Tick-borne fever (TBF), caused by Anaplasma phagocytophilum transmitted by the sheep tick, is a significant welfare and production concern in upland sheep farming across Europe.
Tick-borne fever causes acute and sustained welfare compromise in affected sheep. The high fever — often exceeding 41°C — causes profound depression, loss of appetite, and weakness. Pregnant ewes that contract TBF may abort, causing physical and potentially psychological distress. The immune suppression that follows TBF infection creates a window of heightened vulnerability during which secondary infections, including the painful joint disease tick pyaemia, establish readily. Lambs affected by tick pyaemia may develop swollen, painful joints and become unable to walk or nurse, resulting in starvation and chronic pain. In upland farming systems where ticks are endemic, proactive tick management — including targeted grazing management, appropriate acaricide timing, and breeding for tick resistance — substantially reduces the welfare burden associated with this disease.