1. Introduction

Malaria remains the foremost cause of morbidity and mortality in the tropics [1]. In 2023, over 50% of the world’s population at risk of infection and 95% of the malaria burden were reported in sub-Saharan countries [2, 3]. Increased funding for malaria interventions in the last decade has resulted in reduced malaria parasite transmission rates [4]. However, the benefits achieved with the scaled-up antimalaria interventional measures require comprehensive surveillance and monitoring to ensure continued gains in each and every World Health Organization (WHO) member country [5].

A notable increase in malaria prevalence in the coastal region of Kenya according to Kenya National Malaria Indicator Survey (KNMIS) of 2016 jolted the national and county governments to find out what could be the environmental or social economic drivers attributable to the sudden rise of malaria cases [6]. Mosquito and human factors normally determine rates of new infections with malaria parasites [7, 8]. Anopheles breeding is often affected by biotic as well as abiotic factors such as land cover, rainfall, humidity, wind, edaphic, altitude, topography, and temperature which can also be used to forecast the risk of malaria transmission [9, 10]. Significant malaria prevalence may be presumed in zones with higher temperatures and substantial amounts of rainfall [11]. These suitable environmental conditions promote higher fecundity in anopheline species as well as rapid malarial parasite reproduction within the mosquitoes’ bodies [10, 12]. Coincidentally, no sudden change in soil and climatic conditions had been reported in the recent past [13, 14]. Highly cultivated areas have increased favourable habitats for most of the primary vectors, which prefer sunlight and nonforested areas [15]. Therefore, clearing bushes, keeping of livestock animals, farming food and cash crops, and development of urban centers may affect malaria transmission levels [16]. Although reduced hygienic conditions in urban areas may advance vector breeding in some instances, say for Anopheles stephensi, urbanized centers are likely to have reduced suitable mosquito breeding sites [1, 17, 18]. Nevertheless, positive human behaviors such as prompt and accurate testing for malaria and immediate access to antimalarial drugs if diagnosed positive are vital towards reducing risk [19, 20].

Epidemiology of vector-borne diseases is often influenced by livelihood activities and human movements, which impact positively or negatively on malaria risk in its elimination settings [21, 22]. At the same time, economic and social development is being heavily drained by the costly antimalaria campaigns [22, 23]. In high-endemicity areas, there is limited knowledge on how and to what extent extractive industrial projects are impacting or not, the altered epidemiology, and entomology of malaria [24]. Through a variety of proximal and distal factors, mining and other natural resource development and management projects are considered to influence local disease patterns, including malaria [25]. Particularly, malaria vector Anopheles gambiae sensu lato (s.l.) had been reported to exploit favourable habitats created during project-related developments in the modified physical environment [22, 26]. Substandard screening and sanitation of poorly constructed sketchy housing structures expose workers attracted by mining projects to infective mosquitoes’ bites [27]. Increased vector breeding and human–vector contact were exacerbated by lack of drainage resulting to periurban water bodies (e.g., swamps) [28]. In contrast, companies have an interest in keeping their workforce healthy and thus productive by actively creating malaria control and prevention opportunities ([24, 29, 30]). In the recent past gold, diamond, lithium, and copper mines in Democratic Republic of the Congo had positively impacted on surrounding local communities, socioeconomically [25, 31].

A proposal to commercially exploit titanium deposits located in the Kwale Region was presented by the Canadian company Tiomin Resources Inc. to the Kenyan Government, where the latter approved after years of negotiations [32]. Kenya joined the league of mineral exporters in February 2014 [32]. Sadly, limited health care and disease prevention measures have been established despite the widespread expansion of legal titanium mining in coastal areas of Kenya [15]. Investigations have demonstrated that mine-related conflict often revolves around six thematic areas, namely, land ownership, “unfair” compensation, inequitable resource distribution, deteriorating communal health status and environmental degradation, mine-induced poverty, and human rights abuses [29]. It is often expected that mine developers will as well finance tangible educational, social and health-related projects and services. Impact of the above-mentioned issues can be minimized through corporate social responsibility (CSR) towards full pacification of age-old diseased and impoverished local communities [32, 33].

