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Chronic Wasting Disease (CWD) in Cervids


Introduction

Chronic Wasting Disease (CWD) is a progressive, fatal neurodegenerative disease affecting cervids such as deer, elk, moose, and reindeer. It belongs to the group of transmissible spongiform encephalopathies (TSEs), similar to Bovine Spongiform Encephalopathy (BSE) and Scrapie. CWD is characterized by weight loss, behavioral changes, neurological dysfunction, and eventual death. The disease is of increasing concern due to its spread in wild and farmed cervid populations.

Etiology
Causative Agent

CWD is caused by abnormal prion proteins (PrPSc), which are misfolded forms of the normal cellular prion protein (PrPC).

Agent Characteristics
  • Proteinaceous infectious agent (no nucleic acid)
  • Highly resistant to environmental degradation
  • Persists in soil and organic matter for long periods
  • Capable of inducing misfolding of normal prion proteins
Epidemiology
Species Affected
  • White-tailed deer
  • Mule deer
  • Elk (wapiti)
  • Moose
  • Reindeer (caribou)
Transmission
  • Direct contact between infected and susceptible animals
  • Environmental contamination (soil, feed, water)
  • Exposure to saliva, urine, feces, and carcasses
Environmental Persistence
  • Prions can remain infectious in the environment for years
  • Soil may act as a reservoir
Incubation Period
  • Long incubation period (typically 1.5–3 years or more)
Risk Factors
  • High-density populations (wild or farmed cervids)
  • Contaminated environments
  • Movement of infected animals
Pathogenesis
Entry and Initial Replication

Prions enter via ingestion and initially replicate in lymphoid tissues such as tonsils and Peyer’s patches.

Systemic Spread
  • Spread via lymphatic and nervous systems
  • Accumulation in central nervous system and peripheral tissues
Neurodegeneration
  • Spongiform changes in brain tissue
  • Neuronal loss and gliosis
  • No significant inflammatory response
Clinical Signs
Early Signs
  • Subtle behavioral changes
  • Reduced interaction with herd
Progressive Signs
  • Progressive weight loss (“wasting”)
  • Excessive salivation
  • Increased drinking and urination (polydipsia/polyuria)
  • Listlessness
Neurological Signs
  • Ataxia
  • Tremors
  • Difficulty standing
  • Abnormal posture
Disease Course
  • Gradual progression over months
  • Always fatal
Summary for Practitioners

CWD should be suspected in cervids showing progressive weight loss and neurological signs, particularly in endemic areas or captive populations.

Postmortem Findings
Gross Lesions
  • Emaciation
  • No specific gross lesions in the brain
Microscopic Lesions
  • Spongiform degeneration (vacuolation) in brain tissue
  • Neuronal loss
  • Gliosis
  • Accumulation of prion protein in brain and lymphoid tissues
Diagnosis
Clinical Diagnosis

Based on clinical signs and epidemiological context; confirmation requires laboratory testing.

Laboratory Diagnosis
  • Postmortem testing of brainstem (obex) and lymphoid tissues
  • Immunohistochemistry for prion detection
  • ELISA screening tests
Differential Diagnosis
  • Malnutrition
  • Parasitism
  • Neurological diseases (e.g., listeriosis)
  • Other chronic wasting conditions
Summary for Practitioners

CWD is a reportable disease in many regions. Surveillance and laboratory confirmation are essential for control programs.

Treatment
General Approach

There is no treatment for Chronic Wasting Disease.

Management
  • Culling of affected animals
  • Restriction of animal movement
  • Proper carcass disposal
Summary for Practitioners

CWD is fatal and untreatable. Control relies entirely on prevention and surveillance.

Control and Prevention
Surveillance
  • Monitoring of wild and farmed cervid populations
  • Testing of harvested or dead animals
Biosecurity
  • Control movement of animals
  • Avoid introduction of infected animals into herds
Environmental Management
  • Minimize contamination of feeding and watering sites
  • Limit congregation of animals
Regulatory Measures
  • Reporting and tracking of cases
  • Control programs and culling policies in affected regions
Summary for Practitioners

Control is challenging due to environmental persistence of prions. Integrated surveillance and management strategies are essential.

Zoonotic Importance

No confirmed cases of transmission of CWD to humans have been reported; however, potential zoonotic risk remains under investigation, and precautions are recommended.

Economic and Ecological Importance

CWD impacts wildlife populations, hunting industries, and farmed cervid operations, leading to economic losses and ecological concerns.

Summary

Chronic Wasting Disease is a fatal prion disease of cervids characterized by progressive weight loss and neurological dysfunction. Control is difficult due to environmental persistence, requiring ongoing surveillance and strict management practices.