Giardia canis: Ultrastructural analysis of G. canis trophozoites transfected with full length G. canis virus cDNA transcripts

Giardia canis virus (GCV) is a double-stranded RNA (dsRNA) virus of the family Totiviridae. In this study, the full length cDNA of the G. canis virus was constructed in pPoly2/sfinot vector and RNA was transcribed in vitro. Virus-free G. canis trophozoites were transfected with in vitro transcribed GCV RNA by electroporation. Transfected trophozoites were cultured for 12, 24, 36, 48, 60, or 72 h post transfection for analysis. The ultrastructures of the transfected trophozoites were determined by transmission electron microscopy. The viral particles were detectable sporadically in the cytoplasm as early as 24 h post transfection, but became evident and wide-spread 36 h post transfection. The number of viral particles increased dramatically from 48 to 60 h. Viral particles were released into the culture medium starting at about 60 h and detectable in nuclei 72 h post transfection. Severe vacuolization was seen in transfected G. canis trophozoites as early as 36 h post transfection and persisted throughout the course of this study. The results of the present study indicate that in vitro transcribed GCV transcripts were capable of infecting Giardia trophozoites, apparently replicated and packaged into mature infectious viral particles which were released from the host.