How does a tick transmit borreliosis? - briefly
During a blood meal, a tick ingests Borrelia bacteria from an infected host, the spirochetes migrate to the tick’s salivary glands, and are introduced into the next host when feeding resumes. Transmission typically requires the tick to stay attached for several hours to allow bacterial migration and injection.
How does a tick transmit borreliosis? - in detail
Ticks act as vectors for the spirochete Borrelia burgdorferi, the causative agent of Lyme disease. Transmission occurs during the blood‑feeding process of infected nymphs or adult females. The sequence of events can be described as follows.
During attachment, the tick inserts its hypostome into the host skin, creating a feeding cavity. Saliva is secreted continuously, containing anticoagulants, anti‑inflammatory compounds and immunomodulatory proteins that facilitate prolonged feeding. The pathogen resides in the tick’s midgut after acquisition from a previous host. When the tick begins to ingest blood, the spirochetes migrate from the midgut lumen toward the salivary glands. This migration is driven by chemotactic signals and involves expression of outer‑surface proteins (e.g., OspA down‑regulation, OspC up‑regulation) that enable passage through the peritrophic matrix and entry into the hemocoel.
Once in the salivary glands, Borrelia multiplies and is released with the saliva into the host’s dermal tissue. Transmission typically requires a minimum feeding duration of 24–48 hours; shorter attachment periods result in lower infection probability because the spirochetes have insufficient time to complete migration. The tick’s saliva also suppresses local immune responses, allowing the bacteria to evade detection and establish infection.
Key factors influencing successful transmission include:
- Presence of Borrelia in the tick’s midgut at the start of feeding.
- Up‑regulation of OspC and other surface proteins facilitating migration.
- Sufficient feeding time for migration and salivary secretion.
- Immunomodulatory components of tick saliva that impair host defenses.
After inoculation, Borrelia disseminates from the bite site via the bloodstream, colonizing various tissues and potentially leading to the characteristic manifestations of Lyme disease. Control measures focus on prompt tick removal, avoidance of prolonged attachment, and use of repellents to reduce exposure.