Competition between strains of Borrelia afzelii in the host tissues and consequences for transmission to ticks

Florian Battilotti,Dolores Genné,Maarten J Voordouw,Anouk Sarr,Ryan O M Rego,Olivier Rais,Marika Rossel

doi:10.1038/s41396-021-00939-5

Abstract

Pathogen species often consist of genetically distinct strains, which can establish mixed infections or coinfections in the host. In coinfections, interactions between pathogen strains can have important consequences for their transmission success. We used the tick-borne bacterium Borrelia afzelii, which is the most common cause of Lyme disease in Europe, as a model multi-strain pathogen to investigate the relationship between coinfection, competition between strains, and strain-specific transmission success. Mus musculus mice were infected with one or two strains of B. afzelii, strain transmission success was measured by feeding ticks on mice, and the distribution of each strain in six different mouse organs and the ticks was measured using qPCR. Coinfection and competition reduced the tissue infection prevalence of both strains and changed their bacterial abundance in some tissues. Coinfection and competition also reduced the transmission success of the B. afzelii strains from the infected hosts to feeding ticks. The ability of the B. afzelii strains to establish infection in the host tissues was strongly correlated with their transmission success to the tick vector. Our study demonstrates that coinfection and competition between pathogen strains inside the host tissues can have major consequences for their transmission success.

Highlights

Most pathogen species are composed of different strains [1], which can vary in traits, such as infection intensity, virulence, and transmission [2,3,4]
Strain NE4049 was isolated from an I. ricinus tick in Switzerland, has multi-locus sequence type (MLST) 679, strain ID number 1887 in the Borrelia MLST database, and ospC major group A10
Eight mice were excluded from the study: two mice died during the experiment, one mouse was not infected, and five mice in the co-infected group only became infected with strain Fin-Jyv-A3. We believe that these five mice were not properly exposed to strain NE4049

Summary

Methods

Ticks, and Borrelia afzelii strainsForty female, 5-week-old, specific pathogen-free Mus musculus BALB/c mice were used in this study. We used BALB/c mice because we have a history of successful experimental infections with this mouse strain [33,34,35]. We used B. afzelii strains NE4049 and Fin-Jyv-A3 in this study because we have a history of successful experimental infections with these two strains [33, 34, 36, 37]. Strain Fin-Jyv-A3 was isolated from a Finnish bank vole, has MSLT 676, strain ID number 1961 in the Borrelia MLST database and oMG A3. We determined that both strains contain all the plasmids necessary to complete the life cycle of B. afzelii (see section 1 in the electronic supplementary material (ESM))

Results

Discussion

Conclusion