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David H Walker

Publications and source records attributed to David H Walker.

At least 73 records · Page 4Linked to original sources
PubMed2003

Clinical manifestations, epidemiology, and laboratory diagnosis of human monocytotropic ehrlichiosis in a commercial laboratory setting.

Clinical, epidemiological, and laboratory diagnostic issues of human monocytotropic ehrlichiosis (HME) were investigated in a retrospective case study conducted at a national reference laboratory (Focus Technologies, formerly MRL Reference Laboratory), and at the University of Texas Medical Branch at Galveston, Texas, during 1997 and 1998. Standard questionnaires were sent to physicians for each laboratory-diagnosed patient 2 days to 2 weeks after immunofluorescent antibody assay results were available. Among the 41 cases for which data were obtained, 32 (78%) were definite cases of HME, and 9 (22%) were probable cases of HME. Tick bite or exposure to ticks was recorded in more than 97% of cases. The most prominent clinical findings were fever, abdominal tenderness, and regional lymphadenopathy. There was an association between age and severity of illness. The main laboratory findings included leukopenia, thrombocytopenia, and elevated aspartate aminotransferase and alanine aminotransferase. Clinical and laboratory findings were nonspecific and were not good predictors of the severity of illness. The 90% of patients who received doxycycline treatment underwent rapid clinical improvement with a favorable outcome. The usual duration of effective treatment with doxycycline was 7 to 10 days. This retrospective study is unique because it was based in a commercial reference laboratory setting that receives specimens from different geographic locations. The clinical and laboratory information from 41 patients provides insight into the epidemiological, clinical, and laboratory characteristics of HME.

Adolescent↗
PubMed2003

Kinetics of antibody response to Ehrlichia canis immunoreactive proteins.

Immunoreactive proteins of Ehrlichia canis and Ehrlichia chaffeensis that have been characterized include a family of 28-kDa major outer membrane proteins (p28) and two large antigenically divergent surface glycoprotein orthologs. We previously demonstrated that recombinant E. canis p28 and the 140- and 200-kDa glycoproteins gp140 and gp200, respectively, react strongly with serum antibodies from suspect canine ehrlichiosis cases that were positive for E. canis by immunofluorescent antibody test and in various phases of acute or chronic infection (J. Clin. Microbiol. 39:315-322, 2001). The kinetics of the antibody response to these potentially important vaccine and immunodiagnostic candidates is not known. Acute-phase serum antibody responses to whole-cell E. canis lysates and recombinant p28, gp140, and gp200 were monitored for 6 weeks in dogs experimentally infected with E. canis. Irrespective of the inoculation route, a T-helper 1-type response was elicited to E. canis antigens consisting of immunoglobulin G2 antibodies exclusively in both acute and convalescent phases in most dogs. Analysis of immuoreactive antigens for peak intensity and relative quantity identified major immunoreactive E. canis antigens recognized early in the infection as the 19-, 37-, 75-, and 140-kDa proteins. Later in infection, additional major immunoreactive E. canis proteins were identified, including the 28-, 47-, and 95-kDa proteins and the recently identified 200-kDa glycoprotein. All dogs had developed antibody against the recombinant gp140, gp200, and p28 in the convalescent phase. Immunoreactivity and antibody response kinetics suggest that major immunoreactive proteins identified are immunodominant, but early recognition suggests increased dominance by some antigens.

Animals↗
PubMed2003

Identification of CD8 T-lymphocyte epitopes in OmpB of Rickettsia conorii.

The 1.2-kb DNA fragment of the Rickettsia conorii outer membrane protein B gene (OmpB(451-846)) was subcloned using site-specific PCR primers and expressed as six smaller fragments: OmpB(458-652), OmpB(595-744), OmpB(595-654), OmpB(645-692), OmpB(689-744), and OmpB(739-848). NCTC cells transfected with a mammalian expression vector expressing the fragments OmpB(689-744) and OmpB(739-848) stimulated immune anti-R. conorii CD8 T lymphocytes, suggesting the presence of CD8 T-lymphocyte-stimulating epitopes on these fragments. In order to further characterize the CD8 T-lymphocyte-stimulatory elements, CD8 T-lymphocyte epitopes on OmpB(689-744) and OmpB(739-848) were mapped by overlapping synthetic peptides. The ability of these synthetic peptides to stimulate immune CD8 T lymphocytes was determined by gamma interferon (IFN-gamma) production and cell proliferation after incubation with simian virus 40-transformed murine vascular endothelial cells in the presence of a 20 micro M solution of each synthetic peptide. Five synthetic peptides, SKGVNVDTV (OmpB(708-716)), ANVGSFVFN (OmpB(735-743)), IVSGTVGGQ (OmpB(749-757)), ANSTLQIGG (OmpB(789-797)), and IVEFVNTGP (OmpB(812-820)), induced secretion of IFN-gamma at significantly higher levels than the controls. Three of these five peptides, SKGVNVDTV (OmpB(708-716)), ANSTLQIGG (OmpB(789-797)), and IVEFVNTGP (OmpB(812-820)), also stimulated the proliferation of immune CD8 T lymphocytes. Significantly higher levels of specific cytotoxic T-lymphocyte killing were observed with the same three synthetic peptides, SKGVNVDTV (OmpB(708-716)), ANSTLQIGG (OmpB(789-797)), and IVEFVNTGP (OmpB(812-820)).

