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. 1995 Nov;33(11):2987–2993. doi: 10.1128/jcm.33.11.2987-2993.1995

Pathogenic, immunologic, and molecular differences between two Ehrlichia risticii strains.

R Vemulapalli 1, B Biswas 1, S K Dutta 1
PMCID: PMC228620  PMID: 8576359

Abstract

Ehrlichia risticii is the causative agent of Potomac horse fever (PHF), an acute infectious disease of horses. In the last few years, there have been several reports of PHF cases occurring even in vaccinated horses. We isolated a new strain of E. risticii (90-12 strain) from a vaccinated horse suffering from clinical PHF. The major pathogenic, immunologic, and molecular differences between the 90-12 strain and the 25-D stain, which was originally isolated during the outbreaks in 1984, were studied. The 90-12 strain was more pathogenic for mice and horses compared with the 25-D strain. In enzyme-linked immunosorbent assay and immunofluorescence assay with mouse and horse antisera of both the strains, two- to fourfold differences were observed between (immunoblot) with mouse and horse antisera and also with the recombinant clone-specific antibodies. Though several antigens were similar in both the strains, there were significant differences between them in the 110-, 85-, 70-, 51-, and 33-kDa antigens. The 85-kDa antigen was present only in the 90-12 strain but cross-reacted with a 50-kDa antigen of the 25-D strain. The 51-kDa antigens of both strains had different migration patterns, Southern blot hybridization of the genome from both the strains with DNA probes made from the 51-, 55-, and clones for both the strains, whereas the probe of the 85-kDa clone showed a completely different pattern. The 16S rRNA gene sequences from the two strains were identical. Neither strain replicated in gamma interferon-treated mouse peritoneal macrophages. In in vitro neutralization assay, sera from the 25-D strain-infected horse neutralized the homologous strain but did not neutralize the 90-12 strain, whereas sera from the 90-12 strain-infected horse neutralized both the strains. In mouse protection experiments, there was complete homologous protection. But in cross-protection, mice immunized with the 25-D strain were only partially protected against challenge with the 90-12 strain, whereas mice immunized with the 90-12 strain were completely protected against the 25-D strain challenge. These results clearly indicate that there are major differences between the 90-12 and 25-D strains which may have implications regarding the vaccine failure for PHF and the development of an efficient vaccine.

