Institute of Molecular Pathogenesis (IMP)

Paratuberculosis, also called „Johne´s disease“, is a chronic inflammatory intestinal disease of domestic and wild ruminants and camelids caused by Mycobacterium avium subsp. paratuberculosis (Map). 

After a latency period of several years, clinical symptoms (diarrhea, weight loss and fatigue) are only visible in the final stage of the disease. Chronic diarrhea is observed in cattle and less frequently in goats and camelids, while sheep are mainly characterized by weight loss and fatigue. However, Map is shed in high amounts via faeces also before clinical symptoms occur. Young animals are most susceptible for infection. Paratuberculosis is spread via trade with clinically healthy, latently infected animals. 

The disease, which is reportable in Germany, has been reported from all regions of the country. Up to now it was detected in cattle, sheep, goats, red deer, roe deer, alpacas, different zoo animals and in a donkey. It causes considerable direct and indirect economic losses which are most severe in dairy herds (reduced milk yield, diminished slaughter value because of weight loss, increased susceptibility to other diseases, direct animal losses). 

The zoonotic potential of the disease is controversial. There is still no scientifically proven evidence of a causal link between Crohn's disease, a chronic inflammatory bowel disease of humans, and paratuberculosis. 

Diagnostics of paratuberculosis is based on the detection of the causative agent in faeces and tissues (jejunum, ileum, ileocaecal valve, gut-associated lymph nodes) or on detection of antibodies in blood serum or milk. Detection of the causative agent is done by bacterioscopy (staining of acid-fast bacilli) or by bacteriological culture followed by identification of genome fragments of Map by PCR. Target regions for PCR can be IS900, f57 and others (Möbius et al., Vet. Microbiol. 126: 324-333, 2008.). Meanwhile, molecular detection of genome fragments of MAP in faecal and tissue samples using quantitative real-time PCR is an established diagnostic method. Different real-time PCR-systems for the direct detection of MAP genome fragments in DNA preparations from different specimen have been approved in Germany.

Furthermore, different ELISA assays for the detection of antibodies against Map in serum and milk samples of cattle and in serum of small ruminants are licensed in Germany.

Because of the chronic course of the disease detection of infected animals is delayed for a long time. Especially in young animals (cattle up to at least 2 years of age) a negative test result does not exclude infection. Even in older animals repeated testing is necessary to increase the detection rate. Prevalence estimation is difficult with the established diagnostic methods.

Cultural and/or molecular biological examination of environmental faecal samples or boot swabs proved a cost-efficient approach for the detection of the paratuberculosis herd status even in low prevalence herds. Antibody detection in serum or milk samples of individual animals is also useful for the classification of the infection status of the herd. Antibody detection in pooled milk samples or bulk milk samples allows the identification of herds with high numbers of MAP shedders.