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Ticks Tick Borne Dis. 2015 Sep;6(6):805-11. doi: 10.1016/j.ttbdis.2015.07.008. Epub 2015 Jul 17.

Pathogenic potential of a Costa Rican strain of 'Candidatus Rickettsia amblyommii' in guinea pigs (Cavia porcellus) and protective immunity against Rickettsia rickettsii.

Author information

1
Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica.
2
Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica; Sección de Virología, Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica.
3
Centro de Investigación en Estructuras Microscópicas, Universidad de Costa Rica, San José, Costa Rica; Escuela de Biología, Universidad de Costa Rica, San José, Costa Rica.
4
Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica; Sección de Entomología Médica, Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica.
5
Servicio de Patología, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica.
6
Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica; Sección de Entomología Médica, Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica. Electronic address: adriana.troyo@ucr.ac.cr.

Abstract

'Candidatus Rickettsia amblyommii' is a spotted fever group rickettsia that is not considered pathogenic, although there is serologic evidence of possible infection in animals and humans. The aim of this study was to evaluate the pathogenic potential of a Costa Rican strain of 'Candidatus R. amblyommii' in guinea pigs and determine its capacity to generate protective immunity against a subsequent infection with a local strain of Rickettsia rickettsii isolated from a human case. Six guinea pigs were inoculated with 'Candidatus R. amblyommii' strain 9-CC-3-1 and two controls with cell culture medium. Health status was evaluated, and necropsies were executed at days 2, 4, and 13. Blood and tissues were processed by PCR to detect the gltA gene, and end titers of anti-'Candidatus R. amblyommii' IgG were determined by indirect immunofluorescence. To evaluate protective immunity, another 5 guinea pigs were infected with 'Candidatus R. amblyommii' (IGPs). After 4 weeks, these 5 IGPs and 3 controls (CGPs) were inoculated with pathogenic R. rickettsii. Clinical signs and titers of anti-Rickettsia IgG were determined. IgG titers reached 1:512 at day 13 post-infection with 'Candidatus R. amblyommii'. On day 2 after inoculation, two guinea pigs had enlarged testicles and 'Candidatus R. amblyommii' DNA was detected in testicles. Histopathology confirmed piogranulomatous orchitis with perivascular inflammatory infiltrate in the epididymis. In the protective immunity assay, anti-Rickettsia IgG end titers after R. rickettsii infection were lower in IGPs than in CGPs. IGPs exhibited only transient fever, while CGP showed signs of severe disease and mortality. R. rickettsii was detected in testicles and blood of CGPs. Results show that the strain 9-CC-3-1 of 'Candidatus R. amblyommii' was able to generate pathology and an antibody response in guinea pigs. Moreover, its capacity to generate protective immunity against R. rickettsii may modulate the epidemiology and severity of Rocky Mountain spotted fever in areas where both species circulate.

KEYWORDS:

Costa Rica; Experimental infection; Guinea pig; Immunity; Rickettsia amblyommii

PMID:
26210090
DOI:
10.1016/j.ttbdis.2015.07.008
[Indexed for MEDLINE]

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