Community-based abdominal ultrasound survey of cystic echinococcosis in Bhutan: prevalence and risk factors

BACKGROUND: Cystic echinococcosis (CE) is a neglected parasitic zoonosis, caused by larvae of the Echinococcus granulosus sensu lato (s.l.) complex. The parasitic transmission cycle is maintained between dog and livestock (ungulates), with humans involved as dead-end hosts. In Bhutan, CE is a recognized public health and veterinary problem; however, the true burden of CE in high-risk communities remains unknown. This study assessed the community-level prevalence, potential risk factors, and awareness of CE in Bumthang District to inform CE control strategies. METHODS: We conducted a cross-sectional, community-based abdominal ultrasound survey (April-July 2025) in four gewogs of Bumthang district using cluster sampling design. We invited all individuals aged ≥ 12 years from the selected villages. The WHO-IWGE ultrasound staging criteria were used to classify the cysts. RESULTS: Among the 3,058 participants with complete data (of 3,077 screened), the cluster-adjusted prevalence of confirmed CE (ultrasound-pathognomonic findings) was 2.58% (95% CI: 1.93-3.44). When cystic lesions (CL) were included, the estimate was 3.66% (95% CI: 2.92-4.59). The liver was the most commonly affected organ (93%), and cyst stages ranged from CE1 to CE5, indicating the presence of both active and inactive infections. Only intermittent dog contact ("sometimes") was independently associated with higher odds of prevalent CE (aOR 1.73, 95% CI 1.04-2.82). Other commonly hypothesized individual-level factors (sex, education, occupation and place of birth) were not independently associated with infection. All participants with CE and other clinically significant ultrasound findings received counselling, stage-appropriate management for CE cases, and appropriate referral and treatment within Bhutan's state-funded free healthcare system. CONCLUSION: CE is prevalent in Bumthang district. Currently, it remains under-recognized, under-reported and a huge detection gap exists between hospital-based passive detection and true community prevalence. The weak discrimination by individual-level risk factors and the pattern of modest village-level clustering are consistent with the environmentally mediated transmission hypothesis. These findings support the need of One Health control strategies including integrated surveillance rather than targeted approaches for high-risk groups.