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Biomedical subjects

D R Roberts

Publications and source records attributed to D R Roberts.

At least 55 records · Page 3Linked to original sources
PubMed1994

Gonotrophic cycle and survivorship of Anopheles pseudopunctipennis (Diptera: Culicidae) in the Tapachula foothills of southern Mexico.

Mark-release-recapture experiments were conducted to determine the length of the gonotrophic cycle and survivorship of Anopheles pseudopunctipennis Theobald in the Tapachula foothills of southern Mexico. Separate trials with wild-caught females were conducted in the early and late dry season to examine intraseasonal differences. The gonotrophic cycle of insectary-reared, nulliparous females was estimated during the late dry season. A total of 5.4-5.7% of marked females was recaptured. A 3-d gonotrophic cycle was characteristic of wild-caught females, whereas a 4-d gonotrophic cycle was characteristic for insectary-reared females. Engorged, wild-caught females completed oogenesis in approximately 60 h under field conditions. Blood digestion in 23.5% of 2,221 and 21.9% of 1,195 engorged, wild-caught females held in the insectary was not accompanied by egg development. Dissections of these females showed that nearly 85% were nulliparous and presumably pregravid. These statistics plus other field data were used to determine that 60% of all nulliparous entered a pregravid condition. The body size and wing length of gravids was significantly larger than pregravids. Daily survival estimates of 0.875 and 0.884 were calculated for field-collected females during the early and late dry season, respectively.

Animals↗
PubMed1994

Bionomics of adult Anopheles pseudopunctipennis (Diptera: Culicidae) in the Tapachula foothills area of southern Mexico.

Field studies on the bionomics of adult Anopheles pseudopunctipennis Theobald were conducted to assess its relative importance as a primary vector of vivax malaria in southern Mexico. In four malaria endemic villages in a foothill region near Tapachula, Mexico, population densities of A. pseudopunctipennis increased during the dry seasons of 1990 and 1991. The pattern of nocturnal host-seeking activity indoors was unimodal with a late night peak at 0100 hours enhancing its vectorial significance, because it occurred when most residents were asleep and fully exposed to the anophelines. Comparisons of trapping methods showed that a horse-baited trap was more effective than human landing catches or UV light traps. Pit shelters, on the other hand, were more effective than indoor and natural shelter resting collections. Results of enzyme-linked immunosorbent assays performed on wild-caught A. pseudopunctipennis specimens documented the presence of natural infections with the VK210 and new VK247 circumsporozoite polymorphs of P. vivax. These findings verify the importance of A. pseudopunctipennis as a major vector of vivax malaria at higher elevations and extend the geographical range of the VK247 P. vivax polymorph in Mexico.

Animals↗
PubMed1994

Fall acclimation patterns of interior spruce seedlings and their relationship to changes in vegetative storage proteins.

Changes in the content of vegetative storage proteins (VSPs) were monitored in 1-year-old interior spruce (Picea glauca (Moench) Voss x Picea engelmanni Parry complex) seedlings from late summer until midwinter. Seedlings were also monitored for days to terminal bud break (DBB(t)), dry weight fraction and frost hardiness, measured as both index of injury at -18 degrees C (IL(-18 degrees C)) and as the temperature causing 50% foliage electrolyte leakage (LT(50)). During fall acclimation, VSP content, frost hardiness and dry weight fraction increased, whereas DBB(t) decreased. In mid-November, IL(-18 degrees C) reached its lowest value, coinciding with high VSP content and dry weight fraction, and low DBB(t). The LT(50) decreased in a linear manner as dry weight fraction and VSP content increased; r(2) values were 0.69 to 0.81, respectively. The fall accumulation of VSPs was also highly correlated with increased dry weight fraction. The increase in VSP content occurred as seedling photosynthetic capacity declined, but maximum contents were obtained before complete inactivation of the photosynthetic apparatus. The results indicate that VSP accumulation is an integral part of fall acclimation in interior spruce, closely parallels frost hardiness and partially accounts for the increase in dry weight fraction.

