Characterization of double-stranded RNA satellites associated with the Trichomonas vaginalis virus

A special satellite-like RNA of a novel hypovirus from Pestalotiopsis fici broadens the definition of fungal satellite

Satellites associated with plant or animal viruses have been largely detected and characterized, while those from mycoviruses together with their roles remain far less determined. Three dsRNA segments (dsRNA 1 to 3 termed according to their decreasing sizes) were identified in a strain of phytopathogenic fungus Pestalotiopsis fici AH1-1 isolated from a tea leaf. The complete sequences of dsRNAs 1 to 3, with the sizes of 10316, 5511, and 631 bp, were determined by random cloning together with a RACE protocol. Sequence analyses support that dsRNA1 is a genome of a novel hypovirus belonging to genus Alphahypovirus of the family Hypoviridae, tentatively named Pestalotiopsis fici hypovirus 1 (PfHV1); dsRNA2 is a defective RNA (D-RNA) generating from dsRNA1 with septal deletions; and dsRNA3 is the satellite component of PfHV1 since it could be co-precipitated with other dsRNA components in the same sucrose fraction by ultra-centrifuge, suggesting that it is encapsulated together with PfHV1 genomic dsRNAs. Moreover, dsRNA3 shares an identical stretch (170 bp) with dsRNAs 1 and 2 at their 5' termini and the remaining are heterogenous, which is distinct from a typical satellite that generally has very little or no sequence similarity with helper viruses. More importantly, dsRNA3 lacks a substantial open reading frame (ORF) and a poly (A) tail, which is unlike the known satellite RNAs of hypoviruses, as well as unlike those in association with Totiviridae and Partitiviridae since the latters are encapsidated in coat proteins. As up-regulated expression of RNA3, dsRNA1 was significantly down-regulated, suggesting that dsRNA3 negatively regulates the expression of dsRNA1, whereas dsRNAs 1 to 3 have no obvious impact on the biological traits of the host fungus including morphologies and virulence. This study indicates that PfHV1 dsRNA3 is a special type of satellite-like nucleic acid that has substantial sequence homology with the host viral genome without encapsidation in a coat protein, which broadens the definition of fungal satellite.

Multiple Regulations of Parasitic Protozoan Viruses: A Double-Edged Sword for Protozoa

Parasite infections affect human and animal health significantly and contribute to a major burden on the global economy. Parasitic protozoan viruses (PPVs) affect the protozoan parasites' morphology, phenotypes, pathogenicity, and growth rates. This discovery provides an opportunity to develop a novel preventive and therapeutic strategy for parasitic protozoan diseases (PPDs). Currently, there is greater awareness regarding PPVs; however, knowledge of viruses and their associations with host diseases remains limited. Parasite-host interactions become more complex owing to PPVs; however, few studies have investigated underlying viral regulatory mechanisms in parasites. In this study, we reviewed relevant studies to identify studies that investigated PPV development and life cycles, the triangular association between viruses, parasites, and hosts, and the effects of viruses on protozoan pathogenicity. This study highlights that viruses can alter parasite biology, and viral infection of parasites may exacerbate the adverse effects of virus-containing parasites on hosts or reduce parasite virulence. PPVs should be considered in the prevention of parasitic epidemics and outbreaks, although their effects on the host and the complexity of the triangular association between PPVs, protozoans, and hosts remain unclear. IMPORTANCE PPVs-based regulation of parasitic protozoa can provide a theoretical basis and direction for PPD prevention and control, although PPVs and PPV regulatory mechanisms remain unclear. In this review, we investigated the differences between PPVs and the unique properties of each virus regarding virus discovery, structures, and life cycles, focused on the Trichomonas vaginalis virus, Giardia lamblia virus, Leishmania RNA virus, and the Cryptosporidium parvum virus 1. The triangular association between PPVs, parasitic protozoa, and hosts reveals the "double-edged sword" property of PPVs, which maintains a balance between parasitic protozoa and hosts in both positive and negative respects. These studies discuss the complexity of parasitic protozoa and their co-existence with hosts and suggest novel pathways for using PPVs as tools to gain a deeper understanding of protozoal infection and treatment.

