Mathematical and statistical studies of the epidemiology of HIV.
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Acquired Immunodeficiency Syndrome↗
Biomedical subjects
R M Anderson
Publications and source records attributed to R M Anderson.
The antibody recognition profiles of humans naturally infected with Ascaris lumbricoides.
A semi-quantitative analysis of individual human antibody responses to larval Ascaris excretory and secretory (ES) antigens using radioimmunoprecipitation and SDS-PAGE is presented. A significant relationship was observed between the intensity of antibody-precipitated radiolabelled ES antigens and host age. The antibody response profile followed a similar age-related pattern to that of intensity of infection, with blood samples from 5-9-year-old children showing the strongest banding patterns and the heaviest infections. These findings support the hypothesis that the degree of exposure to infective stages of Ascaris is a major determinant of the convex age-intensity profile observed in the community. Considerable heterogeneity was observed in the antibody profiles of individuals, particularly in the recognition of a 14 kD molecule. Positive correlations were observed between the strength of banding at several mol. wts and the worm burdens of individuals. However, the sample size was too small to determine whether these relationships simply reflect age-related profiles or represent independent associations between antibody levels and worm burden. When the data were stratified by age, negative associations between the strength of recognition of some bands and the intensity of infection were suggested and require further study.
Adolescent↗
The influence of different sexual-contact patterns between age classes on the predicted demographic impact of AIDS in developing countries.
A model is developed to describe the spread of HIV within heterosexual communities and the demographic impact of AIDS. The model combines epidemiologic and demographic processes and is designed to mirror the impact of AIDS in sub-Saharan Africa. Refinements on past work in this area include unequal probabilities for transmission from females to males and from males to females, the inclusion of an age- and sex-dependent sexual-partner choice function and distributed incubation plus infectious periods. Numerical studies suggest that unequal transmission probabilities (weighted to a greater probability from males to females than vice versa), and the tendency of males to choose sexual partners of the opposite sex younger than themselves, both act to increase the demographic impact of AIDS over that predicted with equal transmission between the sexes and partner choice restricted within given age classes. Analyses support the conclusions of past work that the epidemic will only have a small detrimental impact on the dependency ratio of a population (the ratio of dependents to working adults) even when a weighting is added to take account of the extra burden imposed by the care of adult AIDS patients. However, a small increase in the ratio can imply a significant rise in the number of dependents within the population. Stimulation studies of the impact of changes in behavior to reduce transmission highlight to the need to induce such changes as early as possible in the course of the epidemic in order to minimize its impact. Directions for future research are discussed emphasizing the need to acquire quantitative data on sexual habits and to construct models to represent heterogeneity in sexual behavior.
Acquired Immunodeficiency Syndrome↗
Development of diabetes attitude scale for health-care professionals.
This article describes the development of a diabetes attitude scale (DAS) that was designed to measure the attitudes of health-care professionals (HCPs). The DAS was developed through the efforts of a national panel of diabetes experts. The panel developed a 60-item scale that was pilot tested and reduced to a 50-item scale. The 50-item scale was then mailed to a national sample of HCPs with an interest in diabetes. The surveys were returned by 633 nurses, 322 dietitians, 116 physicians, and 67 others totaling 1138 returns (a return rate of 54%). The returned surveys were analyzed, and a 31-item DAS composed of 8 subscales resulted. Evidence for the reliability and validity of the 31-item DAS along with the instrument itself are included in this study.
Attitude of Health Personnel↗
Rates of sexual partner change among two pastoralist southern Nilotic groups in east Africa.
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Acquired Immunodeficiency Syndrome↗
Networks of sexual contacts: implications for the pattern of spread of HIV.
This paper examines the influence of sexual contact patterns (mixing matrices) on the pattern of the AIDS epidemic in a male homosexual community via numerical studies of a mathematical model of the transmission dynamics of HIV. A discussion is presented of the range of possible structures of networks of sexual contacts with extremes of assortative (within sexual activity groups) and disassortative (between sexual activity groups) mixing. The assortative mixing extreme is shown to generate the most rapid growth in the incidence of infection in the early stages of the epidemic while the disassortative extreme is shown to generate the epidemic of the largest magnitude over a long period. High within-group mixing (assortative) may generate multi-peak epidemics. The results are discussed in the context of both the interpretation of observed patterns of the spread of HIV and the acquisition of data on sexual contact patterns.
