Strongyloides stercoralis in the non-endemic setting and beyond: an epidemiological, clinical, diagnostic and treatment challenge

Strongyloides stercoralis is a soil-transmitted helminth widely distributed in areas of the world where sewage disposal is inadequate, and human waste contaminates the environment. A peculiar cycle of “autoinfection” causes the indefinite persistence of the infection in the human host, if not properly treated. Therefore, the infection is diagnosed also in areas of temperate climate, as a result of immigration from endemic countries and persistence of autochthonous cases that were acquired in the past, when sanitation was poor. Chronic infection often causes no symptoms or mild non-specific symptoms, although the clinical burden has not yet been well defined. However, immunocompromised people can develop severe complications, related to hyperinfection and dissemination of larva, that are life-threatening. A diagnostic gold standard lacks. Stool microscopy, which is routinely used for the diagnosis of intestinal parasitic infections, has low sensitivity for S. stercoralis, and this is among the causes at the basis of the underestimation of the prevalence of strongyloidiasis. A Cochrane meta-analysis showed that ivermectin has higher efficacy than albendazole and similar tolerability, while having similar cure rates and less adverse events than thiabendazole. Hence, ivermectin is the drug of choice for the treatment of strongyloidiasis in immunocompetent patients. However, there was no conclusive evidence on the different dose schedules of ivermectin, and on the optimal treatment in immunosuppressed patients, especially in case of severe strongyloidiasis. My work aims at addressing some of the main gaps of knowledge about key aspects of strongyloidiasis in the endemic and non-endemic setting. The first chapter of this thesis will bring an up-to-date review of the main epidemiological, clinical, diagnostic and treatment issues in the non-endemic setting, as a general introduction to the many challenges related to this condition worldwide. The second chapter focuses on global epidemiology and includes new estimates of the global prevalence of strongyloidiasis as well as a case-control study assessing the epidemiological characteristics of the infection in Italy. The third chapter proposes a review of clinical and laboratory characteristics of patients with strongyloidiasis at presentation and their evolution after treatment. The fourth chapter relates to the critical issue of diagnosis and includes: a narrative review of available diagnostic tools (their accuracy and potential role), a systematic review with meta-analysis on the accuracy of polymerase chain reaction (PCR) for the diagnosis of strongyloidiasis, and a diagnostic study evaluating the use of serology for the follow up of infected patients. The fifth chapter deals with therapy, with the results of a randomized controlled trial conducted in European travel clinics that compared different doses of ivermectin for the treatment of chronic strongyloidiasis.

Keywords:B780-tropical-medicine

Project type:PhD project