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Biomedical subjects

R M Anderson

Publications and source records attributed to R M Anderson.

At least 19 recordsLinked to original sources
PubMed1992

Age-dependent choice of sexual partners and the transmission dynamics of HIV in Sub-Saharan Africa.

A mathematical model of the transmission of HIV-1 within heterosexual populations in Sub-Saharan Africa is described and its properties analysed. The model incorporates epidemiological and demographic processes and extends previous work in this area via the inclusion of age and sex dependency in rates of sexual partner change, and sexual partner choice dependent on age. Parameter assignments are made on the basis of current data on the transmission dynamics of HIV-1 and the demography of human populations in Africa. Both age-dependent rates of sexual activity and the sexual contact of males with females younger than themselves act to enhance the predicted demographic impact. With realistic parameter values, the model suggests AIDS is able to reverse the sign of population growth rates from positive to negative values over a timescale of a few decades. The sensitivity of this prediction is examined in relation to changes in the pattern of sexual contact between different age classes of females and males, different patterns of change in the age-dependent rate of sexual partner change, different assumptions concerning the doubling time of the epidemic in its early stages, and the relative efficiencies of viral transmission between men and women, and vice versa. The impact AIDS is predicted to have on the number of young and elderly persons as a fraction of the number of productive adults (the dependancy ratio) is examined under various assumptions concerning the weighting to be applied to mirror the burden imposed by the care of those with AIDS. The paper includes an assessment of the influence of the timing of changes in sexual behaviour, or the promotion of the use of condoms, on the predicted course of the epidemic. The paper concludes with a discussion of data needs and the model refinements required to more accurately mirror current understanding of the epidemiology of HIV-1.

Acquired Immunodeficiency Syndrome↗
PubMed1992

The regulation of immunological responses to parasitic infections and the development of tolerance.

It is well established that specific unresponsiveness to immunization can be induced by prolonged exposure to antigenic proteins. More generally, many parasitic infections, such as the helminth worms and the Leishmania parasites, appear to be able to persist in some of their human hosts over long periods of time, via what appears to be an ability to induce defective or inappropriate T-cell responses (= tolerance). Recent research has suggested that cytokines, produced by specific subsets of CD4+ T-cells (characterized by cytokine secretory profiles and growth properties), have an important, and often complex, role in promoting or inhibiting host protective immunity to parasitic infections. By examination of the population dynamics of the stimulation and regulation of cellular responses to infection, via the use of simple mathematical models, we show that nonlinear interactions between CD4+ T-cell subsets and their secreted cytokines can result in either host protection or immunological unresponsiveness, depending on the magnitude and duration of exposure to parasitic infection. Analyses also identify a possible mechanism to explain the stimulation of two separate peaks of enhanced T-cell-mediated responses over a wide range of levels of antigenic exposure.

Animals↗
PubMed1992

The concept of herd immunity and the design of community-based immunization programmes.

The paper focuses on the concepts of transmission success and herd immunity and their relevance to the design of community-based immunization programmes for the control of infectious diseases. Recent work in a number of areas is reviewed, including the influence of mass vaccination on the average age of infection and the incidence of morbidity due to infection and vaccination, the age window of susceptibility and the problems of vaccine programme design in developing countries, the interaction between vaccine efficacy and vaccine safety and the design of vaccination programmes for the control of sexually transmitted infections. Discussions centre on the interplay between an understanding of the transmission dynamics of an infection and the design of community-based control programmes.

Adolescent↗
PubMed1992

Some aspects of sexual behaviour and the potential demographic impact of AIDS in developing countries.

This review examines recent research on the influence of heterogeneity in sexual behaviour on the transmission dynamics of the human immunodeficiency virus (HIV), the aetiological agent of AIDS. Attention is focused on the potential demographic impact of AIDS in developing countries and how this is influenced by the structure of networks of sexual contacts (who mixes with whom), age-dependency in rates of sexual partner change and differences in the ages of female and male sexual partners. Analyses based on the construction of simple and complex mathematical models of the spread of HIV via heterosexual contact serve as a template for the interpretation of observed pattern and as a guide to the major aspects of sexual behaviour that govern the transmission dynamics of the virus. It is argued that much greater attention must be addressed to the quantification of patterns of sexual behaviour in defined communities, despite the many practical problems that surround data collection and interpretation.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Dynamic interaction between CD4+ T cells and parasitic helminths: mathematical models of heterogeneity in outcome.

