CATTLE ( BOS TAURUS) RESIST CHRONIC WASTING DISEASE FOLLOWING ORAL INOCULATION CHALLENGE OR TEN YEARS' NATURAL...

We conducted a 10-yr study to establish whether chronic wasting disease (CWD) was readily transmissible to domestic cattle ( Bos taurus) following oral inoculation or by cohousing cattle with captive cervids in outdoor research facilities where CWD was enzootic. Calves ( n=12) were challenged orally on one occasion using brain homogenate derived from CWD-infected mule deer ( Odocoileus hemionus). Five uninoculated cattle served as unchallenged controls. Two other groups of cattle ( n=10-11/group) were housed outdoors for 10 yr in captive cervid research facilities. The environmentally challenged cattle were exposed to CWD-associated prions through common paddocks, feed, and water and via direct daily contact with known and potentially infected mule deer or wapiti ( Cervus canadensis) throughout the decade-long study period. None of the exposed cattle developed neurologic disease during the study. We euthanized cattle surviving to 10 yr postchallenge and examined all for lesions or disease-associated prion protein (PrP^d) by histopathology, immunohistochemistry, and western immunoblot analysis of central nervous system and lymphoid tissue. None had evidence of PrP^d accumulation. We conclude that the risks of CWD transmission to cattle following oral inoculation or after prolonged exposure to contaminated environments are low.