at 14 villages in a malarious area of southern Mexico. An. albimanus adults were collected weekly in each village using UV-light traps between July 1991 and August 1992. Based on rainfall, the study was divided into 6 seasonal periods. Villages were considered to have high mosquito abundance when >5 mosquitoes per trap per night were collected during any 1 of the 6 seasonal periods. The extension and frequency of 11 land cover types surrounding villages were determined using aerial photographs and subsequently verified through field surveys. Elevation was the main landscape feature that separated villages with low and high mosquito abundance. All villages with high mosquito abundance were below 25 m. Transitional and mangrove land cover types were found only in the high mosquito abundance group. Flooded areas as potential breeding sites and potential adult resting sites in unmanaged pastures were significantly more frequent in areas surrounding villages with high mosquito abundance. No significant differences in density of cattle and horses were found among village groups. Overall, surrounding breeding sites located at low elevations in flooded unmanaged pastures seemed to be the most important determinants of An. albimanus adult abundance in the villages.

Animals↗
PubMed1996

Characterization of Anopheles darlingi (Diptera: Culicidae) larval habitats in Belize, Central America.

Surveys for larvae of Anopheles darlingi Root were conducted in April, May, and August 1994 in riverine habitats of central Belize (Cayo and Belize districts). An. darlingi was present during both the dry and wet seasons. Larvae were encountered most frequently in patches of floating debris along river margins. The floating mats were often formed by bamboo hanging over the banks and dense submersed bamboo roots. Larvae were found less frequently in lake margins, small lagoons, and ground pools with submersed roots and patches of floating leaves or vegetation. In addition to their association with floating debris, larvae of An. darlingi were associated positively with shade and submersed plants in riverine environments. Samples from river habitats showed the larvae of Anopheles albimanus Wiedemann to be strongly associated with sun-exposed sites containing green or blue-green algae. Unlike An. darlingi, An. albimanus was an ubiquitous mosquito, the immatures of which occurred in a wide variety of riverine and nonriverine aquatic habitats. Based on published reports and our experience, the association of An. darlingi with river systems was verified, and its distribution in Central America and Mexico was mapped.

Animals↗
PubMed1996

Predictions of malaria vector distribution in Belize based on multispectral satellite data.

Use of multispectral satellite data to predict arthropod-borne disease trouble spots is dependent on clear understandings of environmental factors that determine the presence of disease vectors. A blind test of remote sensing-based predictions for the spatial distribution of a malaria vector, Anopheles pseudopunctipennis, was conducted as a follow-up to two years of studies on vector-environmental relationships in Belize. Four of eight sites that were predicted to be high probability locations for presence of An. pseudopunctipennis were positive and all low probability sites (0 of 12) were negative. The absence of An. pseudopunctipennis at four high probability locations probably reflects the low densities that seem to characterize field populations of this species, i.e., the population densities were below the threshold of our sampling effort. Another important malaria vector, An. darlingi, was also present at all high probability sites and absent at all low probability sites. Anopheles darlingi, like An. pseudopunctipennis, is a riverine species. Prior to these collections at ecologically defined locations, this species was last detected in Belize in 1946.

Animals↗
PubMed1996

Characterization of Anopheles pseudopunctipennis larval habitats.

A survey of Anopheles pseudopunctipennis larval habitats was performed throughout most of its known geographic range. Eleven key environment variables characterized most larval habitats of this important vector of malaria in the Americas. Larval habitats occurred mainly in valley and foothill areas which were often situated in arid regions. Immatures were found primarily during the dry season in sun-exposed freshwater stream pools with clear, shallow, stagnant water containing abundant filamentous green algae and/or aquatic vegetation.

Animals↗
PubMed1995

Biochemical systematics and population genetic structure of Anopheles pseudopunctipennis, vector of malaria in Central and South America.

An electrophoretic survey of 42 populations of Anopheles pseudopunctipennis collected throughout its known geographic distribution was performed to clarify the taxonomic status of this important malaria vector species. The results indicated strong differences in the allele frequencies of three enzyme loci (glycerol dehydrogenase, 6-phosphogluconate dehydrogenase, and phosphoglucomutase) of the 33 loci analyzed. No fixed electromorphic differences separate the populations of An. pseudopunctipennis. The populations of An. pseudopunctipennis showed little genetic divergence, with Nei distances ranging from 0 to 0.079. A comparison of An. pseudopunctipennis data with either one of three other Anopheles species showed a high genetic distance of 0.335 with a closely related species, An. franciscanus; 0.997 with An. crucians, and 2.355 with An. (Nyssorhynchus) albimanus. Geographic populations of An. pseudopunctipennis were classified into three clusters; one cluster included populations collected in North America (United States and Mexico) and Guatemala, one cluster included populations from Belize and South America (Colombia, Ecuador, Peru, Chile, and Argentina); and one cluster was represented by populations from the Island of Grenada (type-locality of An. pseudopunctipennis). Based on our isozyme analyses, we defined these clusters as three geographic populations of An. pseudopunctipennis. Of the two mainland populations, one extends from the southern United States south through Mexico and Guatemala, and the other extends north from southern South America through Central America to Belize. These two geographic populations converge in southern Mexico and northern Central America. One part of the convergence zone was identified in the area of eastern Guatemala and southern Belize.

Alleles↗
PubMed1995

Predictions of adult Anopheles albimanus densities in villages based on distances to remotely sensed larval habitats.

Remote sensing is particularly helpful for assessing the location and extent of vegetation formations, such as herbaceous wetlands, that are difficult to examine on the ground. Marshes that are sparsely populated with emergent macrophytes and dense cyanobacterial mats have previously been identified as very productive Anopheles albimanus larval habitats. This type of habitat was detectable on a classified multispectral System Probatoire d'Observation de la Terre image of northern Belize as a mixture of two isoclasses. A similar spectral signature is characteristic for vegetation of river margins consisting of aquatic grasses and water hyacinth, which constitutes another productive larval habitat. Based on the distance between human settlements (sites) of various sizes and the nearest marsh/river exhibiting this particular class combination, we selected two groups of sites: those located closer than 500 m and those located more than 1,500 m from such habitats. Based on previous adult collections near larval habitats, we defined a landing rate of 0.5 mosquitoes/human/min from 6:30 PM to 8:00 PM as the threshold for high (> or = 0.5 mosquitoes/human/min) versus low (< 0.5 mosquitoes/human/min) densities of An. albimanus. Sites located less than 500 m from the habitat were predicted as having values higher than this threshold, while lower values were predicted for sites located greater than 1,500 m from the habitat. Predictions were verified by collections of mosquitoes landing on humans. The predictions were 100% accurate for sites in the > 1,500-m category and 89% accurate for sites in the < 500-m category.

Animals↗
PubMed1994

The environment, remote sensing, and malaria control.

Results of studies in California, Mexico and Belize demonstrate the value of remote sensing technology for studying vector-borne diseases. These studies have also shown that it is necessary to fully define the environmental factors associated with the presence of vectors and disease transmission, and to be able to detect these environmental factors with image data. These studies, and other published reports, are demonstrating many potential uses of remotely sensed data in managing and targeting vector and disease control measures.

Aedes↗