Strongyloides stercoralis: a plea for action

Abstract

More than one century later, the key issues regarding this parasite (subsequently renamed Strongyloides stercoralis) are essentially the same, and although researchers have recently given more attention to this infection, systematic action plans still lag behind. There is widespread agreement in the scientific community that its prevalence is largely underestimated [2]. The current estimate of 30 to 100 million infected persons in the world dates back to review articles published between 1989 and 1996 [3], [4], and is cited by most subsequent papers. These figures were mostly based on surveys aimed at defining the prevalence of parasitic infections, without using adequate diagnostic techniques for S. stercoralis. For example, Kato-Katz, a technique that is commonly used in surveys aiming to assess intestinal helminth infections [5], is poorly sensitive for this parasite. Larvae of S. stercoralis in stool are often scanty, and therefore they are most often missed by this technique that examines a small amount of faeces (between 20 and 50 mg, depending on the template). Larvae can be detected by this technique only occasionally, when the larval output is particularly high [6]. More reliable prevalence estimates have been made by geographically confined surveys, using alternative faecal-based diagnostic methods that are much more sensitive such as Baermann or Koga agar plate culture [7], [8]. Serology (ELISA or IFAT) is even more sensitive, but its specificity is less well defined. Problems of cross-reactivity seem to arise especially in areas where other nematodes, particularly filariae, are also endemic. New and promising tools such as serologic methods based on recombinant antigens or PCR are also available in some referral centers. However, the optimal diagnostic strategy, both for epidemiological surveys and for individual diagnosis and screening, has yet to be defined and certainly deserves further research