Ticks harbor and excrete chronic wasting disease prions
Chronic wasting disease (CWD) is a fatal neurodegenerative disease caused by infectious prions (PrP CWD ) affecting cervids. Circulating PrP CWD in blood may pose a risk for indirect transmission by way of hematophagous ectoparasites acting as mechanical vectors. Cervids can carry high tick infestations and exhibit allogrooming, a common tick defense strategy between conspecifics. Ingestion of ticks during allogrooming may expose naïve animals to CWD, if ticks harbor PrP CWD . This study investigates whether ticks can harbor transmission-relevant quantities of PrP CWD by combining experimental tick feeding trials and evaluation of ticks from free-ranging white-tailed deer ( Odocoileus virginianus ). Using the real-time quaking-induced conversion (RT-QuIC) assay, we show that black-legged ticks ( Ixodes scapularis ) fed PrP CWD -spiked blood using artificial membranes ingest and excrete PrP CWD . Combining results of RT-QuIC and protein misfolding cyclic amplification, we detected seeding activity from 6 of 15 (40%) pooled tick samples collected from wild CWD-infected white-tailed deer. Seeding activities in ticks were analogous to 10–1000 ng of CWD-positive retropharyngeal lymph node collected from deer upon which they were feeding. Estimates revealed a median infectious dose range of 0.3–42.4 per tick, suggesting that ticks can take up transmission-relevant amounts of PrP CWD and may pose a CWD risk to cervids.