Abstract
Water scarcity and poor access to potable water are growing concerns in sub-Saharan Africa. This study investigated seasonal variations in microbial contamination and physicochemical properties of surface waterpoints, the primary sources of water in southwestern Kenya, using a cross-sectional environmental surveillance design (May 2024-April 2025). Total coliforms and Escherichia coli isolates were quantified, to assess water safety and ecosystem health using membrane filtration and differential chromogenic agar. Results revealed high microbial contamination in all samples (100% for total coliforms; 62.5% for E. coli), with significantly higher bacterial loads during the wet season. Total coliforms and E. coli averaged 1.13 × 106 CFUs/mL and 1.34 ± 1.26 × 105; and 2.84 × 105 CFUs/mL and 9.82 ± 9.78 × 104, respectively, for wet and dry seasons respectively. Prevalence of E. coli in sampled sites was statistically significant between seasons (χ2(1, N = 28) = 20.57, P < .05). Physicochemical parameters varied seasonally, with the dry season having higher pH, temperature, total dissolved solids and dissolved oxygen, while the wet season had higher conductivity. During the dry season, E. coli and total coliforms were not correlated while in the wet season, a weak but significant correlation existed (r = 0.465, P = .003). Microbial parameters showed no significant correlation with physicochemical variables in either season, emphasising distinct seasonal interaction patterns. MANOVA conducted to assess the influence of water bodies, seasons and their interactions on microbial and physiochemical parameters revealed that water quality was significantly influenced by both water body type and season (P < .001). Total coliforms were significantly influenced by season but not water sources. The presence of unsafe microbial loads and poor water quality highlights public health risks and potentially impact on livestock and livelihoods. These microscale findings, advocate for continuous ecological surveillance and public health monitoring on water quality status and community awareness. We recommend promotion of nature-based indigenous solutions for water and ecosystem management amid climate change.
Introduction
Water as an enabler to development contributes to human wellbeing and survival and resilient ecosystems. 1 Access to clean water is a universal human right 2 and promotes human health and productivity. Despite its significance, this vital finite and irreplaceable 3 resource, continues to face a lot of threats that compromises its availability and quality both temporally and spatially.
Water, Sanitation and Hygiene (WASH) is compromised by poor or lack of water accessibility and infrastructure. 4 It is estimated that close to 2 billion people are devoid of potable water services. 5 This lack of access to adequate potable water, which leads to consumption of contaminated water, is estimated to cause over 1.8 million human deaths and approximately 4 billion cases of illness annually.6,7 Many rapidly developing urban and rural centres in Africa are faced with unsustainable sources of potable water.8-11
Waterborne microorganisms in drinking water are a major public health concern,12-14 especially from human and animal faecal sources.15,16 The pathogens are primarily transmitted through ingestion of contaminated water; contact with urine, body fluids or faecal-oral route transmission of infected animals or indirectly through water or soil contaminated with infected animal exudates and excreta. Increased use of shared water points by humans, livestock and wildlife, predisposes fragile wetlands to ubiquitous zoonotic waterborne and water-related diseases.11,17-19 Waterborne and water-related pathogens of public health importance when ingested can result into severe stomach cramps, bloody diarrhoea, vomiting, kidney failure and death.19-21 Studies reveal that waterborne diseases cause high morbidity and mortality in low- and middle-income countries (LMICs), killing an estimated 4.9 of every 1,000 children who are below 5 years. 22
In Narok County, Kenya and sub-Saharan Africa, available surface water resources are currently decreasing in quality and quantity.23-25 This is attributed to weather variation, global warming and land-use change, water pollution (surface-runoff, industrial waste, agro-based chemicals and human waste), population increase, urbanisation, and poor water resource management.26-28 Article 43(1)(d) of the Constitution of Kenya, 29 provides that ‘every person has the right to clean and safe water in adequate quantities’. The county lags the in provision of potable water as water, sanitation and hygiene (WASH) infrastructure in most rural areas is either poorly developed or non-existent, as less than 10% of Narok County households have access to piped water.10,11 Moreover, environmental hygiene is compromised in Narok as over 50% of Narok residents practice open defecation due to lack of improved sanitary infrastructure in form of pit latrines and toilets,28,30 a scenario that exposes the community to increased incidents of morbidity and compromised health in a shared human–livestock–wildlife landscape. Furthermore, cultural sanitary norms, livestock husbandry in form of pastoralism and wildlife conservation exacerbate environmental pollution, which predisposes the shared multi-use fragile surface water sources to pathogenic faecal pollution and contamination, especially in downstream communities.11,31
Additionally, in Narok West subcounty, the most arid of the 6 Narok sub-counties, close to 70% of the residents’ source water from unimproved surface water points, such as open water pans, rivers and unprotected springs. 11 These surface sources are prone to pollution and contamination by faecal matter. 17 We define open water pans as natural or excavated depressions filled by water and are used by herders to water livestock, farmers for irrigation, water wildlife and other community members for domestic use. Open water pans store surface runoff water and usually lose water through seepage and evaporation.
