http://www.sciencedaily.com/releases/20 ... 072925.htm
Wild Mice Have Natural Protection Against Lyme Borreliosis
Apr. 4, 2013 — Like humans, mice can become infected with Borrelia. However, not all mice that come into contact with these bacteria contract the dreaded Lyme disease: Animals with a particular gene variant are immune to the bacteria, as scientists from the universities of Zurich and Lund demonstrate. Wild mice are the primary hosts for Borrelia, which are transmitted by ticks.
Springtime spells tick-time. Lyme borreliosis is the most common tick-borne disease in Switzerland: around 10,000 people a year become infected with the pathogen. The actual hosts for Borrelia, however, are wild mice. Like in humans, the pathogen is also transmitted by ticks in mice. Interestingly, not all mice are equally susceptible to the bacterium and individual animals are immune to the pathogen. Scientists from the universities of Zurich and Lund headed by evolutionary biologist Barbara Tschirren reveal that the difference in vulnerability among the animals is genetic in origin.
Protective gene variant
Tschirren and colleagues examined wild mice for signs of a Borrelia infection in a large-scale field study. Borrelia afzelii -- the scientific name for the bacteria -- feed on mouse blood. The researchers discovered that mice with a particular variant of the antigen receptor TLR2 were around three times less susceptible toBorrelia. "The immune system of mice with this receptor variant recognizes the pathogen better and can trigger an immune response more quickly to destroy the Borrelia in time," says Tschirren. Infected mice exhibit similar symptoms to humans -- especially joint complaints. Consequently, in the wild infected mice probably do not survive for very long and weakened animals soon fall victim to foxes and birds of prey.
Arms race between mice and Borrelia
The protective gene variant is advantageous for its carriers and, according to the researchers, gradually becoming prevalent in the mouse population. Nonetheless, it is unlikely that all mice will one day be resistant to Borrelia. "The increasing resistance in the host is bound to lead to adaptations in Borrelia," predicts Tschirren. "We can observe the evolutionary adaptation through the rearmament in mice and the pathogen."
People also have the antigen receptor TLR2, but not the resistant gene variant observed in mice. Whether the evolutionary arms race between mice and Borrelia will have repercussions for people remains to be seen. According to Tschirren, the bacterium does not necessarily have to become more aggressive for humans.
STUDY: Proceedings of the Royal Society B: Biological Sciences, 2013; 280 (1759): 20130364 DOI: 10.1098/rspb.2013.0364
http://rspb.royalsocietypublishing.org/ ... 9/20130364
Polymorphisms at the innate immune receptor TLR2 are associated with Borrelia infection in a wild rodent population
Peer R. E. Mittl2 and
+ Author Affiliations
1Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
2Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
3Molecular Ecology and Evolution Laboratory, Department of Biology, Lund University, Sölvegatan 37, 22362 Lund, Sweden
The discovery of the key role of Toll-like receptors (TLRs) in initiating innate immune responses and modulating adaptive immunity has revolutionized our understanding of vertebrate defence against pathogens. Yet, despite their central role in pathogen recognition and defence initiation, there is little information on how variation in TLRs influences disease susceptibility in natural populations. Here, we assessed the extent of naturally occurring polymorphisms at TLR2 in wild bank voles (Myodes glareolus) and tested for associations between TLR2 variants and infection with Borrelia afzelii, a common tick-transmitted pathogen in rodents and one of the causative agents of human Lyme disease. Bank voles in our population had 15 different TLR2 haplotypes (10 different haplotypes at the amino acid level), which grouped in three well-separated clusters. In a large-scale capture–mark–recapture study, we show that voles carrying TLR2 haplotypes of one particular cluster (TLR2c2) were almost three times less likely to be Borrelia infected than animals carrying other haplotypes. Moreover, neutrality tests suggested that TLR2 has been under positive selection. This is, to our knowledge, the first demonstration of an association between TLR polymorphism and parasitism in wildlife, and a striking example that genetic variation at innate immune receptors can have a large impact on host resistance.
FULL TEXT: http://rspb.royalsocietypublishing.org/ ... 30364.full