Assessment of Risk Factors in Synanthropic and Wild Rodents Infected by Pathogenic Leptospira spp. Captured in Southern Chile

Abstract

Leptospirosis is caused by pathogenic Leptospira, and synanthropic and wildlife species of rodents are an important source of infection; however, much of the information about infection progression was obtained from murine models. The aim of this study was to assess infection status and risk factors associated with pathogenic Leptospira in synanthropic and wild rodent species and describe histopathological lesions in several organs from naturally infected animals. In a cross-sectional study, 121 rodents from three synanthropic species and two wild species were trapped in dairy farms in Southern Chile. Liver, heart, kidney, and lungs from trapped animals were fixed in formalin and stained with hematoxylin-eosin. Tissues with lesions consistent with Leptospira infection were tested by immunohistochemistry (IHC) and real-time polymerase chain reaction (qPCR) using the LipL32 antigen. Risk factors were assessed by a conditional mixed-logistic regression model. More than half (56.7%) of the negative reactors to the microscopic agglutination test were identified as infected either by IHC/qPCR. A lower risk of infection compared to the rest of the seasons was found in the fall, and the synanthropic species have a lower risk of infection in comparison with the wildlife species. IHC and qPCR contributed to the identification of pathogenic Leptospira in related histological lesions and 50% more infections than serology.

Keywords: infection status; leptospirosis; rodents.

Figure 1

Dairy farms on which rodent sampling was performed, Region de Los Ríos, Valdivia, Chile.

Figure 2

Histopathological findings compatible with pathogenic Leptospira spp. infection. (a) Lymphoplasmacytic, tubulointerstitial nephritis (H&E, 10×); (b) multifocal to coalescing areas of hemorrhage in the renal cortex (H&E, 10×); (c) diffuse hemorrhage in the lung parenchyma (H&E, 10×); (d) diffuse, lymphoplasmacytic alveolitis (H&E, 10×); (e) sinusoidal dilatation and congestion in the liver (H&E, 10×) (f) mild, lymphoplasmacytic myocarditis (H&E, 40×).

Figure 3

Indirect immunostaining (Anti-LipL32) of pathogenic Leptospira spp. Brown-stained aggregates of filamentous bacteria consistent with Leptospira (pointed out with arrows) in different tissues. (a,b) Tubular lumen and between cells of the tubular epithelium in the kidney (100×); (c,d) lung tissue (10×); (e) liver tissue (10×); (f) heart tissue (100×).