Protozoan viruses

1. PROTOZOAN
VIRUSES

2.  The first clear evidence of viral endosymbionts in parasites was the
discovery by transmission electron microscopy (TEM) of virus-like
particles (vlps) in parasites such as the protozoans Entamoeba
histolytica and Leishmania hertigi (currently Paraleishmania
hertigi).
 Since then, vlps and true viruses have been documented in a variety
of protozoan and helminth parasites that in turn parasitize humans,
animals, plants.
 Now we will focus mainly on the protozoan parasites Trichomonas
vaginalis, Leishmania spp., Giardia duodenalis and Cryptosporidium
spp., And their viral endosymbionts, as model systems to present
and discuss the potential for exploiting their use as native or
manipulated viruses to treat human parasitic diseases together with
the challenges associated with their application.

3. Mostly are small non-enveloped,double stranded, non-
segmented RNA genomes ranging between 5 to 7 kilo
bases (kb).
Shape and size: Spherical or Icosahedral and their
average diameter approximately 30-40 nm.
Within the totiviridae family, 5 genera, Giardiavirus,
Trichomonasvirus, Leishmaniavirus, Totivirus, and
Victorivirus, are currently recognised which share
common characteristics.

4. Their genomes are linear uncapped dsRNA encoding for two
partially overlapping proteins; the capsid protein (CP) and
the RNA-dependent RNA polymerase (RdRp).
The viral genome is never found free in the protozoan cell
and the positive strand viral transcript is synthesized within
the viral particle by CP/RDRP and translocated to the cell
cytoplasm to be translated.
The virions are icosahedral, composed of 120 copies of
capsid protein.

5. • Linear dsRNA genome of 4.6-6.7 kb.
• Contains 2 overlapping ORFs: gag and pol, respectively
encoding CP and RDRP.
• Replication (Cytoplasmic):
1. Virus either remains intracellular (Totivirus)
or attachement to host receptors mediates endocytosis
of virus into host cell (Giardiavirus).
2. Transcription of the dsRNA genome by viral polymerase
occurs inside the virion, so that dsRNA is never exposed
to the cytoplasm. This plus-strand transcript is used as
template for translation.
3. (+)RNAs are encapsidated in a sub-viral particle, in
which they are transcribed to give RNA (-) molecules
with which they become base-paired to produce dsRNA
genomes.
4. Mature virions are transmitted to new cell during cell
division, sporogenesis, cell fusion (Totivirus) or are
released from the host cell (Giardiavirus).

7.  EXAMPLES OF PROTOZOA AND
THEIR VIRUSES:
 A human flagellated protozoan extracellular
parasite Trichomonas vaginalis causative agent of
sexually transmitted disease.
 The virus that may be capable to infect this
protozoa is known as Trichomonas vaginalis
viruses (TVV).
 It was the first virus from a protozoan parasite to
be described and characterised in the 1980s, and
the first for which the full-length genome
sequence was reported.
 Genus:Ttrichomonasvirus
 Family: Totiviridae
 Four main phylogenetically distinct viral species, 1
to 4, have been described, with TVV1 closer to
TVV2 and TVV3 to TVV4.
 Genome size is nearly 4.5 to 4.9kb.

8. LEISHMANIA RNA VIRUS(LRV):
 An icosahedral , encapsidated double –stranded RNA , genome size is 5.3kb
 Family: Totiviridae.
 This virus observed in L. Guyanensis and L. Braziliensis.
 Subtypes-14 (LRV-1 – LRV14).
 Within Leishmania spp., The Leishmania RNA viruses (LRVs) are isolated
mainly from the Leishmania viannia subgenus from South America, and
designated as LRV1 whereas from the old-world Leishmania subgenus (i.E. L.
Aethiopica, L. Major and L. Tropica) were named LRV2.
 Viral replication is cytoplasmic. Replication follows the double-stranded RNA
virus replication model.

9. GIARDIA LAMBLIA ( OR G.
INTESTINALIS OR DUODENALIS):
Flagellated, intestinal protozoan
important causative agent of
diarrheal disease.
Infection occurs after ingestion of
giardial cysts from contaminated
food, water and soil.
The virus that may infect giardia
lambilia called GIARDIA LAMBLIA
VIRUS(GLV).

10.  Giardia lamblia virus (GLV), small, non –enveloped
positive sense dsrna virus (discovered in 1980s).
Virus isolated from the fungus Gigaspora margarita
 It is non- segemented.
Family: Totiviridae
Genome size: approx 6.3 kbp.
GLV particle is the largest, most robust and
thermo-stable among Totiviridae.

11. PURIFICATION OF PROTOZOAN
VIRUSES:
1. PROTOZOAN CULTURES
2. INFECTION WITH VIRUS
3. INCUBATION OF INFECTED PROTOZOAN CELLS
4. HARVEST USING SONICATION AND CENTRIFUGATIONS.

12. REFRENCE LINKS:
viruses of parasitic protozoa - pubmed (nih.gov)
http;//doi/10.1186/borrow et al.Virol J
https://viralzone.expasy.org/161.totiviridae
science direct
ncbi.nlm.nih.gov
youtube

13. THANK
YOU
BY HUMIRA
1ST SEM
MSC MICROBIOLOGY