Transmission electron microscopic observations on ultrastructural alterations in Schistosoma mansoni adult worms recovered from C57BL/6 mice treated with radiation-attenuated vaccine and/or praziquantel in addition to passive immunization with normal and vaccinated rabbit sera against infection

Abstract

Although the current treatment of schistosomiasis relies largely on praziquantel (PZQ), it has not been successful in significantly reducing the overall rate of disease cases, one of the suggested reasons being the inevitable resistance to PZQ. Previous studies showed that radiation-attenuated vaccine provides protection against Schistosoma mansoni in a host of various species. In the present study, we evaluated the effect of various vaccination strategies in C57BL/6 mice, including single or multiple vaccination strategy, subcurative dose (20 mg/kg) of PZQ, and a combination of single vaccination with subcurative dose of PZQ. Treatment either with subcurative dose of PZQ or with a single vaccination of attenuated cercariae (500 per mouse), caused significant reduction in total worm burden, hepatic, and intestinal ova counts of 43.03, 73.2, and 59.5 and 37.97, 52.02, and 26.3%, respectively. Furthermore, tegumental changes were observed. In multiple vaccinated group, there was an extensive lysis in tegumental layers. High deformations in gastrodermis, testis cells, vitelline cells, and oocytes were recorded. Also, this study is to explore the role of humoral immunity using highly resistant rabbits that had been exposed to three immunizations with ultraviolet (UV)-irradiated cercariae (8000 per rabbit in each immunization), and their sera were tested for their ability to transfer protection. The reduction in challenge worm burden had reached 32.76-43.64% when compared with recipients of normal serum or no serum. The reduction in hepatic and intestinal ova counts reached to 74.4 and 71.08% in group immunized with vaccinated rabbit sera. Swelling and extensive lysis of tegumental layers, gastrodermis lumen, spermatocytes, and deformation of oocytes were recorded with more severity than that recorded in normal rabbit sera group. Our findings recorded that multiple vaccination strategy is the most effective strategy then passive transfer of vaccinated rabbit. This gives guiding in the design the appropriate therapeutic strategy.

Ultrastructural alterations in Schistosoma mansoni juvenile and adult male worms after in vitro incubation with primaquine

“…Additionally, the ultrastructural changes in adult male worms included degeneration of the tegument and subtegumental layers as well as shrinkage of the muscle with embedded spines. These findings were in accordance with those of El-Shabasy et al (2015) who confirmed the same ultrastructural transformation of the tegument induced by PZQ.…”

“…Both scanning and transmission electron microscope play an important role in elucidating the detailed morphology and different alterations of the S. mansoni tegument allowing the interpretation of its functionality (Senft & Gibler 1977, El-Shabasy et al 2015). These methods have been employed by several researchers (de Oliveira et al 2012, El-Shabasy et al 2015) and help to explain the mechanisms of action of anti-schistosomal drugs.…”

“…These methods have been employed by several researchers (de Oliveira et al 2012, El-Shabasy et al 2015) and help to explain the mechanisms of action of anti-schistosomal drugs. The normal S. mansoni tegument is an essential interface between the parasite and the intravascular environment in the host (El-Shabasy et al 2015).…”

“…Although alterations in the surface ultrastructure of schistosome worms have received little attention, several investigators have used them for evaluating anti-schistosomal drugs (El-Shabasy et al 2015). As male worms are more sensitive to anti-schistosomal drugs than females are (Shaw & Erasmus 1987), the current study is the first to document the alterations in the tegumental surface of 21-day-old juvenile and adult male worms of S. mansoni following primaquine treatment at different concentrations in vitro by a detailed temporal examination using both scanning and transmission electron microscopy.…”

Ultrastructural study on morphology of Schistosoma spindale by Scanning electron microscopy (SEM)

“…The detection and identification of these helminths are done by morphological characterization. Moreover, a complete understanding of micro-morphological features plays an important role in the development of vaccines (Degheidy and Shalaby, 2010) and alterations in the ultrastructure of schistosome worms are useful for evaluation of anti-schistosomal drugs (El-Shabasy et al, 2015) for which there is a necessity of understanding normal ultrastructural morphology. Scanning Electron microscopy (SEM) allows better characterization of taxonomically significant structures and is important for generating a more precise species identification and the confirmation, description and/or redescription of species of nematodes (Rebello et al, 2012).…”