Journal Article↗
PubMed1994

Insecticide resistance issues in vector-borne disease control.

Vector-borne diseases are an increasing cause of death and suffering worldwide. Efforts to control these diseases have been focused on the use of chemical pesticides, but arthropod resistance (whether physiological, biochemical, or behavioral) to pesticides is now an immense practical problem. The pharmacokinetic interactions of pesticides with arthropods, mechanisms of resistance, and the strengths and shortcomings of different resistance test methods are briefly reviewed. Using malaria control as an example, the differences between the efficacy of insecticide-sprayed houses in reducing malaria transmission, and the actual effect of such treatments on vectors are discussed. Reduced malaria transmission as a result of spraying house walls occurs through some combination of killing vectors that land on sprayed walls (insecticidal effect) and by preventing vectors from entering or remaining inside long enough to bite (behavioral effects). Both insecticidal and behavioral effects of insecticides are important, but the relative importance of one versus the other is controversial. Field studies in Africa, India, Brazil, and Mexico provide persuasive evidence for strong behavioral avoidance of DDT by the primary vector species. This avoidance behavior, exhibited when malaria vectors avoid insecticides by not entering or by rapidly exiting sprayed houses, should raise serious questions about the overall value of current physiological and biochemical resistance tests. The continued efficacy of DDT in Africa, India, Brazil, and Mexico, where 69% of all reported cases of malaria occur and where vectors are physiologically resistant to DDT (excluding Brazil), serves as one indicator that repellency is very important in preventing indoor transmission of malaria. This experience with DDT has implications for future control efforts because pyrethroids also stimulate avoidance behaviors in arthropods. Each chemical should be studied early (before broad-scale use) to define types of action against vector species by geographic area, especially for impregnated bed net applications. The problems for vector control created by use of insecticides in agriculture and the potential for management of resistance in both agriculture and vector-borne disease control are discussed.

Agrochemicals↗
PubMed1994

Remote sensing as a landscape epidemiologic tool to identify villages at high risk for malaria transmission.

A landscape approach using remote sensing and geographic information system (GIS) technologies was developed to discriminate between villages at high and low risk for malaria transmission, as defined by adult Anopheles albimanus abundance. Satellite data for an area in southern Chiapas, Mexico were digitally processed to generate a map of landscape elements. The GIS processes were used to determine the proportion of mapped landscape elements surrounding 40 villages where An. albimanus abundance data had been collected. The relationships between vector abundance and landscape element proportions were investigated using stepwise discriminant analysis and stepwise linear regression. Both analyses indicated that the most important landscape elements in terms of explaining vector abundance were transitional swamp and unmanaged pasture. Discriminant functions generated for these two elements were able to correctly distinguish between villages with high and low vector abundance, with an overall accuracy of 90%. Regression results found both transitional swamp and unmanaged pasture proportions to be predictive of vector abundance during the mid-to-late wet season. This approach, which integrates remotely sensed data and GIS capabilities to identify villages with high vector-human contact risk, provides a promising tool for malaria surveillance programs that depend on labor-intensive field techniques. This is particularly relevant in areas where the lack of accurate surveillance capabilities may result in no malaria control action when, in fact, directed action is necessary. In general, this landscape approach could be applied to other vector-borne diseases in areas where 1) the landscape elements critical to vector survival are known and 2) these elements can be detected at remote sensing scales.

Animals↗
PubMed1994

Remote sensing of tropical wetlands for malaria control in Chiapas, Mexico.

