In the event you were hoping things would get better before they got worse, a groundbreaking new study published in Scientific Reports is indicating that things seem to be working in the opposite direction. At least for now.
The research has since confirmed that Chronic Wasting Disease (CWD), a fatal prion disease affecting deer, can be transmitted from mother to fetus in free-ranging white-tailed deer populations. This discovery, as outlined in the study aptly titled, "Vertical transmission of chronic wasting disease in free-ranging white-tailed deer populations," is now reshaping our understanding of how this devastating disease spreads in the wild and poses new challenges for wildlife management.
Chronic Wasting Disease, often dubbed "zombie deer disease," is caused by misfolded proteins called prions that attack the nervous system, leading to progressive deterioration and death in cervids like white-tailed deer. Historically, CWD transmission was thought to occur primarily through horizontal routes: direct contact between animals or indirect exposure to prions lingering in the environment, such as in contaminated soil or plants. These prions are notoriously resilient, persisting for years and driving outbreaks in endemic areas across the United States and Canada.
While experimental studies in captive animals, like muntjac deer and sheep, hinted at the possibility of maternal (vertical) transmission - where prions pass from mother to offspring during pregnancy - evidence in wild populations was scarce. This gap left wildlife managers focusing on curbing horizontal spread through measures like culling, surveillance, and restrictions on baiting or feeding deer. The new study, however, provides the first direct evidence of in utero transmission in free-ranging deer, revealing a previously under-appreciated pathway that could ultimately amplify CWD’s spread.
Researchers examined 28 pregnant white-tailed does from CWD-endemic regions, alongside controls from a non-endemic area in Georgia. They analyzed maternal tissues (lymph nodes, uterus, placentomes, amniotic fluid) and fetal tissues (brain, thymus, liver, spleen) using advanced prion detection methods.
The study’s results are striking. Researchers found that 31% of CWD-positive mothers had at least one infected fetus. To establish that CWD could be spread, researchers then inoculated tissues from whitetail fetuses into lab mice, with most subsequently developing the disease.
The research team's experiment revealed a more nuanced understanding of CWD transmission during pregnancy. They observed that in some cases, one twin fetus would have CWD prions while the other did not. Similarly, CWD-positive does with infectious prions in their reproductive tissue did not always transmit them to their fetuses, leading researchers to believe that a potential role for genetics in determining a deer's susceptibility to CWD might be a possibility.
What’s it all mean?
Well, we’re not entirely sure. Until now, CWD management has centered on horizontal transmission, with vertical transmission considered a minor or unproven factor in wild populations. This study upends that view by confirming that infectious prions can indeed cross the placental barrier in free-ranging deer, establishing vertical transmission as a viable and significant pathway.
While horizontal transmission remains the dominant mode of CWD spread, vertical transmission adds a “silent” amplifier that complicates eradication. The researchers have stated that further studies are likely required to quantify its population-level impact and explore how genetic factors influence transmission risk.
