A team of scientists just added chronic wasting disease to the long list of infectious diseases that ticks can carry and possibly transmit. A new study, published in the Scientific Reports journal, shows that black-legged ticks harbor and even excrete the mis-folded proteins, or “prions”, that give rise to the always-fatal neurodegenerative disease in whitetail deer and other cervid species. It also explored the possibility that deer are spreading CWD amongst themselves by inadvertently ingesting engorged ticks while grooming one another.
According to the study, the researchers used a sampling of some 2,000 hunter-harvested deer heads from Wisconsin in order to achieve their findings. Of those 2,000 dead heads, 174 were infested with ticks, and 15 of those tested positive for CWD. They examined the deer blood inside the ticks on the CWD-infected heads and detected active prions in 6 of them. They also noted that—during the engorgement phase, when ticks can swell to 100 times their unfed body weight—the parasites were excreting those prions back into their hosts’ ear tissue.
“Natural modes of indirect transmission of CWD among free-ranging cervids remain poorly examined and may perpetuate … increases and broad geographic spread of the disease,” the study reads. “The presence of [prions] in blood may pose a risk for indirect transmission by way of … parasites acting as mechanical vectors, as cervids can carry high tick infestations and exhibit [social] grooming.”
Whether or not a deer can actually contract CWD by ingesting a prion-harboring tick during grooming activity isn’t clearly understood at this point. But they’re known to get the disease from other CWD-infected substances in the environment—like the saliva of CWD-infected animals found in the soil in areas where deer tend to congregate.
In the laboratory, the team of scientists fed black-legged ticks a CWD-infected “blood meal” and found that those ticks readily absorbed prions and excreted the prions once fully engorged. They even measured the prion loads from each fed tick and determined that the arachnids held “transmission-relevant amounts and may pose a CWD risk to cervids.”
There are still a lot of unanswered questions about the role that ticks might be playing in the inexorable march of CWD across the North American landscape. But the authors of this study hope their findings could open doors for future research. “We have identified a potential mechanical vector of CWD not previously evaluated for whitetail deer,” they wrote. “These findings and implications may prove useful for CWD research and adaptive management efforts moving forward as we advance our understanding of ecologically relevant drivers of CWD dynamics.”