Antigen specific urinary immunoglobulin in reservoir hosts of leptospirosis

Authors: Nally, Jarlath; Hornsby, Richard; Alt, David

Submitted to: Veterinary Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2021
Publication Date: 9/1/2021
Citation: Nally, J.E., Hornsby, R.L., Alt, D.P. 2021. Antigen specific urinary immunoglobulin in reservoir hosts of leptospirosis. Veterinary Sciences. 8(9). Article 178. https://doi.org/10.3390/vetsci8090178.
DOI: https://doi.org/10.3390/vetsci8090178

Interpretive Summary: Leptospirosis is a zoonotic disease caused by an atypical bacterium, Leptospira. Leptospirosis causes abortion, premature birth, and stillbirth in cattle, but the mechanisms of disease are not well understood. Continued disease transmission is facilitated by infected cattle which are typically asymptomatic and shed Leptospira intermittently from their kidneys via urine into the environment where they can survive in suitable moist conditions. Detecting and diagnosing cattle that shed leptospires is difficult. Other animals also shed Leptospira from their kidneys via urine in a similar manner, including rats which transmit the disease to humans and other animals. In this manuscript, we used a rat model of leptospirosis to demonstrate that the shedding of Leptospira from rats was accompanied by urinary antibody. This antibody reacts with the Leptospira shed in urine and has the potential to be used not only as a diagnostic assay, but also facilitate the identification of antigens expressed by leptospires during host infection. Given our findings in rats, we extended our studies to include naturally infected cattle and confirmed similar results. Understanding the interaction between Leptospira and the bovine urinary system is essential in determining the mechanisms of continued disease maintenance and transmission.

Technical Abstract: Domestic and wild animal species act as reservoir hosts of leptospirosis, a global zoonotic disease affecting more than one million people annually and causing significant morbidity and mortality in domestic animals. In contrast to incidental hosts which present with an array of clinical manifestations, reservoir hosts are typically asymptomatic and can shed leptospires from chronically infected kidneys via urine for extended periods of time. Renal excretion of leptospires occurs despite evidence of a humoral and cellular immune response, and is reflective of the unique biological equilibrium that exists between certain animal species and specific serovars of Leptospira. In this manuscript we demonstrate that urinary excretion of pathogenic leptospires is accompanied by the presence of antigen specific urinary immunoglobulin. In rats experimentally infected with L. interrogans serovar Copenhageni, using the intraperitoneal or conjunctival route of inoculation, urinary IgG specific for protein antigens was detectable within one week. Rat urinary IgG was not bound to urinary derived leptospires. In cattle that were naturally exposed to, and infected with L. borgpetersenii serovar Hardjo, urinary IgA specific for protein antigens was detected. Collectively, these results demonstrate that urinary excretion of immunoglobulin specific for leptospires is a hallmark of reservoir hosts of infection, and that urinary Ig can be used to diagnostically identify antigens of Leptospira expressed during persistent renal colonization.