Intra-uterine transmission of Mycobacterium avium subsp paratuberculosis in subclinically affected red deer (Cervus elaphus)

Abstract

AIM: To determine the rate of transmission of Mycobacterium avium subsp paratuberculosis (M. ptb) from hind to fetus in utero, and the risk of transmission from dam to fawn via infected colostrum and milk in subclinically affected red deer hinds.

METHODS: Hinds were sourced from farms in Otago or Southland and selected for the study if they were positive to the immunoglobulin G1 (IgG1) modified enzyme-linked immunosorbent assay (ELISA) (Paralisa) and exhibited no clinical signs of Johne's disease. The hinds (n=35) were sent to a deer slaughter premises (DSP; n=31) or were killed on-farm (n=4). All post-mortem samples were collected from the fetus first and then from the dam, taking care to avoid cross contamination between samples. Fresh samples (n=185) were collected for culture, and tissue samples (n=72) were collected from 24 hinds and their fetuses for histopathological examination.

RESULTS: A total of 24/35 hinds selected were suitable for inclusion in the study. Eighteen of these pregnant hinds were culture-positive for M. ptb, and 14 of these had culture-positive fetuses, representing a transmission rate of 78% (95% confidence interval (CI) =0.58–0.98) from dam to fetus. Of the 16 mammary glands sampled, 11 (69%) were culture-positive for M. ptb while 12/15 (80%) mammary lymph nodes sampled were also culture-positive.

CONCLUSIONS: This study demonstrated a high rate of transmission of M. ptb from dam to fetus in red deer, and a potential risk of transmission to fawns suckling from mothers that are subclinically affected with Johne's disease.

KEY WORDS:

• Red deer
• Cervus elaphus
• Johne's disease
• Mycobacterium paratuberculosis
• intra-uterine transmission
• mammary gland

Acknowledgements

The authors would like to acknowledge DEEResearch and the Foundation for Research Science and Technology for funding this study. We are grateful to the owners of the animals for making them available, and the DSP management for their collaboration. We acknowledge the skill and expertise of the people in the Disease Research Laboratory, Otago University, for carrying out the serological tests, and the Tb Diagnostic Laboratory, AgResearch Wallaceville, for the bacterial culturing. We would also like to acknowledge the assistance provided by Jamie Ward and Marjorie Orr during the necropsies and collection of tissues, and to Peter Johnstone for statistical analyses.