Incidentally, malaria prevalence in the coastal region had shot from 4% in 2015 to 7.6% (as percentage of all first outpatient visits) in 2017 [34]. This begged the question: What are the contributing factors towards this sudden spike in higher malaria prevalence in the Kenyan coastal region [35, 36]. Fundamental changes in the ability of Anopheles mosquitoes to vector malaria may have been caused by shifts in mosquito feeding and resting behavior connected to insecticide-treated bed net coverage [18, 37]. Changes in land use, housing structures, and/or climate could have shifted microclimatic dynamics associated with Plasmodium transmission. Mining regions with disused mining sites contribute a lot to malaria endemicity due to displacement and proliferation of mosquito breeding sites, high human migrations, and lack of adequate antimalaria activities [9, 10]. Specific vector control measures must be introduced to decimate this upcoming source of malaria in Kenya [38]. The study was aimed at determining the malaria prevalence and parasitemia density among residents and migrants in the five different sites of investigation, namely, the control (C) site with no dam, sugarcane, nor mining; the dam (D) site, the sugarcane (S) site, the mining (M) site, and the dam–sugarcane–mining (DMS) site.

2. Materials and Methods

2.2. Study Site

The study was conducted in endemic Kwale County in the coast province of Kenya, a malaria mesohypoendemic zone (Figure 1). Kwale County borders Tanzania to the south-west and the Indian Ocean to the east. The area is often hot and humid all year round with an annual mean temperature range of 22°C–34°C, average relative humidity range of 70%–80%, and annual rainfall range of 900–1500 mm. Altitude ranges from 0 to 462 m above sea level. Both malaria and lymphatic filariasis are endemic in the study area. Kwale residents experience moderate to high malaria transmission. Studies undertaken along the Kenyan coast have reported a yearly increase in malaria admissions and childhood mortalities [13].

3. Results

3.2. Malaria Prevalence in the Five Selected Study Sites

Overall, the malaria positivity rate was 22.9% (95% CI: 20.4–25.6) by RDT and 20.1% (95% CI: 17.8–22.7) by microscopy. P. falciparum observation by RDT was highest in the DMS site 33.7% (95% CI: 27.8–40.8) followed by the S site with 26.8% (95% CI: 21.6–33.4), D site with 23.3% (95% CI: 18.3–29.6), M site 17.6% (95% CI: 13.0–23.8), and the least being the C site with 11.0% (95% CI: 7.3–16.7) (Figure 2).

3.3. Parasitemia Density in the Five Study Sites

The overall parasitemia density from microscopy results was 8.4 (95% CI: 6.2–11.3) with a site-specific parasitemia density of 18.7 (95% CI: 11.2–31.2), 8.6 (95% CI: 4.7–15.7), 7.1 (95% CI: 3.7–13.3), 3.7 (95% CI: 1.3–10.6), and 3.1 (95% CI: 1.5–6.6) for DMS, S, D, M, and C sites, respectively (Figure 3). The highest parasitemia density was found in the DMS site where all the selected human activities were undertaken.

4. Discussion

Dam creation is often aimed at storing water for use domestically in cooking and washing activities and agriculturally in irrigating gardens and farms. Incidentally, such dams become habitation grounds for water living animals and plants. Among the water-living animals are the mosquitoes in the larva stage which mature and later as adult forms transmit various pathogenic organisms [10]. Of our interest is the transmission of P. falciparum by Anopheles mosquito. Mosquitos are known to oviposit their eggs in fresh or salty water bodies [41].