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Selected References

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  1. Anderson B. E., Dawson J. E., Jones D. C., Wilson K. H. Ehrlichia chaffeensis, a new species associated with human ehrlichiosis. J Clin Microbiol. 1991 Dec;29(12):2838–2842. doi: 10.1128/jcm.29.12.2838-2842.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Bhardwaj N., Nash T. W., Horwitz M. A. Interferon-gamma-activated human monocytes inhibit the intracellular multiplication of Legionella pneumophila. J Immunol. 1986 Oct 15;137(8):2662–2669. [PubMed] [Google Scholar]
  3. Biswas B., Mukherjee D., Mattingly-Napier B. L., Dutta S. K. Diagnostic application of polymerase chain reaction for detection of Ehrlichia risticii in equine monocytic ehrlichiosis (Potomac horse fever). J Clin Microbiol. 1991 Oct;29(10):2228–2233. doi: 10.1128/jcm.29.10.2228-2233.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Byrne G. I., Lehmann L. K., Landry G. J. Induction of tryptophan catabolism is the mechanism for gamma-interferon-mediated inhibition of intracellular Chlamydia psittaci replication in T24 cells. Infect Immun. 1986 Aug;53(2):347–351. doi: 10.1128/iai.53.2.347-351.1986. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Chaichanasiriwithaya W., Rikihisa Y., Yamamoto S., Reed S., Crawford T. B., Perryman L. E., Palmer G. H. Antigenic, morphologic, and molecular characterization of new Ehrlichia risticii isolates. J Clin Microbiol. 1994 Dec;32(12):3026–3033. doi: 10.1128/jcm.32.12.3026-3033.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Dutta S. K., Myrup A. C., Rice R. M., Robl M. G., Hammond R. C. Experimental reproduction of Potomac horse fever in horses with a newly isolated Ehrlichia organism. J Clin Microbiol. 1985 Aug;22(2):265–269. doi: 10.1128/jcm.22.2.265-269.1985. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Dutta S. K., Penney B. E., Myrup A. C., Robl M. G., Rice R. M. Disease features in horses with induced equine monocytic ehrlichiosis (Potomac horse fever). Am J Vet Res. 1988 Oct;49(10):1747–1751. [PubMed] [Google Scholar]
  8. Dutta S. K., Rice R. M., Hughes T. D., Savage P. K., Myrup A. C. Detection of serum antibodies against Ehrlichia risticii in Potomac horse fever by enzyme-linked immunosorbent assay. Vet Immunol Immunopathol. 1987 Jan;14(1):85–92. doi: 10.1016/0165-2427(87)90077-8. [DOI] [PubMed] [Google Scholar]
  9. Dutta S. K., Shankarappa B., Mattingly-Napier B. L. Molecular cloning and analysis of recombinant major antigens of Ehrlichia risticii. Infect Immun. 1991 Mar;59(3):1162–1169. doi: 10.1128/iai.59.3.1162-1169.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Dutta S. K., Shankarappa B., Thaker S. R., Mattingly-Napier B. L. DNA restriction endonuclease cleavage pattern and protein antigen profile of Ehrlichia risticii. Vet Microbiol. 1990 Oct;25(1):29–38. doi: 10.1016/0378-1135(90)90090-i. [DOI] [PubMed] [Google Scholar]
  11. Holland C. J., Ristic M., Cole A. I., Johnson P., Baker G., Goetz T. Isolation, experimental transmission, and characterization of causative agent of Potomac horse fever. Science. 1985 Feb 1;227(4686):522–524. doi: 10.1126/science.3880925. [DOI] [PubMed] [Google Scholar]
  12. Kagaya K., Watanabe K., Fukazawa Y. Capacity of recombinant gamma interferon to activate macrophages for Salmonella-killing activity. Infect Immun. 1989 Feb;57(2):609–615. doi: 10.1128/iai.57.2.609-615.1989. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Kahler S. Transmission is unsolved mystery of equine monocytic ehrlichiosis. J Am Vet Med Assoc. 1989 Jun 15;194(12):1681-5, 1687. [PubMed] [Google Scholar]
  14. Kaylor P. S., Crawford T. B., McElwain T. F., Palmer G. H. Passive transfer of antibody to Ehrlichia risticii protects mice from ehrlichiosis. Infect Immun. 1991 Jun;59(6):2058–2062. doi: 10.1128/iai.59.6.2058-2062.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Kemmerich B., Small G. J., Pennington J. E. Relation of cytosolic calcium to the microbicidal activation of blood monocytes by recombinant gamma interferon. J Infect Dis. 1986 Nov;154(5):770–777. doi: 10.1093/infdis/154.5.770. [DOI] [PubMed] [Google Scholar]
  16. Messick J. B., Rikihisa Y. Inhibition of binding, entry, or intracellular proliferation of Ehrlichia risticii in P388D1 cells by anti-E. risticii serum, immunoglobulin G, or Fab fragment. Infect Immun. 1994 Aug;62(8):3156–3161. doi: 10.1128/iai.62.8.3156-3161.1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Olsen G. J., Woese C. R. Ribosomal RNA: a key to phylogeny. FASEB J. 1993 Jan;7(1):113–123. doi: 10.1096/fasebj.7.1.8422957. [DOI] [PubMed] [Google Scholar]
  18. Park J., Rikihisa Y. Inhibition of Ehrlichia risticii infection in murine peritoneal macrophages by gamma interferon, a calcium ionophore, and concanavalin A. Infect Immun. 1991 Oct;59(10):3418–3423. doi: 10.1128/iai.59.10.3418-3423.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Park J., Rikihisa Y. L-arginine-dependent killing of intracellular Ehrlichia risticii by macrophages treated with gamma interferon. Infect Immun. 1992 Sep;60(9):3504–3508. doi: 10.1128/iai.60.9.3504-3508.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Rikihisa Y., Perry B. D. Causative ehrlichial organisms in Potomac horse fever. Infect Immun. 1985 Sep;49(3):513–517. doi: 10.1128/iai.49.3.513-517.1985. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Rikihisa Y., Wada R., Reed S. M., Yamamoto S. Development of neutralizing antibody in horses infected with Ehrlichia risticii. Vet Microbiol. 1993 Jul;36(1-2):139–147. doi: 10.1016/0378-1135(93)90135-t. [DOI] [PubMed] [Google Scholar]
  22. Shankarappa B., Dutta S. K. Production and characterization of monoclonal antibodies to Ehrlichia risticii. Am J Vet Res. 1989 Jul;50(7):1145–1149. [PubMed] [Google Scholar]
  23. Stothard D. R., Clark J. B., Fuerst P. A. Ancestral divergence of Rickettsia bellii from the spotted fever and typhus groups of Rickettsia and antiquity of the genus Rickettsia. Int J Syst Bacteriol. 1994 Oct;44(4):798–804. doi: 10.1099/00207713-44-4-798. [DOI] [PubMed] [Google Scholar]
  24. Turco J., Winkler H. H. Gamma-interferon-induced inhibition of the growth of Rickettsia prowazekii in fibroblasts cannot be explained by the degradation of tryptophan or other amino acids. Infect Immun. 1986 Jul;53(1):38–46. doi: 10.1128/iai.53.1.38-46.1986. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Turco J., Winkler H. H. Isolation of Rickettsia prowazekii with reduced sensitivity to gamma interferon. Infect Immun. 1989 Jun;57(6):1765–1772. doi: 10.1128/iai.57.6.1765-1772.1989. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Turco J., Winkler H. H. Selection of alpha/beta interferon- and gamma interferon-resistant rickettsiae by passage of Rickettsia prowazekii in L929 cells. Infect Immun. 1990 Oct;58(10):3279–3285. doi: 10.1128/iai.58.10.3279-3285.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Weisburg W. G., Dobson M. E., Samuel J. E., Dasch G. A., Mallavia L. P., Baca O., Mandelco L., Sechrest J. E., Weiss E., Woese C. R. Phylogenetic diversity of the Rickettsiae. J Bacteriol. 1989 Aug;171(8):4202–4206. doi: 10.1128/jb.171.8.4202-4206.1989. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. van der Kolk J. H., Bernadina W. E., Visser I. J. Een paard seropositief ten opzichte van Ehrlichia risticii. Tijdschr Diergeneeskd. 1991 Jan 15;116(2):69–72. [PubMed] [Google Scholar]

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