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Prevalence of Zoonotic Bacterial Pathogens and Associated Risk Factors among Cage-Cultured Nile Tilapia (Oreochromis Niloticus) in Mwanza Gulf of Lake Victoria, Tanzania
(NM-AIST, 2025-08) Komba, Richard
Aquaculture has the potential to improve global food and nutrition security, but climate change and poor practices can lead to chemical accumulation and zoonotic bacterial pathogens. This study aimed to identify the prevalence of zoonotic bacterial pathogens and associated risk factors in cage-cultured Nile tilapia in Mwanza Gulf, Lake Victoria, Tanzania. A total of 210 Nile tilapia (Oreochromis niloticus) samples were collected from cages distributed in three districts: Nyamagana (60), Ilemela (70) and Misungwi (80). Tissue samples from the gills, skin, kidney and liver were examined for zoonotic pathogenic bacterial infections. Bacterial isolation and identification were performed using standard conventional bacteriological methods. Additionally, a structured questionnaire was administered to 120 fish farmers to gather information on aquaculture practices, fish health status, and disease management. Water and sediment quality in cage-cultured and control sites were assessed using established physicochemical and sediment analysis procedures. Nine genera of bacteria were identified, including Salmonella spp. (12.5%), Klebsiella spp., Pseudomonas spp. (23.5%), Lactococcus spp. (16.9%), Bacillus spp. (14.7%), Shigella spp., E. coli, Streptococcus spp., and Staphylococcus spp. (16.7%). The gills had the highest bacterial
prevalence (28.6%), followed by the liver (16.7%), skin (12.9%) and kidney (6.7%). Bacterial isolates were most prevalent in cages in Ilemela (44.1%), followed by Misungwi (34.6%) and Nyamagana (21.3%), and with significant differences noted (p < 0.001). Additionally, analysis showed that most farms had high stocking densities (> 8 fish/m², 44.4%) and reared Nile tilapia (Oreochromis niloticus) (67.7%). Few farmers regularly measured water quality (16.7%) or removed dead fish daily (20.8%). Key factors influencing total mortality included stocking density (p = 0.013), fish species (p = 0.031), dead fish disposal methods (p = 0.023), and predator bird control (p = 0.016). Water samples from both cage-cultured and control sites showed no significant differences in quality (p > 0.05). Farmed fish and their aquatic environments harbor potentially pathogenic and zoonotic bacteria, posing significant risks to public health and leading to considerable economic losses. Therefore, the implementation of optimal management practices, along with strict biosafety and biosecurity measures, is essential.
Detection of Rift Valley Fever Virus Interepidemic Activity in Lower Moshi Area of Kilimanjaro Region, Northeastern Tanzania: A Community Survey
(NM-AIST, 2025-08) Kumalija, Medard
Rift Valley fever virus (RVFV) is a zoonotic viral disease of public health importance that affects livestock, wildlife and humans, mainly in sub-Saharan Africa. Despite its public health importance, the ways in which RVFVs circulate during the inter-epidemics (IEPs) stages and potentially spread to new areas remain unclear. The IEPs are the period during which transmissions pass without being detected, whereas surveillance is not performed. This study aimed to compare the rates of exposure to RVFV and RVFV infection among humans, goats and mosquito vectors in an agricultural and pastoral community in the lower Moshi area of the Moshi rural district. The area is located along the Great Rift Valley and is characterized by animal maintenance and heavy seasonal rains, making it swampy and favoring mosquito reproduction throughout. Although the spread of RVFV by mosquito vectors to animals and humans during interepidemic periods has been established, less is known about the roles that animals, humans, and vector mosquitoes play in maintaining the virus during IEPs. The reservoirs in the IEPs have become an area of interest for research. Therefore, a cross-sectional study survey was conducted in Lower Moshi in the Kilimanjaro region from June to December 2020. The RVFV exposure was determined via the detection of IgG/IgM to RVFV via a competitive enzyme-linked immunosorbent assay (cELISA), whereas infection was determined via real-time quantitative polymerase chain reaction (RT‒qPCR). In humans, male sex was more related to RVFV seropositivity than female sex was (χ² = 5.351; p=0.030). People aged 50 years and above were seropositive (χ² =14.430; p=0.006). The RVFV seropositivity in goats was related to increased seropositivity in humans (χ² =6.003; p=0.021, χ² =23.213; p=0.000 and 27.053; p=0.000). The RVFV antibody concentrations were only marginally higher in humans than in goats [t (112) =0.526; p=0.60)]. The RT‒qPCR revealed that goats presented the highest RVFV infection rate (4.1%), followed by humans (2.6%), Aedes aegypti (2.3%), and the Culex pipiens complex (1.5%). Similarly, a greater proportion of goats (23.3%) were RVFV seropositive than were humans (13.2%). These findings suggest that northeastern Tanzania may serve as a persistent hotspot for RVF transmission and call for the implementation of integrated, health-based active surveillance strategies targeting livestock, humans and vectors. Enhanced diagnostics, targeted vaccination and climate-informed risk mapping are recommended to enable timely interventions and reduce the likelihood of future RVF outbreaks.