Malaria, transmitted by anopheline mosquitoes, remains a serious health problem in the tropics. Most malaria eradication efforts focus on control of anopheline vectors. These efforts include the NASA Di-Mod project, whose current goal is to integrate remote sensing, geographic information systems (GIS), and field research to predict anopheline mosquito population dynamics in the Pacific coastal plain of Chiapas, Mexico. Field studies demonstrate that high larval production of Anopheles albimanus, the principal malaria vector in the plain, can be linked to a small number of larval habitat-types, determined by larval sampling and cluster analysis of wetlands in the coastal plain. Analysis of wet and dry season Landsat Thematic Mapper (TM) satellite imagery identified 16 land cover units within an 185-km2 study area in the coastal zone. A hierarchical approach was used to link the larval habitat-types with the larger land cover units and make predictions of potential and actual low, medium, and high anopheline production. The TM-based map and GIS techniques were then used to predict differences in anopheline production at two villages, La Victoria and Efrain Gutierrez. La Victoria was predicted to have much higher Anopheles albimanus production, based upon a 2-10 times greater extent of medium- and high-producing land cover units in its vicinity. This difference between villages was independently supported by sampling (with light traps) of adults, which were 5-10 times more abundant in La Victoria.

Animals↗
PubMed1994

Bionomics of larval populations of Anopheles pseudopunctipennis in the Tapachula foothills area, southern Mexico.

The population dynamics of Anopheles pseudopunctipennis larvae were studied in a foothill region near Tapachula, Mexico. Systematic surveillance of wet-season and dry-season habitats was conducted during 1990 and 1991. Sampling along transects of the Coatan River was employed to quantify habitat availability and population densities of larvae during the dry season. During the wet season, larvae were most abundant in temporary habitats, such as seepage springs, rain pools, and pools in stream and river margins. The temporary habitats disappeared during the dry season, which occurred concurrent with increasing densities of larvae in dry-season habitats within transects along the Coatan River. The great abundance of the dry-season riverine habitats, viz., small pools with filamentous algae, resulted in peak densities of host-seeking adult populations in villages associated with the river. During both seasons, there were significant associations between the presence and abundance of larvae and habitats containing filamentous algae, and secondarily with selected aquatic and semiaquatic plants. There was a significant correlation between mean numbers of larvae per habitat and mean numbers of breeding sites in the transects. Overall, An. pseudopunctipennis larvae were very abundant during the dry season and relatively uncommon during the wet season.

Animals↗
PubMed1993

Industrial exposure to 1,3-butadiene in monomer, polymer and end-user industries.

Researchers from the National Institute for Occupational Safety and Health (NIOSH) of the Centers for Disease Control and Prevention conducted an extent-of-exposure study of 1,3-butadiene monomer, polymer and end-user industries to assess occupational exposure to butadiene and to evaluate control technologies. The findings of the exposure assessment are reported here. Walk-through surveys were conducted in 11 monomer, 17 polymer and two end-user plants; in-depth industrial hygiene surveys were conducted at four monomer, five polymer and two end-user plants. Airborne exposure concentrations of butadiene were determined for various job categories by personal sampling. The samples were analysed by a new method developed at NIOSH that is sensitive to 0.2 microgram per sample. A total of 687 personal (full-shift and short-term) and 232 area samples were taken. The results indicate that all exposures were well below the current permissible exposure limit of the US Occupational Safety and Health Administration of 1000 ppm. The US Occupational Safety and Health Administration (1990) has proposed a new standard that would reduce exposure to 2 ppm. Exposures ranged from less than 0.005 ppm to 374 ppm, and 3.7% of the samples contained more than 10 ppm, 7.8% more than 2 ppm but less than 10 ppm and 88.5% less than 2 ppm. We recommend means for reducing exposure by the use of engineering controls.

Air Pollutants, Occupational↗
PubMed1993

Host selection patterns of Anopheles pseudopunctipennis under insecticide spraying situations in southern Mexico.

