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

Background Strongyloides stercoralis is a neglected soil-transmitted helminth that occurs worldwide and 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 population aged 6 years and above. S. stercoralis was diagnosed using a serological diagnostic test detecting antigens in urine. Data on demography, hygiene and knowledge about helminth infection were collected. S. stercoralis prevalence among 7,246 participants with complete data record was 30.5% and ranged across provinces between 10.9% and 48.2%. The parasite was ubiquitous in Cambodia, with prevalence rates below 20% only in five south-eastern provinces. Infection risk increased with age both in men and women although girls aged less than 13 years and women aged 50 years and above had lower odds of infection than their male counterparts. Open defecation was associated with higher odds of infection while declaring having some knowledge about health problems caused by worms was protective. Infection risk was positively associated with night maximum temperature, minimum rainfall, and distance to water, and negatively associated with land occupied by rice fields. Conclusions / Significance S. stercoralis infection is ubiquitous and rampant in Cambodia. The parasite needs to be addressed by control programs delivering ivermectin. However the high cost of this drug in Cambodia currently precludes control implementation. Donations, subsidization or the production of affordable generic production are needed so S. stercoralis, which infests almost a third of the Cambodian population, can be addressed by an adequate control program. Authors Summary The threadworm, Strongyloides stercoralis, is a most neglected worm infection transmitted through infective larvae on the soil. Threadworms occur worldwide and particularly in tropical climates. It may cause long-lasting and potentially fatal infections due to its ability to replicate within its host. This study aimed to assess the risk of threadworm infection in at the national level in Cambodia. We conducted a nation-wide community-based parasitological survey among the population aged 6 years and above. The threadworm was diagnosed using a serological diagnostic test detecting antigens in urine. Data on demography, hygiene and knowledge about helminth infection were collected. The threadworm infection risk was calculated by using geostatistical models to predict its geographical distribution in Cambodia. About one third (30.5%) of the enrolled study participants (n=7,246) were infected with threadworms. The lowest and hightest infection rates a province level was 10.9% and 48.2%, respectively. Prevalence rates below 20% were found only in five south-eastern provinces. The risk of an infection with threadworms increased with age in men and women. Open defecation was associated with higher risk of infection while declaring having some knowledge about health problems caused by worms was protective. Furthermore, the threadworm infection risk was positively associated with environmental factors such as night maximum temperature, minimum rainfall, and distance to water, and negatively associated with land occupied by rice fields. Threadworm infection is highly prevalent in Cambodia and adequate control measures are warranted, including access to treatment, in order to address the burden of this NTD in Cambodia.