Molecular interactions of plant viral satellites

Plant viral satellites fall under the category of subviral agents. Their genomes are composed of small RNA or DNA molecules a few hundred nucleotides in length and contain an assortment of highly complex and overlapping functions. Each lacks the ability to either replicate or undergo encapsidation or both in the absence of a helper virus (HV). As the number of known satellites increases steadily, our knowledge regarding their sequence conservation strategies, means of replication and specific interactions with host and helper viruses is improving. This review demonstrates that the molecular interactions of these satellites are unique and highly complex, largely influenced by the highly specific host plants and helper viruses that they associate with. Circularized forms of single-stranded RNA are of particular interest, as they have recently been found to play a variety of novel cellular functions. Linear forms of satRNA are also of great significance as they may complement the helper virus genome in exacerbating symptoms, or in certain instances, actively compete against it, thus reducing symptom severity. This review serves to describe the current literature with respect to these molecular mechanisms in detail as well as to discuss recent insights into this emerging field in terms of evolution, classification and symptom development. The review concludes with a discussion of future steps in plant viral satellite research and development.

Trichomonas vaginalis Virus Among Women With Trichomoniasis and Associations With Demographics, Clinical Outcomes, and Metronidazole Resistance

BACKGROUND

Trichomonas vaginalis virus (TVV) is a non-segmented, 4.5-5.5 kilo-base pair (kbp), double-stranded RNA virus infecting T. vaginalis. The objectives of this study were to examine the TVV prevalence in US Trichomonas vaginalis isolates and TVV's associations with patient demographics, clinical outcomes, and metronidazole resistance.

METHODS

Archived T. vaginalis isolates from the enrollment visits of 355 women participating in a T. vaginalis treatment trial in Birmingham, Alabama, were thawed and grown in culture. Their total RNA was extracted using a Trizol reagent. Contaminating, single-stranded RNA was precipitated using 4.0 M Lithium Chloride and centrifugation. The samples were analyzed by gel electrophoresis to visualize a 4.5 kbp band representative of TVV. In vitro testing for metronidazole resistance was also performed on 25/47 isolates obtained from the women's test of cure visits.

RESULTS

TVV was detected in 142/355 (40%) isolates at the enrollment visit. Women with TVV-positive (TVV+) isolates were significantly older (P = .01), more likely to smoke (P = .04), and less likely to report a history of gonorrhea (P = .04). There was no association between the presence of clinical symptoms or repeat T. vaginalis infections with TVV+ isolates (P = .14 and P = .44, respectively). Of 25 test of cure isolates tested for metronidazole resistance, 0/10 TVV+ isolates demonstrated resistance, while 2/15 TVV-negative isolates demonstrated mild to moderate resistance (P = .23).

CONCLUSIONS

Of 355 T. vaginalis isolates tested for TVV, T. vaginalis isolates tested for TVV, the prevalence was 40%. However, there was no association of TVV+ isolates with clinical symptoms, repeat infections, or metronidazole resistance. These results suggest that TVV may be commensal to T. vaginalis.

Trichomonas vaginalis virus: a review of the literature

Trichomonas vaginalis (TV) is a parasitic protozoan responsible for the sexually transmitted infection trichomoniasis. Trichomonas vaginalis virus (TVV) is a nonsegmented, 4.5-5 kbp, double-stranded RNA virus, from the Totiviridae family, which inhabits TV. A capsid protein consisting of 120 subunits is covered in channels aiding in RNA release. TVV is closely associated with the Golgi complex and is transmitted vertically. TVV has four subspecies, TVV1, TVV2, TVV3, and TVV4. The clinical significance of TVV and its effect on the pathogenicity of TV is not well known. We performed a systematic review of the literature on TVV to better understand its clinical significance and its role in the pathogenesis of TV.

Prospective study of effect modification by Toll-like receptor 4 variation on the association between Trichomonas vaginalis serostatus and prostate cancer

PURPOSE

In previous studies, we observed a positive association between Trichomonas vaginalis serostatus and risk of prostate cancer, particularly aggressive cancer, which we hypothesized might be due to T. vaginalis-mediated intraprostatic inflammation and cell damage. To explore this hypothesis further, we investigated effect modification by Toll-like receptor 4 (TLR4) variation on this association. We hypothesized that TLR4 variation might serve a marker of the anti-trichomonad immune response because T. vaginalis has been shown to elicit inflammation through this receptor.