Studies of host selection patterns of Anopheles pseudopunctipennis were conducted in villages in foothills near Tapachula, Mexico. Based on 2 years of collections, 53.8 and 86.1% of all engorged females resting inside houses were found to contain human blood. Estimates of weighted and unweighted human blood indices, including data from outdoor resting collections, varied from 29.5 to 54.7%. Humans and dogs were the more common blood sources for all An. pseudopunctipennis mosquitoes, accounting for 96% of blood meals tested. Results of analyses of host preference through estimates of forage ratios (FRs) indicated that the large numbers of blood meals from humans and dogs were more reflective of host availability than host preference. An FR of less than 1 indicated that, in terms of host availability, proportionately fewer An. pseudopunctipennis females fed on humans than other large animal hosts. In contrast, FRs of 15-20 and 5-7 revealed strong selective biases for horses and pigs as sources of blood meals, respectively. The proportion of outdoor-resting, blood-engorged females containing human blood declined markedly after houses were sprayed with DDT. This response to house spraying is attributed to an excito-repellency effect of DDT.

Animals↗
PubMed1993

Apparent changes in the abundance and distribution of Anopheles species on Grenada island.

Results of a recent survey of the 3 species of Anopheles mosquitoes, Anopheles (Nyssorhynchus) aquasalis, Anopheles (Nyssorhynchus) argyritarsis, and Anopheles (Anopheles) pseudopunctipennis, on the island of Grenada are contrasted with the only other published survey of these species on Grenada, which was published in 1938. Results suggest that a significant change in the abundance and distribution of each species has occurred over this period. Physical characteristics of the aquatic habitats for each species are described and compared.

Animals↗
PubMed1993

Preliminary observations on the changing roles of malaria vectors in southern Belize.

A survey for larval and adult Anopheles mosquitoes was conducted in Toledo District of southern Belize during August-September 1992. We surveyed for larvae in 145 habitats and conducted paired indoor-outdoor collections of adult mosquitoes landing on humans at 6 houses. In 1940-41, Kumm and Ram reported Anopheles darlingi females to be the most common Anopheles mosquitoes inside houses and reported no specimens of Anopheles vestitipennis in southern Belize. In our 1992 survey we found no An. darlingi mosquitoes either as adults or larvae. More An. vestitipennis females were captured indoors than outdoors, whereas most Anopheles albimanus and Anopheles apicimacula females were captured outdoors. All 3 species were represented occasionally in 145 collections of larvae from diverse habitats. Anopheles vestitipennis now appears to be a potentially important vector of malaria during the wet season in Toledo District.

Animals↗
PubMed1993

Dynamics of population densities and vegetation associations of Anopheles albimanus larvae in a coastal area of southern Chiapas, Mexico.

Spatial and seasonal variations on Anopheles albimanus larval densities and their plant associations were investigated in larval habitats in southern Mexico between April 1989 and May 1990. Thirty-four plant groups were dominant in larval habitats. Dense larval populations were associated with 3 genera of plants, Cynodon, Echinocloa and Fimbristylis and no larvae were found in habitats with Salvinia and Rhizophora. Low significant positive or negative associations were documented with the other 12 plant genera. Larval habitats were classified according to the morphology of their dominant plants. Higher larval densities were observed in the groups characterized by relatively short emergent vegetation. The distribution of habitat-types within 5 identified vegetation units showed a significantly dependent relationship. For the entire study period, highest larval densities were detected in flooded pasture/grassland vegetation units. For all vegetation units, higher larval densities were found when the dominant plant type covered between 25-50% of the breeding site. The integration of data from habitat-types into vegetation units did not result in loss of information.

Animals↗
PubMed1992

An automated system for testing the accuracy of patient-controlled analgesia devices.

A system was developed to test the accuracy of patient-controlled analgesia devices in situations simulating clinical use. Bolus requests are made automatically at predetermined intervals, and the infusate delivered is measured and recorded without the need for operator presence. To ensure clinical relevance, the bolus request times used in this study corresponded to a pattern typical of those requested by patients on the ward. Graseby, Abbott Provider 5500 and IVAC patient-controlled analgesia devices were tested and found to deliver reasonably accurately over a 24 h period. However, when an infusion was started in an unprimed system or after a period of no bolus requests in a bolus-only mode the Graseby and IVAC machines under-delivered. This system provides a means of testing patient-controlled analgesia devices operating in any delivery mode.

