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Biomedical subjects

R M Anderson

Publications and source records attributed to R M Anderson.

At least 109 records · Page 6Linked to original sources
PubMed1997

Heterogeneities in the transmission of infectious agents: implications for the design of control programs.

From an analysis of the distributions of measures of transmission rates among hosts, we identify an empirical relationship suggesting that, typically, 20% of the host population contributes at least 80% of the net transmission potential, as measured by the basic reproduction number, R0. This is an example of a statistical pattern known as the 20/80 rule. The rule applies to a variety of disease systems, including vector-borne parasites and sexually transmitted pathogens. The rule implies that control programs targeted at the "core" 20% group are potentially highly effective and, conversely, that programs that fail to reach all of this group will be much less effective than expected in reducing levels of infection in the population as a whole.

Animals↗
PubMed1997

Epidemic thresholds and vaccination in a lattice model of disease spread.

We use a lattice-based epidemic model to study the spatial and temporal rates of disease spread in a spatially distributed host population. The prevalence of the disease in the population is studied as well as the spread of infection about a point source of infection. In particular, two distinct critical population densities are identified. The first relates to the minimum population density for a epidemic to occur, whilst the second is the minimum population density for long-term persistence to occur. Vaccination regimes are introduced that are used to measure the impact of spatially and nonspatially dependent intervention strategies. Specifically we show how a ring of vaccinated susceptibles, of sufficient thickness, can halt the spread of infection across space.

Animals↗
PubMed1997

The kinetics of immunological responses to microfilariae in a murine host: experimental and mathematical studies.

We present a mathematical model which is used to interpret the dynamics of the immunological response of a mouse host to infection with the filarial worm Onchocerca lienalis. The model mimics changes in worm burden over time post-infection and after reinfection and its behaviour provides a good description of experimental results. Measured production of T-cells and eosinophils is also compared with the predictions of the model. Our results show that the immune response mechanism proposed on the basis of experimental results, involving CD4+ T-cells and eosinophil destruction of the parasite, is supported by the insights gained from the mathematical model. Also, using the parameters estimated to describe the primary infection dynamics, the degree of acquired immunity to secondary infection is also well described by the model. Our analysis highlights the importance of obtaining quantitative measures of the many rate parameters involved in even the simplest interpretations of immunological responses to parasitic infection.

Animals↗
PubMed1997

Recent upturn in mortality in rural Zimbabwe: evidence for an early demographic impact of HIV-1 infection?

OBJECTIVES: To describe recent mortality trends in rural Zimbabwe and to assess the impact of HIV-1 infection. METHOD: Comparative, cross-sectional, retrospective, demographic survey with 1-year follow-up. Parallel HIV-1 surveillance. Comparison of results with 1992 national census and vital registration data and results from mathematical model-based population projections. SETTING AND PARTICIPANTS: Residents of 929 (745 revisited in 1995) households in two rural areas of Manicaland Province, Zimbabwe, with contrasting HIV-1 prevalence: Honde and Rusitu valleys. Subjects gave information on parental survival for 2320 resident children. Female residents aged 13-49 years (n = 1237) provided information on birth histories and child survival. Consenting women attending local antenatal clinics (n = 487) provided blood samples for HIV-1 screening and demographic information. MAIN OUTCOME MEASURES: HIV-1 prevalence in pregnant women; per capita death registration rates; incidence of parental death for children aged under 8 years; infant mortality and age-specific death probabilities. RESULTS: HIV-1 prevalence was high in each study area. Death registration and age-specific mortality have begun to rise. The largest increases were seen in the area of higher HIV-1 prevalence (Honde) and among younger adults, particularly men. Incidence of parental death was observed to be rising. Increases in registered deaths were concentrated among HIV-1-associated causes. CONCLUSIONS: The observed increases in mortality by age, sex and cause of death were consistent with those expected early in a severe HIV-1 epidemic, on the basis of mathematical model projections and observations elsewhere in Africa. Further rises in mortality, particularly among women and young children, and consequent increases in orphanhood, are to be expected in rural areas of Zimbabwe.

Adolescent↗
PubMed1997

The natural history of syphilis. Implications for the transmission dynamics and control of infection.

