Strongyloides stercoralis: Spatial distribution of a highly prevalent and ubiquitous soil-transmitted helminth in Cambodia

Abstract

Background: Strongyloides stercoralis is a neglected soil-transmitted helminth that occurs worldwide, though it is particularly endemic in tropical and subtropical areas. It can cause long-lasting and potentially fatal infections due to its ability to replicate within its host. S. stercoralis causes gastrointestinal and dermatological morbidity. The objective of this study was to assess the S. stercoralis infection risk and, using geostatistical models, to predict its geographical distribution in Cambodia.

Methodology / principal findings: A nation-wide, community-based parasitological survey was conducted among the Cambodian population, aged 6 years and older. S. stercoralis was diagnosed using a serological diagnostic test that detects IgG antibodies in urine. Data on demography, hygiene and knowledge about helminth infection were collected. S. stercoralis prevalence among 7,246 participants with a complete data record was 30.5%, ranging from 10.9% to 48.2% across provinces. The parasite was ubiquitous in Cambodia; only five south-eastern provinces had prevalence rates below 20%. Infection risk increased with age for both men and women, although girls under the age of 13 and women aged 50 years and over had lower odds of infection than their male counterparts. Open defecation was associated with higher odds of infection, while having some knowledge of the health problems caused by worms was a protective factor. Infection risk was positively associated with nighttime maximum temperature, minimum rainfall, and distance to water; it was negatively associated with land occupied by rice fields.

Conclusions / significance: S. stercoralis infection is rampant in Cambodia. Control programs delivering ivermectin are needed to manage the parasite. However, the high cost of this drug in Cambodia currently precludes the implementation of control initiatives. Donations, subsidies or affordable generics are needed so that S. stercoralis, which infects almost a third of the Cambodian population, can be addressed through an adequate control program.

Fig 1. Map of Cambodian provinces.

This map was created with ArcGIS version 10.0 (ESRI; Redlands, CA, USA) specifically for this study by Forrer et al.

Fig 2. Provincial-level S. stercoralis prevalence in 25 provinces of Cambodia.

Data were obtained from a 2016 cross-sectional survey of 7,246 participants aged 6 years and older, living in 249 villages across Cambodia.

Fig 3. Map of Cambodia showing observed S. stercoralis prevalence in the 249 study villages.

Data were obtained from a 2016 cross-sectional survey of 7,246 participants aged 6 years and older, living in 249 villages across Cambodia. This map was created with ArcGIS version 10.0 (ESRI; Redlands, CA, USA) and displays the results obtained specifically from this study by Forrer et al.

Fig 4. Smoothed age-prevalence of S. stercoralis, Cambodia.

Data were obtained from a cross-sectional survey conducted in 2016 among 7,246 participants aged 6 years and older, living in 249 villages across Cambodia. Restricted cubic splines were used. Data are stratified for males (A) and females (B). Uncertainty is expressed as 95% confidence interval (CI).

Fig 5. Map of the predicted prevalence (median) of S. stercoralis in Cambodia.

Predictions were obtained with the geostatistical model shown in Table 3, based on survey data collected in 2016 from 7,246 participants aged 6 years and older, living in 249 villages across Cambodia. This map was created with ArcGIS version 10.0 (ESRI; Redlands, CA, USA) and display the results obtained specifically from this study by Forrer et al.

Fig 6. Lower (A) and upper (B) estimates of predicted S. stercoralis prevalence in Cambodia.

The lower and upper estimates are the 2.5% CI and the 97.5% CI, respectively. This map was created with ArcGIS version 10.0 (ESRI; Redlands, CA, USA) and display the results obtained specifically from this study by Forrer et al.