Prevalence rate and risk factors of human cystic echinococcosis: A cross-sectional, community-based, abdominal ultrasound study in rural and urban north-central Chile

Author summary Human cystic echinococcosis (CE) is a parasitic disease caused by Echinococcus granulosus s.l. complex; its cycle involves canids and livestock, mainly sheep. It is endemic in areas with extensive livestock breeding activities, where close contact occurs between humans and the domestic dog-livestock parasite cycle. After ingestion of parasite eggs, people may develop fluid-filled cysts, mainly in the liver. CE is a neglected disease, which causes significant socioeconomic impact mainly on poor communities worldwide. Prevalence data in many affected areas is lacking or largely underestimated, partly because human cases typically do not reach medical attention or official disease records. We determined the prevalence of abdominal CE by ultrasound population-based screening in volunteers residing in urban and rural localities of the Monte Patria Municipality, Limari province, Coquimbo region, which is an E. granulosus s.l. endemic area of northern Chile, and assessed the risk factors associated with human infection. We performed an ultrasound survey on 2,439 people residing in thirteen localities and found an overall prevalence of 1.6% (95% CI 1.1-2.2). A higher risk of infection was associated with residing in rural localities, older age and drinking non-potable water. CE cysts were either in active or inactive stages in equal proportions and 84.6% of infected volunteers were newly diagnosed with CE. Our findings will serve to support the implementation of cost-effective diagnostic, treatment and control strategies and to improve the epidemiological surveillance system for CE in Chile. Background Cystic echinococcosis (CE) caused by Echinococcus granulosus sensu lato (s.l.) is a neglected and underdiagnosed parasitic zoonosis that has a significant socioeconomic impact on rural communities relying on livestock farming. CE is endemic across Latin America, including Chile, where the Coquimbo region exhibits a relatively high record of hospital-based human cases and infected animals. However, the incidence of hospitalized CE cases may underestimate the real burden of infection in a population, since the majority of cases never reach medical attention or official disease records. Methodology/Principal findings In 2019, a cross-sectional, community-based study was conducted with the objectives of estimating for the first time the prevalence of human abdominal CE using abdominal ultrasound (US) screening in volunteers residing in urban and rural localities of the Monte Patria municipality located in Limari province, Coquimbo region, Chile, and identifying the risk factors associated with human infection. Pre-screening activities included a 16-h lecture/hands-on training aimed at rural physicians that focused on the diagnosis of CE by US, based on current WHO recommendations. A total of 2,439 (similar to 8% of municipality inhabitants) people from thirteen target localities were screened by abdominal US in June-July 2019. We found an overall CE prevalence of 1.6% (95% CI 1.1-2.2) with a significantly higher likelihood of infection in rural localities, older age classes and people drinking non-potable water; 84.6% of infected volunteers were newly diagnosed with CE. Cysts were either in active or inactive stages in equal proportions; active cysts were detected in all age classes, while 95.7% of inactive cysts occurred in >40 years-old subjects. Conclusions/SignificanceThis is the first US survey aimed at detecting human infection caused by Echinococcus granulosus s.l. in Chile. Our findings indicate a high CE prevalence in the area, and contribute to define the demographic and behavioral risk factors promoting the transmission of the parasitic infection within target communities. Our results support the implementation of cost-effective strategies for the diagnosis, treatment and control of CE, and the need to improve the epidemiological surveillance system in Chile.

Automated summary

This study determined the prevalence of human abdominal cystic echinococcosis (CE) using ultrasound screening in a region of northern Chile and identified the risk factors associated with infection. The results showed a high prevalence of CE in the area and provide support for the implementation of cost-effective diagnostic, treatment, and control strategies.