The new science of molecular biology provides a vital diagnostic technique, IS900 PCR. This and other tests for Johne's disease become available as commercial kits. Availability of commercial kits allows development and standardization of state and national control programs.

The new age of paratuberculosis research was ushered in with the discovery of a genetic element unique to M. paratuberculosis. This nucleotide sequence in the chromosomal DNA of the organism was simultaneously and independently discovered by Des Collins in New Zealand and the research team led by J.J. McFadden in England in 1989. The sequence was found to be an insertion element and was designated IS900. It was the first insertion element ever reported in mycobacteria. The importance of this discovery was its enabling the development of genetic tools for the detection of M. paratuberculosis without having to cultivate the bacterium on laboratory media, a process typically requiring 12 to 16 weeks.

Today, IS900-based "gene probes" are providing new and intriguing information on the ecology and host range of this intestinal pathogen. Most provocative are reports that M. paratuberculosis is found in the tissues of over half of humans with Crohn's disease. This chronic, untreatable intestinal disease bears marked clinical and pathological similarity to Johne's disease. To date, the cause of Crohn's disease is unknown.

Researchers around the globe developed several other diagnostic tests many of which became both validated and commercialized in the 1990s. Among the most widely used is the absorbed ELISA, a test for serum antibodies. Multiple companies around the world currently market diagnostic kits based on the absorbed ELISA technique (IDEXX Laboratories, Inc, USA; ImmuCell, USA; Synbiotics, USA; CSL Limited, Australia; SVANOVA, Sweden; and Institut Porquier, France). Agar-gel immunodiffusion (AGID) technology also was adopted and commercialized for serologic diagnosis of paratuberculosis in cattle, sheep and goats (ImmuCell, USA).Automated culture methods were adapted from products designed to detect M.tuberculosis in humans and the BACTEC system (Becton-Dickinson, USA) became a mainstay of for routine culture of M.paratuberculosis in some countries. The Australian immunologist, Paul Wood, developed a method for detecting cellular immune responses to infectious agents based on the principle of measuring gamma-interferon released from peripheral blood leukocytes (Bovigam, CSL Limited).

The availability of multiple diagnostic tests for paratuberculosis gave veterinarians the tools needed to operate effective paratuberculosis prevention and control programs. Australia was the first to establish comprehensive programs to identify herds that were paratuberculosis-free, or of low risk of being infected, to facilitate safe trade of animals. The cattle Market Assurance Program (MAP), as it referred to, is being expanded to include sheep, goats, llamas and alpacas. The Animal Health Service of The Netherlands was next to design and promote national programs for control of bovine paratuberculosis. The USA, with leadership provided by a special committee of the U.S. Animal Health Association called the National Johne's Working Group, created a Voluntary Johne's Disease Herd Status Program modeled after the Dutch and Australian programs. Individual states in the U.S. are moving toward adoption of this program.

The International Association for Paratuberculosis has become even more vital as an organization that facilitates the exchange of scientific information among researchers and regulatory veterinarians operating paratuberculosis control programs in different countries. Animal agriculture owes a deep debt of gratitude to the foresight of Rod Chiodini and Richard Merkal for starting this organization.

What does the future hold?

Since the first recognition of paratuberculosis as a disease entity roughly 100 years ago, the infection has emerged as a common and troublesome disease of multiple animal species. It will likely take almost that long to get it under control, and it will take global efforts. The open question of whether M. paratuberculosis is zoonotic looms large for animal agriculture. The answer to this question will affect how actively, and by what methods, veterinarians in cooperation with animal agriculture work to control this infectious disease. The answer to this question will also affect whether animal agriculture must bear the brunt of the costs to battle this disease or whether society at large should contribute to addressing it as well.