Salt-bearing fumarole deposits in the summit crater of Oldoinyo Langai, Northern Tanzania: Interaractions between natrocarbonatite lava and meteoric water

Oldoinyo Lengai in the Northern Tanzania rift is the only active nephelinite-carbonatite stratovolcano. We report the discovery of thermonatrite, aphthitalite, halite and sylvite fumarole deposits on recent natrocarbonatite lava flows erupted in the summit crater during the wet season. These salt deposits occur as delicate, concave fringes or tubes that line the cooling cracks in the lava flows and consist of intergrowths of euhedral crystals. The presence of a dark altered zone, depleted in halides and alkalies, adjacent to cooling cracks and observations of steam fumaroles emanating from the fractures suggest that the salts are formed by sublimation from saturated vapours generated by the extrusion of lavas over meteoric water. The crystallisation sequence recorded in the salts suggests that mixing between meteoric steam and magmatic CO2 and H2S occurs at high temperatures resulting in the sublimation of carbonates and sulphates. At lower temperatures the vapours are dominated by meteoric steam and sublimate halides. The high solubility of the fumarole salts within meteoric water and their formation only during the wet season implies that these are ephemeral deposits that are unlikely to be preserved in the geological record. © 2001 Elsevier Science B.V. All rights reserved

Mapping of Bancroftian Filariasis in Cameroon: Prospects for Elimination

<div><p>Background</p><p>Lymphatic filariasis (LF) is one of the most debilitating neglected tropical diseases (NTDs). It still presents as an important public health problem in many countries in the tropics. In Cameroon, where many NTDs are endemic, only scant data describing the situation regarding LF epidemiology was available. The aim of this study was to describe the current situation regarding LF infection in Cameroon, and to map this infection and accurately delineate areas where mass drug administration (MDA) was required.</p><p>Methodology</p><p>The endemicity status and distribution of LF was assessed in eight of the ten Regions of Cameroon by a rapid-format card test for detection of <i>W</i>. <i>bancrofti</i> antigen (immunochromatographic test, ICT). The baseline data required to monitor the effectiveness of MDA was collected by assessing microfilariaemia in nocturnal calibrated thick blood smears in sentinel sites selected in the health districts where ICT positivity rate was ≥ 1%.</p><p>Principal findings</p><p>Among the 120 health districts visited in the eight Regions during ICT survey, 106 (88.3%) were found to be endemic for LF (i.e. had ICT positivity rate ≥ 1%), with infection rate from 1.0% (95% CI: 0.2–5.5) to 20.0% (95% CI: 10–30). The overall infection rate during the night blood survey was 0.11% (95% CI: 0.08–0.16) in 11 health districts out of the 106 surveyed; the arithmetic mean for microfilaria density was 1.19 mf/ml (95% CI: 0.13–2.26) for the total population examined.</p><p>Conclusion/significance</p><p>ICT card test results showed that LF was endemic in all the Regions and in about 90% of the health districts surveyed. All of these health districts qualified for MDA (i.e. ICT positivity rate ≥ 1%). Microfilariaemia data collected as part of this study provided the national program with baseline data (sentinel sites) necessary to measure the impact of MDA on the endemicity level and transmission of LF important for the 2020 deadline for global elimination.</p></div

LF infection rate by circulating antigen and mf detection according to the surveyed villages in the South-West Region of Cameroon.

<p>LF infection rate by circulating antigen and mf detection according to the surveyed villages in the South-West Region of Cameroon.</p

LF infection rate by circulating antigen and mf detection according to the surveyed villages in the Centre Region of Cameroon.

<p>LF infection rate by circulating antigen and mf detection according to the surveyed villages in the Centre Region of Cameroon.</p

Crude endemicity levels of LF antigenaemia and microfilariaemia, and intensity of infection by Region, sex, and age group in Cameroon.

<p>Crude endemicity levels of LF antigenaemia and microfilariaemia, and intensity of infection by Region, sex, and age group in Cameroon.</p