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D J Rogers

Publications and source records attributed to D J Rogers.

At least 55 records · Page 3Linked to original sources
PubMed1997

A generic population model for the African tick Rhipicephalus appendiculatus.

We present a simulation population model for the African tick Rhipicephalus appendiculatus, based on previous analyses of the mortality factors most closely correlated with observed population changes at 11 sites in equatorial and South Africa. The model incorporates temperature-dependent rates of egg production and development, climate-driven density-independent mortality rates, particularly during the adult-larval stage, and density-dependent regulation of both nymphs and adults. Diapause is also included for tick populations in southern Africa. The model successfully describes both the seasonality and annual range of variation in numbers of each tick stage observed at each of 4 test sites in Uganda, Burundi and South Africa. Sensitivity analysis showed that the final version of the model is robust to 4-fold variation in most parameter values (that were per force based on informed guesses), but is more sensitive to the regression coefficients determining density-dependent interstadial mortality (that were derived from analysis of field data). The model is able to predict the seasonality of ticks from a site in Kenya where a full prior population analysis was not possible because only adults and nymphs had been counted. The model is potentially applicable to other species of ticks, both tropical and temperate, to predict tick abundance and seasonality as risk factors for tick-borne diseases.

Animals↗
PubMed1997

Lectins for drug delivery within the oral cavity--investigation of lectin binding to oral mucosa.

The aim of this study was to identify receptors present on the buccal mucosa in order to select appropriate lectins that will allow the retention of a dosage form within the oral cavity. Studies using human buccal cells, the avidin-biotin-complex/diaminobenzidine method for identifying lectin binding and a microdensitometer to allow a semi-quantitative analysis of stain intensity, showed a wide diversity of lectin receptors. Kinetic studies of lectin binding to buccal cells revealed significant binding after 20 s, particularly for lectins from Pisum sativum and Arachis hypogaea. A significant reduction in lectin binding was observed after exposing buccal cells to a series of lectin solutions pre-treated with a large excess of secretor or non-secretor saliva. However when bound to the buccal cells, there was little displacement of lectins on exposure to either saliva types. Further studies on rat oral tissue suggested that the lectins appeared to bind to varying degrees on whole oral epithelial surfaces although differences in binding between this and the human buccal cell model were evident. It was concluded that a wide range of possible target receptors for lectins are present on rat oral epithelium and human buccal cells. Lectin binding to these receptors can be affected by the exposure time and the presence of saliva.

Administration, Oral↗
PubMed1996

Remotely sensed surrogates of meteorological data for the study of the distribution and abundance of arthropod vectors of disease.

This paper gives an overview of how certain meteorological data used in studies of the population dynamics of arthropod vectors of disease may be predicted using remotely sensed, satellite data. Details are given of the stages of processing necessary to convert digital data arising from satellite sensors into ecologically meaningful information. Potential sources of error in these processing steps are also highlighted. Relationships between ground-measured meteorological variables (saturation deficit, ground temperature and rainfall) and data from both the National Oceanic and Atmospheric Administration's, polar-orbiting, meteorological satellites and the geostationary, Meteosat satellite are defined and examples detailed for Africa. Finally, the current status of existing satellite platforms and future satellite missions are reviewed and potential data availability discussed. How such satellite-based predictions have proved valuable in understanding the distribution of tsetse fly species in Côte d'Ivoire and Burkina Faso will be the subject of a future review.

Africa↗
PubMed1996

Predicting the distribution of tsetse flies in West Africa using temporal Fourier processed meteorological satellite data.