On the other hand, humans, animals and plants need water to quench their thirst. Green plants are the source of cell sap for male mosquitoes which in turn fertilize female mosquitoes for the latter to oviposit fertilized eggs which hatch into aquatic free-swimming larvae. Mosquito larva growth depends on watered niches with dissolved nutrients [42]. Mosquito larvae are habitual filter feeders. They have fan-like mouth brushes that sweep water at their mouths from in front of them. In this mechanism, they sieve out small particles of decomposing materials and microorganisms, which they then eat. Some larvae in Stages 3 and 4 are known to eat other mosquito larvae in Stages 1 and 2 [43]. Female adult mosquito populations are hematophagous and hence suck blood from humans and animals within 5-km radius or even further if carried away with the help of strong coastal monsoon winds. Humans and animals coming to draw water or drink, respectively, are precious blood-carrying commodities to the malaria vector. The blood meal yields high levels of iron as hemoglobin in erythrocytes and as ferric transferrin [43]. The female mosquito uses the heme-iron part and the globulin-protein part to supply nutrients for viable egg production. Most importantly, iron is required for optimal egg development and viable offspring. Therefore, water environments are crucial for malaria vectors to thrive. Particularly, presence of a dam not only provides mosquitoes with breeding environments but such sites also attract humans and animals for their blood-feeding activities towards self-sustenance and generational continuity [44].

Sugar faming involves land selection, farmer recruitment, land preparation, seed cane stem seed selection and planting, crop maintenance, irrigation in some regions, harvesting, transportation, and cane weighing [16]. Land selection and preparation often necessitate uprooting of trees, clearing of bushes, and plowing and harrowing the land until a clear land is suitable for sugar stem seed planting, activities which engage machines and humans as well. Shallow puddles and pools of water before or during planting of sugarcane are often fertile sites for oviposition of malaria vector eggs, and larval occupation and growth into mature pupa and adults emerge. Subsequent activities equally demand animal, human, or mechanized labor, situations which offer continued blood meal sources for the female mosquitoes. Sugarcane stem and leaves also provide feeding points for male mosquitoes, hence the increased potency of their longer and slender sperms leading to higher fecundity [45, 46]. Both larval nutrition and adult nutrition significantly affect mosquito fecundity [47]. It is known that blood meal quantity and source can influence mosquito fecundity [48]. Intake of carbohydrates can influence egg production while blood meal source and quantity taken by adult mosquitoes determine fecundity [48]. Filled up ventral diverticulum or crop with plant sugar meals can compete for space in the midgut for blood meals and thereby reduce blood meal intake and fecundity among mosquitoes [49]. Sugarcane stems, leaves, and floral parts are also resting places for both male and female mosquitoes. Digesting of blood by female mosquitoes is usually an energy-expending process, hence the nonflight restful mode and posture during these midgut-specific miR-1174 functions of the midgut through its target gene serine hydroxymethyltransferase (SHMT) enzyme whose depletion causes female mosquitoes to lose their flight ability and die within 48 h of a blood meal [50, 51]. Therefore, rest for female mosquitoes is very important for effective digestion of a blood meal and viable egg production.

Modern mining procedures involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, and final reclamation or restoration of the land after the mine is closed [22]. During prospecting of crude ores, various technologically identified suspected earth points are opened up, most of which yield negative results leading to movements to fresh grounds and repeating the same procedure until a positive crude ore is discovered. Once discovered, the digging up using earth-moving tools and machines is normally heightened. Micro as well as macro freshly opened up earth points are often left gaping wide which fill up with water once rains fall. The stagnated water shelter, broods, and breeds millions of malaria vector eggs which hatch into larvae [52, 53]. Larvae in turn produce pupae and adults. When female mosquitoes quest for blood meals and suck Plasmodium-infected blood meal from humans and animals, with more than a minimum number of the malaria agents enough to cause an infection, the sporogonic cycle of parasites’ multiplication in the mosquito begins, while in the mosquito’s stomach, the microgametes penetrate the macrogametes generating zygotes. The zygotes in turn become motile and elongated (ookinetes) which invade the midgut wall of the mosquito where they develop into oocysts. The oocysts grow, rupture, and release sporozoites, which make their way to the mosquito’s salivary glands. Inoculation of the sporozoites into a new human host perpetuates the exoerythrocytic and erythrocytic stages of malarial agents’ life cycle. Workers in mines includes miners, office and security staff, transporters, supervisors, managers, visitors, caterers, and business men and women directly or indirectly related to the mining activities [22]. These workers not only supply blood meals to mosquitos but also provide malarial agents to the blood-questing female mosquito if one is suffering from malaria.