Population Density and Extent of Harvesting of Warburgia Ugandensis (Sprague) in Northern Tanzania: Implications for Conservation
(NM-AIST, 2025-06) Mollel, Letan
Warburgia ugandensis, commonly known as Osokonoi and Endoroniki in Maa, is highly overexploited medicinal plant for commercial purposes. Despite its significant therapeutic potential, unsustainable harvesting practices threatened its survival thereby risking local extinction in its native range areas. This study aimed to assess the population density, distribution, and extent of harvesting of Warburgia ugandensis across its native ranges, land use types, and elevation gradients in Northern Tanzania. Meanwhile, it assessed ethno- botanical uses and conservation measures of Warburgia ugandensis across its native range areas in northern Tanzania. Data were collected from 128 plots each measuring 1ha within species native range areas (Kilimanjaro, Monduli, Ketumbeine, Gelai, and Longido) while
open-ended questionnaires were administered to 221 randomly chosen respondents. Data were analyzed using the Kruskal-Wallis test, post hoc (Dunn test), Generalized Linear Models (GLMs), and Descriptive Statistics. Land use types significantly influenced population density, with Forest Reserves recording the highest mean density of 6.485 stems/ha compared to grazing land with 1.833 stems/ha. Elevation also influenced density, with higher densities at 2001-2500 m compared to 1000-1500 m. A significant variation in the extent of harvesting was revealed with Ketumbeine experiencing extensive debarking and root cutting. Community knowledge of Warburgia ugandensis medicinal uses was highest around Kilimanjaro, with gastrointestinal disorders and cough being the most common ones. Respondents’ perceptions of species utilization were high in Gelai and Monduli, while Ketumbeine and, Longido revealed more variability. Community awareness of conservation measures for the species was notably high in Kilimanjaro compared to Monduli. The study underscores the need for targeted conservation efforts, in areas where the species is over-exploited, particularly Ketumbeine, and Longido while taking into consideration soil topography, climate factors, and sustainable harvesting practices.
