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The prevalence of BJD (Bovine Johne's Disease).
The following is a list of references that gives some detail on the prevalence of BJD (Bovine Johne's Disease) in cattle herds in various countries across the world. Unfortunately, since research into this topic has not been conducted everywhere, data is not available for all countries.
For a thorough discussion of the global prevalence of Johne's Disease, by continent and by country, see the paper "Johne's Disease - The International Perspective".
In the UK, where the prevalance of Johne's disease in cattle was recorded to be 3.5%, an average of 7% of supermarket milk supplies were contaminated with Mycobacterium paratuberculosis DNA. At peak times of the year, up to 25% of supermarket milk supplies were contaminated.
In some parts of the USA, very high prevalance rates of Johne's disease(18%) have been recorded. This is most likely caused by intensive modern farming practices, where higher numbers of cattle are grazed on smaller plots of land. Since infection with paratuberculosis is spread through contact with contaminated faeces (i.e. cowpats), these intensive practices increase the chances of cross contamination between animals in a herd.
Since the milk from an entire herd is likely to be pooled together (in tankers) for transport to pasteurization processing plants, the herd prevalence figure (i.e. the number of herds in a region that contain infected animals) is more likely to indicate the level of contamination of milk.
Johne's Disease - The International Perspective
Johne's Disease on U.S. Dairy Operations
Epidemiology of Johne's Disease
Economic Significance of BJD (Bovine Johnes Disease)
Dire Warnings about Johne's Disease: A Wake-up call for the dairy industry?
Yanking Johne's Chain
Epidemiology of Crohn's Disease