Competition between strains ofBorrelia afzeliiinside the rodent host and the tick vector

Abstract

Multiple-strain pathogens often establish mixed infections inside the host that result in competition between strains. In vector-borne pathogens, the competitive ability of strains must be measured in both the vertebrate host and the arthropod vector to understand the outcome of competition. Such studies could reveal the existence of trade-offs in competitive ability between different host types. We used the tick-borne bacterium Borrelia afzelii to test for competition between strains in the rodent host and the tick vector, and to test for a trade-off in competitive ability between these two host types. Mice were infected via tick bite with either one or two strains, and these mice were subsequently used to create ticks with single or mixed infections. Competition in the rodent host reduced strain-specific host-to-tick transmission and competition in the tick vector reduced the abundance of both strains. The strain that was competitively superior in host-to-tick transmission was competitively inferior with respect to bacterial abundance in the tick. This study suggests that in multiple-strain vector-borne pathogens there are trade-offs in competitive ability between the vertebrate host and the arthropod vector. Such trade-offs could play an important role in the coexistence of pathogen strains. rspb.royalsocietypublishing.org Proc. R. Soc. B 285: 20181804

Competition Between Strains of Borrelia afzelii in Immature Ixodes ricinus Ticks Is Not Affected by Season

“…In a previous study, we investigated competition between two strains of B. afzelii (Fin-Jyv-A3 and NE4049) in the rodent host Mus musculus and in the tick vector I. ricinus (Genné et al, 2018). We tested the effects of interstrain competition on two phenotypes of B. afzelii: strain-specific host-to-tick transmission and strain-specific spirochete load in ticks.…”

“…Borrelia afzelii strains NE4049 and Fin-Jyv-A3 were chosen for this study because both strains are highly infectious to rodent hosts (Genné et al, 2018). Strains NE4049 and Fin-Jyv-A3 were obtained from an I. ricinus nymph in Neuchatel, Switzerland and from a bank vole (Myodes glareolus) in Jyväskylä, Finland, respectively.…”

“…Numerous studies have investigated interactions between pathogen strains in the vertebrate host (Bruce et al, 2000;de Roode et al, 2005a;Bell et al, 2006;Harrison et al, 2006;Pollitt et al, 2011;Reif et al, 2014). In contrast, studies on interstrain interactions in the arthropod vector are rare (Reif et al, 2014;Pollitt et al, 2015;Genné et al, 2018), but these studies have shown that these interactions exist and that they influence the performance of the pathogen strains inside the arthropod vector. The population dynamics of vector-borne pathogens inside their arthropod vectors are also highly dependent on abiotic factors, such as temperature (Sternberg and Thomas, 2014).…”

“…In areas where Lyme borreliosis is endemic, mixed infections in the nymph are common (Qiu et al, 2002;Pérez et al, 2011;Durand et al, 2015Durand et al, , 2017. A recent experimental infection study found that strains of B. afzelii experience competition inside I. ricinus nymphs (Genné et al, 2018). The population size of B. afzelii inside the unfed nymph decreases over time suggesting that competition between strains could intensify with increasing nymphal age (Jacquet et al, 2017;Pospisilova et al, 2019).…”

“…We recently used an experimental infection approach to show that strains of B. afzelii experience competition inside I. ricinus nymphs that were 1 month old (Genné et al, 2018). As part of that study, we also collected engorged larvae, and we allowed a subset of nymphs to age under different seasonal treatments (i.e., different temperature and light conditions that represented summer vs. winter), but these ticks were not analyzed until now.…”