Reindeer herd in a snowy landscape, symbolizing CWD transmission.

Chronic Wasting Disease: How Does It Spread Among Reindeer?

Samir D’Costa in Science & Nature September 2025 • 4 min read.

"New research sheds light on the transmission pathways of Chronic Wasting Disease (CWD) in reindeer, revealing potential risks for farmed and wild populations. Uncover the implications for wildlife management and conservation."

Chronic Wasting Disease (CWD) is a significant threat to deer populations, and recent findings have confirmed its presence in reindeer. Understanding how this disease spreads is crucial for managing its impact, particularly in areas where reindeer populations overlap with other cervids like white-tailed deer, mule deer, and elk.

The primary mode of CWD transmission is horizontal, meaning it spreads from one animal to another through contact or contaminated environments. Direct transmission occurs when healthy animals come into close contact with infected animals and their bodily fluids, such as saliva, urine, and feces. Indirect transmission happens when animals are exposed to environments contaminated with infectious materials, like decomposed carcasses.

A 2005 study investigated how CWD spreads among reindeer by examining both direct and indirect transmission routes. This research provides insights into the potential risks faced by reindeer populations in North America, where they share habitats with other cervids known to carry CWD.

Unveiling the Pathways: Direct vs. Indirect CWD Transmission in Reindeer

Reindeer herd in a snowy landscape, symbolizing CWD transmission.

The study, conducted in Alaska, involved challenging reindeer fawns with CWD through intracranial inoculation using brain material from infected elk, mule deer, and white-tailed deer. This initial challenge aimed to confirm the susceptibility of reindeer to CWD, regardless of the source species. Following the initial inoculation, researchers assessed whether CWD could spread to uninoculated reindeer through direct and indirect contact.

Researchers divided reindeer into several groups to study different transmission routes:

Intracranially Inoculated Group: Reindeer in this group were directly injected with CWD-infected brain material to confirm their susceptibility to the disease.
Direct Contact Group: These reindeer were housed in the same pen as the inoculated reindeer, allowing for nose-to-nose contact and potential transmission through bodily fluids.
Indirect Contact Group: This group was housed in separate pens within the same barn, preventing direct physical contact but allowing for potential transmission through the environment (e.g., airborne particles or contaminated surfaces).
Negative Control Group: These reindeer were housed separately to ensure they had no contact with infected animals or contaminated environments.

The researchers monitored all reindeer for clinical signs of CWD over several years. They collected tissue samples to detect the presence of PrPSc, an abnormal prion protein that serves as a marker for CWD infection. These samples were analyzed using immunohistochemistry, Western blot, and ELISA to confirm CWD infection and assess the extent of prion deposition in different tissues.

Implications and Future Directions

The study's findings highlight the potential for CWD to spread among reindeer through both direct and indirect contact. This is particularly concerning for farmed reindeer, where animals are in close proximity, and for wild caribou populations that share habitats with CWD-infected cervids. These results underscore the need for continued monitoring and management efforts to prevent the spread of CWD and protect reindeer populations.

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This article is based on research published under:

DOI-LINK: 10.3201/eid2212.160635, Alternate LINK

Title: Horizontal Transmission Of Chronic Wasting Disease In Reindeer

Subject: Infectious Diseases

Journal: Emerging Infectious Diseases

Publisher: Centers for Disease Control and Prevention (CDC)

Authors: S. Jo Moore, Robert Kunkle, M. Heather West Greenlee, Eric Nicholson, Jürgen Richt, Amir Hamir, W. Ray Waters, Justin Greenlee

Published: 2016-12-01

Everything You Need To Know

What is Chronic Wasting Disease (CWD), and why is it a concern for reindeer populations?

Chronic Wasting Disease (CWD) is a significant threat to deer populations, including reindeer. It spreads through both direct and indirect contact, posing risks to farmed and wild reindeer. The disease is particularly concerning because reindeer populations often overlap with other cervids like white-tailed deer, mule deer, and elk, increasing the potential for transmission. Understanding CWD transmission is crucial for effective management and conservation efforts.

How does Chronic Wasting Disease spread among reindeer?

Chronic Wasting Disease (CWD) spreads among reindeer primarily through horizontal transmission, involving both direct and indirect contact. Direct transmission occurs when healthy reindeer come into close contact with infected animals, exchanging bodily fluids such as saliva, urine, and feces. Indirect transmission happens when reindeer are exposed to environments contaminated with infectious materials, like decomposed carcasses. This dual pathway of transmission makes CWD particularly challenging to control in both farmed and wild populations.

What methods were used in the Alaskan study to investigate Chronic Wasting Disease (CWD) transmission in reindeer?

In the Alaskan study, researchers used several methods to investigate Chronic Wasting Disease (CWD) transmission in reindeer. Initially, reindeer fawns were challenged with CWD through intracranial inoculation using brain material from infected elk, mule deer, and white-tailed deer to confirm their susceptibility. Then, reindeer were divided into groups like the 'Intracranially Inoculated Group', 'Direct Contact Group', 'Indirect Contact Group', and 'Negative Control Group'. The researchers monitored them for clinical signs of CWD and collected tissue samples to detect PrPSc, an abnormal prion protein, using immunohistochemistry, Western blot, and ELISA to confirm CWD infection and assess prion deposition.

What are the implications of direct versus indirect contact in the spread of Chronic Wasting Disease (CWD) among reindeer?

The study's findings indicate that Chronic Wasting Disease (CWD) can spread among reindeer through both direct and indirect contact, but the implications differ. Direct contact, involving bodily fluids, poses a higher risk in close-quartered environments like farmed reindeer populations. Indirect contact, via contaminated environments, affects wild caribou populations sharing habitats with CWD-infected cervids like white-tailed deer, mule deer and elk. Understanding these distinct transmission pathways is crucial for tailoring management efforts to specific reindeer populations, informing strategies for reducing contact rates and environmental contamination.

Given that Chronic Wasting Disease (CWD) can spread through both direct and indirect contact, what future steps are necessary to protect reindeer populations?

Protecting reindeer populations from Chronic Wasting Disease (CWD), requires comprehensive strategies addressing both direct and indirect transmission pathways. For farmed reindeer, measures such as reducing animal density, implementing strict biosecurity protocols to minimize direct contact, and regular testing are essential. In wild caribou populations, continued monitoring to detect CWD prevalence, managing the overlap with other cervids like white-tailed deer, mule deer, and elk, and addressing environmental contamination through carcass management are critical. Further research into prion persistence in the environment and the development of effective mitigation strategies are also needed to safeguard reindeer populations.