UTMB Department of Pathology

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Pathogenesis of Rickettsial Diseases and Human Ehrlichiosis

Rickettsiae and Ehrlichiae are obligately intracellular bacteria. Rickettsial diseases have been one of the major scourges of mankind and they still threaten public health. Human ehrlichiosis is the new emerging disease. My research interest is to study the pathogenesis of rickettsial diseases and human ehrlichiosis using molecular biological methods. We are investigating the mechanisms of host immune evasion by E. chaffeensis, which include modulation of cytokine production and inhibition of phagosome and lysosome fusion.

1. Zhang JZ, Winslow GM, Yu, XJ. Expression of members of the 28-kDa major outer membrane protein family of Ehrlichia chaffeensis during persistent infection. Infect. Immun. 72: 4336-4346, 2004
2. McLeod MP, Qin X, McNeill TZ, Gioia J, Highlander, SK, Fox GE, Karpahty SE, Jiang H, Chao H, Yu XJ, Walker, DH, Weinstock GM. The complete genome of Rickettsia typhi and compararison with R. prowazekii and R. conorii. J. Bacteriol. 186:5842-5855, 2004.
3. Zhang JZ, Sinha M, Luxon BA, and Yu XJ. Survival strategy of obligately intracellular Ehrlichia: novel modulation of immune response and host cell cycles. Infect Immun. 72:498-507, 2004
4. Long, S. W., J. M. Pound, and X. J. Yu. 2004. Ehrlichia prevalence in Amblyomma americanum, Central Texas. Emerg Infect Dis 10:1342-1343, 2004.
5. Long SW, Zhang XF, Zhang JZ, Ruble RP, Teel P, and Yu XJ: Evaluation of transovarial transmission and transmissibility of Ehrlichia chaffeensis (Rickettsiales: Anaplasmataceae) in Amblyomma americanum (Acari: Ixodidae). J. Med. Entomol. 40: 1000-004, 2003
6. Zhang XF, Zhang JZ, Long SW, Ruble, RP, and Yu XJ. Experimental Ehrlichia chaffeensis infection in beagles. J. Med. Microbiol. 52:1021-6, 2003
7. Li Z, Diaz-Montero CM, Valbuena, G, Yu XJ, Olano, JP, Feng HM, and Walker DH: Identification of CD8 T-lymphocyte epitopes in OmpB of Rickettsia conorii. Infect. Immun. 71:3920-3926, 2003
8. Zhang JZ, McBride JW, and Yu XJ. L-selectin and E-selectin expressed on monocytes mediating Ehrlichia chaffeensis attachment onto host cells. FEMS Microbiol. Letters. 227: 303-309, 2003
9. Long S W, Zhang XF, Qi H, Standaert S, Walker DH, Yu XJ: Antigenic variation of Ehrlichia chaffeensis resulting from differential expression of the 28-kDa protein gene family. Infec. Immun. 70:1824-1831, 2002
10. Yu XJ, Zhang X-F, McBride JW, Zhang YL, and Walker DH: Phylogenetic relationships of Anaplasma marginale and Ehrlichia platys to other Ehrlichia determined by GroEL amino acid sequences. Int. J. Syst. Evol. Microbiol. 51:1143-1146, 2001
11. Suksawat J, Yu XJ, Hancock SI, Hegarty BC, Nilkumhang P, Breitschwerdt EB. Serologic and molecular evidence of coinfection with multiple vector-borne pathogens in dogs from Thailand. J. Vet. Intern. Med. 2001
12. McBride JW, Yu XJ, and Walker DH: A conserved transcriptionally active p28 multigene locus of Ehrlichia canis. Gene.254:245-252, 2000
13. Popov VL, Yu XJ, and Walker DH: The120 kDa outer membrane protein of Ehrlichia chaffeensis: preferential expression on dense-core cells and gene expression in Escherichia coli associated with attachment and entry. Microbial Pathogenesis 28:71-80, 2000.
14. Yu XJ, McBride JW, Zhang, XF, Walker DH. 2000. Characterization of the complete transcriptionally active Ehrlichia chaffeensis 28 kDa outer membrane protein multigene family. Gene. 248:59-68, 2000
15. Yu XJ, McBride JW, Diaz CM, and Walker DH. Molecular cloning and characterization of the 120-kDa protein gene of Ehrlichia canis and application of the recombinant 120-kDa protein for serodiagnosis of canine ehrlichiosis. J. Clin. Mcrobiol. 38:369-374, 2000
16. Moron CG, Bouyer DH, Yu XJ, Foil LD, Crocquet-Valdes, and Walker DH: Phylogenetic analysis of the rompB genes of Rickettsia felis and Rickettsia prowazekii European human and North American flying-squirrel strains. Am. J. Trop. Med. Hyg. 62: 598-603, 2000