BACKGROUND: Syphilis remains a significant cause of morbidity in many developing countries and in some areas within North America and Europe. Mathematical models of the transmission dynamics of sexually transmitted infections have provided insights of relevance both to the interpretation of observed epidemiological patterns and to the design of control programs. Their use for the study of syphilis has been limited to date. GOALS AND STUDY DESIGN: The authors investigated the transmission dynamics of syphilis against a template based on the natural history of infection in individual patients with the aim of (1) identifying gaps in our understanding of the biology of infection, and (2) providing insights of relevance to the design of control policies. RESULTS: Analyses reveal that Treponema pallidum has a moderate to high probability of transmission during contact between susceptible and infectious sexual partners. This, combined with questions over the existence of any immunity to reinfection, helps to ensure the long-term persistence of syphilis within "core" activity groups. Patterns of treatment in North America are shown to have significantly altered the relative frequency of individuals in the different stages of disease. CONCLUSIONS: The analyses emphasize the benefits to be gained from treating infected people early in the primary stage of infection to reduce the effective period during which infected people can transmit to others. This form of treatment is beneficial for both the individual and the community. Treatment has greatly altered the incidence of different disease stages, but the full implications of treatment depend on whether immunity is present.

Contact Tracing↗
PubMed1997

A comparison of global versus disease-specific quality-of-life measures in patients with NIDDM.

OBJECTIVE: This study was conducted to compare the Short Form 36 (SF-36) (a global measure of health-related quality of life) and the Diabetes Care Profile (DCP) (a diabetes-specific measure of self-care and diabetes-related quality of life) in patients with NIDDM. RESEARCH DESIGN AND METHODS: This study was conducted as part of a larger study initiated in 1991 using a randomly selected sample of communities, physicians, and patients with diabetes located throughout Michigan. A total of 255 patients with NIDDM participated. The study examined the relationship between the two measures and diabetes variables, such as glycosylated hemoglobin level and number of complications. RESULTS: The SF-36 and the DCP have both common and discrete measurement domains. Both instruments have acceptable subscale reliability. The DCP has predictive validity regarding glycemic control, whereas the SF-36 does not. Both measures correlate with the number of complications for patients who have NIDDM treated with insulin. CONCLUSIONS: This study suggests that for examining relationships within diabetes, e.g., the impact of acute complications and/or regimen on quality of life, the DCP is the appropriate measure. Conversely, when examining relationships between the patient's experience of living with diabetes and quality of life and other chronic diseases, the SF-36 would be an appropriate measure. Both instruments can be used to illuminate the experience and behavior of patients living with and caring for NIDDM.

Adult↗
PubMed1997

Comparison of laboratory test frequency and test results between African-Americans and Caucasians with diabetes: opportunity for improvement. Findings from a large urban health maintenance organization.

OBJECTIVE: To compare African-American and Caucasian patients with preexisting diabetes in a health maintenance organization (HMO) on: 1) frequency with which they received a subset of recommended laboratory tests according to the American Diabetes Association (ADA) consensus guidelines and 2) the results of laboratory test values (glycosylated hemoglobin, cholesterol, and creatinine). RESEARCH DESIGN AND METHODS: A cross-sectional study of 2,312 HMO members with diabetes continuously enrolled during 1991 was conducted using computerized medical record and billing data. Receipt of the ADA recommended tests for glycosylated hemoglobin, cholesterol, and creatinine was compared between African-Americans and Caucasians, stratified by insulin requirements. In addition, group comparisons were made based on the laboratory test results. RESULTS: Less than 20 percent of all subjects received the recommended number of ADA tests. This did not differ by race except for creatinine and cholesterol testing in insulin users only, where African-Americans had more tests. On average, after adjusting for covariates, African-Americans had significantly higher glycosylated hemoglobin and creatinine laboratory values. Both groups had elevated cholesterol values. CONCLUSIONS: The opportunity exists to improve the process of care for both African-Americans and Caucasians with diabetes in an HMO setting. The need to improve glycosylated hemoglobin results and subsequently limit complications is especially pressing among the African-American population.

Black or African American↗
PubMed1997

The effects of temperature, light and water upon the hatching of the ova of Schistosoma japonicum.

Eggs of Schistosoma japonicum were obtained from infected patients' feces from Yujiang City, China to observe the effects of temperature, light and water on the hatching of eggs. The temperature of water and light played important roles on the hatching of S. japonicum, but the type of water did not. A constant temperature of 28 degrees C and electrical light produced the highest rate of hatching, and reproducible results, whereas a temperature of 4 degrees C or 37 degrees C, and the absence of light inhabited the hatching of eggs. The percentage of eggs hatched during the first 8 hours of 24 hours incubation was 94.90%, so that using the hatching rate of the first 8 hours could approximate the total hatching rate of samples.

