Why have ticks become infectious? - briefly
Warmer temperatures, broader host distributions, and fragmented habitats have expanded tick numbers and the prevalence of pathogens they harbor, turning them into more frequent disease vectors. Human intrusion into wildlife zones and altered wildlife management further raise exposure to infected ticks.
Why have ticks become infectious? - in detail
Ticks have acquired a greater capacity to transmit pathogens because multiple ecological and biological processes have converged. Rising temperatures extend the active season of ixodid species, allowing more feeding cycles per year and facilitating the development of pathogens within the vector. Warmer climates also shift geographic ranges northward, exposing naïve wildlife and human populations to tick species that previously were absent.
Human modification of landscapes increases contact between ticks, reservoir hosts, and people. Fragmented forests and suburban gardens create edge habitats where small mammals such as white‑footed mice thrive; these animals serve as efficient reservoirs for bacteria, viruses, and protozoa. Elevated host density shortens the interval between blood meals, accelerating pathogen acquisition and dissemination.
Pathogen adaptation contributes directly to vector competence. Genetic mutations and horizontal gene transfer have produced strains that survive longer in tick midguts, replicate more efficiently, and evade the tick’s immune defenses. Some microorganisms manipulate tick salivary proteins to enhance transmission during feeding.
The tick microbiome influences infection dynamics. Disruption of native bacterial communities—through environmental stressors or exposure to pesticides—can reduce competition, allowing pathogenic species to colonize the vector more readily.
Collectively, climate-driven expansion, altered land use, increased reservoir host abundance, pathogen evolution, and microbiome shifts create conditions in which ticks more frequently acquire and transmit disease agents.