Potential mechanisms of immunoregulation have been investigated for the capacity to generate heterogeneity in the outcome of infection with helminth parasites. We have developed a mathematical model of the interaction between T cell and parasite populations, based on the assumption that activation of a Th1 CD4+ T cell response is required for host resistance. Antigen dose-dependent inhibition of Th1 cell proliferation generates heterogeneity in the outcome of host response to infection, with relatively low levels of exposure inducing resistance, and high levels of exposure associated with host susceptibility. Heterogeneity is additionally predicted in the duration of infection before individuals of the resistant class clear infection, with infection becoming more prolonged as the level of exposure rises. Similar categories of response are predicted if an alternative regulatory mechanism, that of interferon gamma-regulated control of Th1 cell differentiation, is substituted into the model. However, the relationship between level of exposure and duration of infection is reversed. Results are discussed in the context of how these simple models of parasite-immune system interactions might be used to make predictions concerning specific examples of parasitic infection.

Animals↗
PubMed1992

Gonococcal infection, infertility, and population growth: I. Endemic states in behaviourally homogeneous growing populations.

Sexually transmitted diseases such as gonorrhoea are a significant cause of infertility in women when the infection is untreated. They have the potential to alter human population growth rates in many developing countries where sexually transmitted diseases are prevalent due to limited public health facilities for diagnosis and treatment. The authors develop a simple model describing the conditions under which such a disease can exist in a growing population in which sexual partners are chosen at random by proportionate mixing. Using the model, the impact that such a disease could have for a range of possible parameters is examined. Then a full parameter set for gonorrhoea in a developing country is estimated. Analysis demonstrates the significant influence gonococcal infection may have in reducing population growth rate in some communities. For example, the simple model predicts that a prevalence of 20% in sexually active adults results in a 50% reduction in the population growth rate. Finally, the authors discuss how potential control initiatives may change the parameter values that determine transmission and alter the demographic impact of gonorrhoea.

Africa↗
PubMed1992

Gonococcal infection, infertility, and population growth: II. The influence of heterogeneity in sexual behaviour.

Heterogeneity in sexual behaviour has an important influence on the transmission dynamics of sexually transmitted diseases (STDs). The authors describe the development of a simple mathematical model, incorporating such heterogeneity, to investigate the demographic impact of gonorrhoea on human population growth in developing countries where the disease is endemic. Earlier predictions, based on a model with homogeneous mixing, are shown to be in good qualitative agreement with the predictions of a more complex mathematical framework in which the population is stratified both by sex and into two subgroups representing low and high sexual activity, defined on the basis of rates of sexual partner change. Analyses also demonstrate that the pattern of mixing (assortative to random) between the sexual activity classes has an important influence on the predicted prevalence of gonococcal infection in a defined community. The more complex model supports earlier conclusions that gonorrhoea, via its impact on fertility, can significantly reduce net population growth rates.

Adolescent↗
PubMed1992

Effects of expert and non-expert facilitators on the small-group process and on student performance.

At the University of Michigan Medical School in 1990, the authors investigated the effects of faculty facilitators' levels of content expertise on the educational process and learning outcomes of small-group teaching sessions. The study was conducted in a microbiology course for second-year students in which four small-group sessions were used to replace 38 hours of lecture and laboratory time. The interactions between 11 expert and ten non-expert faculty facilitators and 156 students were observed and coded. The students' levels of knowledge and satisfaction were measured. The results indicate that, although significant differences in faculty-student interactions were not observed, the students in the 11 groups led by the content experts had higher levels of satisfaction and higher examination scores.

Attitude↗
PubMed1992

Controversial beliefs about diabetes and its care.

