M. paratuberculosis is naturally resistant to many commonly used antimicrobial drugs. IN VITRO | IN VIVO		Information about the susceptibility of M. paratuberculosis to antimicrobial drugs is minimal. This is largely because treatment of animals with Johne's disease is considered to be too costly.

Drug susceptibility in vitro

M. paratuberculosis has not heretofore been considered a human pathogen. For a review of this issue please visit the page of this website called "Zoonotic potential". However, treatment of Chron's disease patients for M. Paratuberculosis has been tried and results of such studies are described on that page.

It has not been considered economically prudent to treat animals with Johne's disease. The chances of curing the animal are low, the cost of the drugs is high and the meat and milk derived from animals treated with the kind of potent drugs required are not suitable for human consumption. Hence, very little research has been done to establish a profile of drug susceptibility based on laboratory tests (i.e. in vitro drug susceptibility testing).

What can be gleaned from the few published reports can be loosely summarized as follows:

*TB refers to tuberculosis in humans caused by Mycobacterium Tuberculosis.

Readers should understand the many shortcomings of this table:

1) the table is based on very limited amounts of data from different sources and not all of it is consistent.

2) there are antibiotic susceptibility differences among M. paratuberculosis strains.

3) methods for performing drug susceptibility studies on a pathogen that grows so slowly are not well developed.

4) in vitro tests on mycobacteria are notoriously poor at predicting treatment efficacy in vivo (meaning what is predicted to work based on laboratory tests often fails in patients).

Animal treatment

The most comprehensive review of this topic was written by Guy St, Jean (The Veterinary Clinics of North America - Food, volume 12, pages 417-430, July, 1996). The most recent report of attempted treatment of a cow with Johne's disease is found on pages 56-60 of the Proceedings of the 34^th Annual Convention of the American Association of Bovine Practitioners, September 13-15, 2001.

The conclusion from both the review and the recent single case study is that therapy for clinical paratuberculosis in cattle is costly, inconvenient (requires daily medication) and produces remission of clinical signs only, not elimination of the infection. Once treatment stops, the signs of the infection return since the infection was not cured. Costs to treat a 550 Kg cow range from roughly US$1/day for isoniazid to over US$200/day for amikacin. Given that treatment must continue for at least 6 months and that the economic value of most cows is only US$1,000 - US$2,000, it is seldom financially rational to treat cattle with paratuberculosis. In addition, meat and milk from treated cows legally can not be used for human consumption. The one situation where treatment may be useful is to maintain genetically valuable cow long enough to recover embryos.