Risks of Exposure to Contaminant Fluoride among Lactating Mothers and Children (0-24 Months) in Ngarenanyuki Communities in Northern Tanzania
(NM-AIST, 2025-07) Memba, Lucia
This study revealed important information on fluoride contamination of agricultural produce, water, cow and human breast milk, and excretion through urine. Risks of exposure to contaminant fluoride among children and lactating mothers were investigated. Structured questionnaires and 24-hour dietary recall was used to estimate dietary intake. Samples were collected and analyzed for fluoride contents. In all samples, fluoride concentration was determined by using a fluoride ion-selective electrode. Univariate logistic regression analysis was used to correlate dietary fluoride exposure and urinary fluoride excretions in children and breast milk fluoride excretion in lactating mothers. Results identified maize (21.7%), African nightshade (18.4%), and East African highland banana (15.2%) as the most consumed food
crops among lactating mothers; cow’s milk (2.7%) for children aged 6 months, and maize for children aged 7-24 months (9.2%-22.5%). Fluoride mean concentration levels in maize were (0.03±0.01 mg/kg), nightshade (0.081±0.004 mg/kg), East African highland banana (0.025±0.002 mg/kg), domestic water (4.57±0.21 mg/L), public tap water (4.74±0.6 mg/L), cow’s milk (0.34±0.18 mg/L), and human breast milk (0.077±0.03 mg/L). Both domestic water and human milk fluoride levels exceeded WHO safe standards of 1.5 mg/L and 0.002 mg/L, respectively. Dietary exposure among children was found ranged from 0.7±0.02 to 15.60±6.53 mg/kg bw/day, with food crops contributing 62.16%. Lactating mothers’ exposure ranged from 0.621±0.09 to 88.12±25.2 mg/kg bw/day, with food crops contributing 60.3%. The studied
population was exposed to dietary fluoride above the safe levels of 0.01 and 0.05 to 0.07 mg/kg/day by WHO for infants and adults, respectively. Biomarkers of fluoride exposure showed urinary fluoride excretion in children averaged 8.82±1.25 mg/L, with exposure increasing with age (p=0.003), and no significant gender differences (p=0.97). Positive correlations were observed between urinary fluoride excretion and consumption of cow's milk (ρ= 2.3, p<0.0000) and East African highland banana (ρ=-2.5, p<0.0001) in children, and between breast milk fluoride excretion and consumption of cow’s milk (ρ=0.027, p=0.0001), maize (ρ=0.00022, p=0.02), and tap water (ρ=-0.0002, p=0.001) in lactating mothers. The study concludes with recommendations for comprehensive research across seasons, diverse food crops, other exposure routes, and detailed biomarker assessments to fully understand the risks associated with fluoride exposure.
Optimization of Soil Fertility Under Banana-Coffee- Livestock and Maize-Legume Residues Transfer Farming Systems on the Slopes of Mount Kilimanjaro, Tanzania
(NM-AIST, 2025-08) Mhoro, Lydia
Arable land is under more pressure due to consequences of climate change and the growing global human population. Among other things, soil fertility has been most negatively impacted. This study aimed at optimizing nutrient management on the slopes of Mount Kilimanjaro for optimal crop production. The area is distinguished by two major farming systems: the banana- coffee-livestock on the highlands [> 1000 meters above sea level (m.a.s.l.)] and maize-legumes on the lowlands (< 1000 m.a.s.l.) of the slope. Data on soil nutrient management was gathered through a household survey. Soil nutrient quantification was done to assess nutrient balance highland-lowland farming systems. A field experiment was conducted in maize-legume farming to optimize soil nitrogen through inorganic fertilizer and cattle manure. The cost
benefit of the existing farming systems by smallholders were assessed. The demographic results showed that most of agricultural practitioners are adults (> 40 years). The findings showed that the levels of organic carbon (1.22%) and nitrogen (0.14%) were significantly lower (p<0.01) in the lowlands. Additionally, both the highlands and lowlands had considerably reduced extractable phosphorus (P) levels, measuring 9.3 mg kg-1 and 8.2 mg kg-1, respectively. The highland had significantly (p<0.01) less potassium (K+) [0.34 cmol (+) kg-1] than the lowland [0.93 cmol (+) kg-1]. The highlands had a negative balance of N and K, while the lowlands had negative balances of all three nutrients (N, P, and K). The field experiment results showed a significant increase in maize crop yields upon N fertilization, with the highest application rate of urea (75 kg N ha-1) producing the highest grain yields of up to 4.21 and 4.32 t ha-1 in the 2021 and 2023 seasons, respectively. In the lowlands, applying manure resulted in increases in soil total N, OC, extractable P, and exchangeable K of 16.67%, 18.13%, 20.95%, and 6.76%, respectively. The highland farming systems have shown high benefit cost ratio (3.79) compared to lowland (1.20) farming systems. Apart from the efforts of the smallholder farmers on soil fertility management, the study concludes that the sustainability of farming systems on the slope of Mt. Kilimanjaro is at stake, which eventually threatens food security.
Therefore, integrating organic and inorganic inputs can significantly improve crop yields and soil health sustainably.