An example is given of the application of remotely-sensed, satellite data to the problems of predicting the distribution and abundance of tsetse flies in West Africa. The distributions of eight species of tsetse, Glossina morsitans, G. longipalpis, G. palpalis, G. tachinoides, G. pallicera, G. fusca, G. nigrofusca and G. medicorum in Côte d'Ivoire and Burkina Faso, were analysed using discriminant analysis applied to temporal Fourier-processed surrogates for vegetation, temperature and rainfall derived from meteorological satellites. The vegetation and temperature surrogates were the normalized difference vegetation index and channel-4-brightness temperature, respectively, from the advanced, very-high-resolution radiometers on board the National Oceanic and Atmospheric Administration's polar-orbiting, meteorological satellites. For rainfall the surrogate was the Cold-Cloud-Duration (CCD) index derived from the geostationary, Meteosat satellite series. The presence or absence of tsetse was predicted with accuracies ranging from 67%-100% (mean = 82.3%). A further data-set, for the abundance of five tsetse species across the northern part of Côte d'Ivoire (an area of about 140,000 km2), was analysed in the same way, and fly-abundance categories predicted with accuracies of 30%-100% (mean = 73.0%). The thermal data appeared to be the most useful of the predictor variables, followed by vegetation and rainfall indices. Refinements of the analytical technique and the problems of extending the predictions through space and time are discussed.

Africa, Western↗
PubMed1995

The use of an alcometer in clinical forensic practice.

Forensic physicians are at times required to provide a professional opinion on a person's degree of intoxication through alcohol, particularly with regard to fitness for interview by the police. Inherent to these assessments is an estimation of the blood alcohol concentration (BAC). Most forensic physicians rely on taking a history regarding recent alcohol consumption and a clinical assessment to estimate the BAC. We report a study in which the BAC of 118 detainees was estimated and compared with the BAC measured by an alcometer. Our estimations were accurate in 66% of cases. Most errors resulted from underestimating the BAC. Additionally, we attempted to determine fitness for interview using a single measurement of the BAC without a clinical assessment. 19% of those who were assessed as unfit for interview had a BAC of less than the UK legal limit for driving (currently 80 mg%) and 37% considered fit, had a BAC above that level. We conclude that the routine use of alcometers would enhance the practice of forensic medicine but could not replace its role in the assessment of levels of alcohol intoxication.

Journal Article↗
PubMed1995

Child sexual abuse--the interface with genitourinary medicine.

Whenever a child is seen in a genitourinary clinic the possibility that the child is the victim of child sexual abuse must be considered. This article considers the definition and postulated prevalence of child sexual abuse in England and Wales. A proposed management plan is then detailed with a review of the significance of the medical findings. Finally consideration is given to the ethical dilemmas which such cases pose.

Adolescent↗
PubMed1995

Lectin from Codium fragile ssp. tomentosoides conjugated to colloidal gold: a new histochemical reagent.

A new histochemical reagent has been developed utilising a lectin from a marine alga for the first time. Colloidal gold was coupled to the N-acetyl-alpha-D-galactosamine specific lectin from the green alga Codium fragile ssp. tomentosoides. The lectin--gold conjugate bound to the membranes of blood-group A1 human erythrocytes which were used as a model system. The bound complex could be detected, readily, by transmission electron microscopy. This novel reagent incorporating a lectin of low molecular weight (15 kDa) has potential value for studies of cell-surface topography of a variety of tissues.

Chlorophyta↗
PubMed1994

Tsetse flies and their control.

The authors use a quantitative modelling framework to describe and explore the features of the biology of tsetse flies (Glossina spp.) which are important in determining the rate of transmission of the African trypanosomiases between hosts. Examples are presented of the contribution of previous research on tsetse to quantified epidemiological and epizootiological understanding, and areas of current ignorance are identified for future study. Spatial and temporal variations in risk are important (but rarely-studied) determinants of the impact of trypanosomiasis on humans, domestic animals and agricultural activities. Recent grid-based sampling surveys to Togo provide valuable data sets on tsetse, cattle and trypanosomiasis throughout the country. A combination of ground-based meterological and remotely-sensed satellite data, within linear discriminant analytical models, enables description of the observed distributions of the five species of tsetse occurring in Togo, with accuracies of between 72% (Glossina palpalis and G. tachinoides) and 98% (G. fusca). Abundance classes of the two most widespread species, G. palpalis and G. tachinoides, are described with accuracies of between 47% and 83%. This is especially remarkable given the relatively small differences between the average values of the predictor variables in areas of differing fly abundance. Similar analyses could be used to predict the occurrence and abundance of flies in other areas, which have not been surveyed to date, in order to plan tsetse control campaigns or explore development options. Finally, some recent tsetse control campaigns are briefly reviewed. The shift of emphasis from fly eradication to fly control is associated with a devolution of responsibility for control activities from central government to local areas, communities or even individuals. The future role of central governments will remain crucial, however, in determining the areas in which different control options are practised, in facilitating control by local communities and in protecting controlled areas from re-invasion by flies from other areas.