World Health Organization (WHO) and World Organisation for Animal Health has approved various physiochemical levels of water for human and animal consumption, with deviations likely to result in illness, reduced productivity and jeopardise livelihoods. Conversely, Kenya’s National Research Agenda for 2008-2030, 32 advocates for environmental research in a myriad of areas including water resources and pollution, environmental health and public health. It postulated that the human disease burden (morbidity and mortality) attributed to zoonosis is projected to increase, including those attributed to gastro-intestinal ailments. 33 Sadly, most of these have not been quantified in the global south, including Kenya and its arid and semi-arid lands. 34 Moreover, there is a growing dearth of knowledge in relation to the spatial temporal variation of surface water resources in Kenya’s arid and semi-arid lands (ASALs) including Narok, vis-à-vis the waterborne and water-related pathogen loads, One Health implications (human, animal, and ecosystem), and remedial medical policy reforms which the study seeks to attempt to fill. In view of these, the main premise of this study was to establish systematic seasonal prevalence of water quality on surface water sources in the shared human-animal landscape of Narok. This quantitative hydro-ecological baseline risk assessment in the ASAL human-livestock-wildlife landscape of Narok West subcounty, Narok County, Kenya (May 2024 to April 2025) is critical for environmental monitoring and microbial pollution, for public health importance. Specifically, our study sought to: (i) establish prevalence of E. coli isolates in surface waters; (ii) assess influence bacterial loads by season and water sources; and (iii) determine seasonal microbial and physicochemical relationships across sampling periods and surface water bodies. The study was guided by the hypotheses: (i) there was significant variation of E. coli isolates in shared surface waters; (ii) bacterial loads are significantly influenced by seasons and water sources; and (iii) significant microbial and physicochemical variations occur across sampling seasons and within shared surface water sources.
Materials and Methods
Study Area
Narok West subcounty, classified as semi-arid23,25 spans 17,944 km2 and is located south-west of Kenya in Narok County (Figure 1) . It is characterised by a bimodal annual rainfall ranging between 300 and 1,000 mm, 35 influenced by the Intertropical Convergence Zone and topographic relief from Lake Victoria.36,37 Ambient temperature range between 18°C in the highlands and 28°C in the lowlands, with a mean of 25°C. 38 Annual potential evaporation is about 1,820 mm, with a daily evaporation at 165 mm per day during the hot dry season. 39 The dominant plant is leleshwa (Tarchonanthus camphoratus), thorn scrub, sansevieria grass and scattered patches of forest. 40 The region is currently witnessing a decrease in annual rainfall and an increase in ambient temperatures.40,41 The subcounty lies within the Greater Maasai Mara Serengeti Ecosystem, a critical migratory corridor for wildlife.42,43 In relation to geology, the area is characterised by vertisol, cambisol, ferralsol and lithosol/rock outcrops. 44 The study area is dominated by the Maasai ethnic community, 45 who predominantly engage in pastoralism, wildlife tourism/conservation and crop farming as socio-economic activities. 46 The subcounty is a fragile ASAL currently witnessing increased land degradation, fragmentation and natural resource use conflicts attributed to changing land tenure.47-49

Map of Africa, Kenya and Narok West subcounty.
Selection of Sampling Sites
The study was conducted from May 2024 to April 2025. The sampling sites were selected through stratified random convenience sampling to represent the diverse landscape, based on surface water type (river or OWP), access and major water use/surrounding anthropogenic activity in the landscape (Figure 1). The sampling sites were geo-located using a handheld Global Positioning System (GPS) receiver (Garmin e-Trex 10, Olathe, USA; Figure 2). The geological coordinates and description of the sites are given in Table 1. Twenty-eight (28) surface open water points comprising 20 OWPs and 8 rivers, each with a single sampling point were sampled. The sampling sites were either in private or communal lands. 50 All sampling sites were open access, multi-use, accessible and used by humans, livestock and wildlife.

