The Rinconada Lake System (RLS) as a Potential Reservoir of Protozoan Parasites in Camarines Sur, Philippines

Protozoan and helminthic parasitism remain significant health and economic burdens, particularly in developing countries such as the Philippines. This study evaluated the Rinconada Lake System (RLS) in Camarines Sur, comprising Lakes Buhi, Bato, and Baao, as a potential reservoir for medically important parasites. Microscopic examination of surface water samples from 20 stations revealed no helminthic ova, which may have settled in sediments, but detected potential coccidian oocysts of Cryptosporidium spp. (55%, 11/20) and Cyclospora sp. (40%, 8/20). Culture-based detection of free-living amoeba was at 60% (36/60), showing organisms resembling Acanthamoeba spp. (35% or 21/60) significantly linked to Lake Baao and Lake Bato (P < 0.01) likely reflecting greater anthropogenic influence. The metabarcoding confirmed the presence of protozoan parasites in the lakes, such as Echinamoeba sp. and Vermamoeba vermiformis, while no helminthic parasites were detected using current methods. Additional microbial eukaryotes of medical relevance, such as fungi and algae, were also identified. Retrospective analysis of the available health records from surrounding communities showed that Entamoeba histolytica was the most documented case for 4 years (47.8% or 75/157), followed by various helminthic infections (49.7% or 78/157), predominantly caused by Ascaris lumbriocoides. There was no significant association with the patient's residence or sex, except for significantly higher cases in those aged 0-10 years. In conclusion, findings suggest that the RLS may serve as an environmental reservoir for opportunistic protozoan parasites, while its role in helminthic transmission requires further investigation. Based on current evidence, emphasis on surveillance and mitigation strategies in communities surrounding the RLS, especially for protozoan parasites, is highly recommended.