In a three year study concluded in 2011 AgResearch have investigated the hypothesis that MAP subverts responses in the gut immune system to ensure its survival in the host. This was found to be the case.  In the study of both naturally and experimentally infected adult cows and calves severity of disease was associated with a disregulated immune response and a failure to recognise MAP as foreign by the Toll like receptors TLR1 and TLR2, proteins which are responsible for initiating effective immune responses to the invasion of pathogens.   The study has provided valuable information on markers to identify MAP infection at early and late time-points in the disease which may aid genetic studies and have application in the development of new diagnostics.  Publication of the findings from this study is now underway.

Molecular marker studies have indicated that resistant and susceptible phenotypes in deer can potentially be distinguished by the nature of gene expression in response to MAP challenge in vitro.  Researchers at the University of Otago have developed technology to study macrophages, a type of white cell key to immune response and found that susceptible animals show a dysfunctional, hyper-inflammatory response to infection, while resistant animals contain the infection in a more controlled manner.

The 2011 Annual report outlines research highlights from the JDRC program since 2008.

Advances in strain typing MAP have been used to survey approximately 350 beef, dairy, deer and sheep samples collected from 2008-2010.  Of the 20 type C and 8 type S sub-strains identified in New Zealand to date, this analysis indicated that only 3 major subtypes are responsible for most infections in this collection of samples; one type C strain in deer, a second type C strain in dairy cattle and a third type S strain found in sheep and beef cattle.  There is clear evidence from the study that MAP is transmitted between species and that the profile of disease varies regionally through the nation.  A small number of samples were also found to contain more than one strain type, indicating that animals can be infected on more than one occasion.

A characteristic of Johne’s disease is the wide range of levels of infection found in animals in the different stages of the disease. In the pre-clinical stages, where the animal is infected but not displaying symptoms, very few bacteria (MAP) are present in tissues and few if any are detectable in faeces. In contrast, enormous numbers can be present an animal displaying clinical symptoms. Counting the number of organisms in tissue and faecal samples is key to understanding the level of infection of an animal, but is difficult because the bacteria is difficult to handle in the laboratory and notoriously slow growing. JDRC funded research to improve the ability to count bacteria has been successful, for all but animals shedding very low numbers of bacteria. AgResearch Scientists have shown how their culture and PCR technique for pooled faecal samples can be used as cost beneficial diagnostics for determining the MAP infection status of herds and flocks.