Map Narok West subcounty and sampling points.
Description of Sampled Water Bodies (Coordinates – Geographic WGS84).
Water Sampling for Physicochemical and Bacteriological Parameters
Physicochemical parameters were collected in-situ from 28 surface water points using a calibrated handheld HI-98194 Multiparameter Waterproof Meter field sonde (USA). The sonde probes were submerged in the water sampling point at a depth of 10 cm from the surface and the readings were taken directly by reading from the screen. Before sampling at each point, the probes were cleaned with deionised water. The in situ variables noted were dissolved oxygen (DO; %/mg/L), temperature (Temp.; °C), electrical conductivity (EC; μS/cm), pH, and total dissolved solids (TDS; mg/L).
Aseptic polyethylene bottles were used for microbial water sampling and collection from multi-use surface waters, 10 to 15 cm below the water surface. 51 Caution was taken to reduce rising sediments when filling the bottles since sediments harbour settled microbes. 52 Water sampling was conducted in triplicate 4 times per site (twice during wet season and twice during dry season). All water samples collected were stored in a cool box with ice and transported to Biological Sciences Laboratory at the Maasai Mara University for quantitative microbial assessment within 24 hours.
Culture and Enumeration of Coliforms
Using Eppendorf pipettes (Germany) and serial dilution technique, 50 μL aliquots water were filtered through sterile cellulose acetate membrane filters (47 mm diameter and 0.45 μm porosity; Millipore, County Cork, Ireland) by a sterile BioVAc 330B laboratory 3-branches stainless steel vacuum filter (China). Thereafter, the filter papers were placed in selective agar-filled Petri dishes in duplicate and incubated. Differential culture media (HiCrome™ Chromogenic Coliform Agar, India) incubated for 24 hours at 37°C was used to morphologically distinguish visible E. coli coliforms (dark-blue pigmentation) from other non-faecal indicator bacteria (bright pink/red colonies; Figure 3). ATCC 29522 E. coli was used as a positive control. Visible colonies (both purple/blue and pink/red) were enumerated using a colony counter and reported as colony forming units (CFUs) per 100 mL surface water following incubation.

Phenotypical identification and enumeration of E. coli and CFUs using differential culture media (HiCrome™ CCA) upon incubation at 24 hours at 37°C. E. coli coliforms (dark-blue pigmentation) from other non-faecal indicator bacteria (bright pink/red).
Data Analysis
The data was collected, cleaned and entered in SPSS version 27 which was used in carrying out the analysis. Values of physicochemical and bacteriological variables were summarised using means and standard deviations. Pearson correlation analysis was used to assess the existence of relationships between microbial and physicochemical parameters. Multivariate analysis of variance (MANOVA) and Tests of Between-Subjects Effects were used to assess the effect of water body (OWP and river), season (dry and wet), and their interaction on microbial and physicochemical parameters, with P < .05 significance level.
Results
Microbial and Physicochemical Water Quality
Cumulatively, there was a 100% (n = 112) and 62.5% (n = 70) rate of encountering CFUs and E. coli isolates in the surface water points within Narok West. Prevalence of E. coli in the sampled sites was statistically significant, (χ2(1) = 20.57, P < .05). Seasonally, there were nuanced findings based on the bacterial loads and physicochemical parameters (Table 2) . The dry season had higher pH, temperatures and TDS than wet season which exhibited higher mean total CFUs and E. coli loads together with conductivity and dissolved oxygen. Seasonal analysis of microbial quantities against water bodies revealed that rivers had higher total CFUs and E. coli loads during the wet season as opposed to dry season (Table 3). This was also evident for E. coli loads, though higher E. coli loads were established during dry season (Table 2) were found. Moreover, during the dry season, both open water pans and rivers had higher pH, temperature, DO and TDS than during the wet season. Only conductivity was higher during the wet season as opposed to dry season, for both rivers and open water pans. The study established that seasonally, both rivers and OWPs in the landscape had lower CFUs and E. coli loads, with lower pH, temperature, conductivity, DO and TDS during the dry season as opposed to wet season. Conversely, concerning surface water sources, rivers had more total coliform and E. coli loads, conductivity, DO and TDS in the wet season. The landscape witnessed higher CFUs, pH, temperature, conductivity, DO and TDS in rivers as opposed to open water pans during dry season, unlike E. coli. However, seasonality, all measured variables were higher in rivers during the wet season.
