Table 1. Viral endosymbionts of protozoa can affect parasitic pathogenesis.

Protozoon	Viral endosymbiont	Virus type	Impact on parasite	Effect on parasitic pathogenesis	Proposed mechanism of action
Cryptosporidium spp.	Cryspovirus (Csp1) [10]	Partitiviridae (dsRNA)	Up-regulation of parasitic fecundity [10].	Increase	Unknown
Trichomonas vaginalis	TVV [11]	Totiviridae (dsRNA)	Modulation of parasitic metabolism and immunogenicity [12].	Increase	Interaction with host TLR3 proinflammatory signaling [13]
Leptomonas seymouri	Lepsey NLV1 [14]	Narnaviridae (ssRNA+)	Unknown	Unknown	Unknown
Phytomonas spp.	PserNV1 [15]	Narnaviridae (ssRNA+)	Unknown	Unknown	Unknown
Giardia spp.	GLV [16]	Totiviridae (dsRNA)	Unknown	None	Unknown
Leishmania (Viannia)	LRV1 [17]	Totiviridae (dsRNA)	Modulation of parasitic metabolism, virulence, and immunogenicity. [18,19]	Increase	Interaction with host TLR3 proinflammatory signaling and modulation of the NLRP3 inflammasome. [17]
Leishmania (Leishmania)	LRV2 [20]	Totiviridae (dsRNA)	Unknown	Unknown	Unknown

dsRNA, double-stranded RNA; GLV, Giardia lamblia virus; LRV1, Leishmania RNA virus 1; LRV2, Leishmania RNA virus 2; NLV1, narna-like virus 1; PserNV1, Pser Narna virus 1; TLR3, Toll-like receptor 3; TVV, Trichomonas vaginalis virus.