Unique Strain of Rickettsia parkeri Associated with the Hard Tick Dermacentor parumapertus Neumann in the Western United States.

In 1953, investigators at the Rocky Mountain Laboratories in Hamilton, MT, described the isolation of a spotted fever group Rickettsia (SFGR) species from Dermacentor parumapertus ticks collected from black-tailed jackrabbits (Lepus californicus) in northern Nevada. Several decades later, investigators characterized this SFGR (designated the parumapertus agent) by using mouse serotyping methods and determined that it represented a distinct rickettsial serotype closely related to Rickettsia parkeri; nonetheless, the parumapertus agent was not further characterized or studied. To our knowledge, no isolates of the parumapertus agent remain in any rickettsial culture collection, which precludes contemporary phylogenetic placement of this enigmatic SFGR. To rediscover the parumapertus agent, adult-stage D. parumapertus ticks were collected from black-tailed jackrabbits shot or encountered as roadkills in Arizona, Utah, or Texas from 2011 to 2016. A total of 339 ticks were collected and evaluated for infection with Rickettsia species. Of 112 D. parumapertus ticks collected in south Texas, 16 (14.3%) contained partial ompA sequences with the closest identity (99.6%) to Rickettsia sp. strain Atlantic rainforest Aa46, an SFGR that is closely related or identical to an SFGR species that causes a mild rickettsiosis in several states of Brazil. A pure isolate, designated strain Black Gap, was cultivated in Vero E6 cells, and sequence analysis of the rrs, gltA, sca0, sca5, and sca4 genes also revealed the closest genetic identity to Rickettsia sp. Atlantic rainforest Aa46. Phylogenetic analysis of the five concatenated rickettsial genes place Rickettsia sp. strain Black Gap and Rickettsia sp. Atlantic rainforest Aa46 with R. parkeri in a distinct and well-supported clade.IMPORTANCE We suggest that Rickettsia sp. Black Gap and Rickettsia sp. Atlantic rainforest Aa46 represent nearly identical strains of R. parkeri and that Rickettsia sp. Black Gap or a very similar strain of R. parkeri represents the parumapertus agent. The close genetic relatedness among these taxa, as well as the response of guinea pigs infected with the Black Gap strain, suggests that R. parkeri Black Gap could cause disease in humans. The identification of this organism could also account, at least in part, for the remarkable differences in severity ascribed to Rocky Mountain spotted fever (RMSF) among various regions of the American West during the early 20th century. We suggest that the wide variation in case fatality rates attributed to RMSF could have occurred by the inadvertent inclusion of cases of milder disease caused by R. parkeri Black Gap.

Cardiac Tropism of Borrelia burgdorferi: An Autopsy Study of Sudden Cardiac Death Associated with Lyme Carditis.

Fatal Lyme carditis caused by the spirochete Borrelia burgdorferi rarely is identified. Here, we describe the pathologic, immunohistochemical, and molecular findings of five case patients. These sudden cardiac deaths associated with Lyme carditis occurred from late summer to fall, ages ranged from young adult to late 40s, and four patients were men. Autopsy tissue samples were evaluated by light microscopy, Warthin-Starry stain, immunohistochemistry, and PCR for B. burgdorferi, and immunohistochemistry for complement components C4d and C9, CD3, CD79a, and decorin. Post-mortem blood was tested by serology. Interstitial lymphocytic pancarditis in a relatively characteristic road map distribution was present in all cases. Cardiomyocyte necrosis was minimal, T cells outnumbered B cells, plasma cells were prominent, and mild fibrosis was present. Spirochetes in the cardiac interstitium associated with collagen fibers and co-localized with decorin. Rare spirochetes were seen in the leptomeninges of two cases by immunohistochemistry. Spirochetes were not seen in other organs examined, and joint tissue was not available for evaluation. Although rare, sudden cardiac death caused by Lyme disease might be an under-recognized entity and is characterized by pancarditis and marked tropism of spirochetes for cardiac tissues.

Routine argyrophil techniques detect Rickettsia rickettsii in tissues of patients with fatal Rocky Mountain spotted fever.

Rickettsia rickettsii, a bacterial tickborne pathogen that causes Rocky Mountain spotted fever (RMSF), stains poorly or not at all with conventional tissue Gram techniques, and contemporary visualization of the pathogen in formalin-fixed, paraffin-embedded tissues has relied almost entirely on immunohistochemical staining methods that are generally limited to specialized research laboratories or national reference centers. To our knowledge, previously described argyrophil-based histochemical techniques have not successfully detected rickettsiae in formalin-fixed, paraffin-embedded tissues. To investigate the ability of standard silver impregnation techniques to demonstrate the occurrence and distribution of R. rickettsii in tissues of patients with RMSF confirmed by molecular and immunohistochemical methods, three widely recognized and commercially available silver impregnation methods (Warthin-Starry, Steiner, and Dieterle's) were applied to various tissues obtained at autopsy from 10 patients with fatal RMSF. R. rickettsii bacteria were demonstrated in one or more tissues of all patients, using each of the argyrophil-based methods, and appeared as small, dark brown-to-black lanceolate rods, often in pairs and occasionally surrounded by a faint halo. Rickettsiae were identified most consistently in small arteries and arterioles of liver, kidney, and leptomeninges, and were localized predominantly to the cytoplasm of endothelial cells and less often within the internal elastic lamella and smooth muscle of the media. This validation of argyrophilic techniques to detect R. rickettsii demonstrates the utility of inexpensive core histochemical methods in the diagnosis of infectious agents in pathology specimens and may have utility in certain resource-limited settings where RMSF is endemic.