METHODS

We previously genotyped the non-synonymous TLR4 single nucleotide polymorphism (SNP), rs4986790, and determined T. vaginalis serostatus for 690 incident prostate cancer cases and 692 controls in a nested case-control study within the Health Professionals Follow-up Study.

RESULTS

A non-significant suggestion of effect modification was observed by rs4986790 carrier status on the association between T. vaginalis serostatus and prostate cancer risk (p interaction = 0.07). While no association was observed among men homozygous wildtype for this SNP (odds ratio (OR) = 1.23, 95 % confidence interval (CI): 0.86-1.77), a positive association was observed among variant carriers (OR = 4.16, 95 % CI: 1.32-13.1).

CONCLUSIONS

Although not statistically significant, TLR4 variation appeared to influence the association between T. vaginalis serostatus and prostate cancer risk consistent with the hypothesis that inflammation plays a role in this association. Larger studies will be necessary to explore this possible effect modification further.

Genetic characterization of three Cuban Trichomonas vaginalis virus. Phylogeny of Totiviridae family

Trichomonas vaginalis can be infected with double stranded RNA (dsRNA) viruses known as T. vaginalis virus (TVV). This viral infection may have important implications for trichomonal virulence and disease pathogenesis. In this study we identified and genetic characterized three strains of TVVs isolated from T. vaginalis in Cuba. The three new predicted sequences of capsid protein and RNA-dependent RNA polymerase amounted to the previously determined 20 TVV sequences and other 21 viruses of Totiviridae family were used for a phylogenetic analysis. Four distinct monophyletic clades are shown in a phylogenetic tree. One corresponds with TVVs, other with Victorivirus, Leishmaniavirus and Eimeria brunetti virus and, other with viruses of the genus Totivirus and the last with Giardiavirus. The E. brunetti virus is identified in the phylogenetic tree as independent taxon between Leishmaniavirus and Victorivirus isolates, most closely related to Victorivirus. TVV constitute a monophyletic cluster distinguishable from all other viruses in Totiviridae family. This result suggested that TVV may be grouped in a separated genus and not inside of Giardiavirus. TVVs appear to be more closely related to protozoan viruses in the genus Leishmaniavirus and to fungal viruses in the genus Victorivirus than to other protozoan and fungal viruses in Giardiavirus and Totivirus. Among TVVs, four main groups can be recognized within Trichomonasvirus cluster, which correspond with the previous species classification proposed. Further studies, with more TVV strains, especially TVV3 and 4 strains, are needed in order to determine the phylogenetic relationship among Trichomonasvirus genus and specifically if TVV2 and 3 each also constitute a well-delimited group.

Antibodies raised against Bcvir15, an extrachromosomal double-stranded RNA-encoded protein from Babesia canis, inhibit the in vitro growth of the parasite

As part of a search for homologous members of the Plasmodium falciparum Pf60 multigene family in the intraerythrocytic protozoan parasite Babesia canis, we report here the characterization of a cDNA of 1,115 bp, which was designated Bcvir for its potential viral origin. The Bcvir cDNA contained two overlapping open reading frames (ORFs) (ORF1 from nucleotide [nt] 61 to 486 and ORF2 from nt 417 to 919), where Bcvir15, the deduced ORF1 peptide (M(1) to I(141)), is the main expressed product. The Bcvir cDNA was derived from an extrachromosomal dsRNA element of 1.2 kbp that was always found associated with a double-stranded RNA (dsRNA) of 2.8 kbp by hybridization, and no copy of this cDNA sequence was found in B. canis genomic DNA. Biochemical characterization of Bcvir15, by using polyclonal rabbit sera directed against recombinant proteins, indicated that it is a soluble protein which remained associated with the cytoplasm of the B. canis merozoite. Interestingly, purified immunoglobulins from the anti-glutathione S-transferase-Bcvir15 (at a concentration of 160 micro g/ml) induced 50% inhibition of the in vitro growth of B. canis, and the inhibitory effect was associated with morphological damage of the parasite. Our data suggest that the extrachromosomal dsRNA-encoded Bcvir15 protein might interfere with the intracellular growth of the parasite rather than with the process of invasion of the host cell by the merozoite. Epitope mapping of Bcvir15 identified three epitopes that might be essential for the function of the protein.

