Dental fluorosis among people and livestock living on Gihaya Island in Lake Kivu, Rwanda

Background Dental fluorosis is caused by prolonged exposure to excessive fluoride during the period of permanent tooth formation and is characterized by tooth discoloration, pitting, and loss of shape. Communities living near Lake Kivu in Western Rwanda exhibit a high prevalence of dental fluorosis; however, data on prevalence and risk factors are scarce. Methods This cross sectional, quantitative study used a One Health approach to investigate dental fluorosis prevalence among people and livestock and to measure fluoride content in the environment. In 2018, oral health examinations were conducted to assess the prevalence of fluorosis in children (aged 9 to 15 years), cattle and goats residing on Gihaya Island (Rwanda, East Africa). All children and cattle/goats meeting basic eligibility criteria (e.g., island residence) were invited to participate. Presence and severity of dental fluorosis was categorized according to the Dean’s Fluorosis Index. Samples of local foods, water, soil and grass were collected from communal sources and individual households and analyzed for fluoride content using standard laboratory techniques. Descriptive and binomial analyses (Fisher Exact Test) were used to assess this dataset. Results Overall, 186 children and 85 livestock owners (providing data of 125 livestock -23 cattle and 102 goats) participated. Dental fluorosis was recorded in 90.7% of children and 76% of livestock. Moderate to severe fluorosis was observed in 77% children while goats and cattle most often exhibited mild or absent/questionable severity, respectively. Water from Lake Kivu (used primarily for human cooking water and livestock drinking water) contained fluoride levels that were consistently higher than the maximum threshold (1.5 mg/L) recommended by the World Health Organization. Other sources (borehole and rainwater) were within safe limits. All food, soil and grass samples contained fluoride. The highest levels were observed in porridge (0.5 mg/g) and small fishes (1.05 mg/g). Conclusions Altogether, dental fluorosis was highly prevalent among children and goats on Gihaya Island with various food and water sources contributing a cumulative exposure to fluoride. An immediate and coordinated response across human, animal and water professionals is needed to reduce fluoride exposure within safe limits for island residents.

Choice of benthic macroinvertebrate-based metrics for assessing water quality in the littoral zone under anthropogenic disturbance in southern Lake Kivu (Central Africa)

Benthic macroinvertebrates are widely used to assess the ecological quality of fresh waters. This is because they are in direct contact with the aquatic environment and respond differently to pollutants and changes in the watershed, which are difficult to assess by toxicological or chemical monitoring alone. this study used benthic macroinvertebrate parameters to assess the quality of the nearshore waters of lake Kivu. Twenty-six metrics covering various aspects of the community were tested using whisker plots to compare their sensitivity in discriminating between reference and disturbed stations. Nine parameters (% EPT taxa, % Diptera taxa, % Chironomid taxa, % Insect taxa; % no Insects taxa, ratio EPT/Chironomid taxa, % moderate tolerant taxa, % very moderate tolerant taxa, Family Biotic Index) were found to be sensitive and were able to discriminate between reference and disturbed stations. All sensitive metrics, with the exception of the percentage of EPT taxa, were positively and/or negatively correlated with the physico-chemical parameters affected by the changes in the littoral zone. The combined values of the three calculated biotic indices (ASPT, BMWP and FBI) showed that the biological water quality varies from moderate to good in the reference stations and from average to poor in the disturbed stations. It is concluded that metrics based on benthic macroinvertebrates are effective for assessing water quality in the littoral zone of Lake Kivu in the context of the lack of historical water quality databases and specific tools for toxicological assessment. It is suggested to compare the performance of this approach with others currently used in bio-indication.

Natural and human-induced landslides in a tropical mountainous region: the Rift flank west of Lake Kivu (DR Congo)

Tropical mountainous regions are often identified as landslide hotspots with particularly vulnerable populations. Anthropogenic factors are assumed to play a role in the occurrence of landslides in these populated regions, yet the relative importance of these human-induced factors remains poorly documented. In this work, we aim to explore the impact of forest cover dynamics, roads and mining activities on the occurrence of landslides in the Rift flank west of Lake Kivu in the DR Congo. To do so, we compile an inventory of 2730 landslides using © Google Earth imagery, high resolution topographic data, historical aerial photographs from the 1950’s and extensive field surveys. We identify old and recent (post 1950’s) landslides, making a distinction between deep-seated and shallow landslides, road landslides and mining landslides. We find that susceptibility patterns and area distributions are different between old and recent deep-seated landslides, which shows that natural factors contributing to their occurrence were either different or changed over time. Observed shallow landslides are recent processes that all occurred in the past two decades. The analysis of their susceptibility indicates that forest dynamics and the presence of roads play a key role in their regional distribution pattern. Under similar topographic conditions, shallow landslides are more frequent, but of smaller size, in areas where deforestation has occurred since the 1950’s as compared to shallow landslides in forest areas, i.e. in natural environments. We attribute this size reduction to the decrease of regolith cohesion due to forest loss, which allows for a smaller minimum critical area for landsliding. In areas that were already deforested in 1950’s, shallow landslides are less frequent, larger, and occur on less steep slopes. This suggests a combined role between regolith availability and soil management practices that influence erosion and water infiltration. Mining activities increase the odds of landsliding. Mining and road landslides are larger than shallow landslides but smaller than the recent deep-seated instabilities. The susceptibility models calibrated for shallow and deep-seated landslides do not predict them well, highlighting that they are controlled by environmental factors that are not present under natural conditions. Our analysis demonstrates the role of human activities on the occurrence of landslides in the Lake Kivu region. Overall, it highlights the need to consider this context when studying hillslope instability characteristics and distribution patterns in regions under anthropogenic pressure. Our work also highlights the importance of considering the timing of landslides over a multi-decadal period of observation.

