Johne’s Disease in Small Ruminants

Kids may ingest the bacterium, MAP by nursing fecal contaminated teats. (Photo by Laci Jones)

By Barry Whitworth

Most small ruminant producers realize that the number one health problem in sheep and goats is gastrointestinal parasites (GIP) or what is commonly referred to as “worms.” Producers have several tools such as FAMACHA, Five Point Check, or Fecal Egg Counts that assist them in finding and treating animals infected with GIP.

These tools alert producers to compromised animals so that they can intervene with early treatment before the disease progresses too far. Still, on some occasions animals succumb to the “worms” and die. Many assume the treated animal died because the “worms” were resistant to the dewormer used to treat the parasites.

Sometimes this may be the case, but another possibility is that GIP was not the problem. Another disease that is sometimes mistaken for GIP is Johne’s disease. This disease has clinical signs that are very similar to GIP.

Johne’s disease, which is pronounced “yoh-nees,” is a gastrointestinal disease of ruminants that is fatal. The bacterium that causes the illness is Mycobacterium avium subspecies paratuberculosis which is commonly referred to by the acronym MAP. Producers should be aware that Johne’s is a herd disease. This means that if one animal is found ill with MAP, then several more of the normal appearing animals are probably also infected with the organism.

Most animals are infected early in life, but the clinical symptoms of the disease do not appear for many months. The organism is contagious. The bacterium can be transferred from animal to animal within a species such as sheep to sheep or from one ruminant to another ruminant such as cattle to sheep. Non-ruminant species (such as dogs, raccoons, coyotes, etc.) can be infected with MAP, but they usually to do not have any clinical signs. All breeds of sheep and goats are susceptible. Since very few records are kept, no one is sure how widespread the disease is in small ruminants.

MAP is very hardy in the environment. The organism is resistant to heat, cold, moisture, and drying. The bacterium has been found to survive for several months in the soil and water. The organism can be found in grasses fertilized with contaminated manure. Disinfectants that are labeled as “tuberculocidal” may be used for cleaning surfaces, feed troughs or water troughs. However, organic material may inactivate the disinfectant. Composting manure will reduce the number of MAP organisms.

MAP infects the last portion of the small intestines and its lymph nodes. This area is called the ileum. For reasons that have not been explained, the organism begins to replicate and infect more tissue. The immune system responds with inflammation. The ileum thickens, which prevents absorption of nutrients and ultimately results in the animal starving.

Learn more in the November issue!