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Biomedical subjects

D J Rogers

Publications and source records attributed to D J Rogers.

At least 73 records · Page 4Linked to original sources
PubMed1990

Estimation of rates of predation on tsetse.

The levels of natural predation of puparial and adult tsetse flies, Glossina pallidipes Austen, were investigated at Nguruman, Kenya, during January 1989. Puparial experiments involved the production, by individually tubed female flies, of naturally deposited, unhandled puparia in soil cores; handled puparia were obtained from groups of caged flies kept in the normal way. Equal numbers of handled and unhandled puparia were planted out at different densities (1, 2, 4 or 8 per linear metre) in fifty-one natural puparial sites in four major vegetation types. After 10 days puparia were recovered using a soil corer and sieving system. Average predation rates (adjusted for the displacement of puparia by vertebrate activity at the puparial sites) were 9.4% and 7.8% for the two types of puparia during the experiment, equivalent to an average loss of 23.7% of all puparia during a normal 30-day developmental period. Maximum potential predation rates of adult flies were investigated by pinning freshly killed adults at densities of 1, 2, 4 or 8 per m3 to natural vegetation and scoring the results after 24 h. 70% of flies were attacked during this time, by a variety of predators, thought to include both vertebrates and invertebrates. No density dependence was detected in the experiments, either because natural puparial densities were too low for it to occur at this stage of the life cycle or because adult predation levels were too high for it to be detected. Present results are compared and contrasted with previous results for this and another species of tsetse. Calculations of the life-time fertilities of female tsetse suggest that the levels of puparial predation revealed by the present experiments are entirely realistic. Behaviour of the adult flies allows them to escape most of the considerable predation pressure under which they live. How they do so remains a mystery.

Animals↗
PubMed1990

X-ray film digestion: a semi-quantitative assay for proteolytic enzymes used in immunohaematology.

A simple semi-quantitative assay method for proteolytic enzyme solutions used in blood group serology is described. The method is an adaptation of a technique formerly used for assay of faecal trypsin and is based on the digestion of the gelatin coating of unexposed X-ray film. A Spearman rank correlation coefficient of 0.8 was obtained when the X-ray film technique was compared with a spectrophotometric method using azoalbumin as substrate. The method is not suitable as a reference technique or as a substitute for serological control, but is useful for monitoring or comparing enzyme preparations in some circumstances or situations.

Blood Grouping and Crossmatching↗
PubMed1989

Effect of host odours on trap catch composition of Glossina pallidipes in Kenya.

The effect of odour attractants on the composition of samples of Glossina pallidipes Austen was investigated by comparing the age and nutritional status of flies caught in unbaited biconical traps with those caught in traps baited with cow urine and acetone. For both male and female flies, baited traps caught more flies with significantly higher fat content than did unbaited traps. Thus the samples from baited traps were more representative of the population as a whole: males showed a fuller range of the fat/haematin conditions known to occur in the field and proportionately more females were in later stages of the pregnancy cycle, than from unbaited traps.

Animals↗
PubMed1989

The development of analytical models for human trypanosomiasis.

The idea of biological equilibria is presented and applied first to the case of single species populations. Difference and differential descriptions of population changes over time are compared and contrasted. The complications that arise when describing interactions between species are then illustrated for the case of vector-borne diseases, such as malaria. A simple model for malaria is explored and later extended to the case of the African trypanosomiases where more than one vertebrate host species is involved. Appropriate parameter values obtained from the literature are listed, and equilibrium predictions given. These predictions broadly coincide with field experience. A brief description of the analysis of age-prevalence data is given and applied to several sets of data from sites in West, Central and East Africa. In each case the force of infection is extremely low, indicating that a non-human reservoir must be involved in the maintenance of the disease throughout Africa. A final plea is made to integrate the modelling exercise into on-going programmes for disease control or eradication.

Africa↗
PubMed1988

The dynamics of vector-transmitted diseases in human communities.

The development of vector-transmitted disease models and their application to field studies is reviewed. The key concepts of the basic rate of reproduction and disease transmission threshold are explained, and their application to disease control briefly illustrated. The complications involved in producing appropriate models are discussed for the case of the trypanosomatid parasites Leishmania and Trypanosoma that frequently have more than one vertebrate host and are often fatal in the human host. A two-species, vector-borne disease model allows a quantification of the role of animal reservoirs in maintaining human diseases. Human prevalence may be determined more by the parasitological characteristics of wild reservoir species, about which little is generally known, than by any other single feature of the complex interaction between parasites, vectors and hosts. Domestic animals are often ideal reservoirs, maintaining large numbers of vectors and considerably enlarging the parasite pool. When vector-transmitted diseases are fatal to the human host, human and vector dynamics interact in ways which may cause epidemic cycles, low-level endemic equilibria or disease extinction. For both leishmaniasis and trypanosomiasis it is suggested that a very small number of chronic human cases can maintain the disease in the human population over long periods of time between epidemic outbreaks. They may also be important in the maintenance of geographically distinct foci, characteristic of human trypanosomiasis in Africa. Finally there is a plea to establish a tradition of field observation leading to, and being directed by, mathematical models which in turn are modified as the observations accumulate. All too often, one-way traffic between the two results in slow, or misguided, progress.

Animals↗
PubMed1988

A general model for the African trypanosomiases.

