A substantial species barrier is preventing the spread of deadly chronic wasting disease (CWD) seen in deer, elk, and moose to humans, found a study.

CWD, also known as zombie deer disease, is highly transmissible and a type of prion disease -- degenerative diseases found in some mammals and primarily involve brain damage but can also affect the eyes and other organs.

The deadly disease occurs when abnormal proteins fold, clump together, and eventually destroy the central nervous system in the brain.

While CWD has never been found in humans, so far, Creutzfeldt-Jakob Disease (CJD) is the most common form of prion disease among humans.

In the study, scientists from the National Institutes of Health in the US used a human cerebral organoid model to decode the risk of spread in humans.

To validate the model, the team infected the organoids with human CJD prions (positive control).

They then directly exposed the healthy human organoids for seven days with high concentrations of CWD prions from white-tailed deer, mule deer, elk, and normal brain matter (negative control).

The results published in the journal Emerging Infectious Diseases showed none of the organoids became infected with CWD in the six months of observation.

“This indicates that even following direct exposure of human central nervous system tissues to CWD prions, there is a substantial resistance or barrier to the propagation of infection,” according to researchers.

However, they acknowledged that the “emergence of new strains with a lesser barrier to infection remains possible”.

Yet they remain “optimistic that the inference of these current data is that humans are extremely unlikely to contract a prion disease because of inadvertently eating CWD-infected cervid meat”.