Seasonal Descriptive Statistics Across Sampled Water Points.
Dry Season Correlation Analysis of Water Quality Parameters.
P < .05. **P < .01.
Seasonal Correlation Analysis of Water Quality Parameters
Seasonal Pearson correlation analysis was conducted to examine the relationships among microbial and physicochemical parameters, with significant correlations determined at P < .05. During the dry season (Table 3), total coliforms and E. coli exhibited a weak positive correlation, which was not statistically significant. Neither microbial parameter demonstrated significant associations with physicochemical variables. Among physicochemical parameters, several significant correlations were observed. Conductivity correlated positively with temperature (r = .324, P = .015), though weak. pH showed a significant positive correlation with DO (r = .302, P = .024). Conductivity was positively correlated with DO (r = .308, P = .021). Similarly, TDS was significantly positively correlated with DO (r = .350, P = .008), Temperature (r = .335, P = .012) and conductivity (r = .984, P < .01).
In the wet season (Table 4), a weak but statistically significant positive correlation was observed between CFUs and E. coli (r = .465, P = .003). No significant associations were found between microbial parameters and physicochemical variables. Physicochemical parameters displayed several significant relationships. pH correlated positively with temperature (r = .394, P = .003), while DO revealed a positive correlation with temperature (r = .317, P = .017). TDS demonstrated a moderate positive correlation with conductivity (r = .648, P < .01).
Wet Season Correlation Analysis of Water Quality Parameters.
P < .005. **P < .001.
A multivariate analysis of variance (MANOVA) was conducted to assess the influence of water body (OWP and river), season (dry and wet), and their interaction on microbial and physicochemical parameters. The multivariate test statistics indicated significant main effects for both water body (Wilks’ λ = .669, F(7,62) = 4.387, P = .001) and season (Wilks’ λ = .643, F(7,62) = 4.920, P < .001). However, the interaction effect of water body × season was not statistically significant (Wilks’ λ = .811, F(7,62) = 2.062, P = .061).
Having found significant main effects from the MANOVA, a post hoc analysis was conducted for each of the main effects to assess the levels that had a significant difference. The results of these analyses were as shown in Table 5. The results showed that CFUs was significantly influenced by season (P < .001), but not by water body (P = .136). E. coli counts were not significantly affected by water body (P = .727) or season (P = .138). Regarding physicochemical parameters, pH showed a significant effect of water body (P = .001) and season (P = .050). Water temperature was significantly affected by season (P = .025), but not by water body (P = .096).
Tests of Between-Subjects Effects of Water Quality Parameters.
Conductivity was significantly influenced by water body (P = .007), but not by season (P = .170). Dissolved oxygen was significantly affected by water body (P = .003) but not season (P = .098). Total dissolved solids were significantly influenced by water body (P = .011) and not season (P = .801).
Discussion
The overall objective of this study was to establish seasonal variation in microbial and physiochemical water quality on surface water sources in the shared human-animal ASAL of Narok. The study revealed several notable findings. First, it established high encounter rates of CFUs and E. coli isolates in the surface water points within Narok West. Secondly, it revealed bacterial loads are significantly influenced by seasons and water sources. Finally, it revealed nuanced statistically significant seasonal microbial and physicochemical fluctuations within surface water bodies. These findings on the prevalence of coliform forming units and E. coli colonies and physicochemical profile of surface waters of Narok are in correspond to previous studies 31 which established 5.1-9.7 pH ranges and high faecal and non-faecal bacteria in water pans of Narok South subcounty. Additionally, higher faecal indictor bacteria (E. coli) encounters were significant during the wet season compared to with dry-season levels in congruence previous studies.53,54 These high coliform numbers can plausibly be attributed to human excreta, livestock pastoralism and seasonal migration of wildlife, though requires further studies. Moreover, the E. coli loads were higher than those established from Nairobi River, 55 thus could be attributed to surface runoff from open defecation, overflowing and flooding of sanitation amenities, animal waste and wastewater treatment plants. These sources can be established via faecal-source and non-faecal pollution tracking.56-59
High TDS levels in the water points may be attributed to high levels of hydrogen ions found in clay soils, which increase acidity in water pans, 31 though warrants confirmatory tests. Higher bacterial loads during wet season can be attributed to increased introduction of CFUs and E. coli isolates from surface runoff, human excreta and animals waste into the water bodies, 54 while lower mean water temperatures during wet season compared to dry season can be attributed to lower ambient temperatures. Conversely, higher DO during wet season can be because of increased churning of waters during inflows. Our findings negate 60 findings which established that water pans in Baringo had higher pH and conductivity during wet season in comparison to dry season.
