Three Leptospira Strains From Western Indian Ocean Wildlife Show Highly Distinct Virulence Phenotypes Through Hamster Experimental Infection

Abstract

Leptospirosis is one of the most widespread zoonoses worldwide, with highest incidence reported on tropical islands. Recent investigations carried out in a One-Health framework have revealed a wide diversity of pathogenic Leptospira lineages on the different islands of Western Indian Ocean carried out by a large diversity of mammal reservoirs, including domestic and wild fauna. Using golden Syrian hamsters as a model of acute infection, we studied the virulence of Leptospira interrogans, L. mayottensis, and L. borgpetersenii isolates obtained from rats, tenrecs, and bats, respectively. Hamsters were inoculated with 2.108 bacterial cells and monitored for 1 month. The L. interrogans isolate proved to be the most pathogenic while L. mayottensis and L. borgpetersenii isolates induced no clinical symptoms in the infected hamsters. High leptospiral DNA amounts were also detected in the urine and organs of hamsters infected with the L. interrogans isolate while L. mayottensis and L. borgpetersenii isolates mostly failed to disseminate into the organism. In addition, histological damage was more pronounced in the kidneys and lungs of hamsters infected with the L. interrogans isolate. Altogether, these data support that Leptospira strains shed by mammals endemic to this insular ecosystem (L. mayottensis and L. borgpetersenii isolates) are less pathogenic than the L. interrogans rat-borne isolate. These results may provide a relevant framework for understanding the contrasting epidemiology of human leptospirosis observed among Western Indian Ocean islands.

Pathogenic Leptospira and their animal reservoirs: testing host specificity through experimental infection

“…An alternative explanation of our observations is that the absence of renal colonization in rats by the endemic strains could result from some natural incompatibility possibly genetically determined between the bacterium and this alternative vertebrate host: the L. mayottensis and L. borgpetersenii isolates may not be able to adhere to cells of the host kidney tubules of rats and hamsters and organize bacterial biofilms 27,34 . Noteworthily, L. mayottensis has been recently detected in rats from Madagascar but mostly as co-infections with L. interrogans 19 .…”

“…challenging bats and tenrecs with all three isolates, would bring further relevant information although such experiments require accessing to lab colonies of bats and tenrecs, which are very few worldwide. Other biological characteristics of the Leptospira isolates may also account for our results such as attenuated virulence; 27 low growth rate of Leptospira may also hamper L. mayottensis and L. borgpetersenii from chronically infecting mammalian host other than their natural reservoir. Further experiments are needed to solve this issue and unravel factors that may be at play in such interactions.…”

“…Similarly, one may consider that the inability of L. borgpetersenii and L mayottensis recovered from endemic hosts to colonize rats' kidneys may also reflect an attenuated virulence of these isolates. In a previous study 27 , we have shown that the L. interrogans isolate, the same than the one used in the present study, was (i) significantly more virulent than L. mayottensis and L. borgpetersenii (2020) 10:7239 | https://doi.org/10.1038/s41598-020-64172-4 www.nature.com/scientificreports www.nature.com/scientificreports/ isolates and (ii) able to colonize kidneys after experimental infection of the highly sensitive hamsters more efficiently than did the Leptospira isolates recovered from endemic hosts.…”

“…All Leptospira isolates were grown in Ellinghausen-McCullough-Johnson-Harris (EMJH) liquid medium (Difco, Detroit, MI, USA) supplemented with albumin fatty acid supplement (AFAS) (purchased at AO/OIE and National Collaborating Centre for Reference and Research on Leptospirosis Academic Medical Center, Department of Medical Microbiology, Amsterdam) and 5-fluorouracil (5-Fu) at 28 °C (for detailed protocol, see http://dx.doi.org/10.17504/protocols.io.ifccbiw). The isolates were stored at −80 °C or in liquid nitrogen for three to four years and their virulence was restored by two serial passages in hamsters, then stored at −80 °C and passaged less than 5 times before the start of the experiments 27 . The virulence of the three isolates has been tested on hamsters in a previous study in our lab and revealed a higher virulence of L. interrogans compared to the two other strains 27 .…”

“…The isolates were stored at −80 °C or in liquid nitrogen for three to four years and their virulence was restored by two serial passages in hamsters, then stored at −80 °C and passaged less than 5 times before the start of the experiments 27 . The virulence of the three isolates has been tested on hamsters in a previous study in our lab and revealed a higher virulence of L. interrogans compared to the two other strains 27 . infection and sample collection.…”