The alpha-Gpdh polymorphism in the tick Ixodes ricinus: similar diurnal trends in genotypic composition in Irish and Swedish population samples

Key enzymes and proteins of crop insects as candidate for RNAi based gene silencing

RNA interference (RNAi) is a mechanism of homology dependent gene silencing present in plants and animals. It operates through 21-24 nucleotides small RNAs which are processed through a set of core enzymatic machinery that involves Dicer and Argonaute proteins. In recent past, the technology has been well appreciated toward the control of plant pathogens and insects through suppression of key genes/proteins of infecting organisms. The genes encoding key enzymes/proteins with the great potential for developing an effective insect control by RNAi approach are actylcholinesterase, cytochrome P450 enzymes, amino peptidase N, allatostatin, allatotropin, tryptophan oxygenase, arginine kinase, vacuolar ATPase, chitin synthase, glutathione-S-transferase, catalase, trehalose phosphate synthase, vitellogenin, hydroxy-3-methylglutaryl coenzyme A reductase, and hormone receptor genes. Through various studies, it is demonstrated that RNAi is a reliable molecular tool which offers great promises in meeting the challenges imposed by crop insects with careful selection of key enzymes/proteins. Utilization of RNAi tool to target some of these key proteins of crop insects through various approaches is described here. The major challenges of RNAi based insect control such as identifying potential targets, delivery methods of silencing trigger, off target effects, and complexity of insect biology are very well illustrated. Further, required efforts to address these challenges are also discussed.

Pathogenic Landscape of Transboundary Zoonotic Diseases in the Mexico-US Border Along the Rio Grande

Transboundary zoonotic diseases, several of which are vector borne, can maintain a dynamic focus and have pathogens circulating in geographic regions encircling multiple geopolitical boundaries. Global change is intensifying transboundary problems, including the spatial variation of the risk and incidence of zoonotic diseases. The complexity of these challenges can be greater in areas where rivers delineate international boundaries and encompass transitions between ecozones. The Rio Grande serves as a natural border between the US State of Texas and the Mexican States of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. Not only do millions of people live in this transboundary region, but also a substantial amount of goods and people pass through it everyday. Moreover, it occurs over a region that functions as a corridor for animal migrations, and thus links the Neotropic and Nearctic biogeographic zones, with the latter being a known foci of zoonotic diseases. However, the pathogenic landscape of important zoonotic diseases in the south Texas-Mexico transboundary region remains to be fully understood. An international perspective on the interplay between disease systems, ecosystem processes, land use, and human behaviors is applied here to analyze landscape and spatial features of Venezuelan equine encephalitis, Hantavirus disease, Lyme Borreliosis, Leptospirosis, Bartonellosis, Chagas disease, human Babesiosis, and Leishmaniasis. Surveillance systems following the One Health approach with a regional perspective will help identifying opportunities to mitigate the health burden of those diseases on human and animal populations. It is proposed that the Mexico-US border along the Rio Grande region be viewed as a continuum landscape where zoonotic pathogens circulate regardless of national borders.

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.

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.

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

Ixodes ricinus Linnaeus (Acari: Ixodidae) ticks are vectors of numerous infectious diseases in humans and animals. The allozyme variability of MDH and alpha-Gpdh was detected by native polyacrylamide gel electrophoresis in I. ricinus natural populations in three localities in Serbia. Four alleles of Mdh locus (MDH 1, MDH 2, MDH 3 and MDH X) and four alleles of alpha-Gpdh locus (VS, S, F and VF) were detected. Interpopulation differences in Mdh and alpha-Gpdh allele frequencies were statistically insignificant. Significant difference in alpha-Gpdh allele frequencies between males and females was recorded in the largest sample only. Differences in allele frequencies, detected between borreliae-infected and uninfected I. ricinus ticks, were close to the level of statistical significance, especially for alpha-Gpdh locus. Clear significant difference appeared in females when sexes were tested separatelly (P = 0.037). It is interesting that genotypes containing rarer alleles (MDH 1 and S) were infected in higher proportion in comparison to other genotypes. Our results point towards a possible role of Mdh and alpha-Gpdh loci in I. ricinus ticks in the determination of energy requirements for host seeking. Sex differences in alpha-Gpdh allele frequencies suggest that selective pressure, concerning efficiency of reserve materials utilisation, points to alpha-Gpdh rather than to Mdh locus.