A general mathematical model of a vector-borne disease involving two vertebrate host species and one insect vector species is described. The model is easily extended to other situations involving more than two hosts and one vector species. The model, which was developed from the single-host model for malaria described by Aron & May (1982), is applied to the African trypanosomiases and allows for incubation and immune periods in the two host species and for variable efficiency of transmission of different trypanosome species from the vertebrates to the vectors and vice versa. Equations are derived for equilibrium disease prevalence in each of the species involved. Model predictions are examined by 3-dimensional phase-plane analysis, which is presented as a simple extension of the 2-dimensional phase-plane analysis of the malaria model. Parameter values appropriate for the African trypanosomiases are derived from the literature, and a typical West African village situation is considered, with 300 humans, 50 domestic animals and an average population of 5000 tsetse flies. The model predicts equilibrium prevalences of Trypanosoma vivax, T. congolense and T. brucei of 47.0, 45.8 and 28.7% respectively in the animal hosts, 24.2, 3.4 and 0.15% in the tsetse vectors, and a 7.0% infection of humans with human-infective T. brucei. The contribution to the basic rate of reproduction of the human-infective T. brucei is only 0.11 from the human hosts and 2.54 from the animal hosts, indicating that in the situation modelled human sleeping sickness cannot be maintained in the human hosts alone. The animal reservoir is therefore crucial in determining not only the continued occurrence of the disease in humans, but its prevalence in these hosts as well. The effect of changing average fly density on equilibrium disease prevalences is examined, together with the effect of seasonal changes in fly numbers on disease incidence. In a seasonal situation changes in fly mortality rates affect both future population size and infection rate. Peak disease incidence lags behind peak fly numbers, and that in the less favoured host lags behind that in the more favoured host. Near the threshold fly density for disease transmission disease incidence is more changeable than at higher fly densities and may even exceed equilibrium prevalence at the same average fly density (because most hosts are susceptible at the time that fly numbers begin their annual increase).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Thyrotropin-releasing hormone and cyclo (His-Pro)-like immunoreactivities in the cerebrospinal fluids of 'normal' infants and adults, and patients with various neuropsychiatric and neurologic disorders.

Levels of thyrotropin-releasing hormone (TRH) - and cyclo(His-Pro) (CHP)-like immunoreactivities and the activity of enzyme Pyroglutamate aminopeptidase (PAPase) were measured in cerebrospinal fluid (CSF) of over 100 normal adults (NA) and infants, and adult patients with various neurologic and neuropsychiatric disorders (NNDA). Levels of TRH and CHP in CSF of over 70% of the NA group were below 50 and 500 pg/ml respectively. The TRH- and CHP-like immunoreactivities in the remainder of the 30% of NA specimens exhibiting higher peptide concentrations were enzymatically and chromatographically characterized and were found to behave like authentic peptides. The levels of both of these peptides were significantly elevated in the CSF of most of the NNDA patients. An elevation in the CSF level of CHP was significantly correlated with the level of TRH, but not PAPase. Results from this study suggest that CSF elevation of TRH level may be due to a nonspecific response to stress that may be associated with hospitalization, myelogram procedure, and/or the neurologic and neuropsychiatric diseases for which the patients were admitted.

Adult↗
PubMed1986

On the mechanism of fasting-associated elevations in hypothalamic cyclo(His-Pro) content.

Potential mechanism(s) underlying the fasting-associated rise in hypothalamic cyclo(His-Pro) content was explored by examining the effects of 24-hour fasting on: (i) cyclo(His-Pro) synthesis from TRH, (ii) cyclo(His-Pro) metabolism, and (iii) cyclo (His-Pro) secretion by hypothalamic tissue in vitro. The data presented here show that none of these three variables were altered due to fasting. Two additional potential changes that could cause cyclo(His-Pro) elevations during fasting are suggested. These include an in vivo decrease in hypothalamic cyclo(His-Pro) secretion that may not be apparent in vitro, and/or an increase in the synthesis of cyclo(His-Pro) from a precursor(s) other than TRH.

Aminopeptidases↗
PubMed1985

Trypanosomiasis 'risk' or 'challenge': a review.

Definitions of the term 'challenge' as applied to the African trypanosomiases are reviewed. Data from one West and one East African site show simple linear relationships between the incidence of trypanosomiasis in both humans and animals, and either the amount of man-tsetse contact, or the Apparent Density of flies. Data from a number of East African sites are analysed and show a linear relationship between the mean Berenil Index of cattle and the logarithm of the challenge, where challenge is the simple product of Apparent Density and mean fly infection rate. Apparent Density is a more variable element of total challenge than is infection rate. The results of field studies are analysed to show that Berenil has a short prophylactic effect, lasting for about 22 days in cattle. When allowance is made for this effect there is a direct, apparently linear relationship between the daily probability of infection of cattle and total challenge, the latter varying over almost three orders of magnitude. Variations in tsetse fly density account for about 50% of the variability of Apparent Density. Hence the latter is a crude estimate of the former. Seasonal and density-related changes in the availability of flies to human catchers could account for the inadequacies of the fly-round technique in assessing fly density and/or challenge. Evidence at present available suggests that trypanotolerant cattle are more likely to be an economic alternative to drug-treated zebu at higher rather than lower challenge levels. Whether either type of animal could profitably be raised in areas of the highest challenge and without some form of tsetse control remains an open question.

Africa, Eastern↗