Analgesia, Patient-Controlled↗
PubMed1991

Characterisation of oligosaccharides from Drosophila melanogaster glycoproteins.

An analysis of the released oligosaccharides from a membrane glycoprotein preparation of third instar larvae (3rdIL), and purified larval serum protein 2 (LSP2) from Drosophila melanogaster was performed. Sequential exoglycosidase digestion in combination with high-resolution gel permeation chromatography and partial acetolysis indicated the presence of two series of oligomannosides; one of these series was unusual and characterized by the presence of a core alpha 1-6 linked fucose, the other was a typical mammalian oligomannose series containing the following isomers -D1, -D2, -D12, -D123 and -CD123 as well as the unprocessed Man9GlcNAc2 structure. Conventional oligomannose could only be detected in the LSP2 sample. This study opens the way to use powerful molecular and classical genetic techniques to analyse the control and functional significance of glycosylation in higher organisms.

Animals↗
PubMed1991

Storage protein changes during zygotic embryogenesis in interior spruce.

The major storage proteins isolated from protein bodies of embryo tissues of interior spruce Picea glauca (Moench) Voss/Picea engelmanii Parry had apparent molecular weights of 41, 35, 33, 24 and 22 kD. Minor proteins of 30 and 27.5 kD were also observed. Based on their solubility characteristics, the 41 kD protein was identified as a water and buffer-soluble albumin, and the 35, 33, 24 and 22 kD proteins were characterized as buffer-insoluble, high salt-soluble globulins. Two-dimensional electrophoresis revealed each protein was composed of several isoelectric variants. Developmentally specific accumulation of storage proteins was observed during embryogenesis. The 41 kD protein only accumulated during the later stages of cotyledon maturation, whereas the other storage proteins began to accumulate during the early stages of embryo development. All storage proteins showed major accumulations during cotyledon maturation.

Journal Article↗
PubMed1991

Quality of blood prepared for autotransfusion in primary cemented total hip replacement.

We have measured levels of contaminants (products of cell lysis and other substances) in blood salvaged from patients undergoing primary cemented total hip replacement. Washing of this blood removed an average of 91.4% of the free haemoglobin mass, reduced white cell lysozyme concentrations by 86% and almost totally eliminated fats and particulate matter. Osmotic fragility was significantly improved by washing although not to control levels.

Anticoagulants↗
PubMed1991

A dipstick ELISA for rapid detection of human blood meals in mosquitoes.

A dot-enzyme-linked immunosorbent assay, dot-ELISA, that allows for identification of human blood meals in mosquitoes in less than 2 h is presented. Strips of mylar-backed nitrocellulose paper, the dipstick, may be inoculated with anti-human capture antibody, blocked, dried and stored for at least 3 months before use. The Dipstick ELISA consistently detected human blood meals at 24 h post-blood meal in frozen Anopheles mosquitoes and at 32 h post-blood meal on samples eluted off filter-paper smears. This ELISA detects human IgG at dilutions of 1:25,600, and produces strong positive results at dilutions between 1:400 and 1:12,800. The Dipstick ELISA is highly specific, and no false positives were detected when tested against cow, horse, goat, dog, cat, pig, rabbit, mouse, rat, chicken, raccoon and opossum sera. All reagents for the assay are commercially available. The Dipstick ELISA meets requirements for a rapid and simple assay for the identification of human blood meals and should have particular application to short-term field studies and emergency epidemiological investigations. A modified protocol, the Trough ELISA, which treats dipsticks jointly in disposable pipet troughs during the conjugate and substrate steps, was developed and produced as a kit. The Trough ELISA produces 1-4% random false positives, and we recommend that the Trough ELISA not be used.

Animals↗