Morphometric characteristics of four important fish species from the Rwandan side of Lake Kivu

Inland fisheries are important socio-economic resources for rural communities in Africa. In Rwanda, about two million people directly depend on capture fisheries from Lake Kivu. Sustainable fisheries management requires monitoring of population dynamics that help devise effective intervention strategies. However, the relevant data such as length-length and length-weight relationships do not exist for most of the key species in Lake Kivu. The present study generated morphometric and body weight data for Limnothrissa miodon (n=82), Lamprichthys tanganicanus (n=55), Haplochromis vittatus (n=51) and Haplochromis graueri (n=34) from Lake Kivu. Length-weight relationships (W=aLb) were highly significant for all species (p < 0.0001), high adjusted R2 = 78 to 98% of the variance in weight explained by total length. Negative allometric length-weight relationships were found with regression slope (b) values of 2.7 for Limnothrissa miodon, 2.8 for H. graueri, and 2.8 for L. tanganicanus, and positive (b=3.4) for Haplochromis vittatus. Length-length relationships were highly significant for all species (p ≤ 0.0001), except for the relationship between total and caudal length for L. miodon, and total and caudal peduncle length for L. tanganicanus, both not significant at p > 0.05. The highest R2 was for the relationships between total and standard length for H. vittatus, and total and fork length for L. tanganicanus. No description of length-length relationships exists for these species in literature or in FishBase database. The data generated in the current study will be used to assess changes in fish populations over time.

Geochemical Characterization of Nyamyumba Hot Spring, Northwest Rwanda

Hot spring is a hot water that is naturally occurring on the surface from the underground and typically heated by subterranean volcanic activity and local underground geothermal gradient. There are four main hot springs in Rwanda such as: Kalisimbi, Bugarama, Kinigi and Nyamyumba former name Gisenyi hot springs. This research focused on the geochemical analysis of Nyamyumba hot springs located near the fresh water of Lake Kivu. Nyamyumba hot springs are located in the western branch of the East African Rift System and they are located near Virunga volcanic complex, explaining the rising and heating of water. The concentrations of Sulfate, Iron, Ammonia, Alkalinity, Silica, Phosphate, Salinity, Alkalinity, and Conductivity using standard procedures were measured. The results showed that hot spring water has higher concentrations of chemicals compared to Lake Kivu water and the geochemistry of these hot springs maybe associated with rock dissolution by hot water. The measured parameters were compared with World Health Organization (WHO) standards for recreational waters and it has been identified that Nyamyumba hot spring are safe to use in therapeutic activities (Swimming).

Vibrio cholerae multifaceted adaptive strategies in response to bacteriophage predation in an endemic region of the Democratic Republic of the Congo

Bacteriophage predation of toxigenic Vibrio cholerae O1 (the causative agent of cholera) has been linked with seasonal patterns of disease and with clinical response to infection in humans 1-4. However, we still lack a clear demonstration of how the interplay between bacteria and bacteriophage can influence shifts in strain populations. We analyzed toxigenic V. cholerae O1 isolated from patients in the Great Lakes, a cholera endemic region of the Democratic Republic of the Congo (DRC), between 2013-2017. Bayesian phylogeography shows that all strains derived from the East Africa T10 introduction event5, consistent with establishment of a regional endemic focus, and identified two major lineages, with the most recent correlating to ST515, a cholera cluster previously found in the Lake Kivu and expanding northward6. We also identified a novel ICP1 bacteriophage, genetically distinct from previous ICP1 isolates detected in Asia 7,8, from stool samples of cholera patients. The presence of phages in specific regions of the DRC resulted in the independent emergence, along both internal and external branches of the cholera phylogeny, of distinct mutational pathways in genes of the O1 biosynthetic gene cluster associated with phage resistance. Our data evidence, for the first time, V. cholerae multi-peaked adaptive landscape during outbreaks, and a complex co-evolutionary dynamic linked to presence of predatory phages

Questioning territories and identities in the precolonial (nineteenth-century) Lake Kivu region

Throughout Africa, contemporary boundaries are deemed ‘artificial’ because they were external impositions breaking apart supposedly homogeneous ethnic units. This article argues that the problem with the colonial borders was not only that they arbitrarily dissected African societies with European interests in mind, but also that they profoundly changed the way in which territoriality and authority functioned in this region, and therefore they affected identity. The presumption that territories could be constructed in which ‘culture’ and ‘political power’ neatly coincided was influenced by European ideas about space and identity, and privileged the perceptions and territorial claims of those ruling the most powerful centres in the nineteenth century. Thus, this article questions assumptions that continue to influence contemporary views of the Lake Kivu region. It shows that local understandings of the relationship between space and identity differed fundamentally from state-centred perspectives, whether in precolonial centralized states or colonial states.