Human strongyloidiasis: identifying knowledge gaps, with emphasis on environmental control

Abstract

Strongyloides is a human parasitic nematode that is poorly understood outside a clinical context. This article identifies gaps within the literature, with particular emphasis on gaps that are hindering environmental control of Strongyloides. The prevalence and distribution of Strongyloides is unclear. An estimate of 100-370 million people infected worldwide has been proposed; however, inaccuracy of diagnosis, unreliability of prevalence mapping, and the fact that strongyloidiasis remains a neglected disease suggest that the higher figure of more than 300 million cases is likely to be a more accurate estimate. The complexity of Strongyloides life cycle means that laboratory cultures cannot be maintained outside of a host. This currently limits the range of laboratory-based research, which is vital to controlling Strongyloides through environmental alteration or treatment. Successful clinical treatment with antihelminthic drugs has meant that controlling Strongyloides through environmental control, rather than clinical intervention, has been largely overlooked. These control measures may encompass alteration of the soil environment through physical means, such as desiccation or removal of nutrients, or through chemical or biological agents. Repeated antihelminthic treatment of individuals with recurrent strongyloidiasis has not been observed to result in the selection of resistant strains; however, this has not been explicitly demonstrated, and relying on such assumptions in the longterm may prove to be shortsighted. It is ultimately naive to assume that continued administration of antihelminthics will be without any negative long-term effects. In Australia, strongyloidiasis primarily affects Indigenous communities, including communities from arid central Australia. This suggests that the range of Strongyloides extends beyond the reported tropical/subtropical boundary. Localized conditions that might result in this extended boundary include accumulation of moisture within housing because of malfunctioning health hardware inside and outside the house and the presence of dog fecal matter inside or outside housing areas.

Strongyloidiasis: A Disease of Socioeconomic Disadvantage

“…Currently, it is estimated that between 30–100 million people are infected by Strongyloides worldwide [ 2 , 88 ]. There is however a general consensus amongst the scientific community that the prevalence is underestimated due to inadequate diagnostic techniques [ 88 ], and the lack of sensitivity in tests for S. stercoralis and the similarity of its symptoms to other diseases result in great underestimation of the infection and 300 million people infected globally is probably a more accurate estimate [ 47 , 89 ]. Misclassification of the disease may also be contributing to the underestimation of its prevalence.…”

The National Strongyloides Working Group in Australia 10 workshops on: commendations and recommendations

“…Currently, clinical approaches to treating strongyloidiasis are the focus of interventions. However, understanding the environmental factors that allow the nematode to survive in the environment (soil, wet areas inside and outside the house, and waste water reservoirs) and to be transmitted to people, will increase the number of tools at our disposal for preventing and controlling the disease 29 . This is particularly important if ivermectin resistance emerges in S. stercoralis , as it has in sheep infected with S. papillosus 30 …”

“…Each Aboriginal community or region needs a program to eliminate the disease devised and led by the community 19,29 . In other groups, a standardised process for identifying infected individuals, treating them, and monitoring for cure, is required.…”

“…Each Aboriginal community or region needs a program to eliminate the disease devised and led by the community. 19,29 In other groups, a standardised process for identifying infected individuals, treating them, and monitoring for cure, is required. Advocacy includes identifying opportunities to extend collaboration and joint approaches with other communities, groups and agencies fighting similar diseases, such as hookworm, where joint efforts could be more effective.…”

Advocating for both Environmental and Clinical Approaches to Control Human Strongyloidiasis

“…However, to date, there has been no progress made mostly due to the gaps in knowledge regarding S. stercoralis treatment and control [22]. Investigation into transmission hot-spots is currently being undertaken [23].…”