Abstract
Prion diseases are rare neurodegenerative diseases of humans and animals with a lethal evolution. Several cell types found on the human skin, including keratinocytes, fibroblasts and lymphocytes, are susceptible to the abnormal infective isoform of the prion protein, which transforms the skin to produce a potential target for prion infection. Iatrogenic transmission of CreutzfeldtβJakob disease was also recognized after corneal transplants in humans, and scrapie was successfully transmitted to mice after ocular instillation of infected brain tissue, confirming that these new routes, as well as cerebral inoculation and oral ingestion, could be important in prion infections. Animal prion infections, such as scrapie (sheep) and βmad cow diseaseβ (cattle), have shown a pattern of horizontal transmission in farm conditions and several ectoparasites have been shown to harbor prion rods in laboratory experiments. Fly larvae and mites were exposed to brainβinfected material and were readily able to transmit scrapie to hamsters. New lines of evidence have confirmed that adult flies are also able to express prion proteins. Because ocular and cerebral myiases and mite infestation are not rare worldwide, and most cases are caused by fly larvae or hay mites that usually affect sheep and cattle, it is important to discuss the possibility that these ectoparasites could eventually act as reservoirs and/or vectors for prion diseases.