Animals↗
PubMed1996

A scaling analysis of measles epidemics in a small population.

We present a detailed analysis of the pattern of measles outbreaks in the small isolated community of the Faroe Islands. Measles outbreaks in this population are characterized by frequent fade-out of infection resulting in long intervals when the disease is absent from the islands. Using an analysis of the distribution of epidemic sizes and epidemic durations we propose that the dynamical structure observed in the measles case returns reflects the existence of an underlying scaling mechanism. Consequently the dynamics are not as purely stochastic as is usually thought for epidemiological systems of this sort. We use a lattice-based epidemic model to provide a theoretical estimate of the scaling exponents and show that a conventional compartmental SEIR model is unable to reproduce this result. The methods discussed in this paper are general and represent a novel way to consider the dynamics of any other communicable disease where there is frequent fade-out in the case returns.

Denmark↗
PubMed1996

Low-efficacy HIV vaccines: potential for community-based intervention programmes.

To combat the spread of HIV, progress on vaccine development is eagerly awaited. Haynes in this series has described the progress made so far with various vaccine types. This article describes how mathematical modelling techniques can be used to predict the likely impact of low-efficacy vaccines in community transmission of the virus. The answers are often not what one would predict by intuition alone, and they have great bearing on the likely success of such vaccination strategies.

AIDS Vaccines↗
PubMed1996

Transmission dynamics and epidemiology of BSE in British cattle.

A comprehensive analysis of the bovine spongiform encephalopathy (BSE) epidemic in cattle in Great Britain assesses past, present and future patterns in the incidence of infection and disease, and allows a critical appraisal of different culling policies for eradication of the disease.

Age Factors↗
PubMed1996

Mass vaccination to control chickenpox: the influence of zoster.

The impact of transmission events from patients with shingles (zoster) on the epidemiology of varicella is examined before and after the introduction of mass immunization by using a stochastic mathematical model of transmission dynamics. Reactivation of the virus is shown to damp stochastic fluctuations and move the dynamics toward simple annual oscillations. The force of infection due to zoster cases is estimated by comparison of simulated and observed incidence time series. The presence of infectious zoster cases reduces the tendency for mass immunization to increase varicella incidence at older ages when disease severity is typically greater.

Adolescent↗
PubMed1996

Viral dynamics in vivo: limitations on estimates of intracellular delay and virus decay.

Anti-viral drug treatment of human immunodeficiency virus type I (HIV-1) and hepatitis B virus (HBV) infections causes rapid reduction in plasma virus load. Viral decline occurs in several phases and provides information on important kinetic constants of virus replication in vivo and pharmacodynamical properties. We develop a mathematical model that takes into account the intracellular phase of the viral life-cycle, defined as the time between infection of a cell and production of new virus particles. We derive analytic solutions for the dynamics following treatment with reverse transcriptase inhibitors, protease inhibitors, or a combination of both. For HIV-1, our results show that the phase of rapid decay in plasma virus (days 2-7) allows precise estimates for the turnover rate of productively infected cells. The initial quasi-stationary phase (days 0-1) and the transition phase (days 1-2) are explained by the combined effects of pharmacological and intracellular delays, the clearance of free virus particles, and the decay of infected cells. Reliable estimates of the first three quantities are not possible from data on virus load only; such estimates require additional measurements. In contrast with HIV-1, for HBV our model predicts that frequent early sampling of plasma virus will lead to reliable estimates of the free virus half-life and the pharmacological properties of the administered drug. On the other hand, for HBV the half-life of infected cells cannot be estimated from plasma virus decay.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Power laws governing epidemics in isolated populations.

Temporal changes in the incidence of measles virus infection within large urban communities in the developed world have been the focus of much discussion in the context of the identification and analysis of nonlinear and chaotic patterns in biological time series. In contrast, the measles records for small isolated island populations are highly irregular, because of frequent fade-outs of infection, and traditional analysis does not yield useful insight. Here we use measurements of the distribution of epidemic sizes and duration to show that regularities in the dynamics of such systems do become apparent. Specifically, these biological systems are characterized by well-defined power laws in a manner reminiscent of other nonlinear, spatially extended dynamical systems in the physical sciences. We further show that the observed power-law exponents are well described by a simple lattice-based model which reflects the social interaction between individual hosts.

Denmark↗