How do ticks become infected with diseases? - briefly
Ticks pick up pathogens while ingesting blood from infected hosts, and certain microbes can also be passed from adult females to their eggs or transferred between neighboring ticks feeding on the same animal.
How do ticks become infected with diseases? - in detail
Ticks acquire pathogens through several biologically defined pathways that operate at distinct stages of their life cycle. The most common route is ingestion of infected blood while feeding on vertebrate hosts. When a larva, nymph, or adult attaches to a host that carries a microorganism—such as bacteria, viruses, or protozoa—the pathogen enters the tick’s gut, crosses the midgut barrier, and disseminates to salivary glands. Subsequent feeding events allow the tick to transmit the agent to new hosts.
Key mechanisms of pathogen acquisition include:
- Transstadial transmission – the pathogen survives the molt from one developmental stage to the next (e.g., larva to nymph). This ensures continuity of infection despite the tick’s intermittent feeding pattern.
- Transovarial transmission – infected females pass the microorganism to their offspring via eggs. This vertical route sustains infection in tick populations even when vertebrate hosts are scarce.
- Co‑feeding transmission – adjacent ticks feeding simultaneously on the same host exchange pathogens without systemic infection of the host. The proximity of feeding sites facilitates direct pathogen transfer.
- Environmental uptake – certain agents can be acquired from contaminated substrates, such as soil or vegetation, when ticks crawl through infected material. This route is less common but documented for some rickettsial species.
The internal journey of a pathogen involves crossing several physiological barriers. After ingestion, the organism must traverse the peritrophic matrix, invade midgut epithelial cells, and enter the hemocoel. From there, it reaches the salivary glands, where it is stored in secretory vesicles ready for injection during the next blood meal. Successful navigation of these steps depends on specific molecular interactions between tick and pathogen, including surface proteins that mediate adhesion and immune evasion.
Factors influencing infection rates include host competence, tick species specificity, feeding duration, and environmental temperature. Longer attachment periods increase the probability of pathogen uptake and transmission. Temperature affects both tick metabolism and pathogen replication, thereby modulating the efficiency of the infection process.
Overall, the combination of horizontal acquisition from hosts, vertical passage to progeny, and occasional environmental uptake creates a robust system that maintains disease agents within tick populations and facilitates their spread to new vertebrate hosts.