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D H Walker

Publications and source records attributed to D H Walker.

264 records · Page 15Linked to original sources
PubMed1970

Morphological variants of coliphage P1.

Lysates of P1 from all hosts tested contained at least three morphological variants with respect to head size. These were termed "big" (P1B), "small" (P1S), and "minute" (P1M). Since successive clonings of plaques isolated on many different hosts failed to change the proportions of the variants, we concluded that the production of variants was a function of the P1 genome rather than that of the host. In the electron microscope, the heads appeared to be icosadeltahedra, having face-to-face head diameters of 86 +/- 2 nm, 65 +/- 2 nm, and 47 +/- 2 nm. Assuming the head capsids to be composed of the same protein subunits, these diameters were compatible with T = 16, 9, and 4 with a lattice constant (intercapsomere distance) of 12 to 13 nm. The tails of all variants were morphologically indistinguishable. Each consisted of a hollow tail tube surrounded by a contractile sheath attached to the head by means of a "head-neck connector" which could be a specialized vertex capsomere. In CsCl gradients, a number of bands were observed. One band contained the majority of P1B particles and 99% of the plaque-forming units. Two other bands contained P1S particles whose densities suggested a content of about 40 and 60% of the complete P1B genome. The less dense of these two bands also contained defective P1B particles with a calculated content of only 60% of the complete genome. The P1S particles tested injected their deoxyribonucleic acid (DNA) into host cells and killed them. Genetic markers contained in this band could be rescued by infectious P1B particles, confirming the evidence of Ikeda and Tomizawa that this fraction contains P1 DNA.

Agar↗
PubMedDate not supplied

Chronic granulomatous disease involving the central nervous system.

Two male sibling infants died following a short course of lethargy and obtundation after a lifelong history of persistent, unrelenting diarrhea. Postmortem examination revealed extensive necrosis and early granuloma formation in the liver, spleen, lungs, and lymph nodes as well as in the central nervous system. To our knowledge, this fulminant clinical course, with documentation of granulomatous CNS lesions, has not been reported in patients with chronic granulomatous disease of childhood.

Brain↗
PubMedDate not supplied

Emergence of the ehrlichioses as human health problems.

Ehrlichiae are small, gram-negative, obligately intracellular bacteria that reside within a phagosome. The first human ehrlichial infection was recognized in the United States in 1987. It was later shown to be caused by a new species, Ehrlichia chaffeensis. In 1994, an ehrlichial pathogen within neutrophils that is closely related to the known veterinary pathogens E. equi and E. phagocytophila was found to infect humans. Molecular methods were required to detect, characterize, and identify these fastidious and uncultivated bacteria. Subsequently, E. chaffeensis infection was documented in more than 400 patients in 30 states, Europe, and Africa. Likewise, approximately 170 cases of human granulocytic ehrlichiosis have been diagnosed, most since 1994, predominantly in the upper midwestern and northeastern states, but also in northern California. The disease caused by ehrlichiae is generally undifferentiated but is often associated with leukopenia, thrombocytopenia, and elevated serum hepatic transaminase levels in tick-exposed patients. Infection ranges from subclinical to fatal; tetracycline appears to be an effective therapy. The emergence of these two newly recognized tickborne infections as threats to human health is probably due to increased clinical cognizance, but as in other emerging tickborne infections, it is likely that the rapid increase in identified cases signals a true emergence of disease associated with a changing vector-host ecology.

Animals↗
PubMedDate not supplied

Molecular characterization of a novel Rickettsia species from Ixodes scapularis in Texas.

A novel Rickettsia species of undetermined pathogenicity was detected in Ixodes scapularis. DNA sequencing showed the highest nucleotide sequence similarities with R. australis for the 17 kDa gene, R. helvetica for gltA, and R. montana for rompA. The new organism, provisionally designated as genotype Cooleyi, is highly divergent in three conserved genes from recognized Rickettsia species.

Animals↗
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Dual infection with Ehrlichia chaffeensis and a spotted fever group rickettsia: a case report.

Well-documented cases of simultaneous human infection with more than one tick-borne pathogen are rare. To our knowledge only two dual infections have been reported: simultaneous human infection with the agent of human granulocytic ehrlichiosis and Borrelia burgdorferi and simultaneous human infection with B. burgdorferi and Babesia microti (1-2). Rocky Mountain spotted fever has long been known to be endemic in North Carolina; cases of human ehrlichial infection were recognized there soon after Ehrlichia chaffeensis was recognized as an important cause of tick-borne disease in the southeastern United States. Because both Rocky Mountain spotted fever and ehrlichiosis are prevalent in North Carolina, occasional cases of simultaneous human infection by rickettsial and ehrlichial agents would not be surprising; however, no such cases seem to have been reported.

Adult↗
PubMedDate not supplied

Identification of rickettsiae in cutaneous biopsy specimens from dogs with experimental Rocky Mountain spotted fever.

Direct immunofluorescence reaction for Rickettsia rickettsii was performed on formalin-fixed, paraffin-embedded cutaneous biopsy specimens collected from dogs with experimental Rocky Mountain spotted fever (RMSF). A technique of trypsin digestion of deparaffinized, rehydrated sections was successful in demonstrating discrete, immunofluorescent organisms in endothelia and adjacent vessel walls in the dermis. R rickettsii was identified only in grossly evident dermal lesions (macular rash or oral vesicles) and was not apparent in randomly collected biopsy specimens from clinically normal inguinal skin. These results suggest that clinical application of this technique for diagnosis of RMSF may be limited in dogs without cutaneous lesions.

Animals↗
PubMedDate not supplied

Epidemiology and ecology of rickettsial diseases in the People's Republic of China.

Since 1949, information on rickettsial diseases in the People's Republic of China has been virtually nonexistent in the West. This is the first comprehensive review of the ecology and epidemiology of Chinese rickettsial diseases to be published outside the People's Republic. At least five rickettsioses exist in China: scrub typhus, murine typhus, epidemic typhus, Q fever, and one or more spotted fever-group (SFG) rickettsioses. Although epidemic typhus has been controlled and scrub typhus has abated in many areas, murine typhus, Q fever, and SFG rickettsiosis are important public health problems. Serologic surveys indicate high prevalences of antibodies to Coxiella burnetii, Rickettsia tsutsugamushi, and SFG rickettsiae in some regions; these rickettsiae have been isolated from humans, arthropods, and animals. Doxycycline has emerged as the best treatment for murine typhus, epidemic typhus, and scrub typhus. China offers both opportunities and challenges for the investigation and alleviation of the problems of rickettsial diseases.

Adult↗