Trichomonas vaginalis: evaluating capsid proteins of dsRNA viruses and the dsRNA virus within patients attending a sexually transmitted disease clinic

Some isolates of Trichomonas vaginalis, the number one, non-viral sexually transmitted disease agent, are infected with one or several distinct double stranded (ds)-RNA virus. Immune rabbit anti-capsid serum (IRS) reacted with the capsid protein of purified dsRNA virus of a subset of the virus-infected T. vaginalis isolates. A monoclonal antibody (mAb) that recognized the capsid protein reactive with the IRS was generated. Analysis of the virus capsid protein of virus-infected isolates by probing nitrocellulose blots with mAb revealed diversity among immunoreactivity and in the size of the reactive capsid protein. Despite difficulties in visualizing virus within parasites by cross-section electron microscopy, gold-conjugated mAb readily labeled the cytoplasm of virus-positive trichomonads. Finally and importantly, isolates infecting patients attending an STD clinic, 75% of which were virus-positive isolates, had capsid protein of the same size detected by mAb present in all dsRNA viruses.

Visualization of new virus-like-particles in Trichomonas vaginalis

In the present work, we demonstrate virus-like particles (VLPs) with various morphological variations in Trichomonas vaginalis. The VLPs were distinct based on size, shape and electron density, with VLPs being either electron-dense or electron-lucent. We used electron microscopy thin sections of several T. vaginalis strains virus-infected, and also negative staining of fractions obtained after purification by CsCl buoyant density gradient centrifugation. The particles observed in fractions are identical to those previously described, but by thin sections, we found new forms. The shapes found were icosahedral, spherical and oblong, and the sizes varied from 33 to 120nm in diameter with the most common VLP being spherical and having a size range from 83 to 104nm. The VLPs were found in the cytoplasm closely associated with the Golgi complex, with some VLPs budding from the Golgi, and other VLPs were detected adjacent to the plasma membrane. Unidentified cytoplasmic inclusions were observed in the region close to the VLPs and Golgi. Clusters of the already described icosahedral virus were also observed in the cytoplasm, although less frequently. These results indicate that T. vaginalis organisms may be infected with different dsRNA viruses simultaneously.

Trichomonas vaginalis: observation of coexistence of multiple viruses in the same isolate

Trichomonas vaginalis is a flagellated, parasitic protozoan that inhabits the urogenital tract of humans. Some isolates of T. vaginalis are infected with a double-stranded RNA (dsRNA) virus, which was described in the literature as homogeneous icosahedral viral particles with an isometric symmetry and 33 nm in diameter. This study examined in detail the viral particles in T. vaginalis isolate 347 and describes a heterogeneous population of viral particles. The different dsRNA viruses were only observed after a change in the technique. The sample was prepared by the negative staining carbon-film method directly onto freshly cleft mica. The detected viruses ranged in size from 33 to 200 nm. Among the shapes observed were filamentous, cylindrical, and spherical particles. These results show that T. vaginalis may be a reservoir for several different dsRNA viruses simultaneously.

Clinical and microbiological aspects of Trichomonas vaginalis

Trichomonas vaginalis, a parasitic protozoan, is the etiologic agent of trichomoniasis, a sexually transmitted disease (STD) of worldwide importance. Trichomoniasis is the most common nonviral STD, and it is associated with many perinatal complications, male and female genitourinary tract infections, and an increased incidence of HIV transmission. Diagnosis is difficult, since the symptoms of trichomoniasis mimic those of other STDs and detection methods lack precision. Although current treatment protocols involving nitroimidazoles are curative, metronidazole resistance is on the rise, outlining the need for research into alternative antibiotics. Vaccine development has been limited by a lack of understanding of the role of the host immune response to T. vaginalis infection. The lack of a good animal model has made it difficult to conduct standardized studies in drug and vaccine development and pathogenesis. Current work on pathogenesis has focused on the host-parasite relationship, in particular the initial events required to establish infection. These studies have illustrated that the pathogenesis of T. vaginalis is indeed very complex and involves adhesion, hemolysis, and soluble factors such as cysteine proteinases and cell-detaching factor. T. vaginalis interaction with the members of the resident vaginal flora, an advanced immune evasion strategy, and certain stress responses enable the organism to survive in its changing environment. Clearly, further research and collaboration will help elucidate these pathogenic mechanisms, and with better knowledge will come improved disease control.