Lesions from elk hoof disease are generally limited to an elk’s feet. Signs the disease spreads to cause infection throughout the body (called systemic infection) have been very limited. Only mild inflammation has been observed in some internal organs unless elk have secondary infections, such as from trauma, associated with severe debilitation.
Despite the lack of systemic infection, the disease may be exerting changes in molecular factors and processes around the DNA that regulate genome activity independent of DNA sequence in cells throughout the body. These modifications, called epigenetic changes, alter which genes are turned on or turned off, which in turn modifies what proteins are made by the body.
In a study recently published in the journal Scientific Reports, we worked with Dr. Michael Skinner and colleagues in the WSU School of Biological Sciences to conduct cutting-edge research investigating epigenetic changes in female and male elk with and without treponeme-associated hoof disease (TAHD). Sufficient samples were available to scientifically detect a difference in both Roosevelt and Rocky Mountain elk females that were diagnosed with TAHD versus those without TAHD.
The observed epigenetic changes are hypothesized to be a result of infection with TAHD. Epigenetic changes were associated with some human diseases that have been recently investigated. Additionally, some of the epigenetic changes were close to genes known to be associated with bacterial infection.
If these epigenetic changes are systemic, as we suspect, the changes could be passed through the germline (sperm and egg) to future generations and alter their susceptibility to TAHD. However, it is unknown whether those future generations would be more or less susceptible to the disease.
An alternative explanation for the observed epigenetic changes could be due to exposure to environmental contaminants. In previous studies, Dr. Skinner and colleagues have detected epigenetic changes associated with contaminants, such as herbicides, that are passed through generations and are associated with increases in the occurrence of detrimental health impacts in laboratory animals; however, these have not been infectious diseases, such as TAHD. We suspect that the epigenetic changes are a result of the body responding to infection with TAHD in a similar way that the laboratory animals responded to environmental contaminants.
Appropriate single cell type tissues are challenging to collect from free-ranging elk, but we were able to sample normal tendon from the lower limb of elk carcasses submitted for TAHD surveillance from a range of geographic areas. In the future, a non-invasive test for live elk using a cheek swab could be developed to sample more elk and potentially follow disease occurrence in individuals over time. However, this is intensive and costly research, and the benefits would need to be weighed against other research priorities to determine the projects most likely to benefit elk and reduce the negative impacts of TAHD.
More information on the study is available in a WSU press release.