Proceeds from mining are used by the benefitting community to improve infrastructural, social, and educational amenities [54]. Good roads and means of transport contribute to faster access of health centers when one is seeking treatment. Financial enablement allows community members to purchase drugs as well as vector control gadgets such as insecticide-treated nets, repellants, and coils. Stone-walled and concrete-floored houses have been found to reduce indoor mosquito densities. Screened windows, ventilations, and eaves cut off malaria vector access to humans living in the building structure, hence reducing human–mosquito contact hours. Access to primary, secondary, and tertiary education equips community members with knowledge, skills, attitudes, and practices leading to behavior change towards disease diagnosis, treatment, prevention, and control, including malaria. A relationship exists between a positive change in knowledge, attitude, and practices and decline in malaria prevalence [22].

Social corporate responsibility by the mining company includes environment issues such as mined site reclamation and rehabilitation. We found out a well-executed Tiomin mining company reclamation and rehabilitation of mine dune process which were later returned to the community for reuse as agricultural land, recreational activities, and/or man-made forest reserves (Figure 4). Indigenous and exotic grass, herbs, and/or trees were planted and well taken care of resulting into rush green grass lawns and forests which were environmentally fit for habitation (Figure 5).

All this may explain why the study populations in the DMS site had the highest Plasmodium positivity and parasite burden. The interplay between the environment, climate, and living organisms triggers a chain of exchanges of malarial agents between living organisms and vectors [5]. Correspondingly, agricultural livelihood activities, travelling, and outdoor social gatherings are linked to increased risk of malaria infection due to prolonged contact with mosquito vectors where standard preventive interventions may not be particularly effective. Notably, movements related to agriculture-like large-scale migration of laborers searching for economic opportunities play role in malaria epidemiology.

5. Conclusion

Malaria morbidity and burden were highest in the combined study site of dam, sugarcane, and mining human activities. Sugarcane farming and dam construction were a significant driver in Plasmodium sp. prevalence as well as parasite burden, as compared to C and M site; hence, anthropogenic activities affect positivity rates and parasite densities. Therefore, the higher the anthropogenic activities, the higher the malaria incidences and burden. Well thought out, tailored, planned, and implemented mitigation measures per anthropogenic activity can reduce malaria transmission intensities as demonstrated in the titanium study site. Mitigation measures such as flattening excavated sites, rehabilitating mine dunes by planting grass and trees, and prompt malaria diagnosis and treatment by a titanium mining company did bear fruits and resulted to reduced malaria infection rates. Even with continued social economic anthropogenic activities, residents can still live with insignificant Plasmodium infections and mosquito bites if proper mosquito control measures are seriously, intentionally, and deliberately undertaken by both the public and private sectors and partnerships thereof.

6. Recommendation

Characterized relational interplay between these anthropogenic activities and P. falciparum parasitemia may be useful in developing tailored strategies towards optimized malaria control interventions in areas with or without anthropogenic activities. Against new infections, residents may use long-lasting insecticide-treated nets (LLINS), wear body covering clothes, and use insecticide repellants, screened windows and eaves, or closed eaves which have been demonstrated to be still effective as it was in the wealthier mining populations in the M site. To reduce vector densities, residents may use larvicides or biocontrol agents such as Bacillus thuringiensis israelensis (Bti) in larval breeding sites in sugar farms, surrounding water reservoirs, and flattening and rehabilitation of mining areas after excavations as well as planting grass and trees in reclaimed sand dunes, as done by a titanium (Tiomin) mining company in Msambweni County, Kwale, Kenya.

Disclosure

The funders had no role in the study design, data collection and analysis, decision to publish, nor the preparation of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Author Contributions

E.G., JudyM., C.O., S.N., and the late E.M. participated in the development of the study, design of the protocol, and project implementation. C.M., JumaM, B.C., and S.A. participated in information and sample collection and laboratory analysis. C.O. carried out statistical analysis. The late E.M. provided overall scientific guidance. All authors participated in the initial review of the final manuscript.

Funding

The financial support for this research was provided by the Government of Kenya through Internal Research Grant (IRG) # KEMRI/IRG/028/2017/18 (L-0665).