Transmission electron microscopic observation on ultrastructural alterations in Schistosoma japonicum caused by mefloquine

Abstract

The purpose of the study was to explore the ultrastructural alterations of adult Schistosoma japonicum induced by mefloquine. Eight out of ten mice infected with 60–80 S. japonuicum cercariae for 35 days were treated orally with mefloquine at a single dose of 400 mg/kg. Four groups of two mice were killed at 8 h, 24 h, 3 days, and 7 days post-treatment, and schistosomes were collected by perfusion technique, fixed, and examined under a transmission electron microscope. Schistosomes obtained from the remaining two mice served as control. Eight hours after mefloquine 400 mg/kg was administered to the infected mice, various alterations in the tegument and subtegument tissues of both male and female worms were seen, which included focal lysis of tegmental matrix resulted in vacuole formation, decrease in rod-like and discoid-like secretary bodies, light swelling or focal lysis of musculature, extensive lysis of internal structure of sensory organelles, and appearance of vacuole or myelin-like structure in perinuclear cytoplasm of syncytium and epithelial cells. In vitelline cells of female worms, the most significant alteration was extensive lysis or fusion of vitelline balls in vitelline droplets and decrease in granular endoplasmic reticulum Twenty-four hours post-treatment, damage to the tegument and subtegument tissues had increased in severity. In male worms, the most prominent alterations were emergence of large vacuoles in the tegument, detachment of cytoplasmic process from the tegumental surface, focal collapse of internal structure of sensory organelle, and loss of definition of syncytium and gut epithelial cell. In female worms, focal lysis in tegumental matrix, musculatures, and parenchymal tissues resulted in emergence of vacuole or myelin-like structure, reduction of nucleoli, fusion of partial nuclear membrane together with cytoplasm in epithelial cell, and lysis of interstitial tissues among the vitelline cells which were universal. Three and 7 days post-treatment, besides the aforementioned alterations, the significant damage to the male worms were disrupted outer plasma membrane detached from the cytoplasmic process, swelling of individual cytoplasmic process, extensive swelling and focal lysis in the musculature, parenchymal tissues and perinuclear cytoplasm of syncytium, accompanied by emergence of swollen mitochondria, vacuoles, and myelin-like structure, and severe damage to gut epithelial cell. In female worms, apart from disruption of outer plasmic membrane in cytoplasmic process, severe swelling of tegumental matrix accompanied by emergence of vacuoles, swollen mitochondria and myelin-like structure, focal lysis of heterochromatin and nucleoli, disappearance of microvilli in gut epithelial cells, and emergence of myelin-like structures in vitelline cells were observed. The results indicate that administration of mefloquine to mice infected with adult S. japonicum exhibits an extensive damage to the ultrastructure in tegument and subtegument tissues including syncytium, gut epithelial cells, parenchymal tissues, and vitelline cells of schistosomes.