When do ticks capable of transmitting encephalitis appear? - briefly
Encephalitis‑transmitting ticks are most active from late spring to early autumn, with nymphs emerging in May‑June and adults appearing from July through October.
When do ticks capable of transmitting encephalitis appear? - in detail
Ticks that are vectors of tick‑borne encephalitis (TBE) become active during the warm months when temperature and humidity reach levels that support questing behavior. In most of Europe and parts of Asia, the activity period follows a predictable seasonal pattern:
- Spring emergence (April–May): Nymphs, which are most responsible for human transmission, begin to quest after overwintering. Their small size makes them difficult to detect, increasing infection risk.
- Summer peak (June–July): Adult females and remaining nymphs reach maximum activity. Daily temperatures between 15 °C and 25 °C and relative humidity above 70 % create optimal conditions.
- Early autumn (August–September): A second, often smaller, surge of nymphal activity occurs before the onset of cooler weather. Adults may still be active, especially in shaded, moist habitats.
- Winter dormancy (October–March): Tick activity declines sharply. Adults and larvae enter diapause, remaining hidden in leaf litter, moss, or soil until temperatures rise again.
Geographic variations modify this timeline. In northern latitudes (e.g., Scandinavia, Baltic states) the season may start later (May) and end earlier (September). In southern regions (e.g., the Balkans, parts of Russia) activity can begin in March and extend into October, sometimes with a continuous presence of questing ticks.
Key environmental drivers include:
- Temperature: Sustained daily averages above 10 °C trigger metabolic activity; extreme heat (>30 °C) reduces questing due to desiccation risk.
- Humidity: High ground‑level moisture prevents water loss; tick density drops when relative humidity falls below 60 %.
- Photoperiod: Lengthening daylight in spring signals the end of diapause for nymphs and larvae.
- Host availability: Peaks in small‑mammal populations (rodents) in spring and early summer provide blood meals for nymphs, while larger mammals (deer) support adult females later in the season.
Monitoring programs typically record tick abundance using flagging or dragging methods weekly during the active months. Data show that the highest infection rates for TBE virus correspond with the nymphal peak, reinforcing the need for heightened personal protection (protective clothing, repellents, tick checks) during April through July in most endemic areas.