Disease Outbreaks↗
Measles, mumps, and rubella vaccine: what coverage to block transmission?
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Age Factors↗
The transmission dynamics of human immunodeficiency virus (HIV).
The paper first reviews data on HIV infections and AIDS disease among homosexual men, heterosexuals, intravenous (IV) drug abusers and children born to infected mothers, in both developed and developing countries. We survey such information as is currently available about the distribution of incubation times that elapse between HIV infection and the appearance of AIDS, about the fraction of those infected with HIV who eventually go on to develop AIDS, about time-dependent patterns of infectiousness and about distributions of rates of acquiring new sexual or needle-sharing partners. With this information, models for the transmission dynamics of HIV are developed, beginning with deliberately oversimplified models and progressing--on the basis of the understanding thus gained--to more complex ones. Where possible, estimates of the model's parameters are derived from the epidemiological data, and predictions are compared with observed trends. We also combine these epidemiological models with demographic considerations to assess the effects that heterosexually-transmitted HIV/AIDS may eventually have on rates of population growth, on age profiles and on associated economic and social indicators, in African and other countries. The degree to which sexual or other habits must change to bring the 'basic reproductive rate', R0, of HIV infections below unity is discussed. We conclude by outlining some research needs, both in the refinement and development of models and in the collection of epidemiological data.
Acquired Immunodeficiency Syndrome↗
Epidemiological parameters of HIV transmission.
Epidemiological data on the main determinants of the transmission potential of HIV-1 in specific at risk groups in slowly accumulating, but many uncertainties remain.
Acquired Immunodeficiency Syndrome↗
The distribution of the incubation period for the acquired immunodeficiency syndrome (AIDS).
This paper contains details of methods and full results of estimates of the incubation period of acquired immunodeficiency syndrome (AIDS) that were outlined in a previous paper by Medley et al. (Nature, Lond. 328, 719 (1987)). The original model is modified to assess the influence of age and sex on the incubation period: age, but not sex, is statistically significant. The difficulties associated with interpretation of these data, and the additional information that would be required to resolve these difficulties are discussed.
Acquired Immunodeficiency Syndrome↗
Possible demographic consequences of AIDS in developing countries.
Simple mathematical models of the transmission dynamics of HIV that incorporate demographic and epidemiological processes to assess the potential impact of AIDS on human population growth and structure in developing countries suggest that AIDS is capable of changing population growth rates from positive to negative values over timescales of a few decades. The disease is predicted to have little if any impact on the dependency ratio of a population, defined as the number of children below age 15 years and elderly people over 64 years, divided by the number of adults between 15 to 64 years.
Acquired Immunodeficiency Syndrome↗
Neuropathology in glutaric acidaemia type 1.
The neuropathology in three cases of glutaric acidaemia type 1 is presented. All three showed extensive neuronal loss in the caudate nucleus and the putamen, with only small numbers of large neurons surviving. The globus pallidus showed moderate shrinkage and gliosis but no conspicuous decreases in neurons. Severe spongiform change was seen in many regions, involving predominantly white matter. These features are very similar to some cases described previously in familial striatal degeneration in childhood, but are different from other cases. If found in a brain at autopsy, they should lead to studies to diagnose glutaric acidaemia type 1 retrospectively, so that accurate genetic counselling and prenatal diagnosis in future pregnancies can be offered.
Child↗
Predisposition of humans to infection with Schistosoma mansoni: evidence from the reinfection of individuals following chemotherapy.
In a study of faecal egg counts of Schistosoma mansoni from 359 people of all ages from a rural Kenyan community, a positive association was demonstrated between infection intensity in individuals before treatment and reinfection intensity in the same individuals 9 months after treatment in certain age groups of the sampled population. Consequences and possible causes of these observations are discussed in terms of the epidemiology and control of schistosomiasis.
Adolescent↗
The neurotoxicity of tunicamycin.
The neurotoxicity of tunicamycin, an inhibitor of glycosylation of glycoproteins and a potential anti-tumour agent, was investigated by injection of the chemical directly into the lateral ventricle of the brain of rats. A delayed neurological syndrome developed due to anoxic necrosis of brain cells and spongy degeneration of the white matter. In many brains the lesion had the characteristic features of an infarct. Since the predominant lesion was vascular, the action of tunicamycin on blood vessels was investigated in vitro using rabbit aortic rings. In this system the normal relaxation response to acetylcholine in aortic rings pre-contracted with noradrenaline was progressively inhibited as exposure of the ring to tunicamycin increased from 2 h to 5 h. This relaxation response depends on the release of endothelium-derived relaxing factor from endothelial cells. Hence it is proposed that the important primary target in tunicamycin neurotoxicity is endothelial cells of the brain microvessels.
