Long term effect of municipal solid waste amendment on soil heavy metal content of sites used for periurban agriculture in Ngaoundere, Cameroon

An assessment of the impact of amendment using untreated municipal solid wastes on the trace element contents of periurban areas soils was carried out in  Ngaoundere. Waste samples were collected in November and soil samples were collected in November, January, April and July. Heavy metal total concentrations in urban wastes differed significantly among sites and ranged from 0.48 to 7.64 mg/kg for Cd, 38.3 to 236 mg/kg for Cu, 44.06 to 58.03 mg/kg for Ni, 117 to 528 mg/kg for Pb and 270 to 2110 mg/kg for Zn. These levels were out of the critical level for agricultural use at Camp prison (for Pb and Zn), Norvegien (for Cd, Cu and Zn), and Sabongari Gare site (for Cd, Cu and Zn). The levels of Ni in urban wastes from all sites and the levels of all heavy metals in urban wastes from Douze Poteaux site were lower than the critical level. The results revealed that the soil total  concentrations of Cu, Zn, Cd and Pb were below the typical agricultural soil critical level for the soil control and out of the critical level for amended soils. The levels of Ni were found to be within the normal range at all sites. The highest available  concentration of Zn (139.17 mg/kg) was found in November, Fe (843.23 mg/kg) and Pb (38.82 mg/kg) in January and Cu (19.09 mg/kg) and Ni (8.98 mg/kg) in July.  The available concentrations of Cd did not differ among periods. The highest   bioavailable factor (BF) of Zn, Ni and Pb was found at Douze Poteaux site and of Cd and Cu at Sabongari Gare site.Key words: Heavy metals, soils, municipal solid wastes, amendment, bioavailability factor

Unusual localization of blood-borne loa loa microfilariae in the skin depends on microfilarial density in the blood: Implications for onchocerciasis diagnosis in coendemic areas.

BACKGROUND: The diagnostic gold standard for onchocerciasis relies on identification and enumeration of (skin-dwelling) Onchocerca volvulus microfilariae (mf) using the skin snip technique (SST). In a recent study, blood-borne Loa loa mf were found by SST in individuals heavily infected with L. loa, and microscopically misidentified as O. volvulus due to their superficially similar morphology. This study investigates the relationship between L. loa microfilarial density (Loa MFD) and the probability of testing SST positive. METHODS: A total of 1053 participants from the (onchocerciasis and loiasis coendemic) East Region in Cameroon were tested for (1) Loa MFD in blood samples, (2) O. volvulus presence by SST, and (3) Immunoglobulin (Ig) G4 antibody positivity to Ov16 by rapid diagnostic test (RDT). A Classification and Regression Tree (CART) model was used to perform a supervised classification of SST status and identify a Loa MFD threshold above which it is highly likely to find L. loa mf in skin snips. RESULTS: Of 1011 Ov16-negative individuals, 28 (2.8%) tested SST positive and 150 (14.8%) were L. loa positive. The range of Loa MFD was 0-85 200 mf/mL. The CART model subdivided the sample into 2 Loa MFD classes with a discrimination threshold of 4080 (95% CI, 2180-12 240) mf/mL. The probability of being SST positive exceeded 27% when Loa MFD was >4080 mf/mL. CONCLUSIONS: The probability of finding L. loa mf by SST increases significantly with Loa MFD. Skin-snip polymerase chain reaction would be useful when monitoring onchocerciasis prevalence by SST in onchocerciasis-loiasis coendemic areas