How does a tick become infected with borreliosis? - briefly
A tick acquires Borrelia spirochetes during a blood meal from an infected reservoir host such as rodents or birds, where the bacteria colonize its midgut. The pathogens then migrate to the salivary glands, enabling transmission to subsequent hosts during later feedings.
How does a tick become infected with borreliosis? - in detail
Ticks acquire the Lyme disease spirochete during blood meals from infected vertebrate hosts. The pathogen, Borrelia burgdorferi sensu lato, resides in the host’s bloodstream and skin. When an unfed nymph or adult attaches to a host, saliva containing anti‑coagulant and immunomodulatory proteins creates a feeding site. During this prolonged attachment, spirochetes migrate from the host’s capillaries into the tick’s mouthparts and then into the midgut lumen.
Inside the midgut, the bacteria encounter a microenvironment that triggers expression of outer‑surface proteins (e.g., OspA, OspC). These proteins facilitate adherence to the midgut epithelium and protect the spirochetes from digestive enzymes. As the tick continues feeding, the blood meal expands, and the midgut epithelium remodels, allowing spirochetes to detach, proliferate, and migrate toward the salivary glands.
The migration to the salivary glands involves a second set of surface proteins (primarily OspC) that interact with salivary gland receptors. Once within the salivary ducts, the spirochetes are released into the host’s skin during subsequent feeding phases, completing the transmission cycle.
Key steps in the acquisition process:
- Attachment of the tick to an infected host.
- Ingestion of spirochete‑laden blood.
- Passage of bacteria into the midgut lumen.
- Activation of bacterial surface proteins for midgut colonization.
- Proliferation and migration toward the salivary glands.
- Transfer of bacteria into the host during later feeding stages.
Environmental factors such as temperature, host density, and tick developmental stage influence the efficiency of each step. Successful colonization depends on the compatibility of bacterial strains with the tick species and the immune status of the host from which the blood meal is taken.