Vesicular Stomatitis Virus

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Classification

• ‘’’Realm’’’: ‘’Riboviria’’,
• ‘’’Kingdom’’’: ‘’Orthornavirae’’,
• ‘’’Phylum’’’: ‘’Negarnaviricota’’,
• ‘’’Class’’’: ‘’Monjiviricetes’’,
• ‘’’Order’’’: ‘’Mononegavirales’’,
• ‘’’Family’’’: ‘’Rhabdoviridae,
• ‘’’Genus’’’: ‘’Vesiculovirus’’ [1].

Species

NCBI: [1]

“Vesicular Stomatitis Virus”

Two serotypes of VSV exist: the Vesicular Stomatitis Virus New Jersey serotype (VSNV), which is predominantly found in North America and known for causing vesicular lesions in livestock [2], as well as the Vesicular Stomatitis Virus Indiana serotype (VSIV), which is more commonly associated with outbreaks in cattle, horses, and swine, primarily in the United States [3, 4].

2. Description and significance

Vesicular Stomatitis Virus (VSV) is a virus representing a significant pathogen within the agricultural sector. VSV causes vesicular stomatitis, a contagious disease that impacts livestock health and productivity, and in rare cases, humans [5]. Beyond its pathogenic role, VSV possesses a genomic core often used to produce pseudotyped viruses—recombinant particles with a core genome and envelope proteins originating from different viruses. These biological features provide the means to modernize virology research by mimicking wild-type viruses in lower biosafety level (BSL) laboratories [6]. Despite the ubiquity of VSV on Earth, the exact mechanisms through which VSV induces disease are not fully understood. Since VSV is rare in humans and non-livestock species, its long-term effects are incompletely understood due to limited research into potential chronic infections or post-infection complications. Ongoing research aims to develop effective vaccines and therapeutic strategies to combat VSV [5].

3. Genome structure

VSV possesses a non-segmented, 11,161-nucleotide long genome made up of a negative-stranded RNA that encodes five structural proteins [3, 4]:

1. N (nucleoprotein), which is 1269 nucleotides and encapsulates the viral RNA, forming the nucleocapsid;
2. P (phosphoprotein), which is 798 nucleotides and plays a role in viral replication and transcription, and serves as a cofactor for the RNA polymerase;
3. M (matrix protein), which is 690 nucleotides and is involved in the assembly and budding of new virions;
4. G (envelope glycoprotein), which is 1536 nucleotides and made of 511 amino acids. It is glycosylated at positions 178 and 335 and contains covalently-linked fatty acid in the cytoplasmic domain. The G protein is responsible for receptor binding and membrane fusion during entry into host cells;
5. L (large polymerase protein), which is 6330 nucleotides and functions as the RNA-dependent RNA polymerase for viral replication.

The genome features a 47-nucleotide leader sequence at the 3' end and a 57-nucleotide trailer sequence at the 5' end [7]. In between the protein-coding regions are conserved sequences at gene junctions that are critical for initiating and terminating transcription during replication [8]. Notably, intergenic spacers between the G-L protein coding sequences are 14–22 nucleotides in length. These regions of RNA are highly conserved, whereby the genomic sequence of VSV strains found in the United States exhibited little genetic variation to strains that originated in Central America [3].

4. Cell structure

The ‘’Rhabdoviridae’’ family of viruses is characterized by a bullet-shaped morphology and single-stranded RNA genome [9, 10]. VSV’s viral envelope is composed of a lipid bilayer derived from the host cell membrane, studded with glycoprotein spikes (G proteins) that mediate attachment to host cells, as well as matrix proteins (M) that play a role in virus assembly and budding. Inside the envelope, the viral core contains the nucleocapsid, which is comprised of the viral RNA genome encapsulated by the nucleoprotein (N) and associated with the phosphoprotein (P) [11]. The matrix protein (M) lies between the nucleocapsid and the envelope, playing a key role in the structural integrity and budding process of the virus [9].

