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Gene Review

vapA  -  virulence-associated 15-17 kDa antigen

Rhodococcus equi

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Disease relevance of vapA


High impact information on vapA

  • Recent sequencing of the virulence plasmid identified a putative pathogenicity island encoding a novel family of seven Vap proteins including VapA [5].
  • Isolates of R. equi from pneumonic foals typically contain large, 85- or 90-kb plasmids encoding a highly immunogenic virulence-associated protein (VapA) [6].
  • A recombinant, plasmid-cured derivative expressing wild-type levels of VapA failed to replicate in macrophages and remained avirulent for both mice and foals [6].
  • However, expression of VapA alone is not sufficient to restore the virulence phenotype [6].
  • The transcriptional start site of vapA was determined to be a cytidine located 226 bp upstream from the vapA initiation codon [1].

Chemical compound and disease context of vapA


Biological context of vapA


Anatomical context of vapA

  • Linear B-cell epitopes of the Rhodococcus equi virulence-associated protein (VapA) were mapped using a synthetic peptide bank in this study [11].
  • We developed a DNA vaccine expressing the vapA gene (pVR1055vapA) that induced an anamnestic response characterized by virulence associated protein A (VapA)-specific IgG antibodies in sera and bronchoalveolar lavage fluid (BALF) as well as VapA-specific proliferation of pulmonary lymphocytes when tested in adult ponies [12].
  • R. equi and VapA were identified within the lungs of both fetuses, and its distribution correlated with lesions [10].
  • 1. The plasmid construct expressed VapA in a COS-7 cell line [13].
  • Most strains associated well with HeLa cells and no relationship was found with plasmid status and possession of VapA [14].

Associations of vapA with chemical compounds

  • Use of adjuvants (aluminium hydroxide, iscoms) interfered markedly with the immunogenic properties of the VapA based antigen, in the case of aluminium hydroxide by apparently driving a Th2 type of response [4].

Analytical, diagnostic and therapeutic context of vapA

  • The expression of VapA, as monitored by Western blotting, was completely dependent on the presence of virR [1].
  • Immunization of mice with the lipid-modified VapA purified by SDS-PAGE fractionation or with acetone precipitated VapA protein following TX-114 extraction resulted in significantly enhanced clearance from the liver and spleen following intravenous challenge [8].
  • The strains were tested by PCR for the presence of 15- to 17-kDa virulence-associated protein antigen (VapA) and 20-kDa virulence-associated protein antigen (VapB) genes [15].
  • B-Cell epitope mapping of the VapA protein of Rhodococcus equi: implications for early detection of R. equi disease in foals [11].
  • Restriction enzyme analysis of the virulence plasmids of VapA-positive Rhodococcus equi strains isolated from humans and horses [16].


  1. The LysR-type transcriptional regulator VirR is required for expression of the virulence gene vapA of Rhodococcus equi ATCC 33701. Russell, D.A., Byrne, G.A., O'Connell, E.P., Boland, C.A., Meijer, W.G. J. Bacteriol. (2004) [Pubmed]
  2. Pathogenesis and virulence of Rhodococcus equi. Hondalus, M.K. Vet. Microbiol. (1997) [Pubmed]
  3. VapA-negative Rhodococcus equi in a dog with necrotizing pyogranulomatous hepatitis, osteomyelitis, and myositis. Cantor, G.H., Byrne, B.A., Hines, S.A., Richards, H.M. J. Vet. Diagn. Invest. (1998) [Pubmed]
  4. Assessment of the immunogenic potential of Rhodococcus equi virulence associated protein (VapA) in mice. Prescott, J.F., Patterson, M.C., Nicholson, V.M., Morein, B., Yager, J.A. Vet. Microbiol. (1997) [Pubmed]
  5. Deletion of vapA encoding Virulence Associated Protein A attenuates the intracellular actinomycete Rhodococcus equi. Jain, S., Bloom, B.R., Hondalus, M.K. Mol. Microbiol. (2003) [Pubmed]
  6. Role of the 85-kilobase plasmid and plasmid-encoded virulence-associated protein A in intracellular survival and virulence of Rhodococcus equi. Giguère, S., Hondalus, M.K., Yager, J.A., Darrah, P., Mosser, D.M., Prescott, J.F. Infect. Immun. (1999) [Pubmed]
  7. Use of a virulence-associated protein based enzyme-linked immunosorbent assay for Rhodococcus equi serology in horses. Prescott, J.F., Fernandez, A.S., Nicholson, V.M., Patterson, M.C., Yager, J.A., Viel, L., Perkins, G. Equine Vet. J. (1996) [Pubmed]
  8. Molecular characterization of a lipid-modified virulence-associated protein of Rhodococcus equi and its potential in protective immunity. Tan, C., Prescott, J.F., Patterson, M.C., Nicholson, V.M. Can. J. Vet. Res. (1995) [Pubmed]
  9. Virulence-associated protein-specific serum immunoglobulin G-isotype expression in young foals protected against Rhodococcus equi pneumonia by oral immunization with virulent R. equi. Hooper-McGrevy, K.E., Wilkie, B.N., Prescott, J.F. Vaccine (2005) [Pubmed]
  10. Two cases of equine abortion caused by Rhodococcus equi. Szeredi, L., Molnár, T., Glávits, R., Takai, S., Makrai, L., Dénes, B., Del Piero, F. Vet. Pathol. (2006) [Pubmed]
  11. B-Cell epitope mapping of the VapA protein of Rhodococcus equi: implications for early detection of R. equi disease in foals. Vanniasinkam, T., Barton, M.D., Heuzenroeder, M.W. J. Clin. Microbiol. (2001) [Pubmed]
  12. Analysis of anamnestic immune responses in adult horses and priming in neonates induced by a DNA vaccine expressing the vapA gene of Rhodococcus equi. Lopez, A.M., Hines, M.T., Palmer, G.H., Knowles, D.P., Alperin, D.C., Hines, S.A. Vaccine (2003) [Pubmed]
  13. Assessment in mice of vapA-DNA vaccination against Rhodococcus equi infection. Haghighi, H.R., Prescott, J.F. Vet. Immunol. Immunopathol. (2005) [Pubmed]
  14. Association with HeLa cells by Rhodococcus equi with and without the virulence plasmid. de la Peña-Moctezuma, A., Prescott, J.F. Vet. Microbiol. (1995) [Pubmed]
  15. Characterization of virulence plasmids and serotyping of rhodococcus equi isolates from submaxillary lymph nodes of pigs in Hungary. Makrai, L., Takayama, S., Dénes, B., Hajtós, I., Sasaki, Y., Kakuda, T., Tsubaki, S., Major, A., Fodor, L., Varga, J., Takai, S. J. Clin. Microbiol. (2005) [Pubmed]
  16. Restriction enzyme analysis of the virulence plasmids of VapA-positive Rhodococcus equi strains isolated from humans and horses. Nicholson, V.M., Prescott, J.F. J. Clin. Microbiol. (1997) [Pubmed]
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