Our findings reveal that surface water sources, the primary sources of water including for domestic use in Narok County, are not suitable for direct human consumption based on bacterial and physicochemical properties. Additionally, recreational activities in these waters such as swimming should be limited as ingestion of water (swallowing) predisposes the residents to faecal-oral transmission of waterborne pathogens and other gastrointestinal parasites.11,61-63 Furthermore, since these sources are prone to pollution,11,17,64,65 Narok County should invest in providing potable water for its residents to avert waterborne diseases in the face of changing weather and environment.66,67 In areas where access to potable water is unavailable, active awareness of water treatment modes should be encouraged. Furthermore, community members should be made aware of the negative impacts of direct consumption of water from surface water sources. 68 This can aid in reducing regional, national and global waterborne disease burden. 69 Additionally, further studies on E. coli anti-microbial resistance (AMR) levels within the shared multi-use water points are required.70-72
In relation to established water parameters and livestock productivity, we noted that seasonal levels of pH in surface waters were within marginable permissible levels for cattle and other livestock, though not ideal. In as much as TDS levels below 500 mg/L is considered safe for livestock, higher variations witnessed during dry season might lead to diarrhoea, temporary digestive issues and mineral related deficiencies including stunted growth among calves, lambs and kids. However, in relation to CFU and E. coli levels, the surface waters of Narok West subcounty were above recommended levels. These high microbial levels could potentially reduce livestock productivity and subsequently affect livestock keepers’ livelihoods. Furthermore, since mature livestock might possess some resistance to common waterborne pathogens, the high E. coli loads in the water can affect young animals due to immature immune systems and manifest in form of severe diarrhoea, dehydration, and fatalities. This would result in economic losses due to veterinary costs and reduced productivity. It is worth noting that studies have revealed that calves drinking microbial contaminated water put on less weight than those drinking clean water. 73 With Narok being a beef and dairy production hub, it is prudent that clean water be made available for livestock, in the pursuit of maximising productivity. During our study, it was noted with concern that waters from some rivers and open water pans are being used for horticulture irrigation. This practice could potentially affect food safety and quality, especially for those vegetables and fruits eaten raw, poorly washed and/or undercooked.74-76
With recommended pH range of livestock water being 6.5 to 8.5, levels exceeding 8.5 might cause alkalosis in ruminants. This can result in reduced feed digestibility and nutrient absorption leading to reduced milk yield and / or weight gain, thus not suitable for prolonged consumption. While water temperature between 10 and 25°C is generally acceptable for livestock, as it encourages intake, warmer water temperatures exhibited during dry season can result in microbial contamination and proliferation (>25°C) including cyanobacteria. In relation to conductivity, levels below 1,000 µs/cm are considered generally safe for livestock with ranges approaching or exceeding 1000 µs/cm could pose risks to livestock in form of diarrhoea, reduced water intake and mineral imbalances especially wet season.
Our findings established that DO levels were lower during the dry season as compared to the wet season. Low DO levels can support anaerobic bacteria and increase waterborne pathogenic risks, reduce consumption and impact productivity through reduced hydration. The observed low DO levels can be attributed to decomposition of organic matter, dead algal blooms or introduction of nutrient rich runoff. 77 Low DO levels (<2-3 mg/L) render water hypoxic and thus unsuitable for aquaculture, especially during dry season.
Study Limitations
Seasonal precipitation, river flows, water source dimensions and sources of microbial pollution were beyond the scope of the study. Previous studies have noted changes in rainfall precipitation attributed to weather variation 28 in the study area, which subsequently would affect river flows and water source dimensions. In relation to microbial varieties, we were limited to total coliform forming units and E. coli colony counts as opposed to faecal coliforms and enterococci counts. Finally, since the ecosystem is quite extensive coupled by paucity of data of number of OWPs and limited resources (finances, time and equipment), this study sought to establish baseline data on surface water sources and recommends further studies.
