Comparative value of blood and skin samples for diagnosis of spotted fever group rickettsial infection in model animals

Abstract

The definitive diagnosis of spotted fever group (SFG) rickettsioses in humans is challenging due to the retrospective nature and cross reactivity of the serological methods and the absence of reliable and consistent samples for molecular diagnostics. Existing data indicate the transient character of bacteremia in experimentally infected animals. The ability of arthropod vectors to acquire rickettsial infection from the laboratory animals in the absence of systemic infection and known tropism of rickettsial agents to endothelial cells of peripheral blood vessels underline the importance of local infection and consequently the diagnostic potential of skin samples. In order to evaluate the diagnostic sensitivity of rickettsial DNA detection in blood and skin samples, we compared results of PCR testing in parallel samples collected from model laboratory animals infected with Rickettsia rickettsii, Rickettsia parkeri and Rickettsia slovaca-like agent at different time points after infection. Skin samples were collected from ears – away from the site of tick placement and without eschars. Overall, testing of skin samples resulted in a higher proportion of positive results than testing of blood samples. Presented data from model animals demonstrates that testing of skin samples from sites of rickettsial proliferation can provide definitive molecular diagnosis of up to 60–70% of tick-borne SFG rickettsial infections during the acute stage of illness. Detection of pathogen DNA in cutaneous samples is a valuable alternative to blood-PCR at least in model animals.

Clinical and serological evaluation of capybaras (Hydrochoerus hydrochaeris) successively exposed to an Amblyomma sculptum-derived strain of Rickettsia rickettsii

“…Regardless, it must be emphasized that techniques employing the direct detection of rickettsial DNA in bloodstream are not sensitive enough to determine bacteremic periods, especially in less severe infection courses. www.nature.com/scientificreports www.nature.com/scientificreports/ Rickettsia DNA amplification was achieved in skin samples from all capybaras during primary infection (6-26 DPI), which is similar with those results registered by Levin et al 34 in skin biopsies from R. rickettsii-infected guinea pigs (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). It is remarkable that in some capybaras (no.…”

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

“…Surprisingly, rickettsiae persisted in this location for at least 14 days following intraperitoneal inoculation of the organism. Investigators previously noted the presence of rickettsial DNA in the pinnae of rodents collected in the field (28) and in guinea pigs experimentally infected by tick bite or intraperitoneal inoculation with R. parkeri, R. rickettsii, or Rickettsia slovaca (29). The observation of rickettsial aggregates in the dermis of the pinnae also complements the propensity of SFGR to multiply preferentially at temperatures slightly below normal body temperatures (30), such as those observed in the skin of rabbit pinnae (31).…”

Vector Tick Transmission Model of Spotted Fever Rickettsiosis

“…14 Additional work has provided preliminary data toward the development of an immunocompetent rhesus macaque model using intradermal inoculation of R. parkeri during A. maculatum feeding with eschar formation and increased inflammatory markers in serum. 15 Guinea pig animal models also have been used to determine a few aspects of transmission and disease presentation 16,17 ; however, the guinea pig model has several significant limitations with respect to investigations of the immune response and disease pathways in the vertebrate host because of a paucity of reagents for this species, lack of gene knockout animals, and a paucity of inbred animals for adaptive transfer experiments. Although many aspects of rickettsial diseases have been studied using animal models, the complex interaction among the infected vector tick, the host, and the pathogen has not been addressed experimentally because of the absence of a tick transmission mouse model of SFG rickettsiosis that mimics naturally occurring infection that is essential for studying the natural events of immunity and pathogenesis of these tick-borne diseases.…”