17. McBride JW, Yu XJ, and Walker DH: Glycosylation of homologous immunodominant protein of Ehrlichia chaffeensis and Ehrlichia canis. Infect. Immun. 68:13-18, 2000
18. Zhang JZ, Fan MY, Yu XJ, and Raoult D: Phylogenetic analysis of the Chinese Rickettsia isolate BJ-90. Emerg.Infect.Dis. 6:432-433, 2000
19. McBride JW, Yu XJ, Walker DH: Molecular cloning of a conserved major immunoreactive 28-kilodalton protein gene of Ehrlichia canis: a potential serodiagnostic antigen. Clin. Diagn. Lab. Immunol. 6:392-399, 1999
20. Yu XJ, Crocquet-Valdes PA, Cullman LC, Popov VL, and Walker DH. Comparison of Ehrlichia chaffeensis recombinant proteins for diagnosis of human monocytotropic ehrlichiosis. J. Clin. Microbiol. 37: 2568–2575, 1999
21. Yu XJ, McBride JW, Walker DH: Genetic diversity of the 28-kilodalton outer membrane protein of human isolates of Ehrlichia chaffeensis. J. Clin. Microbiol. 37:1137-1143, 1999
22. Billings AN, Yu XJ, Teel PD, Walker DH: Detection of a spotted fever group rickettsia in Amblyomma cajennense (Acari: Ixodidae) in south Texas. J Med Entomol 35:474-478, 1998
23. Sexton DJ, Corey GR, Carpenter C, Kong LQ, Gandhi T, Breitschwerdt E, Hegarty B, Chen S-M, Feng H-M, Yu XJ, Olano J, Walker DH, Dumler JS: Dual infection with Ehrlichia chaffeensis and a spotted fever group rickettsia: A case report. Emerg. Infect. Dis. 4:311-316, 1998
24. Yu XJ, Piesman JF, Olson JG, Walker DH: Geographic distribution of different genetic types of Ehrlichia chaffeensis. Am. J. Trop. Med. Hyg. 56:679-680, 1997.
25. Yu XJ, Crocquet-Valdes PA, Cullman LC, Walker DH: Cloning and sequencing of the gene for a 120-kDa immunodominant surface protein of Ehrlichia chaffeensis. Gene 184:149-154, 1997
26. Yu XJ, Walker DH: Sequence and characterization of an Ehrlichia chaffeensis gene encoding 314 amino acids highly homologous to the NAD A enzyme. FEMS Letters 154:53-58, 1997
27. Chen S-M, Yu XJ, Popov VL, Westerman EL, Hamilton FG, Walker DH: Genetic and antigenic diversity of Ehrlichia chaffeensis: comparative analysis of a novel human strain from Oklahoma and previously isolated strains. J. Infect. Dis. 175:856-863, 1997
28. Zavala-Velazquez JE, Yu XJ, Walker DH: Unrecognized spotted fever group rickettsiosis masquerading as dengue fever in Mexico. Am. J. Trop. Med. Hyg. 55:157-159, 1996
29. Yu XJ, Crocquet-Valdes P, Cullman LC, Walker DH: The recombinant 120-kDa protein of Ehrlichia chaffeensis, a potential diagnostic tool. J. Clin. Microbiol. 34:2853-2855, 1996
30. Yu XJ, Raoult D: Monoclonal antibodies to Afipia felis-a putative agent of cat scratch disease. Am. J. Clin. Pathol. 101:603-606, 1994
31. Yu XJ, Raoult D: Serotyping Coxiella burnetii isolates from acute and chronic Q fever patients by using monoclonal antibodies. FEMS Microbiol Letters 117:15-20, 1994
32. Eremeeva M, Yu XJ, Raoult D: Differentiation among spotted fever group rickettsiae species by analysis of restriction length polymorphism of PCR-amplified DNA. J. Clin. Microbiol. 32:803-810, 1994
33. Yu XJ, Brouqui P, Dumler JS, Raoult D: Detection of Ehrlichia chaffeensis in human tissue by using a speceis-specific monoclonal antibody. J. Clin. Microbiol. 31:3284-3288, 1993
34. Yu XJ, Jin Y, Fan MY, Xu GM, Liu QH, Raoult D. Genotypic and antigenic identificaiton of two new strains of spotted fever group rickettsiae isolated from China. J. Clin. Microbiol. 31:83-88, 1993
35. Walker DH, Liu QH, Yu XJ, Li H, Taylor C, Feng HM: Antigenic diversity of Rickettsia conorii. Am. J. Trop. Med. Hyg. 47:78-86, 1992
36. Yu XJ, Walker DH, Jerrells TR: Polypeptides constituting the antigenic basis for identification of Rickettsia sibirica species by the standard serotyping method for spotted fever group rickettsiae. Acta Virol. 34:71-79, 1990
37. Uchida T, Yu XJ, Uchiyama T, Walker DH: Identification of a unique spotted fever group rickettsia from humans in Japan. J. Infect. Dis. 159:1122-1126, 1989
38. Fan M-Y, Yu XJ, Walker DH: Antigenic analysis of Chinese strains of spotted fever group rickettsiae by protein immunoblotting. Am. J. Trop. Med. Hyg. 39:497-501, 1988

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