As of 2013, no evidence has been found of transmission to humans from deer, nor by eating animals in the deer family, but both channels remain a subject of public health surveillance and research. Researchers in July 2019 stated that "with all the research on the malignity of prions, and the permanence of prions in the wider environment, and their resistance to destruction and degradation, it is necessary to reduce the potential sources of exposure to CWD." In fact an APHIS scientist observed that, while the longevity of CWD prion is unknown, the scrapie prion has been measured to endure for 16 years. The PrPCWD protein is insoluble in all but the strongest solvents, and highly resistant to digestion by proteases. PrPCWD converts the normal protein PrPC into more of itself upon contact, and binds together forming aggregates. Prusiner noted in 2001 that