Preliminary data demonstrated that M. paratuberculosis is equally susceptible to UV inactivation as other bacteria. When 105 - 106 M. paratuberculosis were suspended in sterile deionised water, 4mWs/cm2 UV light was sufficient to achieve a 1 log10 reduction in viable counts, and at UV doses greater than 15 mWs/cm2 , complete disinfection was achieved (E.J.B. Manning and M.T. Collins, unpublished data). Earlier studies concerning the effects of natural sunlight on mycobacteria in the environment indicate that sunlight (presumably UV radiation) decreases the survival rate and that M. paratuberculosis is more resistant to the adverse effects of sunlight than M. bovis. However, recent work in Australia indicates that UV light has minimal effect on M. paratuberculosis viability in soil spiked with the organism.