Amidou Samie

Pathogen-specific burdens of community diarrhoea in developing countries: a multisite birth cohort study (MAL-ED)

BACKGROUND Most studies of the causes of diarrhoea in low-income and middle-income countries have looked at severe disease in people presenting for care, and there are few estimates of pathogen-specific diarrhoea burdens in the community. METHODS We undertook a birth cohort study with not only intensive community surveillance for diarrhoea but also routine collection of non-diarrhoeal stools from eight sites in South America, Africa, and Asia. We enrolled children within 17 days of birth, and diarrhoeal episodes (defined as maternal report of three or more loose stools in 24 h, or one loose stool with visible blood) were identified through twice-weekly home visits by fieldworkers over a follow-up period of 24 months. Non-diarrhoeal stool specimens were also collected for surveillance for months 1-12, 15, 18, 21, and 24. Stools were analysed for a broad range of enteropathogens using culture, enzyme immunoassay, and PCR. We used the adjusted attributable fraction (AF) to estimate pathogen-specific burdens of diarrhoea. FINDINGS Between November 26, 2009, and February 25, 2014, we tested 7318 diarrhoeal and 24 310 non-diarrhoeal stools collected from 2145 children aged 0-24 months. Pathogen detection was common in non-diarrhoeal stools but was higher with diarrhoea. Norovirus GII (AF 5·2%, 95% CI 3·0-7·1), rotavirus (4·8%, 4·5-5·0), Campylobacter spp (3·5%, 0·4-6·3), astrovirus (2·7%, 2·2-3·1), and Cryptosporidium spp (2·0%, 1·3-2·6) exhibited the highest attributable burdens of diarrhoea in the first year of life. The major pathogens associated with diarrhoea in the second year of life were Campylobacter spp (7·9%, 3·1-12·1), norovirus GII (5·4%, 2·1-7·8), rotavirus (4·9%, 4·4-5·2), astrovirus (4·2%, 3·5-4·7), and Shigella spp (4·0%, 3·6-4·3). Rotavirus had the highest AF for sites without rotavirus vaccination and the fifth highest AF for sites with the vaccination. There was substantial variation in pathogens according to geography, diarrhoea severity, and season. Bloody diarrhoea was primarily associated with Campylobacter spp and Shigella spp, fever and vomiting with rotavirus, and vomiting with norovirus GII. INTERPRETATION There was substantial heterogeneity in pathogen-specific burdens of diarrhoea, with important determinants including age, geography, season, rotavirus vaccine usage, and symptoms. These findings suggest that although single-pathogen strategies have an important role in the reduction of the burden of severe diarrhoeal disease, the effect of such interventions on total diarrhoeal incidence at the community level might be limited.

Inhibitory properties of selected South African medicinal plants against Mycobacterium tuberculosis.

ETHNOPHARMACOLOGICAL RELEVANCE Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB) is the most commonly notified disease and the fifth largest cause of mortality. One in 10 cases is resistant to treatment in some areas. Several plants are used locally to treat TB-related disease. AIMS OF THE STUDY The aim was to screen selected South African medicinal plants used to treat TB and related symptoms by traditional healers for antimycobacterial activity. MATERIALS AND METHODS Ethnobotanical information on these plants was obtained. Crude acetone, methanol, hexane and ethanol extracts of 21 selected medicinal plants obtained in Venda, South Africa were screened for their ability to inhibit MTB H(37)Ra and a clinical strain resistant to first-line drugs and one second-line drug using tetrazolium microplate assay to determine the minimum inhibitory concentration (MIC). Results were analyzed using Microsoft Excel 2007 and One way ANOVA; p<0.05 was considered for statistical significance. RESULTS Few acetone extracts were active against MTB with MIC under 100 microg/mL. Four plants showed lower MIC values; Berchemia discolor Klotzsch Hemsl 12, 5 microg/mL on H(37)Ra and 10.5 microg/mL on the clinical isolate, Bridelia micrantha Hochst. Baill (25 microg/mL), Warbugia salutaris Bertol. F Chiov (25 microg/mL), and Terminalia sericea Burch ex D. F (25 microg/mL) on both H(37)Ra and clinical isolate. However, the roots of Ximenia caffra Sond. Var. caffra, barks of Sclerocarya birrea (A Rich) Hochst, Asclepias fruticosa L, tubers of Allium sativum L, leaves of Carica papaya L, Solanum panduriforme E. Mey C, and roots of Securidaca longepedunculata Fresen gave MIC greater than 100 microg/mL. CONCLUSION The acetone extracts of Berchemiadiscolor, Bridelia micrantha, Terminalia sericea and Warbugia salutaris could be important sources of mycobactericidal compounds against multidrug-resistant MTB.

