Tackling Johne's around the world
While the human risk of contracting Johne's is unclear, many researchers and countries continue to search for new eradication methods.
by Ken Olson
The author is outreach coordinator for the Johne's Disease Integrated Program.
Dairy and beef cattle, sheep, goats, water buffalo, camels, llamas, alpacas, farmed deer and various wildlife species around the world are all impacted by Johne's disease. The 11th International Colloquium on Paratuberculosis (ICP) attracted 297 participants from 49 nations to Sydney, Australia, to discuss the latest research findings on the disease, its causative agent Mycobacterium avium subspecies paratuberculosis (MAP), and programs being used to control it.
At this year's ICP, 240 oral and poster presentations were made during the scientific sessions. Several international research consortia, including the Johne's Disease Integrated Program (JDIP) in the U.S., Para TB Tools in the European Union and the Johne's Disease Research Consortia of New Zealand, have developed multidisciplinary teams that leveraged resources to move the research agenda forward.
Human impact still suspect
One reason for worldwide interest in Johne's is the still unresolved questions related to human health impacts. Conference presentations confirmed that livestock producers incur significant costs from the disease but provided no final answers on human health issues. Several papers did provide additional insights and possible reasons for concern. This may be part of the reason why, when asked near the end of the conference, approximately 10 percent of those present indicated they believe MAP to "definitely be zoonotic" and 90 percent said "potentially zoonotic."
An area of growing concern is the presence of MAP in infant formula worldwide. Cyprus and UK workers reported finding live MAP in 9.4 percent of the commercial samples they tested and MAP DNA in 21.9 percent. This was from a relatively small number of samples (35), but they came from 11 different formula producers. Given the susceptibility of neonatal animals of multiple species to MAP, this raised concerns. Some nations are gearing their programs toward being able to assure international buyers that the infant formula they produce utilizes milk that comes from very low-risk herds.
Work from Japan using a mouse model showed that the MAP antigen alone (dead MAP) can cause intestinal inflammation that closely resembles that associated with Crohn's disease. If confirmed by other workers, this would raise concern because even if pasteurization effectively killed MAP there would still be a risk of infection.
Researchers from the University of Minnesota demonstrated that MAP is capable of producing spores. This may be one way the organism survives pasteurization. In addition, a Norwegian study found, from biopsy samples taken from patients with active Crohn's disease, they had many cells that would react to MAP and trigger a cellular immune response similar to that which leads to intestinal inflammation associated with Crohn's.
Survey work from Argentina, Australia, Brazil, Cameroon, Canada, Chile, India, Iran, Korea, New Zealand, the U.S. and several European countries documented the presence of MAP in a variety of species and products. New research tools are providing insights into the organism and why it is so challenging to address but also ways that we may more effectively deal with it in the future.
Genotyping has shown that strains isolated from Crohn's patients are consistent with bovine strains. It has also shown that there are frequently multiple strains on a farm. This may be a reason that vaccination and control programs face challenges. What is effective against one strain may not work against another that is present at the same location. As we look at ways to deal with the disease, there is work from several countries on improved diagnostics and vaccines.
Breeding programs may also play a role. Researchers from New Zealand verified breed differences in resistance to infection for farmed deer. Work in cattle and other species is progressing and may play a role in the future. One diagnostic tool that seemed intriguing is a "Lab on a chip" that was reported by workers from Tennessee. (For more, read Hoard's Has Heard on page 227 of the April 10, 2012, issue.) The work, funded in part by JDIP, shows promise for an on-site detection tool for Johne's and potentially other diseases. Other work shows promise of earlier positive animal detection. Many challenges remain, but progress is being made on a variety of fronts.
Countries take varied approaches
Producer programs from several countries were highlighted. All have a strong emphasis on education as well as the use of risk assessments and management plans (RAMP), and milk ELISA testing is widely used. Most countries, like the U.S., are seeking to control the disease and limit its spread. Japan appears to be the most aggressive in seeking to eradicate the disease, but Holland's processors are making annual testing and culling compulsory for their farmers.
Some programs, like the one in Ontario, Canada, provide an incentive for culling positive animals. The Ontario program, funded jointly by industry and government, subsidizes testing as long as specific requirements are met. Producers must test all lactating animals, complete a RAMP and submit a copy to the program administrator. In addition, all high-titer cows must be removed from the population, meaning they cannot go to another herd or into the food chain.
Demonstration herds in Minnesota, Texas and Ontario showed that following recommended management practices does work. Clinical cases and prevalence estimates have been reduced. The focus areas are calving pens, calf rearing and limiting entry to the herd of animals from high-risk herds. A variety of educational tools are also being provided.
A web-based system (My Healthy Herd) that addresses Johne's disease and other infectious disease is being provided in Great Britain. Visit www.myhealthyherd.co.uk/ to get a taste. A U.S. program, JD RAP, released in 2012, provides producers with an introduction to the risk assessment process. It allows input of data that customizes the program to their operation. It is available at www.jdrap.org.
A postconference tour provided an opportunity to see other dairy and animal health innovations. The New South Wales Centre for Animal and Plant Biosecurity, located on the Elizabeth Macarthur Agricultural Institute, has been updated and expanded to provide a state-of- the-art diagnostic lab for the state.
For more information on the meeting, visit www.paratuberculosis.info, which is the website of the International Association for Paratuberculosis. Proceedings from the 11th ICP, as well as earlier colloquia and additional Johne's-related information, are available in the publications' area of the site. The next ICP will be held June 22 to 26, 2014, in Parma, Italy.