Animals↗
An investigation of hookworm infection and reinfection following mass anthelmintic treatment in the south Indian fishing community of Vairavankuppam.
Hookworm infections, as assessed by counting worms expelled following anthelmintic treatment and by egg output, were found to be of low prevalence and intensity in a South Indian fishing community. The initial overall prevalence of infection in the community was 43%, and the average burden was estimated at 2.2 hookworms per person. The age profiles of prevalence and intensity differed between males and females, with the latter harbouring significantly higher levels of infection. Children of both sexes under 10 years of age rarely harboured hookworms. Treatment with pyrantel pamoate was estimated to be 91% effective in clearing hookworm infections. Egg counts made on stools collected during an 11-month period of reinfection indicated that female patients became reinfected soon after treatment, while little hookworm egg excretion was observed in males during the observation period following treatment. Females acquired a significantly higher number of worms during the reinfection period compared with males, although the average burden in females reached only 28% of the initial, pre-treatment level. The hookworm population consisted of predominantly Necator americanus, and less than 10% of Ancylostoma duodenale. The parasites were highly aggregated within the host population with 10% of the community harbouring over 65% of the total hookworms. Low values of the negative binomial aggregation parameter, k, (indicating extreme over-dispersion) were recorded in groups stratified by age and sex. Highly significant positive correlations were observed between the initial (pre-treatment) and reinfection worm burdens of female (but not of male) patients. It is suggested that occupational practices related to walking through areas contaminated with hookworm larvae play an important role in generating the observed patterns of infection within this community.
Adult↗
The importance of host age and sex to patterns of reinfection with Ascaris lumbricoides following mass anthelmintic treatment in a South Indian fishing community.
Analysis of egg and worm counts of Ascaris recorded at various intervals following a mass anthelmintic treatment programme in a South Indian fishing community is presented. Three indices of infection in the community are compared, namely the prevalence and intensity of egg output (at 2, 6 and 11 months following treatment) and the number of worms expelled following an 11 month period of reinfection. Detailed examination of these measurements revealed significant associations with patient sex and age. The age-prevalence profile of Ascaris infection changed little over time (except immediately following treatment) with the peak prevalence found in the 5-9 year age group. Although 85% of both males and females harboured Ascaris initially, the prevalence following 11 months reinfection was decreased, due to a significantly lower proportion of males being reinfected. By the 11th month of reinfection, the age-intensity profiles of egg output were similar to those observed at initial treatment in the older age groups (10 years and above) and in male children (less than 10 years). However, a dramatic increase in the egg output of female children, greatly exceeding the initial mean, was observed within a 6 month period of reinfection. The intensity of egg output did not accurately reflect the abundance of Ascaris recovered via drug-induced expulsion following an 11 month period of reinfection. Although the egg output attained preintervention levels, the average worm intensity reached only half the initial value. The trends in the sex- and age-intensity profiles were consistent at the two sampling dates and showed similar patterns to the egg output curves. The relevance of the results to helminth control and the monitoring of reinfection is discussed.
Adolescent↗
The use of mathematical models in the epidemiological study of infectious diseases and in the design of mass immunization programmes.
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Communicable Diseases↗
Measles in developing countries. Part I. Epidemiological parameters and patterns.
This paper presents a review of published data concerning the epidemiology of measles in developing countries. Simple mathematical models provide a framework for data analysis and interpretation. The analyses highlight differences and similarities in the patterns of transmission of the measles virus in developed and developing countries. Whilst the rate of loss of maternally derived immunity to measles is broadly similar, the average age at infection is much lower, and case fatality rates are much higher in developing countries. Data analysis also serves to illustrate inter-relationships between different kinds of epidemiological data. Thus, for example, in order to correctly interpret an age stratified serological profile from a developing country it is necessary to have information on the rate of decay of maternal antibodies and age specific case fatality rates. To determine the probable impact of a given vaccination programme, information on the birth rate in the community concerned is also required. A discussion is given of the epidemiological data required in order to effectively design a community based vaccination programme aimed at the eradication of measles.
Adolescent↗