Relationship between negative skin test with Johnin after vaccination and post mortem findings

Area of Science:

• Veterinary Immunology
• Bacteriology
• Animal Health

Background:

• Paratuberculosis (Johne's disease) is a chronic intestinal infection in ruminants.
• Vaccination against paratuberculosis is a strategy to control the disease.
• The efficacy of diagnostic tests in vaccinated animals can be affected by the vaccine itself.

Purpose of the Study:

• To evaluate the diagnostic performance of the intradermal Johnin skin test in cattle vaccinated against paratuberculosis.
• To determine if vaccination influences the interpretation of skin test results.

Main Methods:

• 176 cattle vaccinated with a whole-cell inactivated Mycobacterium paratuberculosis vaccine were skin tested.
• Intradermal Johnin testing was performed between 5 and 14 months of age.
• Post-mortem examinations using histological, microscopical, and cultural techniques confirmed infection status.

Main Results:

• A statistically significant association (P = 0.008) was found between negative skin test results and positive post-mortem findings.
• This indicates that vaccinated cattle may yield false-negative results on skin testing.
• The study highlights potential challenges in diagnosing paratuberculosis in vaccinated herds.

Conclusions:

• The intradermal Johnin skin test may be less reliable for detecting paratuberculosis in cattle vaccinated with a whole-cell inactivated vaccine.
• Vaccination status must be considered when interpreting diagnostic test results for Johne's disease.
• Further research into alternative or modified diagnostic approaches for vaccinated cattle is warranted.