5. Metabolic processes

VSV is an obligate intracellular parasite that relies on the host cellular machinery for its metabolic processes, notably for replication and transcription [12]. This virus primarily infects mammalian cells, including livestock such as cattle, horses, and pigs. VSV enters the host cell through receptor-mediated endocytosis, facilitated by the G protein on the surface of VSV that binds to specific receptors on the host cell membrane [11]. Upon entering a host cell, the viral envelope fuses with the cellular membrane, releasing the nucleocapsid into the cytoplasm. Once inside the cell, the viral RNA is transcribed and replicated by the L protein. The VSV genome is transcribed in the 3’ to 5’ direction in the order N, P, M, G, and L [8]. The mRNA is then translated into viral proteins using the host's ribosomes [12]. The newly synthesized proteins are subsequently assembled into new virions in the cytoplasm. The M protein plays a crucial role in this process by interacting with the N and G proteins before the new virions bud off from the host cell, acquiring their lipid envelope in the process and ready to infect new cells [12].

6. Ecology

VSV is found in various geographic regions, including South and Central America and in southern Mexico. The virus is transmitted by insect vectors such as biting midges (‘’Culicoides’’) and black flies (‘’Simulidae’’) [13]. It can also spread through direct contact or insect bites. VSV is considered endemic in certain areas, with periodic seasonal outbreaks often occurring in areas with high populations of susceptible animals, such as cattle, horses, and pigs.

Environmental factors, including temperature and humidity, can influence the survival of the virus in nature, as well as the behavior of vectors (e.g. insects) that transmit VSV. VSV tends to survive longer at lower temperatures, remaining viable for extended periods in cooler environments, mainly during winter [14]. However, at higher temperatures, the replication rate of the virus increases. Thus, lower temperatures reduce the speed at which VSV spreads, but lengthens the time of spread. Likewise, high humidity can enhance the stability of the virus on surfaces, increasing the likelihood of transmission through contact. Conversely, low humidity can reduce the virus's ability to remain infectious on surfaces [14].

7. Pathology

VSV causes vesicular stomatitis, a contagious viral disease that mainly infects livestock, such as horses, cattle, and pigs [15]. It can also infect other animals like sheep, goats, llamas, alpacas, and occasionally, humans. Vesicular stomatitis is accompanied by a varying array of clinical symptoms: excessive salivation and fever are frequently the first noticeable signs of infection in cattle and horses, while reduced activity is often the first sign in swine [5]. Vesicles (i.e. blister-like sores) that develop on the tongue, the oral mucosa, teats, and coronary bands of cattle and horses quickly rupture and cause large ulcers that become secondarily infected, leaving behind painful erosions. In horses, tongue lesions are most pronounced; in swine, vesicular lesions on the snout and coronary bands are most common. There is no specific treatment for VSV. Lesions typically heal within 7–10 days. Human VSV infections result in influenza-like symptoms or localized vesicular lesions, primarily among those handling infected animals [5, 15].

Infection begins when the virus enters the host through mucosal surfaces or skin abrasions, followed by replication in local tissues and spread to regional lymph nodes and subsequently disseminating throughout the body via the bloodstream [12]. The immune response to VSV includes the production of neutralizing antibodies, but infection can still occur due to antigenic diversity among different VSV strains [16].

8. Current Research

Current research on VSV has focused on understanding antiviral strategies and incorporating VSV into vaccine vectors for therapeutic development. Genome studies are another major area of research on VSV, to uncover the genetic diversity of various VSV strains. Much of the genomic research is based on outbreaks, most recently an outbreak in Colorado in 2019 [3].

