Expanding the hygiene hypothesis: early exposure to infectious agents predicts delayed-type hypersensitivity to Candida among children in Kilimanjaro

Does the immune system of milk increase activity for infants experiencing infectious disease episodes in Kilimanjaro, Tanzania?

INTRODUCTION

Multiple studies have reported that milk immune content increases for infants experiencing infectious disease (ID) episodes, suggesting that the immune system of milk (ISOM) offers enhanced protection when needed to combat ID.

METHODS

To test the hypothesis that ISOM content and/or activity increases during an infant's ID episode, we characterized milk secretory immunoglobulin A (sIgA; a major ISOM constituent) and in vitro interleukin-6 (IL-6) responses to Salmonella enterica and Escherichia coli, as system-level biomarkers of ISOM activity, in a prospective study among 96 mother-infant dyads in Kilimanjaro, Tanzania.

RESULTS

After control for covariates, no milk immune variables (sIgA, Coef: 0.03; 95% CI -0.25, 0.32; in vitro IL-6 response to S. enterica, Coef: 0.23; 95% CI: -0.67, 1.13; IL-6 response to E. coli, Coef: -0.11; 95% CI: -0.98, 0.77) were associated with prevalent ID (diagnosed at the initial participation visit). Among infants experiencing an incident ID (diagnosed subsequent to the initial participation), milk immune content and responses were not substantially higher or lower than the initial visit (sIgA, N: 61; p: 0.788; IL-6 response to S. enterica, N: 56; p: 0.896; IL-6 response to E. coli, N: 36; p: 0.683); this was unchanged by exclusion of infants with ID at the time of initial participation.

CONCLUSION

These findings are not consistent with the hypothesis that milk delivers enhanced immune protection when infants experience ID. In environments with a high burden of ID, dynamism may be less valuable to maternal reproductive success than stability in the ISOM.

Frequency of Candida spp. in the Oral Cavity of Asymptomatic Preschool Mexican Children and Its Association with Nutritional Status

Malnutrition is a public health problem in developing countries, affecting the child population, which favors the appearance of infections such as oral candidiasis. In Mexico, information on the presence of oral colonization by Candida spp. in asymptomatic children is scarce. The present study aimed to determine the presence of Candida spp. in the oral cavity of asymptomatic preschool Mexican children and its association with their nutritional status. A sample of oral mucosa was obtained using a sterile swab and then inoculated in Sabouraud dextrose agar with antibiotics, and the yeast growth was phenotypically identified. The anthropometric profile of children was performed based on the guidelines of the International Society for the Advancement of Kinanthropometry. In addition, eating habits were investigated. The possible associations between the variables were determined through the chi-square test (IC95%, p < 0.05) (GraphPad Prism 8.0). Among the 743 assessed children (403 boys and 340 girls), the average age was 4.6 years, and the average nutritional status was normal (53.7%), followed by undernutrition (28.4%), overweight (12.4%) and obesity (5.5%). In 52 children, Candida was isolated, and the identified species were C. albicans (87.8%), C. glabrata (11.5%), C. krusei (5.8%) and C. parapsilosis (1.9%). The frequency of colonization was greater in males of six years (69.23%). There was no significant association between the colonization by Candida spp. and the nutritional status; however, a relation was observed with a high intake of simple carbohydrates.

From Infections to Anthropogenic Inflicted Pathologies: Involvement of Immune Balance

A temporal trend can be seen in recent human history where the dominant causes of death have shifted from infectious to chronic diseases in industrialized societies. Human influences in the current "Anthropocene" epoch are exponentially impacting the environment and consequentially health. Changing ecological niches are suggested to have created health transitions expressed as modifications of immune balance from infections inflicting pathologies in the Holocene epoch (12,000 years ago) to human behaviors inflicting pathologies beginning in the Anthropocene epoch (300 years ago). A review of human immune health and adaptations responding to environmental (biological, chemical, physical, and psychological) stresses, which are influenced by social conditions, emphasize the involvement of fluctuations in immune cell subsets affecting influential gene-environment interactions. The literature from a variety of fields (anthropological, immunological, and environmental) is incorporated to present an expanded perspective on shifts in diseases within the context of immune balance and function and environmental immunology. The influences between historical and contemporary human ecology are examined in relation to human immunity. Several examples of shifts in human physiology and immunity support the premise that increased incidences of chronic diseases are a consequence of human modification of environment and lifestyle. Although the development of better health care and a broader understanding of human health have helped with better life quality and expectancy, the transition of morbidity and mortality rates from infections to chronic diseases is a cause for concern. Combinations of environmental stressors/pollutants and human behaviors and conditions are modulating the immune-neuroendocrine network, which compromises health benefits.