Animals↗
PubMed2003

Fatal spotted fever rickettsiosis, Minas Gerais, Brazil.

The emergence and reemergence of a serious infectious disease are often associated with a high case-fatality rate because of misdiagnosis and inappropriate or delayed treatment. The current reemergence of spotted fever rickettsiosis caused by Rickettsia rickettsii in Brazil has resulted in a high proportion of fatal cases. We describe two familial clusters of Brazilian spotted fever in the state of Minas Gerais, involving six children 9 months to 15 years of age; five died. Immunohistochemical investigation of tissues obtained at necropsy of a child in each location, Novo Cruzeiro and Coronel Fabriciano municipalities, established the diagnosis by demonstration of disseminated endothelial infection with spotted fever group rickettsiae. The diagnosis in the two fatal cases from Coronel Fabriciano and the surviving patient from Novo Cruzeiro was further supported by immunofluorescence serologic tests.

Adolescent↗
PubMed2003

Human monocytotropic ehrlichiosis, Missouri.

To determine the incidence, clinical and laboratory characteristics, and utility of molecular diagnosis of human monocytotropic ehrlichiosis (HME) in the primary care setting, we conducted a prospective study in an outpatient primary care clinic in Cape Girardeau, Missouri. One hundred and two patients with a history of fever for 3 days (>37.7 degrees C), tick bite or exposure, and no other infectious disease diagnosis were enrolled between March 1997 and December 1999. HME was diagnosed in 29 patients by indirect immunofluorescent antibody assay and polymerase chain reaction (PCR). Clinical and laboratory manifestations included fever (100%), headache (72%), myalgia or arthralgia (69%), chills (45%), weakness (38%), nausea (38%), leukopenia (60%), thrombocytopenia (56%), and elevated aspartate aminotransferase level (52%). Hospitalization occurred in 41% of case-patients. PCR sensitivity was 56%; specificity, 100%. HME is a prevalent, potentially severe disease in southeastern Missouri that often requires hospitalization. Because clinical presentation of HME is nonspecific, PCR is useful in the diagnosis of acute HME.

Acyltransferases↗
PubMed2003

Aponomma hydrosauri, the reptile-associated tick reservoir of Rickettsia honei on Flinders Island, Australia.

Rickettsia honei is the etiologic agent of Flinders Island (Australia) spotted fever. The tick Aponomma hydrosauri is associated with reptiles and is the arthropod reservoir for this rickettsia on Flinders Island. The rickettsia appears to be maintained in the tick via vertical transmission. Of 46 ticks examined, 29 (63%) were positive for spotted fever group rickettsiae by detection of the citrate synthase gene by a polymerase chain reaction (PCR). From the positive tick samples, seven were sequenced and found to be 100% homologous with R. honei. Of 17 reptiles examined, none had evidence of rickettsiae by PCR or culture of blood.

Animals↗
PubMed2002

Bone morphogenetic proteins and spinal fusion.

Bone morphogenetic proteins (BMPs) have increasingly become a focus of research in the laboratory, with animal models, and in human clinical trials for the treatment of spinal disorders. Basic science research has elucidated the putative mechanism of action of BMPs, and the efficacy of BMPs in inducing bone formation has been evaluated in multiple animal models of anterior and posterior spinal fusion. Not only has BMP been shown to improve the quality and amount of bone formation when used as a supplement to autograft, it has also been shown to promote superior fusion in the absence of autograft, even in high-risk fusion models involving the use of nicotine or nonsteroidal antiinflammatory agents. Both completed and ongoing clinical trials have demonstrated the efficacy of recombinant BMP, leading to the first BMP product being approved for clinical use earlier this year. Animal models and clinical trials have also been used to evaluate the safety of BMPs. Although few complications have been reported, BMPs can induce heterotopic bone formation, especially when placed adjacent to exposed neural elements. Potentially more serious, antibody formation has been seen in up to 38% of patients in some clinical trials. No clinical sequelae have been reported despite the development of antibodies against BMP, a naturally occurring human protein implicated in processes other than osteoinduction. The future directions of biological manipulation of the osteoinduction process include further understanding of the interactions of the BMP subtypes, the interactions of BMP with its receptors, and exploring other molecules capable of osteoinduction.

