title: The zoonotic potential of Mycobacterium avium spp. paratuberculosis: a systematic review.
abstract: BACKGROUND
  The zoonotic potential of Mycobacterium avium ssp. paratuberculosis (MAP) has been debated for almost a century because of similarities between Johne's Disease (JD) in cattle and Crohn's disease (CD) in humans. Our objective was to evaluate scientific literature investigating the potential association between these two diseases (MAP and CD) and the presence of MAP in retail milk or dairy products using a qualitative systematic review.
  
  
  METHODS
  The search strategy included 19 bibliographic databases, 8 conference proceedings, reference lists of 15 articles and contacting 28 topic-related scientists. Two independent reviewers performed relevance screening, quality assessment and data extraction stages of the review.
  
  
  RESULTS
  Seventy-five articles were included. Among 60 case-control studies that investigated the association between MAP and CD, 37 were of acceptable quality. Twenty-three studies reported significant positive associations, 23 reported non-significant associations, and 14 did not detect MAP in any sample. Different laboratory tests, test protocols, types of samples and source populations were used in these studies resulting in large variability among studies. Seven studies investigated the association between CD and JD, two challenge trials reported contradictory results, one cross-sectional study did not support the association, and four descriptive studies suggested that isolated MAP is often closely related to cattle isolates. MAP detection in raw and pasteurized milk was reported in several studies.
  
  
  CONCLUSIONS
  Evidence for the zoonotic potential of MAP is not strong, but should not be ignored. Interdisciplinary collaboration among medical, veterinary and other public health officials may contribute to a better understanding of the potential routes of human exposure to MAP.
authors.affiliation: Policy Advice and Effectiveness Program, Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, Guelph, ON. lisa_waddell@phac-aspc.gc.ca
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Waddell
authors.forename: Andrijana
authors.initials: A
authors.lastname: Rajić
authors.forename: Jan
authors.initials: J
authors.lastname: Sargeant
authors.forename: Janet
authors.initials: J
authors.lastname: Harris
authors.forename: Rocio
authors.initials: R
authors.lastname: Amezcua
authors.forename: Lindsay
authors.initials: L
authors.lastname: Downey
authors.forename: Susan
authors.initials: S
authors.lastname: Read
authors.forename: Scott A
authors.initials: SA
authors.lastname: McEwen
mesh_terms: D000818:Animals; D002417:Cattle; D003424:Crohn Disease / Q000382:microbiology*; D006801:Humans; D009164:Mycobacterium Infections / Q000635:transmission*; D016927:Mycobacterium avium subsp. paratuberculosis / Q000302:isolation & purification*; D010283:Paratuberculosis / Q000382:microbiology / Q000635:transmission*; D011634:Public Health; D012307:Risk Factors; D015047:Zoonoses / Q000382:microbiology / Q000635:transmission*