A recombinant form of VSV lacking the glycoprotein gene, known as ΔG-VSV, has been used in the creation of pseudotyped viruses [17]. Pseudotyped viruses, also known as pseudoviruses, can either be replication-competent, able to replicate in vivo, or replication-defective, unable to replicate in vivo. ΔG-VSV-based pseudoviruses often fall into the latter category, as lacking the glycoprotein gene renders it unable to form an infective vector in host cells. Recently during the COVID-19 pandemic, VSV-ΔG-based pseudoviruses were explored as a potential vaccine platform [18]. By utilizing the spike protein of the SARS-CoV-2 virus, the recombinant pseudovirus mimics the entry methods of the SARS-CoV-2 virus while retaining the reduced pathogenicity of VSV. This facilitates the development of antibodies against the SARS-CoV-2 spike proteins, while protecting against infections by the wild-type SARS-CoV-2 virus [18].

The VSV glycoprotein, VSV-G, is also used independently in targeted delivery systems. The use of VSV-G facilitates specific binding and fusion without the need for additional viral components [19]. A recent study demonstrated that vesicles constructed solely from VSV-G can deliver CRISPR-Cas9 in vivo. CRISPR-Cas9-based therapies benefit from such delivery systems, as they require precise and controlled gene editing. Direct delivery of the Cas9 protein avoids the nonspecific DNA cleavage associated with plasmid-based long-term expression. Furthermore, despite the high efficiency of viral vectors, the potential for insertional mutagenesis and the issues related to long-term expression make them less ideal [19]. The use of vesicles composed solely of VSV-G avoids the problems associated with viral vectors, while still maintaining their delivery efficiency. By combining the precision of CRISPR-Cas9 with the efficient delivery offered by VSV-G vesicles, this method represents a promising step towards targeted gene editing applications [19].

Recent advancements in targeted therapies are focusing on refining delivery mechanisms to increase specificity and safety. One key area of focus is modifying viral components, such as the VSV glycoprotein, to target receptors overexpressed on cancer cells. For example, by engineering VSV-G to recognize the Her2/Neu receptor, which is commonly overexpressed in certain types of breast cancer, researchers are working toward creating more precise therapeutic options [20]. This approach has the potential to significantly reduce off-target effects by selectively targeting cancerous cells while sparing healthy tissues. Moreover, this strategy extends beyond breast cancer treatment. It reflects a broader trend in cancer therapies—designing viruses and other delivery vehicles to home in on cancer-specific markers. By targeting markers like Her2/Neu, these modified viruses could drive the advancement of more effective and less toxic treatments. Additionally, combining this approach with technologies like CRISPR-Cas9 could enhance precision in targeting cancer cells at the genetic level, providing multifaceted strategies to cure cancer while minimizing unintended side effects [20].

9. References

[1] National Center for Biotechnology Information (NCBI). (1988). Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information. Retrieved Oct 17, 2024.

[2] Mead, D. G., K. R. Lovett, M. D. Murphy, S. J. Pauszek, G. Smoliga, E. W. Gray, R. Noblet, J. Overmyer, and L. L Rodriguez. 2009. “Experimental Transmission of Vesicular Stomatitis New Jersey Virus From Simulium Vittatum to Cattle: Clinical Outcome Is Influenced by Site of Insect Feeding." Journal of Medical Entomology. 46(4):866–872.

[3] Bertram, M. R., C. Rodgers, K. Reed, L. Velazquez-Salinas, A. Pelzel-McCluskey, C. Mayo, and L. Rodriguez. 2023. “Vesicular Stomatitis Indiana Virus Near-Full-Length Genome Sequences Reveal Low Genetic Diversity during the 2019 Outbreak in Colorado, USA.” Frontiers in Veterinary Science. 10:1-5.

[4] Rodrı́guez, L. L. 2002. “Emergence and Re-Emergence of Vesicular Stomatitis in the United States.” Virus Research. 85(2):211–219.

[5] Rashmir-Raven, A. M. 2018. "Disorders of the Skin." Equine Internal Medicine. 4th ed. Elsevier. 1159–1216.

[6] Thimmiraju, S. R., J. T. Kimata, and J. Pollet. 2024. “Pseudoviruses, a Safer Toolbox for Vaccine Development against Enveloped Viruses.” Expert Review of Vaccines. 23(1):174–185.