Animals↗
PubMed2002

Current status of immune mechanisms of killing of intracellular microorganisms.

The interaction between intracellular pathogens and the mammalian host follows different pathways that reflect evolved survival mechanisms of both the pathogen and the host to assure each one's own survival. From the host's perspective, different immune mechanisms predominate at different stages of infection. Both phagocytic and non-phagocytic target cells participate in microbial uptake and, in some cases, intracellular destruction. In addition, the development of specific immunity ensures sustained activation of intracellular microbicidal mechanisms in the target cells, and induction of apoptotic or lytic target cell death by cytotoxic T lymphocytes. From the pathogen's perspective, different evasion strategies are employed to counteract host defenses. Understanding microbial survival strategies and the immune mechanisms that result in killing of intracellular pathogens will deepen our insight into the pathogenesis of infection that could be applied towards the development of effective vaccination and immunotherapy.

Animals↗
PubMed2002

Human ehrlichioses.

Human ehrlichioses represent one of the best examples of newly emergent infectious diseases in which the classic triad of host, infectious agent, and environment are intertwined closely. These pathogens have existed for eons on the planet, and some were described as veterinary pathogens decades ago. Because of dramatic increases of deer and small mammal populations in certain areas and the subsequent increased populations of particular blood-feeding ticks, the risk of developing these diseases is higher than before. Increasing human populations in suburban areas and increased immunosuppressed populations (transplant patients, human immunodeficiency virus patients, and cancer survivors) also have increased risk of developing severe forms of these diseases.

Anaplasma↗
PubMed2002

Mechanisms of immunity against rickettsiae. New perspectives and opportunities offered by unusual intracellular parasites.

Investigation of the biology, pathology and immunology of rickettsial diseases offers new insights useful not only for the field of rickettsiology, but more importantly for the understanding of general principles of host-intracellular parasite relationships and, in particular, the immune interaction between endothelial cells and immune cells in the context of infection.

Animals↗
PubMed2002

Antigenic variation of Ehrlichia chaffeensis resulting from differential expression of the 28-kilodalton protein gene family.

The transcriptional activity and allele variation of the 28-kDa outer membrane protein gene (p28) of Ehrlichia chaffeensis were analyzed to determine the mechanism of the antigenic variation of the 28-kDa outer membrane proteins. Reverse transcriptase PCR amplification of mRNA indicated that 16 of the 22 members of the p28 multigene family were transcribed. Amino acid sequence analysis indicated that the p28-19 protein was produced in vitro in the Arkansas strain. The p28-19 gene and its promoter region were sequenced and compared in 12 clinical isolates of E. chaffeensis to determine allele variation. The variation of the p28-19 gene among the isolates is limited to three types represented by strains Arkansas, 91HE17, and Sapulpa, respectively. These results indicate that the majority of the p28 genes are active genes and that antigenic variation of the E. chaffeensis 28-kDa proteins may result from differential expression of the p28 gene family members rather than gene conversion.

Alleles↗
PubMed2002

Identification and functional analysis of an immunoreactive DsbA-like thio-disulfide oxidoreductase of Ehrlichia spp.

Novel homologous DsbA-like disulfide bond formation (Dsb) proteins of Ehrlichia chaffeensis and Ehrlichia canis were identified which restored DsbA activity in complemented Escherichia coli dsbA mutants. Recombinant Ehrlichia Dsb (eDsb) proteins were recognized by sera from E. canis-infected dogs but not from E. chaffeensis-infected patients. The eDsb proteins were observed primarily in the periplasm of E. chaffeensis and E. canis.

Animals↗
PubMed2002

Rickettsia felis in Ctenocephalides spp. fleas, Brazil.

In June 2000, suspected cases of Brazilian spotted fever (BSF) occurred in Coronel Fabriciano Municipality, Minas Gerais State, Brazil. Pooled fleas collected near two fatal cases contained rickettsial DNA. The nucleotide sequence alignment of the 391-bp segment of the 17-kDa protein gene showed that the products were identical to each other and to the R. felis 17-kDa gene, confirming circulation of R. felis in Brazil.

Animals↗