Schistosomiasis: cercarial finding and recognizing of human hosts as a prerequisite of invasion.

Abstract

SUMMARYSchistosomiasis occurs in 80 primarily tropical and subtropical countries. It is transmitted to humans and animals by Schistosoma cercariae during freshwater contact. Parasite stages adapt and switch between molluscs, water, and mammals, where worms sustain parasitism. We reviewed research on larvae encountering humans published in PubMed, Embase, and Web of Science until May 2024. Larvae perform intermittent active/tail-first and passive/body-first swimming with arc-like re-encountering upon host approaches. Skin contacts occur spontaneously or through stimulants. Schistosoma mansoni, expressing chemokinesis, lingers in upper-middle warm clear water. Schistosoma haematobium, showing negative photo-orientation, remains in upper-lower, cooler, clear-muddy freshwater. Schistosoma japonicum stays stimuli-wise non-responsive in shallow muddy habitats. Attachment triggers of S. mansoni and S. haematobium are amino acids and temperature, respectively. S. japonicum adheres at random. Temperature gradient, ceramides, and acylglycerols stimulate the epidermal remaining of S. mansoni; solid hydrophobic surfaces trigger S. haematobium and S. japonicum. Temperatures of ≥36°C, ≥40°C, and 37°C guide S. mansoni, S. haematobium, and S. japonicum creeping for entering. Permeation aligns with schistosomula transformation by glycocalyx removal, heptalaminate membrane conversion, and tail stripping off and advances mechanically and enzymatically through acetabular glands. Skin and bloodstream navigation follows increasing L-arginine and D-glucose and parasite adjustment ventral-wards. Head gland enzymes facilitate epidermal-dermal transitioning for cutaneous exiting and vasculature accessing. Skin responds with anti-parasitic, anti-inflammatory edematous infiltrations. Schistosoma reacts by evasion through hormones, neurotransmitters, enzymes, and specialized proteins, among others. The findings, building largely on in vitro experiments, aim to facilitate the development of field-suitable prevention and control measures in support of the World Health Organization 2021-2030 Roadmap on Neglected Tropical Diseases.