Animals↗
PubMed1993

Distribution of tsetse and ticks in Africa: past, present and future.

The current concern over the effects of global warming has rekindled interest in the neglected topic of vector distribution. In order to predict the future, however, we must first comprehend the past and present. In this review, David Rogers and Sarah Randolph discuss the alternative biological and statistical approaches to understanding the present-day distributions of vectors, and make predictions about how these might change with global warming.

Journal Article↗
PubMed1993

Monitoring trypanosomiasis in space and time.

The paper examines the possible contributions to be made by Geographic Information Systems (GIS) to studies on human and animal trypanosomiasis in Africa. The epidemiological characteristics of trypanosomiasis are reviewed in the light of the formula for the basic reproductive rate or number of vector-borne diseases. The paper then describes how important biological characteristics of the vectors of trypanosomiasis in West Africa may be monitored using data from the NOAA series of meteorological satellites. This will lead to an understanding of the spatial distribution of both vectors and disease. An alternative, statistical approach to understanding the spatial distribution of tsetse, based on linear discriminant analysis, is illustrated with the example of Glossina morsitans in Zimbabwe, Kenya and Tanzania. In the case of Zimbabwe, a single climatic variable, the maximum of the mean monthly temperature, correctly predicts the pre-rinderpest distribution of tsetse over 82% of the country; additional climatic and vegetation variables do not improve considerably on this figure. In the cases of Kenya and Tanzania, however, another variable, the maximum of the mean monthly Normalized Difference Vegetation Index, is the single most important variable, giving correct predictions over 69% of the area; the other climatic and vegetation variables improve this to 82% overall. Such statistical analyses can guide field work towards the correct biological interpretation of the distributional limits of vectors and may also be used to make predictions about the impact of global change on vector ranges. Examples are given of the areas of Zimbabwe which would become climatically suitable for tsetse given mean temperature increases of 1, 2 and 3 degrees Centigrade. Five possible causes for sleeping sickness outbreaks are given, illustrated by the analysis of field data or from the output of mathematical models. One cause is abiotic (variation in rainfall), three are biotic (variation in vectorial potential, host immunity, or parasite virulence) and one is historical (the impact of explorers, colonizers and dictators). The implications for disease monitoring, in order to anticipate sleeping sickness outbreaks, are briefly discussed. It is concluded that present data are inadequate to distinguish between these hypotheses. The idea that sleeping sickness outbreaks are periodic (i.e. cyclical) is only barely supported by hard data. Hence it is even difficult to conclude whether the major cause of sleeping sickness outbreaks is biotic (which, in model situations, tends to produce cyclical epidemics) or abiotic.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Modelling the effect of feeding-related mortality on the feeding strategy of tsetse (Diptera: Glossinidae).