Conclusion
The study showed seasonal microbial and physicochemical parameters in surface water bodies in an ASAL region in sub-Saharan Africa, in the face of weather variability. 28 It revealed high bacteria loads and physicochemical levels above approved WHO levels. These high levels are likely to predispose humans and animals to waterborne diseases of public health importance, thus resulting in increased human morbidity and mortality vis-à-vis reduced livestock productivity and livelihood losses. Cumulatively, these could dent the attainment of national, regional, and global agenda ranging from the Kenyan Vision 2030 78 ; The African Union Agenda 2063 79 ; International Decade for Action 2018-2028: Water for Sustainable Development; International Decade of Sciences for Sustainable Development: 2024-2033; and a myriad of UN SDGs 2 including UN SDG 3: Good health and well-being; SDG 6: Clean water and sanitation; SDG 14: Life below water; SDG 15: Life on land; SDG 16: Peace, Justice and Strong Institutions; and SDG 17: Partnerships for the Goals. We advocate for adoption, management and improvement of water conservation strategies8,80 such as rainwater harvesting, fencing of multiple use open water pans and provision of alternative water points to avoid soiling by animals and reduce disturbing sediments 65 as these harbour pathogens and could possibly result into increased waterborne disease infections. We also call for incorporation of local indigenous knowledge systems and nature-based solution practices into water resource management, and periodic spatiotemporal physicochemical and microbial assessments of surface wetlands. Lastly, in a bid to ensure consumption of potable water, we emphasise the need for effective water, sanitation and hygiene campaigns with support from all water and sanitation sector stakeholders.
Recommendation
We propose increased access to potable water and awareness creation on the demerits of direct consumption of water from surface water sources. We also propose further studies on ecosystem health in relation to pathogenic waterborne diseases including E. coli anti-microbial resistance analysis of ubiquitous waterborne pathogens within the waterbodies. This should include seasonal prevalence of waterborne diseases in the face of changing weather and climate, horticultural food safety attributed to irrigated surface waters use vis-à-vis community knowledge, attitude and practices on water, sanitation and hygienic practices in the landscape. Using the Information, Education, and Communication strategy, community members should be made aware of water quality within surface water points and empowered on how to improve public health, making informed decisions and adopting healthy behaviours. We recommend concerted efforts to protect water points from point and non-point contamination, with the communities taking a lead. Through interagency collaboration, Kenya’s Ministry of Health in collaboration with Ministry of Water, Sanitation and Irrigation, Ministry of Environment, Climate Change and Forestry, county governments and public-private health sector players should develop, fund, build capacity and implement national microbial water quality monitoring framework which will conduct ecological health assessments including faecal-source and non-faecal pollution tracking.
Footnotes
Acknowledgements
We extend gratitude to the community of Narok where the sampling was done; Francis Koya and Sammy Yegon (community laymen and translators); together with Fanuel Onyango (Water Quality and Pollution Control Officer at Water Resource Authority, Lake Victoria Basin Area) who assisted with in situ water sampling. We acknowledge Brian O. Otiego for developing the sampling point map. Lastly, we thank George Njoroge, Jamlick Lepaa Mpakany and Faith Jepkemei Waswala for assisting in the preparation and analysis of the microbial samples.
AI Acknowledgement
No generative AI was used in the preparation of this manuscript.
Ethical Considerations
The study protocols and procedures were approved by Egerton University Institutional Scientific and Ethics Review Committee (EUISERC/APP/327/2024); and National Commission for Science, Technology and Innovation (NACOSTI/P/24/35318).
Author Contributions
BMW conceptualized the idea, conducted the study, did data curation together with formal analysis, administered the project, validated results, developed the draft document together with review & editing. GPO helped in methodology, supervision, and reviewing & editing developed document. RO was instrumental in funding acquisition, supervision, and reviewing & editing developed document. PW contributed to the study’s methodology, supervision, and reviewing & editing developed document. All authors provided intellectual input to the drafts, read and approved the final version of the manuscript.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was partially supported by a National Geographic Society Grant NGS-98595R-23 to RA for water collection and bacteriology.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
