Declining soil transmitted helminth detections in an Australian tropical region

Soil-transmitted helminths (STHs), are recognised neglected tropical diseases and have been endemic in patients in tropical Northern Australia. We reviewed the temporal trends in detections of STHs and Hymenolepis nana in faecal samples from Northern Territory (NT) Government Health facilities, representing patients with acute illnesses and comorbidities between 2008 and 2018. Ascaris lumbricoides is not detected in patients in the NT. The number of faecal samples examined yearly was relatively constant with a median of 4458 (range 4246-4933). Faecal samples from patients under the age of 5 years declined by 45% over the 11 years of the study. Detections of Trichuris trichiura, Strongyloides spp., and hookworm ova fell significantly by 89% (p<0.001), 71% (p<0.001), and 43% (p<0.01), respectively, over the 11 years. Detections of H. nana declined by 33% absolutely, but not significantly, when assessed relative to the reduction in faecal samples from patients under the age of 5 years. The marked reduction in STH numbers coincided with a 10-fold increase in NT dispensing of ivermectin, predominantly used for scabies control, in widely geographically spaced locations throughout the NT, over the 11 years of the study. Our data support previous findings of the beneficial collateral effects of ivermectin therapy. Ivermectin is not recognised as having anti-cestode activity, hence the continued presence of H. nana endemically in the NT, suggests declines in STHs are not related to other changes in health hardware or existing mass drug administration programs. The reduction in T. trichiura detections may not be explained by this association, as unlike Strongyloides spp., the anti-helminthic effect of ivermectin has been less marked.