Longitudinal Pathogenesis Study of Young Red Deer (Cervus elaphus) after Experimental Challenge with Mycobacterium avium subsp. paratuberculosis (MAP)

Paratuberculosis progresses more quickly in young red deer than in sheep or cattle. This study describes the clinical, immunological and pathological changes over a 50-week period in fourteen 4-month-old red deer that received heavy oral challenge with Mycobacterium avium subsp. paratuberculosis (MAP). At 4 and 12 weeks post challenge they were anaesthetized and a section of jejunal lymph node was surgically removed for culture, histopathology, and genetic studies. All 14 deer became infected, none were clinically affected, and they had varying degrees of subclinical disease when killed at week 50. Week 4 biopsies showed no paratuberculosis lesions, but MAP was cultured from all animals. At weeks 12 and 50 histopathological lesions ranged from mild to severe with corresponding low-to-high antibody titres, which peaked at 12–24 weeks. IFN-γ responses peaked at 8–15 weeks and were higher in mildly affected animals than in those with severe lesions. 1. Introduction Paratuberculosis (Johne’s disease), caused by Mycobacterium avium subsp. paratuberculosis (MAP), can cause significant loss of production in red deer (Cervus elaphus) on farms in New Zealand [1, 2]. Young deer are particularly susceptible [3] and clinical disease often occurs in 8–27-month-old animals [1], compared with 2–4 years in sheep and cattle. Clinically affected young deer typically have diarrhoea, lose weight, and have some thickening of the small intestines and grossly enlarged mesenteric lymph nodes, often with tuberculosis-like caseous lesions [2]. Although early immune responses have been studied in cattle [4, 5] and in sheep [6], there is little published information about the progression of disease and immunological responses over the 12 months after challenge with MAP in red deer. Early innate and acquired immune responses are thought to play important roles in determining the pathogenesis and severity of the disease. An experimental paratuberculosis challenge model for red deer has been developed to reproduce a typical range of disease outcomes from mild subclinical infection to clinical disease [7]. This challenge model has been used to study the dose response and differences in susceptibility of deer to ovine and bovine strains of MAP [8], protective efficacy of vaccines [9], and age susceptibility [3]. The two main objectives of this study were to monitor the clinical, immunological, and pathological changes over the course of a year and to collect biopsy samples of jejunal lymph node at three time points for future study of gene expression related to