Assessment of Environmental Enteropathy in the MAL-ED Cohort Study: Theoretical and Analytic Framework

Individuals in the developing world live in conditions of intense exposure to enteric pathogens due to suboptimal water and sanitation. These environmental conditions lead to alterations in intestinal structure, function, and local and systemic immune activation that are collectively referred to as environmental enteropathy (EE). This condition, although poorly defined, is likely to be exacerbated by undernutrition as well as being responsible for permanent growth deficits acquired in early childhood, vaccine failure, and loss of human potential. This article addresses the underlying theoretical and analytical frameworks informing the methodology proposed by the Etiology, Risk Factors and Interactions of Enteric Infections and Malnutrition and the Consequences for Child Health and Development (MAL-ED) cohort study to define and quantify the burden of disease caused by EE within a multisite cohort. Additionally, we will discuss efforts to improve, standardize, and harmonize laboratory practices within the MAL-ED Network. These efforts will address current limitations in the understanding of EE and its burden on children in the developing world.

Microbiologic Methods Utilized in the MAL-ED Cohort Study

A central hypothesis of The Etiology, Risk Factors and Interactions of Enteric Infections and Malnutrition and the Consequences for Child Health and Development (MAL-ED) study is that enteropathogens contribute to growth faltering. To examine this question, the MAL-ED network of investigators set out to achieve 3 goals: (1) develop harmonized protocols to test for a diverse range of enteropathogens, (2) provide quality-assured and comparable results from 8 global sites, and (3) achieve maximum laboratory throughput and minimum cost. This paper describes the rationale for the microbiologic assays chosen and methodologies used to accomplish the 3 goals.

Epidemiology and Impact of Campylobacter Infection in Children in 8 Low-Resource Settings: Results From the MAL-ED Study

In a multisite birth cohort study, we document a high burden of Campylobacter infection using enzyme immunoassay, demonstrate an association between Campylobacter and linear growth shortfalls and both increased intestinal permeability and intestinal and systemic inflammation, and identify potential interventions.

Norovirus Infection and Acquired Immunity in 8 Countries: Results From the MAL-ED Study

This longitudinal, multisite study reports a high prevalence of norovirus infection and norovirus-positive diarrhea and describes patterns of age acquisition, disease severity, genogroup-specific immunity, and relationships between norovirus and undernutrition in the first 2 years of life.

In-vitro cytotoxicity and antimicrobial activities, against clinical isolates of Campylobacter species and Entamoeba histolytica, of local medicinal plants from the Venda region, in South Africa

Abstract In the quest for alternative treatments against Campylobacter jejuni and Entamoeba histolytica, which are both aetiological agents of diarrhoea world-wide, the in-vitro activities against the two pathogens of extracts of 18 South African medicinal plants have recently been assessed. Forty extracts from the 18 plant species were prepared and tested against 110 clinical isolates of Campylobacter spp. In addition, extracts from eight of the plant species were tested against a standard strain (HM-1:IMSS) of E. histolytica, and the cytotoxicity of each of 19 extracts from 15 of the plant species was explored using Vero cell cultures and microdilution assays. At least one extract of each plant species investigated was found to be active against some of the Campylobacter isolates. Extracts of Lippia javanica and Pterocarpus angolensis had the highest antibacterial activity, each giving a minimum inhibitory concentration (MIC) of 90 μg/ml. Of the extracts tested against E. histolytica, however, only those of P. angolensis and Syzigium cordatum were found to have anti-amoebic activity, with MIC of 1.2 and 7.5 mg/ml, respectively. Although most of the extracts showed little toxicity against Vero cells, with most of the median inhibitory concentrations (IC50) recorded exceeding 400 μg/ml, an extract of Bauhinia galpini was quite toxic, with an IC50 of just 2.7 μg/ml. Acetone and methanol extracts of several of the plants show promise as templates for the design of new anti-diarrhoeal therapies.

