How does a tick get infected with borreliosis? - briefly
Ticks become carriers by ingesting Borrelia‑infected blood from small mammals or birds during a blood meal; the spirochetes colonize the tick’s gut, then move to the salivary glands to be transmitted in later feedings.
How does a tick get infected with borreliosis? - in detail
Ticks acquire the spirochete that causes Lyme disease while feeding on infected vertebrate reservoirs. The process unfolds through several defined stages.
During the larval blood meal, a naïve tick attaches to a host that carries Borrelia bacteria in its bloodstream. The spirochetes enter the tick’s midgut lumen and adhere to the gut epithelium via outer‑surface proteins (e.g., OspA). Within the gut, the bacteria multiply and persist through the molt that transforms the larva into a nymph.
When the infected nymph begins its next blood meal, environmental cues trigger the spirochetes to down‑regulate OspA and up‑regulate OspC, facilitating migration from the midgut to the salivary glands. The bacteria are then secreted with saliva into the host’s skin, establishing a new infection.
Key points of the infection chain:
- Reservoir hosts – small mammals (especially white‑footed mice), certain birds, and occasionally larger mammals provide the initial source of Borrelia in the ecosystem.
- Acquisition phase – larvae feed on an infected host; spirochetes colonize the gut.
- Transstadial maintenance – the pathogen survives the larva‑to‑nymph molt; no significant transovarial transmission occurs.
- Transmission phase – during the nymphal or adult blood meal, spirochetes move to the salivary glands and are inoculated into the new host.
- Environmental factors – humidity, temperature, and host density influence tick activity and the likelihood of acquiring the pathogen.
The result is a cycle in which each successive tick stage can act as a vector, provided it feeds on an infected reservoir during its previous stage. This mechanism underlies the spread of Lyme disease in endemic regions.