Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Pharmaceutical Sciences



Research Advisor

Maria Gomes-Solecki, DVM


Hassan Almoazen, PhD Rudragouda Channappanavar, PhD James B. Dale, MD Michael M. Meagher, PhD Richard J. Webby, PhD


host pathogen interaction; immune response, Leptospira, Leptospirosis, pathogenesis


Leptospirosis is a zoonotic disease transmitted from reservoir hosts like rodents to other animals and humans, who are incidental hosts. This infection is prevalent in the areas of Southeast Asia, Africa and South America. Inactivated Leptospira serovars vaccines are available in endemic areas but they have certain limitations such as serovar specificity and short-term protection. Antibiotics are effective treatment strategies useful at least during early stages of infection. Early diagnosis of Leptospirosis is difficult due to lack of accessible laboratory and point of care tests and due to clinical similarities with other diseases. Thus, it is important to understand host-Leptospira interactions which comprise host immunity, bacterial virulence, and pathogenesis. Transmission of Leptospira can occur directly or indirectly through environmental sources such as contaminated urine. Outbreaks have been reported from occupational exposure, natural disasters, and recreational activities. Immune responses during early or acute Leptospirosis remains unexplored. The host immunity plays an important role in combating Leptospira spp by involving different immunomodulators that activate specific immune cells. In our study, we investigated the early immune responses after pathogenic and saprophytic Leptospira infection. We observed an elevated chemo-cytokine response with pathogenic L. interrogans infection whereas only a few chemokines were upregulated during saprophytic L. biflexa infection. Moreover, pathogenic L. interrogans infection led to splenomegaly due to recruitment of major myeloid cells to the spleen. The innate immune response consisting of macrophages, neutrophils, NK cells effectively eradicated saprophytic L. biflexa, which did not disseminate in blood, whereas pathogenic Leptospira engaged the involvement of both innate and adaptive immune responses as the former is not sufficient to eradicate them. Consequently, pathogenic Leptospira further disseminates to different organs and promote to disease progression. Our results suggest that infection with pathogenic and saprophytic Leptospira is characterized by a differential immune response. The elevated immune response after L. biflexa exposure during early infection determined in the first study led us to posit that exposure to saprophytic Leptospira may act as an immune booster and could provide protection during subsequent pathogenic Leptospira infection. Our aim was to determine if pathogenic L. interrogans infection led to significant disease after single and double exposure of mice to saprophytic L. biflexa. We found that 75% of mice survived L. interrogans infection after single exposure to L. biflexa, while no deaths were observed in infected mice after double exposure to L. biflexa. An increase in IgG subsets suggested an antibody mediated response specific against L. interrogans. Immunophenotyping in spleen after double exposure to L. biflexa in infected mice showed an elevation in B cells, helper T cells with an increase in early effector and effector response with reduction in cytotoxic T cells. Thus, prior saprophytic L. biflexa exposure protected mice from infection with pathogenic L. interrogans serovar Copenhageni. Previous reports have suggested the possibility of venereal transmission of Leptospira in cattle, sheep, horse, and boars. Although, these studies have detected the presence of spirochetes and their viability in the testes and vaginal fluid of these animals such studies have not been performed in mice. Analysis of Leptospira dissemination and colonization of sex organs in rodents is of significant value as it queries the possibility of mammal-to-mammal venereal transmission. The aim of our study was to evaluate the presence and viability of Leptospira interrogans in testes of mice using models of infection that we previously developed. The aim of our study was to evaluate the presence and viability of Leptospira interrogans in testes of mice using models of infection that we previously developed. This was confirmed by qPCR for the Copenhageni serovar after lethal infection of C3H/HeJ mice. In this model, no histopathological changes were noticed in testis. We further studied persistence of serovar Copenhageni in C3H/HeJ testes after lethal and sublethal infection, with different doses of leptospires. No viable leptospires were recovered from testes of lethally infected mice. However, we found live culturable Leptospira in testes of sublethally infected mice at the acute phase but not at 15 days post infection, which corresponds to the chronic phase of renal colonization. The data suggest that colonization of testes with live and potentially infectious leptospires is transient and limited to the spirochetemic phase of infection. Further studies are necessary to evaluate if presence of Leptospira in testes of mice leads to excretion in semen and to venereal transmission to female mice.

Declaration of Authorship

Declaration of Authorship is included in the supplemental files.




2022-011-Shetty-DOA.pdf (221 kB)
Declaration of Authorship

Available for download on Wednesday, June 12, 2024