Determinants and impact of Giardia infection in the first 2 years of life in the MAL-ED birth cohort

Summary In a multisite birth-cohort study, Giardia spp were detected by enzyme immunoassay at least once in two-thirds of the children. Early persistent infection with Giardia, independent of diarrhea, was associated with deficits in both weight and length at 2 years of age.

The prevalence of Cryptosporidium spp. oocysts in wild mammals in the Kruger National Park, South Africa.

This study determined the prevalence of Cryptosporidium spp. oocysts in faecal samples from elephant (Loxodonta africana), buffalo (Syncerus caffer) and impala (Aepyceros melampus) in the Kruger National Park (KNP) and an adjacent game reserve in South Africa. Two of the study areas were in close proximity to rural communities on the western KNP boundary and the third study area was located in the centre of the KNP. Fresh stool samples (n=445) were collected and tested using an immunofluorescent antibody test (IFA) for Cryptosporidium parvum. A total of 278 of these were randomly selected (approximately 90 samples per wildlife species) and tested with the modified Ziehl Neelsen staining technique (ZN) for Cryptosporidium spp. The prevalence of Cryptosporidium spp. was highest in elephants (25.8% [95% confidence interval: 17.3, 35.9]), compared to buffalo (5.5% [1.8, 12.4]) and impala (4.3% [1.2, 10.5]). C. parvum showed similar patterns, being most prevalent in elephants (4.2% [1.5, 8.8]), compared to buffalo (1.4% [0.2, 5.1]) and impala (1.9% [0.4, 5.3]). 29 samples, including ZN positive and IFA positive samples, were retested using a real time PCR (rtPCR) technique. Of the 28 ZN-positive samples, 14 (50%) were positive with rtPCR and of the 9 IFA-positive samples 6 (67%) were confirmed positive by rtPCR. The prevalence of Cryptosporidium oocysts was significantly higher in both of the two study areas adjacent to the western KNP boundary compared to the area in the centre of the KNP (OR=3.2 [1.2, 9.0]; P=0.024). Our study demonstrates for the first time the presence of Cryptosporidium spp. in wildlife in South Africa. The transmission of this parasite between wildlife, domestic animals and humans is a plausible hypothesis and represents a potential risk for immunodeficient human populations.

Seroprevalence of Entamoeba histolytica in the context of HIV and AIDS: the case of Vhembe district, in South Africa's Limpopo province

Abstract In a recent study in northern South Africa, the seroprevalence of Entamoeba histolytica infection among 257 HIV-positive and 117 HIV-negative individuals was determined, using an ELISA for the detection of antibodies reacting with the parasites galactose/–acetyl-D-galactosamine(Gal/GalNAc)-inhibitable adherence lectin. Overall, 34.0% of the 374 participants (36.1% of the females and 28.1% of the males) were found seropositive for E. histolytica. Although all age-groups were affected by the amoebic pathogen, the subjects aged 50–59 years had the highest seroprevalence (69.2%). The seroprevalence of E. histolytica was also significantly higher among the HIV-positive subjects than among the HIV-negative (42.8% v. 14.5%; χ2=28.65; P<0.0001). Among the HIV-positive subjects, those with fewer than 200 CD4+ cells/μl were relatively more likely to be seropositive for E. histolytica (60.3% v. 43.8%; χ2=4.016; P=0.045). This is the first report indicating a positive association between E. histolytica infection and HIV in South Africa. Further studies, for example to determine the occurrence of diarrhoea or liver abscess in the study area, in relation to seropositivity for E. histolytica and/or HIV, are now needed.