Equine Johne's Disease
Johne’s disease is a chronic granulomatous disease of the gastrointestinal tract of domestic and wild herbivores due to Mycobacterium avium species, particularly Mycobacterium avium subspecies paratuberculosis. These pathogenic mycobacteria are embedded in their food supply.
Most of our understanding of Johne's disease has been derived from the dairy industry. Disease in cattle is due to Mycobacterium avium subspecies paratuberculosis (Map). In contrast, disease in horses is due to Mycobacterium avium subspecies avium (MA) or Mycobacterium avium complex (Mac). Map is theorized to have evolved from Mycobacterium avium subspecies avium (Ma).
IS1311 is present in the vast majority of pathogenic mycobacterium. A long evolutionary time span is suggested by the presence of mutations in some of the IS1311 elements. IS1311 is present in Ma as well as Map. Primers based upon the IS1311 insertion sequence that identify both Ma variants and Map are encompassed in the direct and nested FecaMap® direct and nested fecal Map PCR test.
Current mycobacterium serological test identify only Map. Equine diagnosis of infection/disease or confirmation of a culture isolate as being Ma or Mac can be achieved by either using the FecaMap® nested or real-time PCR tests or IS1311 insertion sequence confirmation.
Clinical Disease in Horses
Recognition of Johne's disease in horses has been delayed owing to:
- Rarity with which horses with enteritis or colic come to necropsy, and
- Relative lack of environmental stress and/or nutritional compromise that undermines an animal's immune status.
Disease usually presents as anterior enteritis. Jejunal and/or ileal masses due to diseased gut tissue cause an obstruction of the gastrointestinal tract. The blockage may, in turn, result in a necrotizing enterocolitis that unmasks the underlying cause.
Why is Mycobacterium avium infection identification important?
The majority of animals that ingest pathogenic mycobacteria experience only transient active infection. Whether infection is arrested or progresses is determined by its cell-mediated immunity that stop future replication of the mycobacteria. Steps that enhance host immunity increase the probability of converting active infection into latent infection.
ITN is a dietary supplement developed by a group of veterinary nutrition experts designed to do just that: enhance the immune response. Use of ITN in cows with advanced Johne’s disease and low body scores resulted in:
- Cessation of diarrhea
- Reduced fecal shedding
- Prolongation of life
- Potential reversal of gastrointestinal pathology after prolonged utilization
What ITN dietary supplementation does is increase the probability that the horse’s host defense mechanisms will be successful in arresting mycobacterium replication.