Londoño AF, Mendell NL, Walker DH, Bouyer DH. A biosafety level-2 dose-dependent lethal mouse model of spotted fever rickettsiosis: Rickettsia parkeri Atlantic Rainforest strain.
PLoS Negl Trop Dis 2019;
13:e0007054. [PMID:
31216274 PMCID:
PMC6602283 DOI:
10.1371/journal.pntd.0007054]
[Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 07/01/2019] [Accepted: 05/21/2019] [Indexed: 11/28/2022] Open
Abstract
Background
The species of the Rickettsia genus are separated into four groups: the ancestral group, typhus group, transitional group and spotted fever group. Rickettsia parkeri, a spotted fever group Rickettsia, has been reported across the American continents as infecting several tick species and is associated with a relatively mild human disease characterized by eschar formation at the tick feeding site, regional lymphadenopathy, fever, myalgia and rash. Currently, there are several mouse models that provide good approaches to study the acute lethal disease caused by Rickettsia, but these models can only be performed in an animal biosafety level 3 laboratory. We present an alternative mouse model for acute lethal rickettsial disease, using R. parkeri Atlantic Rainforest strain and C3H/HeN mice, with the advantage that this model can be studied in an animal biosafety level 2 laboratory.
Principal findings
In the C3H/HeN mouse model, we determined that infection with 1x106 and 1x107 viable R. parkeri Atlantic Rainforest strain organisms produced dose-dependent severity, whereas infection with 1x108 viable bacteria resulted in a lethal illness. The animals became moribund on day five or six post-infection. The lethal disease was characterized by ruffled fur, erythema, labored breathing, decreased activity, and hunched posture, which began on day three post-infection (p.i.) and coincided with the peak bacterial loads. Significant splenomegaly (on days three and five p.i.), neutrophilia (on days three and five p.i.), and thrombocytopenia (on days one, three and five p.i.) were observed.
Significance
Since R. parkeri is used at biosafety level 2, the greatest advantage of this inbred mouse model is the ability to investigate immunity and pathogenesis of rickettsiosis with all the tools available at biosafety level 2.
Rickettsia is a bacterial genus that contains distinct species that are transmitted by arthropods. Many of these agents produce infection and disease in humans. The illness can range from very severe, such as Rocky Mountain spotted fever caused by Rickettsia rickettsii to mild human disease characterized by eschar formation at the tick feeding site and less severe symptoms caused by Rickettsia parkeri and often apparently asymptomatic seroconversion as observed with R. amblyommatis. To study these diseases, animal models are invaluable, and mouse models offer the best advantages for studies of immunity and pathogenesis because of the availability of immunologic reagents and gene knockout animals. Several mouse models are available for the study of the acute lethal disease produced by these bacteria, providing the opportunity to test different treatments and vaccine candidates. However, work with these models requires an animal biosafety level 3 laboratory. In this report, we present an alternative mouse model with R. parkeri Atlantic Rainforest strain available for investigation in a biosafety level 2 laboratory to study an acute dose-dependent lethal spotted fever group rickettsial disease with the advantage that experiments can be performed at this biosafety level.
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