Researchers from the University of Wisconsin-Madison have made a significant discovery, indicating that ticks may play a role in the transmission of chronic wasting disease (CWD) among deer in Wisconsin. The study, led by Heather Inzalaco from the Wisconsin Cooperative Wildlife Research Unit, focused on the potential for ticks to harbor the transmissible protein particle responsible for CWD.
Chronic wasting disease is caused by prions, pathogenic agents that can spread among deer through contact with contaminated soil, urine, saliva, blood, and feces. Prions induce abnormal folding of proteins, primarily in the brain, inhibiting their normal functions. Over time, the accumulation of the CWD prions leads to severe brain damage and eventually death in deer.
While many studies have examined the role of soil in the spread of CWD, Inzalaco became interested in investigating alternative environmental and behavioral transmission methods. Recognizing ticks as potential parasites affecting deer, Inzalaco explored whether ticks that feed on CWD-infected deer could host and transmit the prions.
Inzalaco noted that ticks naturally seek blood meals from their hosts. She hypothesized that ticks acquiring blood from CWD-infected deer might also carry the prions and questioned whether the prions in ticks could be present in sufficient quantities to spread the disease.
Further intriguing observations emerged when Inzalaco discovered that allogrooming, a common non-aggressive social behavior among deer involving mutual grooming, might be problematic. Allogrooming often involves the removal of ectoparasites such as ticks, potentially leading to the inadvertent consumption of the parasites by other deer.
To investigate the possibility of prions in ticks after feeding on CWD-infected blood, Inzalaco conducted laboratory experiments. Despite encountering challenges with tick behavior in the lab, she demonstrated that ticks not only carried the prions in their blood meal but also harbored sufficient quantities of the agent to potentially infect other animals with CWD. The next step was to examine the phenomenon in a natural setting.
In partnership with the Wisconsin Department of Natural Resources, Inzalaco analyzed ticks collected from deer harvested by hunters and submitted for CWD testing. Among the 176 deer with ticks studied, 15 were positive for CWD. Inzalaco assessed the blood within the ticks taken from infected deer to measure the prion levels they contained.
The study revealed that these engorged ticks from the wild carried transmissible levels of prions, mirroring the findings observed in the lab. This suggests that ticks may serve as mechanical vectors for the spread of CWD, acting as carriers of the disease that could potentially be consumed by other deer.
However, the study did not directly test whether prion-carrying ticks did cause transmission to other deer, leaving room for further investigation.
Enhancing our understanding of the transmission mechanisms of CWD can contribute to better disease management. While treating all wild deer with tick preventatives is impractical, Inzalaco suggests that improved land stewardship could help control tick populations. Maintaining contiguous native plant communities and implementing proper management practices, such as natural fire regimes, have been shown to limit tick populations. Conversely, fragmented ecosystems with invasive plants may facilitate tick proliferation.
Inzalaco also believes that ticks could be utilized as a screening tool for CWD in both wild and farmed deer. While tick testing may not match the accuracy of tissue sampling, the method could provide valuable insights into the disease’s impact on Wisconsin’s deer population.
Ultimately, Inzalaco’s research aims to improve the overall health of ecosystems, benefitting everyone, especially hunters in the state. By recognizing the interconnectedness between humans, animals, and ecosystem functioning, efforts can be made to preserve the natural heritage and mitigate the impact of diseases like CWD.