Lower incidence of respiratory infections among iron-deficient children in Kilimanjaro, Tanzania

Objective: We posited a trade-off in iron nutrition, with iron deficiency decreasing risk for infection by depriving infectious agents of iron while increasing risk for infection by compromising immune protection. We described associations between iron deficiency and prevalent and incident infectious disease episodes and cell-mediated immunity (CMI) among 283 children in Kilimanjaro, Tanzania.

Methodology: Whole blood specimens were evaluated for hemoglobin and dried blood spots (DBS) were evaluated for biomarkers of iron deficiency (transferrin receptor) and inflammation (C-reactive protein and α₁-acid glycoprotein). Prevalent and incident infectious disease episodes were identified by physician’s diagnosis. CMI was evaluated as delayed-type hypersensitivity to Candida albicans (DTH-Candida). Associations between iron status and elevated inflammation, prevalent infectious disease episodes and DTH-Candida were described with logistic regression models; associations between iron status and incident infectious disease episodes were described with Cox proportional hazards models.

Results: Elevated inflammation and diagnosed infectious diseases were more common among children with iron-deficiency anemia (IDA, severe iron deficiency), but not significantly so. The incidence of infectious disease was lowest among children with moderate iron deficiency (iron-deficient erythropoiesis, IDE); this pattern was most apparent for respiratory infections (aHR: 0.24; p: 0.030). DTH-Candida was not compromised among children with any degree of iron deficiency.

Conclusions and implications: We observed no adverse effect of iron deficiency on CMI, but did observe patterns consistent with the hypothesis that moderate iron deficiency protects against respiratory infections and may represent a nutritional adaptation to infectious disease. This suggests that interventions targeting iron deficiency should be coupled with effective infectious disease control measures.

New evidences on the altered gut microbiota in autism spectrum disorders

BACKGROUND

Autism spectrum disorders (ASDs) are neurodevelopmental conditions characterized by social and behavioural impairments. In addition to neurological symptoms, ASD subjects frequently suffer from gastrointestinal abnormalities, thus implying a role of the gut microbiota in ASD gastrointestinal pathophysiology.

RESULTS

Here, we characterized the bacterial and fungal gut microbiota in a cohort of autistic individuals demonstrating the presence of an altered microbial community structure. A fraction of 90% of the autistic subjects were classified as severe ASDs. We found a significant increase in the Firmicutes/Bacteroidetes ratio in autistic subjects due to a reduction of the Bacteroidetes relative abundance. At the genus level, we observed a decrease in the relative abundance of Alistipes, Bilophila, Dialister, Parabacteroides, and Veillonella in the ASD cohort, while Collinsella, Corynebacterium, Dorea, and Lactobacillus were significantly increased. Constipation has been then associated with different bacterial patterns in autistic and neurotypical subjects, with constipated autistic individuals characterized by high levels of bacterial taxa belonging to Escherichia/Shigella and Clostridium cluster XVIII. We also observed that the relative abundance of the fungal genus Candida was more than double in the autistic than neurotypical subjects, yet due to a larger dispersion of values, this difference was only partially significant.

CONCLUSIONS

The finding that, besides the bacterial gut microbiota, also the gut mycobiota contributes to the alteration of the intestinal microbial community structure in ASDs opens the possibility for new potential intervention strategies aimed at the relief of gastrointestinal symptoms in ASDs.

Hay fever, asthma, and eczema and early infectious diseases among children in Kilimanjaro, Tanzania

OBJECTIVES

To investigate the hygiene (or "old friends") hypothesis in a high-infectious disease (ID) environment, rural Kilimanjaro, Tanzania.

METHODS

Among a cross-sectional sample of 2- to 7-year-old children, we collected physician-diagnosed hay fever, asthma, and eczema, history of hospitalization, family size, and household environment information via questionnaire; performed active and passive surveillance for ID; and, evaluated total immunoglobulin E (IgE) and biomarkers of inflammation in dried blood spot specimens. We used regression models to describe patterns in allergic diseases.

RESULTS

Complete information was available for 280 children: 12.5% had been diagnosed with hay fever; 18.9% with eczema; 2.1% with asthma. There was a positive association between hay fever and eczema diagnoses (π² : 4.07; P = 0.044); total IgE was positively associated with eczema (β: 0.24; P = 0.100) and allergic diseases together (β: 0.26; P = 0.042). ID were common: the incidence of any ID diagnosis was 28 per 100 children per month. Hay fever was inversely associated with household animals (OR: 0.27; P = 0.006), and positively associated with earth housing materials (OR: 1.93; P = 0.079) and hospitalization in infancy with an ID (3.16; P = 0.066); patterns were similar when allergic disease outcomes were considered together. Few associations between these predictors and eczema or asthma alone were apparent.

CONCLUSIONS

Allergic diseases were common among children in Kilimanjaro. The inverse association between household animals and allergy is consistent with the hygiene/old friends hypothesis; however, positive associations between allergic diseases and earth housing materials and early hospitalization with ID bear further explanation.

