As warmer weather takes hold, people are spending more time outdoors, bringing them into contact with ticks that substantially threaten public health.
Ticks and tick-borne pathogens represent the greatest vector-borne disease threat in the United States. (Vector-borne diseases are transmitted to humans or animals, often through the bite of a bloodsucking insect.) Here, the deer tick is responsible for most human infections, transmitting seven human pathogens—including viruses, bacteria, and protozoa—that can cause Lyme and other diseases.
But tick-to-human transmission is not evenly distributed across the U.S. Deer tick populations in the Northeast and Midwest commonly bite humans and transmit Lyme disease, whereas Southern deer ticks rarely bite and transmit pathogens.
A new study by the University of Minnesota School of Public Health (SPH) looks at the genetic differences in deer ticks from different geographic areas in the U.S.—differences that may explain the regional disparities in Lyme disease transmission patterns. The study, published in Ecology and Evolution, utilized a cutting-edge technology called nanopore sequencing to analyze the genomes of individual ticks from Minnesota, Pennsylvania, and Texas.
The study uncovered two main findings:
There is genetic divergence across regions. The study identified substantial genetic differences between northern and southern ticks. Southern ticks exhibited higher genetic diversity than northern ticks—suggesting different evolutionary pressures among regions.
Northern ticks possess genetic variants associated with disease transmission. Researchers uncovered genetic variants in the genomes of northern ticks related to the ability to detoxify substances and prevent blood from clotting, which may influence tick behaviors such as host preference and pathogen transmission.
“We wanted to understand why deer ticks in the North tend to bite and transmit Lyme disease, while ticks in the South do not,” says public health doctoral candidate and lead author Jacob Cassens. “We discovered numerous genetic differences between populations, particularly between the northern and southern populations, likely reflecting adaptations to distinct environmental conditions and host species.
“Understanding the molecular mechanisms that shape tick behavior and their ability to transmit diseases is paramount. We believe this study contributes to the expanding availability of genomic resources for ticks, paving the way for innovative strategies that reduce the risks posed to human health.”
Future research in this area will seek to link phenotypic (behavior or physiological) traits to genetic characteristics, exploring the biological factors that underlie the differences in Lyme disease transmission between tick populations.
The information could improve Lyme disease risk assessments and enhance tick-control strategies.
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