• Home
• Administration
  • Chairman's Message
  • Contacts
  • Campus Maps
• Faculty
  • Alphabetical Listing
  • Virology
  • Vector Biology
  • Bacteriology
  • Pathobiology
  • Toxicology
  • Anatomical Pathology
  • Clinical Pathology
• Education
  • Mission Statement
  • Course Catalog
  • Graduate Students
  • Residency Program
  • Post-Doctoral Program
  • Training Grants
  • Handbooks
  • Blackboard
  • Campus Maps
• Research
  • Post-Doctoral Program
  • Center for Biodefense
  • Center for Tropical Diseases
  • Environmental Toxicology
  • Vaccine
  • Core Facilities & Resources
  • Research Histopathology Core
• Clinical
  • Anatomic Pathology
    • Autopsy
    • Cytopathology
    • Neuropathology
    • Surgical Pathology
  • Clinical Pathology
    • Blood Bank
    • Clinical Chemistry
    • Coagulation Consultation Services
    • Hematopathology
    • Microbiology
    • Molecular Diagnostics
    • Tissue Antigen
  • Clinical Pathology Administration
  • Campus Maps
• News/Events
  • UTMB Events Calendar
• Links
  • Previous Homepage
  • Innovative Teaching Technologies Initiative
  • Pathology Microscope Imaging Laboratory

David H. Walker, M.D.

Professor and Chairman, Department of Pathology;
Director, UTMB Center for Biodefense and Emerging Infectious Disease;
Director, WHO Collaborating Center for Tropical Diseases;
Autopsy Attending Pathologist, Department of Pathology

University of Texas Medical Branch
301 University Boulevard
Galveston, TX 77555-0609

Office: (409) 772-3989
Fax: (409) 772-1850
dwalker@utmb.edu

Appointments

Professional Education

Honors

Professional Affiliations

Research Interests

His research interests are broadly in the area of obligatory intracellular bacteria that are transmitted by arthropod vectors.  Two research projects currently funded by the NIH are focused on immune mechanisms against rickettsiae and ehrlichiae and identification of the protein antigens that stimulate immunity.  Although the diseases caused by rickettsiae include many long known and feared life threatening infections such as Rocky Mountain spotted fever and epidemic typhus, elucidation of their molecular composition and effector immune mechanisms remains productive lines of investigation.  In contrast, human ehrlichioses are truly emerging infectious diseases that were unknown until recently and are causing increasingly prevalent, severe infections.  Ehrlichial pathogenesis and immunity are in the process of being discovered and investigated at present for these novel organisms.  His research on immunity pursues hypotheses involving studies of innate immunity including NKT cells, natural killer cells, and γδ T cells, and adaptive immunity including antibodies, endothelial biology, and T regulatory cells.

His investigative armamentarium includes outstanding mouse models of spotted fever and typhus rickettsioses and monocytotropic ehrlichioses, which lend themselves to the study of pathogenesis as well as immunity.  The molecular studies of rickettsiae are focused on rickettsial virulence mechanisms, while the investigations of Ehrlichia chaffeensis, E. canis, E. muris, and Ixodes ovatus Ehrlichia are focused on immunodominant proteins as vaccine candidates.  Other projects include development of vaccines against R. prowazekii, E. canis, and E. chaffeensis, development of new diagnostic tests utilizing patented intellectual property sponsored by the Clayton Foundation, and international collaborations in Mexico, Brazil, Cameroon, and Portugal with opportunities for field and laboratory work in tropical locations.

His research is greatly enhanced by collaborative efforts involving the molecular expertise of Drs. Xuejie Yu, Jere McBride, and Donald Bouyer, the immunologic knowledge and skills of Drs. Gustavo Valbuena and Lynn Soong, the ultrastructural expertise of Dr. Vsevolod Popov, and the cell biology skills of Dr. Juan Olano including confocal microscopy.  New initiatives include vector biology of tick-borne ehrlichial and rickettsial infections.

Selected Publications

Peer-reviewed Aritcles:

