The thermal resistance of Mycobacterium paratuberculosis in raw milk under conditions simulating pasteurization.

Mycobacterium paratuberculosis is the etiologic agent of ruminant paratuberculosis, commonly referred to as Johne’s disease. The disease is characterized by a chronic granulomatous ileocolitis that ultimately terminates in diarrhea, weight loss, debilitation, and death. The disease is transmitted among ruminants predominately through feces when animals are at a young age. In the United States, the national disease prevalence has been suggested to be 2.6% of the dairy and 0.8% of the beef cattle, although regional surveys suggest local prevalences of 11-17%. Cattle infected with M. paratuberculosis shed organisms in feces often at concentrations approaching 10 colonyforming units (cfu) per gram. The environment of an infected herd is therefore considered heavily contaminated. In addition to feces, other body fluids may also shed M. paratuberculosis, including milk. Some studies have suggested that as many as 35% of clinically infected cattle and 11.6% of asymptomatic carriers have detectable quantities of M. paratuberculosis in their milk. In recent years, there has been an interest in the possible association of paratuberculosis and human Crohn’s disease, a chronic granulomatous ileocolitis of unknown etiology. The possible etiological association between these 2 diseases has largely been prompted by the isolation of M. paratuberculosis from human patients with Crohn’s disease in the United States, Australia, The Netherlands, and France. Of the primary groups currently engaged in the culture of human tissues, M. paratuberculosis has been isolated from 20%, 33%, and 38% of patients with Crohn’s disease, but from only 0.8% (1 in 121) of controls. These human isolates have been shown to be of the bovine type rather than of ovine-caprine origin and are indistinguishable from strains isolated from cattle 3,4,9,12,13 Recently, a species-specific insertion sequence in M. paratuberculosis, IS900, was used in the polymerase chain reaction to examine tissues from human patients for the presence of this organism. IS900 was detected in 65% of tissues from patients with Crohn’s disease but in only 12.5% of controls and 4.3% of cases of ulcerative colitis. The finding of IS900 in 12.5% of controls indicates a previously unrecognized environmental distribution of this organism, suggesting that human contact with M. paratuberculosis may be common. 17 The low incidence of M. paratuberculosis in ulcerative colitis patients suggests that colonization of the disrupted or abnormal intestinal mucosa by M. paratuberculosis