Allozyme polymorphism of Mdh and alpha-Gpdh in Ixodes ricinus populations: comparison of borreliae-infected and uninfected ticks

Implications of climate change on the distribution of the tick vector Ixodes scapularis and risk for Lyme disease in the Texas-Mexico transboundary region

BACKGROUND

Disease risk maps are important tools that help ascertain the likelihood of exposure to specific infectious agents. Understanding how climate change may affect the suitability of habitats for ticks will improve the accuracy of risk maps of tick-borne pathogen transmission in humans and domestic animal populations. Lyme disease (LD) is the most prevalent arthropod borne disease in the US and Europe. The bacterium Borrelia burgdorferi causes LD and it is transmitted to humans and other mammalian hosts through the bite of infected Ixodes ticks. LD risk maps in the transboundary region between the U.S. and Mexico are lacking. Moreover, none of the published studies that evaluated the effect of climate change in the spatial and temporal distribution of I. scapularis have focused on this region.

METHODS

The area of study included Texas and a portion of northeast Mexico. This area is referred herein as the Texas-Mexico transboundary region. Tick samples were obtained from various vertebrate hosts in the region under study. Ticks identified as I. scapularis were processed to obtain DNA and to determine if they were infected with B. burgdorferi using PCR. A maximum entropy approach (MAXENT) was used to forecast the present and future (2050) distribution of B. burgdorferi-infected I. scapularis in the Texas-Mexico transboundary region by correlating geographic data with climatic variables.

RESULTS

Of the 1235 tick samples collected, 109 were identified as I. scapularis. Infection with B. burgdorferi was detected in 45% of the I. scapularis ticks collected. The model presented here indicates a wide distribution for I. scapularis, with higher probability of occurrence along the Gulf of Mexico coast. Results of the modeling approach applied predict that habitat suitable for the distribution of I. scapularis in the Texas-Mexico transboundary region will remain relatively stable until 2050.

CONCLUSIONS

The Texas-Mexico transboundary region appears to be part of a continuum in the pathogenic landscape of LD. Forecasting based on climate trends provides a tool to adapt strategies in the near future to mitigate the impact of LD related to its distribution and risk for transmission to human populations in the Mexico-US transboundary region.

Identification of salivary antigenic markers discriminating host exposition between two European ticks: Rhipicephalus sanguineus and Dermacentor reticulatus

To succeed blood meal, ticks inject salivary proteins to mammalian hosts, eliciting an antibody response against these foreign antigens. Although this immune response has been proposed as a surrogate marker of exposure to tick bites, identification of the corresponding antigens remains elusive. For this aim, a comparison by immunoblots of the kinetic IgG responses to protein salivary gland extracts from two European tick species, Rhipicephalus sanguineus or Dermacentor reticulatus, in rabbits was performed. A singularity in the immune patterns was observed according to rabbit exposure status and depending on the antigen source. Six and five bands were found specifically associated to R. sanguineus and to D. reticulatus exposures, respectively. The identity of these salivary antigenic proteins was determined using an original immunoproteomic approach. The utilization of these tick salivary proteins as biomarker candidates to discriminate R. sanguineus and/or D. reticulatus tick exposure or to develop anti-tick vaccines is discussed.

Seasonal and spatial occurrence of glycerol-3-phosphate dehydrogenase variability in Ixodes ricinus (Acari: Ixodidae) populations

Previous results indicate that glycerol-3-phosphate dehydrogenase variability represents the adaptation of Ixodes ricinus L. (Acari: Ixodidae) to fluctuations of environmental conditions, particularly to temperature. Analysis of crucial polymorphisms in I. ricinus Gpdh gene was done by the restriction method, and three different haplotypes were obtained (GPDH441 1, GPDH441 2, and GPDH441 3), corresponding to GPDH alleles detected by allozyme electrophoresis. Differences in GPDH441 haplotype and genotype frequencies were found between samples from open and forest habitats. Significant seasonal variations of GPDH441 haplotype and genotype frequencies were detected in samples from the open habitats. No seasonal variations were observed at forest localities, probably because of the less pronounced amplitude of environmental factors. The possible role of host availability was discussed as an important factor that affects seasonal dynamics and genetic composition of tick populations.

Detection of Borrelia-specific 16S rRNA sequence in total RNA extracted from Ixodes ricinus ticks

A reverse transcriptase - polymerase chain reaction based assay for Borrelia species detection in ticks was developed. The method was based on amplification of 552 nucleotide bases long sequence of 16S rRNA, targeted by Borrelia specific primers. In the present study, total RNA extracted from Ixodes ricinus ticks was used as template. The results showed higher sensitivity for Borrelia detection as compared to standard dark-field microscopy. Method specificity was confirmed by cloning and sequencing of obtained 552 base pairs long amplicons. Phylogenetic analysis of obtained sequences showed that they belong to B. lusitaniae and B. afzelii genospecies. RT-PCR based method presented in this paper could be very useful as a screening test for detecting pathogen presence, especially when in investigations is required extraction of total RNA from ticks.