1. Fang R, Ismail N, Shelite T, WALKER DH.  2009. CD4+CD25+ Foxp3- T regulatory cells produce both IFN-γ and IL-10 during acute severe murine spotted fever rickettsiosis.  Infect Immun. Doi:  10.1128/IAI.00349-09.  PMID 1956386.
2. Jordan JM, Woods ME, Soong L, WALKER DH.  2009.  Rickettsiae stimulate dendritic cells through toll-like receptor 4, leading to enhanced NK cell activation in vivo.  J Infect Dis 199:236-242. PMID 19072551.  PMCID 2613164.
3. Sousa R, Franca A, Doria NS, Belo A, Amaro M, Abreu T, Pocas J, Proenca P, Vaz J, Torgal J,  Bacellar F, Ismail N, WALKER DH.  2008. Host and microbial risk factors and pathophysiology of fatal Rickettsia conorii infection in Portuguese patients. J Infect Dis 198:576-585. PMID 18582199. PMCID 2614375.
4. Thirumalapura NR, Stevenson HL, WALKER DH, Ismail N.  2008.  Protective heterologous immunity against fatal ehrlichiosis and lack of protection following homologous challenge.  Infect Immun 76:1920-1930. PMID 18285501.  PMCID2346691.
5. Stevenson HL, Crossley EC, Thirumalapura N, WALKER DH, Ismail N.  2008.  Regulatory roles of CD1d-restricted NKT cells in the induction of toxic shock-like syndrome in an animal model of fatal ehrlichiosis.  Infect Immun 76:1434-1444. PMID 18212072.  PMCID2292873.
6. Jordan JM, Woods ME, Feng H-M, Soong, L, WALKER DH.  2007. Rickettsiae-stimulated dendritic cells mediate protection against lethal rickettsial challenge in an animal model of spotted fever rickettsiosis.  J Infect Dis 196:629-638.
7. de Sousa R, Ismail N, Nobrega SD, Franca A, Amaro M, Anes M, Pocas J, Coelho R, Torgai J, Bacellar F, WALKER DH.  2007. Intralesional expression of mRNA of interferon-γ, tumor necrosis factor-α, interleukin-10, nitric oxide synthase, indoleamine-2, 3-dioxygenase, and RANTES is a major immune effector in Mediterranean spotted fever rickettsiosis.  J Infect Dis 196:770-781.
8. Fang R, Ismail N, Soong L, Popov VL, Whitworth T, Bouyer DH, WALKER DH.  2007. Differential interaction of dendritic cells with Rickettsia conorii:  Impact on host susceptibility to murine spotted fever rickettsiosis. Infect Immun 75:3112-3123.
9. Ismail N, Crossley E, Stevenson HL, WALKER DH.  2007.  Relative importance of T cell subsets in monocytotropic ehrlichiosis: A novel effector mechanism involved in Ehrlichia-induced immunopathology in murine ehrlichiosis.  Infect Immun 75:4608-4620.
10. Stevenson HL, Jordan JM, Peerwani Z, Wang H-Q, WALKER, DH, Ismail N. 2006. An intradermal environment promotes a protective type-1 response against systemic monocytotropic ehrlichial infection.  Infect Immun 74:4856-4864. 
11. Ismail N, Stevenson HL, WALKER DH. 2006. The role of TNF-a and IL-10 in the pathogenesis of severe murine monocytotropic ehrlichiosis: increased resistance of TNF receptor p55- and p75- deficient mice to fatal ehrlichial infection.  Infect Immun 74:1846-1856.
12. Whitworth T, Popov VL, Yu XJ, Walker DH, Bouyer DH. 2005. Expression of Rickettsia prowazekii pld or tlyC gene in Salmonella enterica serovar typhimurium mediates phagosomal escape. Infect Immun 73:6668-6673.
13. Valbuena G, Jordan JM, WALKER DH. 2004. T cells mediate cross-protective immunity between spotted group rickettsiae and spotted fever group rickettsiae. J Infect Dis 190:1221-1227.
14. Ismail N, Soong L, Valbuena G, McBride JW, Olano JP, WALKER DH. 2004. Overproduction of TNF-a by CD8+ type-1 cells and downregulation of IFN-g production by CD4+ Th1 cells contribute to toxic shock-like syndrome in an animal model of fatal monocytotropic ehrlichioses.  J Immunol 172:1786-1800.
15. Olano JP, Masters E, Hogrefe W, WALKER DH. 2003. Human monocytotropic ehrlichiosis, Missouri. Emerg Infect Dis 9:1579-1586.

Reviews:

1. Valbuena GA, WALKER DH. 2006.  Endothelium as a target for infections.   Annu Rev Pathol Mech Dis 1:171-198.
2. WALKER, DH.  2007. Rickettsiae and rickettsial infections: The current state of knowledge.  Clin Infect Dis 45S:39-44.
3. Dong J, Olano JP, McBride JW, WALKER DH.  2008. Emerging pathogens:  Challenges and success of molecular diagnostics.  J Mol Diag 10:185-197.  PMID 1840306.
4. WALKER DH, Ismail N.  2008.  Emerging and re-emerging rickettsioses:  Endothelial cell infection and early disease events.  Nat Rev Microbiol 6:375-386.  PMID 18414502.

Books:

1. Guerrant RL, WALKER DH, Weller PF.  2011.  Tropical Infectious Diseases:  Principles, Pathogens, and Practice.  3rd Ed   Philadelphia (PA):  Elsevier Churchill, Livingstone.

NIH Biosketch