If the host population is taken to be a dynamic variable (rather than constant, as conventionally assumed), a wider understanding of the population biology of infectious diseases emerges. In this first part of a two-part article, mathematical models are developed, shown to fit data from laboratory experiments, and used to explore the evolutionary relations among transmission parameters. In the second part of the article, to be published in next week's issue, the models are extended to include indirectly transmitted infections, and the general implications for infectious diseases are considered.

Population biology of infectious diseases: Part II

Many studies in sub-Saharan Africa have occasionally reported a higher prevalence of stunting in male children compared to female children. This study examined whether there are systematic sex differences in stunting rates in children under-five years of age, and how the sex differences in stunting rates vary with household socio-economic status. Data from the most recent 16 demographic and health surveys (DHS) in 10 sub-Saharan countries were analysed. Two separate variables for household socio-economic status (SES) were created for each country based on asset ownership and mothers' education. Quintiles of SES were constructed using principal component analysis. Sex differentials with stunting were assessed using Student's t-test, chi square test and binary logistic regressions. The prevalence and the mean z-scores of stunting were consistently lower amongst females than amongst males in all studies, with differences statistically significant in 11 and 12, respectively, out of the 16 studies. The pooled estimates for mean z-scores were -1.59 for boys and -1.46 for girls with the difference statistically significant (p < 0.001). The stunting prevalence was also higher in boys (40%) than in girls (36%) in pooled data analysis; crude odds ratio 1.16 (95% CI 1.12–1.20); child age and individual survey adjusted odds ratio 1.18 (95% CI 1.14–1.22). Male children in households of the poorest 40% were more likely to be stunted compared to females in the same group, but the pattern was not consistent in all studies, and evaluation of the SES/sex interaction term in relation to stunting was not significant for the surveys. In sub-Saharan Africa, male children under five years of age are more likely to become stunted than females, which might suggest that boys are more vulnerable to health inequalities than their female counterparts in the same age groups. In several of the surveys, sex differences in stunting were more pronounced in the lowest SES groups.

/pdf/boys-are-more-stunted-than-girls-in-sub-saharan-africa-a-35c9pzsvj0.pdf

Boys are more stunted than girls in Sub-Saharan Africa: a meta-analysis of 16 demographic and health surveys

Humans diverge from most mammals, including nonhuman primates, by depositing significant quantities of body fat in utero and are consequently one of the fattest species on record at birth. While explanations for the fat layer of human neonates have commonly assumed that it serves as insulation to compensate for hairlessness, empirical support for this hypoth- esis is presently weak. Whether the tissue's abundance at birth and growth changes in adiposity during infancy and childhood might be explained in light of its role as energy buffer has not been assessed, and this possibility is explored through development of a model of fat function and growth centered on two related hypotheses. The first is that the greater adiposity of human neonates is at least partially explainable as an accompaniment of the enlarged human brain, which demands a larger energy reserve to ensure that its obligatory needs are met when the flow of resources from mother or other caretakers is disrupted. The second is that age-related changes in the likelihood of experiencing such disruption have influenced the pattern of investment in the tissue, reflected today in peak adiposity during infancy and a decline to a leaner childhood period. Nutritional disruption is common at birth and until lactation is established, during which time human newborns survive from fats deposited prenatally, suggesting one possible explanation for the early onset of fat deposition. At weaning, the transition from breast milk to supplemental foods and the parallel transition from maternal to endogenous immune protection interact to increase the frequency and impact of nutritional disruption, and this may help explain why newborns devote roughly 70% of growth expenditure to fat deposition during the early postnatal months. Evidence is presented that fat stores are mobilized during infections, hinting at one possible mechanism underlying the association between nutritional status and infectious morbidity and mortality among infants in nutritionally stressed human populations. Consistent with the proposed hypothesis, well-fed infants acquire peak fat reserves by an age of peak prevalence of malnutrition, infectious disease, and fat reserve depletion in less-buffered contexts, and childhood—characterized by minimal invest- ment in the tissue—is a stage of reduced risk of energy stress. The model presented here foregrounds energy storage in adipose tissue as an important life-history strategy and a means to modify mortality risk during the nutritionally turbulent period of infancy. Yrbk Phys Anthropol 41:177-209, 1998. r 1998 Wiley-Liss, Inc.

https://groups.anthropology.northwestern.edu/lhbr/kuzawa_web_files/pdfs/Kuzawa%201998%20yearbook.pdf

Adipose tissue in human infancy and childhood : an evolutionary perspective

This review examines the historical, physiological, clinical, and epidemiohogical evidence to support a method of therapy for children's diarrhea that may be recommended for general acceptance. The understanding and use of fluid and nutritional therapy of acute diarrhea in childhood have progressed over the years to a point where acute mortality can be reduced to nearly zero. At the same time, the ill effects on electrolyte balance and nutrition may be reduced to a minimum. Through use of an oral glucose electrolyte solution with a carefully designed composition, physiologically correct treatment may now be so simplified and inexpensive as to be readily available to the remote, under-served areas of the world where most of the morbidity exists; and be useful as well to more sophisticated settings. The method of therapy recommended in this paper has several important departures from traditional teaching. It advocates rapid restoration of extracehlular fluid with a polyelectrohyte solution containing sodium, base and potassium; use of an oral glucose electrolyte solution for repletion of those not in shock and for maintenance; use of a single oral glucose electrolyte solution for all age groups, regardless of diagnosis; and quite early feeding with tolerated foods. Sodium loads given are generally higher than advocated by standard pediatric teaching. The origins of that teaching and support for the newer approach come from a detailed analysis ofcurrent knowledge in the epidemiological, clinical, and physiological aspects of diarrheal illness. Am. J. Clin. Nutr. 33: 637-663, 1980.

The treatment of acute diarrhea in children. An historical and physiological perspective.

Bacterial contamination in traditional gambian weaning foods

Infection and its effect on growth of young-children - comparison of gambia and uganda

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Infection and its effect on growth of young-children - comparison of gambia and uganda