[7] Pauszek, S. J. and L. L. Rodriguez. 2012. “Full-Length Genome Analysis of Vesicular Stomatitis New Jersey Virus Strains Representing the Phylogenetic and Geographic Diversity of the Virus.” Archives of Virology. 157(11):2247–2251.

[8] Barr, J. N., X. Tang, E. Hinzman, R. Shen, and G. W. Wertz. 2008. “The VSV Polymerase Can Initiate at mRNA Start Sites Located Either up or Downstream of a Transcription Termination Signal but Size of the Intervening Intergenic Region Affects Efficiency of Initiation.” Virology. 374(2):361–370.

[9] Chen, Z., T. J. Green, M. Luo, and H. Li. 2004. “Visualizing the RNA Molecule in the Bacterially Expressed Vesicular Stomatitis Virus Nucleoprotein-RNA Complex.” Structure. 12(2):227–235.

[10] Ge, P., J. Tsao, S. Schein, T. J. Green, M. Luo, and Z. H. Zhou. 2010. “Cryo-EM Model of the Bullet-Shaped Vesicular Stomatitis Virus.” Science. 327(5966):689–693.

[11] Emerson, S. U. 1976. "Vesicular Stomatitis Virus: Structure and Function of Virion Components." In Arber, W., et al. (Eds.). Current Topics in Microbiology and Immunology. Vol. 73, 1–34. Springer.

[12] Ludwig, A., Hengel, H. 2009. "Vesicular Stomatitis Virus Infection." In Lang, F. (Ed.). Encyclopedia of Molecular Mechanisms of Disease. Springer.

[13] Rozo-Lopez, P., Drolet, B., Londoño-Renteria, B. 2018. "Vesicular Stomatitis Virus Transmission: A Comparison of Incriminated Vectors." Insects. 9(4):190.

[14] Guo, L., Yang, Z., Zhang, L., Wang, S., Bai, T., Xiang, Y., Long, E. 2021. "Systematic Review of the Effects of Environmental Factors on Virus Inactivation: Implications for Coronavirus Disease 2019." International Journal of Environmental Science and Technology. 18:2865–2878.

[15] MacLachlan, N. J., Dubovi, E. J. (Eds.). 2017. "Chapter 18 - Rhabdoviridae." Fenner's Veterinary Virology 5th ed. Academic Press. 357–372.

[16] Cobleigh, M. A., Bradfield, C., Liu, Y., Mehta, A., Robek, M. D. 2012. "The Immune Response to a Vesicular Stomatitis Virus Vaccine Vector Is Independent of Particulate Antigen Secretion and Protein Turnover Rate." Journal of Virology. 86(8):4253–4261.

[17] Whitt, M. A. 2010. "Generation of VSV Pseudotypes Using Recombinant ΔG-VSV for Studies on Virus Entry, Identification of Entry Inhibitors, and Immune Responses to Vaccines." Journal of Virological Methods. 169(2):365–374.

[18] Yahalom-Ronen, Y., Tamir, H., Melamed, S., Politi, B., Shifman, O., Achdout, H., Vitner, E. B., et al. 2020. "A Single Dose of Recombinant VSV-ΔG-Spike Vaccine Provides Protection Against SARS-CoV-2 Challenge." Nature Communications. 11:6402.

[19] Mangeot, P.-E., Dollet, S., Girard, M., Joly, S., Peschanski, M., Lotteau, V. 2011. "Protein Transfer Into Human Cells by VSV-G-Induced Nanovesicles." Molecular Therapy. 19(9):1656–1666.

[20] Gao, Y., Bergman, I. 2023. "Vesicular Stomatitis Virus (VSV) G Glycoprotein Can Be Modified to Create a Her2/Neu-Targeted VSV That Eliminates Large Implanted Mammary Tumors." Journal of Virology. 97(6):1–13.


Edited by students of Jennifer Bhatnagar for BI 311 General Microbiology, 2024, Boston University.