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

Abstract

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 Limarí 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 (~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/significance: This 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.

Fig 1. Map of localities of residence of volunteers screened by abdominal ultrasound in the Monte Patria municipality, Limarí province, Coquimbo region, Chile.

Locality names in bold indicate the places where the ultrasound screening hubs were set-up in the study area. (Map made in QGIS Geographic Information System. Open Source Geospatial Foundation Project. http://qgis.osgeo.org. Shapes downloaded from an open source from the Biblioteca del Congreso Nacional, Available at https://www.bcn.cl/siit/mapas_vectoriales/index_html).

Fig 2. Example of a US-hub where abdominal US screening sessions were carried out in the study area.

Fig 3. Prevalence of abdominal cystic echinococcosis according to the locality of residence in the Monte Patria municipality, Limarí province, Coquimbo region, Chile.

Fig 4. Distribution of abdominal cystic echinococcosis (CE) by age classes and prevalence.

Number of volunteers with untreated abdominal CE (including new diagnoses and known but untreated infection) and volunteers with abdominal CE cysts on US who reported previous treatment for an abdominal CE cyst in any body location (bars; left Y axis) and overall prevalence of abdominal CE in the screened population (dotted line; right Y axis) according to age class (X axis). Age classes are expressed in years.

Fig 5. Distribution of the abdominal cystic echinococcosis cyst stages (47 cysts detected in 39 cases) according to the WHO Informal Working Group on Echinococcosis (WHO-IWGE) classification by age classes.

Monte Patria municipality, Limarí province, Coquimbo region, Chile.