Genotypic variation and mixtures of Lyme Borrelia in Ixodes ticks from North America and Europe

Abstract

Background: Lyme disease, caused by various species of Borrelia, is transmitted by Ixodes ticks in North America and Europe. Studies have shown the genotype of Borrelia burgdorferi sensu stricto (s.s.) or the species of B. burgdorferi sensu lato (s.l.) affects the ability of the bacteria to cause local or disseminated infection in humans.

Methodology/principal findings: We used a multilocus PCR electrospray mass spectrometry assay to determine the species and genotype Borrelia from ticks collected in New York, Connecticut, Indiana, Southern Germany, and California and characterized isolates from parts of the United States and Europe. These analyses identified 53 distinct genotypes of B. burgdorferi sensu stricto with higher resolution than ospC typing. Genotypes of other members of the B. burgdorferi sensu lato complex were also identified and genotyped including B. afzelii, B. garinii, B. lusitaniae, B. spielmanii, and B. valaisiana. While each site in North America had genotypes unique to that location, we found genotypes shared between individual regions and two genotypes found across the United States. Significant B. burgdorferi s.s. genotypic diversity was observed between North America and Europe: only 6.6% of US genotypes (3 of 45) were found in Europe and 27% of the European genotypes (3 of 11) were observed in the US. Interestingly, 39% of adult Ixodes scapularis ticks from North America were infected with more than one genotype of B. burgdorferi s.s. and 22.2% of Ixodes ricinus ticks from Germany were infected with more than one genotype of B. burgdorferi s.l.

Conclusions/significance: The presence of multiple Borrelia genotypes in ticks increases the probability that a person will be infected with more than one genotype of B. burgdorferi, potentially increasing the risks of disseminated Lyme disease. Our study indicates that the genotypic diversity of Borrelia in ticks in both North America and Europe is higher then previously reported and can have potential clinical consequences.

Figure 1. B. burgdorferi s.s. genotypes detected in NY, CT, IN, and CA.

The number indicates the genotype and the pie size is relative to the proportion that the genotype was observed compared to all the genotypes in that region. The number of B. burgdorferi samples genotyped in each region was 104 for NY, 61 for CT, 14 for IN, and 9 for CA.

Figure 2. Venn diagrams displaying number of genotypes shared between (A) local, (B) regional, and (C) continental areas.

The local and regional diagrams represent data from field-collected Ixodes ticks containing B. burgdorferi s.s. that were genotyped. The continental Venn diagram incorporates data from all samples (ticks and culture isolates) whose origin was known. The size of the circles is proportional to the number of genotypes in the region.

Figure 3. Detection of multiple B. burgdorferi genotypes in adult I. scapularis ticks.

A) Example of assignment of alleles to a genotype in a mixture. Analysis of sample NY71 from a tick collected in Connetquot, Suffolk County, New York is shown. B) Proportions of the minimum number of B. burgdorferi s.s. genotypes per infected adult Ixodes scapularis tick from Indiana, Connecticut, and New York.