Presumptive detection of Giardia lamblia cysts in borehole water in Gombe metropolis, north-eastern Nigeria: a two-round cross-sectional study with implications for water safety

Giardia lamblia (syn. G. duodenalis, G. intestinalis) is a flagellated intestinal protozoan and a common cause of waterborne diarrhoeal disease. Its environmentally resistant cysts can persist in untreated groundwater, yet boreholes in Nigeria are widely assumed to be safe and are rarely screened for protozoan parasites. We examined borehole water from ten quarters of Gombe metropolis (Malam Inna, Tudun Wada, Pantami, Orji, Tumfure, Bolari, Jekadafari, Nassarawo, Kumbiya Kumbiya and Kagarawal) in a cross-sectional study with two sampling rounds two weeks apart. One 15 L sample was collected per site per round (20 samples in total), concentrated by sedimentation and centrifugation, and examined as unstained normal-saline wet mounts by light microscopy. Samples were scored positive when at least one cyst with morphology consistent with Giardia was seen. Two of 10 samples (20%) were positive in each round; overall, 4 of 20 samples (20%; 95% Wilson CI 8-42%) were positive. Three of ten sites were positive at least once: Jekadafari in both rounds, indicating repeated detection, and Tumfure and Pantami in one round each. Positivity did not differ between rounds (Fisher's exact test, p = 1.000). Because identification relied on morphology alone, without staining, immunofluorescence, PCR or viability testing, and because pH, turbidity and temperature were not measured on site, these results are presumptive detections from a small, non-random sample of boreholes. They nevertheless indicate that the underground origin of borehole water does not by itself guarantee freedom from parasitic contamination. We recommend routine parasitological monitoring, wellhead protection and household water treatment, and molecular confirmation (PCR and genotyping) in follow-up work.