OBJECTIVE: The purpose of this study was to identify specific beliefs that differentiate health-care professionals whose attitudes toward diabetes agreed most strongly with a group of national diabetes experts from those whose attitudes disagreed most strongly. RESEARCH DESIGN AND METHODS: The sample for this study included 271 physicians, 834 nurses, and 546 dietitians who completed a Diabetes Attitudes Survey. The sample included specialists in diabetes care and nonspecialists. Controversial beliefs about diabetes and its care were determined by comparing the beliefs of the 10% of the sample whose attitudes were most concordant (with the national panel) with the beliefs of the 10% of the sample whose attitudes were the most discordant. Ten beliefs met the criteria for being defined as controversial. RESULTS: The most controversial beliefs concerned whether the patient or the physician should be the primary decision maker in diabetes care, the meaning of patient noncompliance, and the seriousness of non-insulin-dependent diabetes mellitus. The 10% of the sample with the most discordant attitudes contained a disproportionately large number of physicians, nonspecialists in diabetes, and health-care professionals who had been in practice longer than the other members of the sample. CONCLUSIONS: This study identifies some important differences in beliefs between younger health-care professionals who specialize in diabetes and older nonspecialists. Such beliefs should be addressed in continuing education programs with the aim being to foster the widespread adoption of a contemporary approach to diabetes care.

Attitude of Health Personnel↗
PubMed1992

The cervical spine in fatal motor vehicle accidents.

Of 100 fatal accident cases involving motor vehicles, 60 showed damage to the cervical spine, involving bony or disc damage in 31 and focal haemorrhages in another 29. In 8 cases, pre-autopsy radiology failed to detect lesions which were found by radiology and pathological examination of the post-autopsy specimen. Most of the lesions missed were at the C6-7 region. In some cases, the initial pathological examination 'missed' laterally placed fractures and small chip fractures. Narrow cervical canals in the elderly indicated advanced spondylosis.

Accidents, Traffic↗
PubMed1992

Laboratory outbreak of Q fever.

An outbreak of Q fever in a university department where sheep placentas were being used for research is described. Of six persons exposed to the sheep, four had positive titers with only one person developing an acute febrile illness and liver disease. This report illustrates the value of the family physician obtaining an occupational history and conducting an outbreak investigation.

Adult↗
PubMed1992

Preliminary studies of sexual networks in a male homosexual community in Iceland.

In this article, we present the preliminary results of a study on sexual networks in a homosexual community in Iceland. The network data are transformed into a mixing matrix, which suggests that the pattern of sexual contact within the community is disassortative (i.e., sexual contacts occur largely between individuals of disparate sexual activity levels). The implications for the spread of human immunodeficiency virus (HIV) in the community are assessed by comparison with epidemics generated by proportionate and assortative (like with like) mixing, using a mathematical model of HIV transmission. The potential magnitude of the epidemic associated with the data is shown to be larger than both proportionate and assortative alternatives, although the early rate of growth is lower for the mixing matrix implied by the data. The assumptions made concerning behavioural changes triggered by alterations in population structure as a consequence of AIDS-induced mortality do not significantly alter the shape of the predicted epidemic. The problems in data acquisition and interpretation are discussed.

Adult↗
PubMed1991

Vaccine safety versus vaccine efficacy in mass immunisation programmes.

In community-wide immunisation programmes against childhood infections there is a conflict between the interests of the individual (vaccine safety and efficacy) and the interests of the community (vaccine uptake and level of herd immunity). Studies suggesting that the complication rate is greater with the high efficacy Urabe Am 9 mumps vaccine than with the lower efficacy Jeryl Lynn vaccine, have led to concern about whether the higher efficacy mumps vaccine should be introduced or retained in nationwide mass immunisation programmes. We describe the use of a mathematical model to assess benefits and risks to both individual and community, and illustrate this method by reference to immunisation programmes based on these vaccines. On the basis of current epidemiological data on viral transmission and vaccine coverage in England and Wales, data on vaccine-associated and infection-associated complication rates, and vaccine efficacies estimated from clinical trials, our analyses suggest there is little to choose between the two vaccines, but that overall performance depends on the level of vaccine coverage in a defined population. In community-based programmes, the greater apparent safety of the Jeryl Lynn vaccine (fewer vaccine-induced complications) is offset by the greater apparent efficacy of the Urabe Am 9 vaccine (fewer complications due to natural infection). The findings suggest that it may not always be in the interests of the community to use the vaccine with the lowest complication rate.

Age Factors↗