Angiostrongylus cantonensis: tegumental and hypodermic alterations of the fourth-stage larvae following administration of tribendimidine in vivo and in vitro.

Angiostrongylus cantonensis is a parasitic pathogen whose forth-stage larvae (L4) parasitize in the central nervous system (CNS) of the human cause severe eosinophilic encephalitis or meningoencephalitis. Previous study indicated an impressive anthelmintic efficacy of tribendimidine (TBD) against CNS parasitized L4 of A. cantonensis. Tegument of the larvae is the first physical barrier to protect them from attack by the host immune system. In the present study, tegumental and hypodermic alterations were observed by scanning electron microscopy and transmission electron microscopy after administration of TBD. During treatment of TBD in vivo, L4 presented wizened side sensor, disappearance of mastoids and longitudinal grain, prominent surface coat, heterogeneous tegumental layers, incompact hypodermic cell junctions, blurred myotube, and small scale of vacuole in a basal layer. After incubation with TBD in vitro, L4 exhibited a swollen side sensor and mastoids disappearance in head end. Abundant tegumental blebs and obvious deformation of both cross-grain and longitudinal grain were detected on the surface, and shrinkage of all tegumental layers, chaotic cell junction, turbid muscle cell, disappearance of myotubes, and vacuole-like changes were visible under the electron microscope. The results implied the potential mechanism of the anthelmintic effect of tribendimidine against L4 of A. cantonensis by direct damages to tegumental and hypodermic.