Prevalence of Borrelia burgdorferi-infected ticks from wildlife hosts, a response to Norris et al

Abstract

In a recent Letter to the Editor, Norris et al. questioned the validity of some of our data reported by Feria-Arroyo et al. The main issue investigated by us was the potential impact of climate change on the probable distribution of the tick vector Ixodes scapularis in the Texas-Mexico transboundary region. As an ancillary issue, an analysis of sequence data for the intergenic spacer of Borrelia burgdorferi was conducted. In the present letter, we provide further evidence supporting our original results, and advocate that extensive study of the population genetics of B. burgdorferi is needed in the Texas-Mexico transboundary region.

Figure 1

Multiple alignments for the flaB DNA sequence analysed from samples collected in the study presented by Feria-Arroyo et al. [ 4 ] together with 5 more samples acquired from the same regions in Texas in different times of the year. In the alignment the corresponding flaB sequences from B. burgdorferi strains B31, N40 and 297 were used as reference. Sequences were aligned using MacVector 13.0.7 (MacVector Inc., North Carolina). GE, LP and MM samples correspond with GEWMA, LPWMA and MMWMA samples.

Figure 2

Multiple alignments for the FlaB amino acid sequence corresponding to the fragment amplified in this study. The corresponding FlaB amino acid sequences from B. burgdorferi strains B31, N40 and 297 were used as reference. Sequences were aligned using MacVector 13.0.7 (MacVector Inc. North Carolina). All sequences were identified as B. burgdorferi FlaB sequences when analyzed using BLAT® (MacVector 13.0.7, MacVector Inc., North Carolina). GE, LP and MM samples correspond with GEWMA, LPWMA and MMWMA samples.

Figure 3

Neighbor-Joining phylogenetic tree of the flaB sequences analysed in this study. For the phylogenetic analyses, ClustalW2 [8] generated preliminary multiple sequence alignments for both the DNA sequences (A) and their respective putative amino acid sequences (B, obtained through the NCBI’s blastx program). These alignments were fed into jModeltTest 2.1.7 [9] and ProtTest 3 [10], programs that perform maximum likelihood (ML) optimization to assess the best-fit models for nucleotide substitution and amino acid substitution, respectively. These results informed the parameter sets to be used in RAxML v1.1 [11], a randomized, accelerated ML phylogenetic tree search program. These ML searches were conducted through 100 inferences of 100 distinct, randomized trees using the general time-reversible (GTR) model with gamma distributed rate heterogeneity for nucleotide data and the LG model with rate heterogeneity for amino acid data. The phylogenetic trees were visualized using FigTree v1.4.2 [12]. Figure Xa demonstrates that BWTX12-16 possesses a widely divergent nucleotide sequence from that of the other sequences, yet Figure Xb shows that the BWTX12-16 amino acid sequence is nested with the other sequences.