Free-living haematophagous insects risk death through host grooming responses or through increased susceptibility to predation whenever they take a bloodmeal. In this paper we investigate the effects of these risks on the feeding strategy of tsetse. A model is presented that allows for death of tsetse by starvation if they do not succeed in feeding within a fixed time (set at 6 days in the first instance) and for mortality specifically associated with feeding. In addition there is background mortality that applies to all flies at all times. The model is used to compute the individual life-time fertility (number of female puparia per female) as a function of the probability of obtaining a meal (indicated by field data to be very high, usually > 0.85 per day) and the day on which flies start to search for a meal. We suggest that the feeding strategy that would be selected for is that which allows the maximum reproductive output. The model shows that this strategy involves making no attempts to feed for 3-4 days after the previous meal and then attempting to feed with the greatest possible probability until a meal is obtained. The predicted feeding interval, obtained independently of any trapping data, agrees closely with all previous estimates from field studies using a variety of methods. Preliminary results from a laboratory experiment reveal an increased risk of predation of recently fed as compared with hungry tsetse. The lower the actual feeding mortality the more frequently will flies be able to feed should conditions so demand. It is adaptive, however, for tsetse to delay attempting to feed for as long as they can, which is made possible by the near certainty of locating and feeding on a host within 1 day, using their sophisticated sensory systems.

Animals↗
PubMed1991

Mortality rates and population density of tsetse flies correlated with satellite imagery.

Tsetse flies are a major constraint on animal production in about 10 million km2 of Africa through their transmission of animal trypanosomiasis. Up to 25 million people are at risk from human trypanosomiasis, or sleeping sickness. Tsetse research has been concentrated on the factors that control the distribution and abundance of these vectors and the means by which their numbers can be reduced. Eradication successes in some countries are insignificant compared with the continental scale of the problem and the long-term reduction in the area infested by tsetse has been negligible. We report here that the mortality rates of tsetse from sites in both West and East Africa, the size of male and female tsetse (related to the mortality rate of the parental female population) along a north-south transect in West Africa, and the abundance of two species of tsetse over the northern half of Côte d'Ivoire, are significantly correlated with data from meterological satellites. This information could be used to predict both the mortality rate and the abundance (key determinants of disease transmission potential) of tsetse over very large areas of the continent and to produce maps of high risk areas of disease transmission for the African trypanosomiases and, by implication, for many other vector-borne diseases.

Africa↗
PubMed1991

The feeding behaviour, activity and trappability of wild female Glossina pallidipes in relation to their pregnancy cycle.

Female Glossina pallidipes Austen trapped with baited NG2B traps were subjected both to detailed ovarian dissection and to nutritional analysis. Using a calibration curve derived from dissected wild-caught, laboratory-held flies, the field females were assigned by discriminant analysis to each day of the pregnancy cycle. Field females were most available to NG2B traps while carrying the first instar larva. The nutritional characteristics of trapped field females over the pregnancy cycle lead to the following main conclusions. (i) Fat levels increase most rapidly during the egg in utero stage, while CRDW increases significantly only during the larval stages, culminating in a 4 mg increase during the last day of the third larval instar. (ii) The haematin content of the flies indicates that females feed at approximately 3-day intervals and may feed on any day of the pregnancy cycle. (iii) The estimated time of feeding during the day corresponds with the observed time of peak activity, both of which are earlier in the day later in the pregnancy cycle. (iv) The rate of fat usage reveals significantly greater flight activity on day 5 of the cycle than on other days, agreeing with the high trappability on this day, and overall females appear to use fat at twice the rate of males. Reproductive data provide a much more accurate picture of the relative sampling efficiency than do nutritional data, although the latter reveal the general trends correctly.

Animals↗
PubMed1991

Mycotoxins in food.

The presence of mycotoxins in a wide range of foodstuffs can lead to many different toxic conditions in both man and domestic animals. The major fungi responsible for producing these toxins are species of Aspergillus, Penicillium, Fusarium and Alternaria, although other genera are involved as well, for example Claviceps, Diplodia and Arthrinium. An overview is given of the major mycotoxins responsible for illnesses following ingestion of contaminated foods, with particular emphasis on the effects produced in humans. Compounds discussed include the aflatoxins, cyclopiazonic acid, tenuazonic acid, the trichothecenes, zearalenone, wortmannin, fumonisins B1 and B2, patulin, ochratoxin A, diplodiatoxin and diplosporin.

Aflatoxins↗