Markedly Elevated Antibody Responses in Wild versus Captive Spotted Hyenas Show that Environmental and Ecological Factors Are Important Modulators of Immunity

Evolutionary processes have shaped the vertebrate immune system over time, but proximal mechanisms control the onset, duration, and intensity of immune responses. Based on testing of the hygiene hypothesis, it is now well known that microbial exposure is important for proper development and regulation of the immune system. However, few studies have examined the differences between wild animals in their natural environments, in which they are typically exposed to a wide array of potential pathogens, and their conspecifics living in captivity. Wild spotted hyenas (Crocuta crocuta) are regularly exposed to myriad pathogens, but there is little evidence of disease-induced mortality in wild hyena populations, suggesting that immune defenses are robust in this species. Here we assessed differences in immune defenses between wild spotted hyenas that inhabit their natural savanna environment and captive hyenas that inhabit a captive environment where pathogen control programs are implemented. Importantly, the captive population of spotted hyenas was derived directly from the wild population and has been in captivity for less than four generations. Our results show that wild hyenas have significantly higher serum antibody concentrations, including total IgG and IgM, natural antibodies, and autoantibodies than do captive hyenas; there was no difference in the bacterial killing capacity of sera collected from captive and wild hyenas. The striking differences in serum antibody concentrations observed here suggest that complementing traditional immunology studies, with comparative studies of wild animals in their natural environment may help to uncover links between environment and immune function, and facilitate progress towards answering immunological questions associated with the hygiene hypothesis.

Breastfeeding over two years is associated with longer birth intervals, but not measures of growth or health, among children in Kilimanjaro, TZ

OBJECTIVES

Breastfeeding has been associated with numerous health and well-being benefits for both children and their mothers, including prolonging the birth interval to the subsequent sibling. The clearest associations between breastfeeding and health outcomes, per se, reflect exclusive breastfeeding in the first months of postnatal life and are most evident during infancy. Fewer studies explore the consequences of breastfeeding for multiple years. In this article, we ask whether breastfeeding for more than 2 years is associated with discernible health and well-being benefits to children.

METHODS

Data were collected from 315 children, aged 2 to 7, and their caretakers residing in Kilimanjaro, Tanzania. Basic demographic and health information was solicited, and anthropometric and blood markers of health were evaluated.

RESULTS

Our results indicate a strong positive relationship between breastfeeding for 2 or more years and interbirth interval, but little evidence for a relationship between prolonged breastfeeding and several indicators of child growth and health.

CONCLUSIONS

We suggest that these relationships may support the recently rekindled birth spacing hypothesis, positing selection for longer interbirth intervals, rather than, or in addition to, more direct health benefits associated with breastfeeding for 2 or more years. Our results may indicate attenuating health benefits associated with longer breastfeeding.

Predictors of delayed-type hypersensitivity to Candida albicans and anti-Epstein-Barr virus antibody among children in Kilimanjaro, Tanzania

We evaluated sex, age, nutritional status, and infectious disease (ID) as predictors of two biomarkers of cell-mediated immunity (CMI), delayed-type hypersensitivity to Candida albicans (DTH-Candida), and anti-Epstein-Barr virus antibody (EBV Ab), among 200 children in Kilimanjaro, Tanzania. DTH-Candida, which decreases with compromised CMI, was positively associated with age (OR: 1.27; 95% CI: 1.02, 1.57) and triceps skinfold (TSF; OR: 1.16; 95% CI: 1.02, 1.26), and inversely associated with height-for-age Z score (HAZ; OR: 0.86; 95% CI: 0.68, 1.08) and diagnosed ID (OR: 0.48; 95% CI: 0.22, 1.08). There was significant interaction between TSF and ID: DTH-Candida exhibited a strong inverse association with ID among children with low TSF (OR: 0.16; 95% CI: 0.05, 0.50) and a strong positive association with TSF among children with ID (OR: 2.64; 95% CI: 1.29, 5.42). EBV Ab, which increases with compromised CMI, was inversely associated with male sex (β: -0.47; 95% CI: -0.70, -0.24) and TSF (β: -0.04; 95% CI: -0.08, 0.00), and positively associated with HAZ (β: 0.06; 95% CI: -0.03, 0.15). Among males, EBV Ab was positively associated with anemia. Among normal HAZ children, EBV Ab was inversely associated with TSF. There was no association between DTH-Candida and EBV Ab. While DTH-Candida provides a direct measure of CMI, our results suggest that interpretation of EBV-Ab among Kilimanjaro children was complicated by its indirect relationship with CMI. Among our sample, CMI increased with age and adequate nutrition and was compromised during acute ID. The suggestive CMI-compromising effect of increasing height-for-age may bear further exploration.