About Johne’s Disease
Johne’s disease, also known as paratuberculosis, is a fatal infectious enteritis caused by the bacterium Mycobacterium avium subspecies paratuberculosis (Map). The disease predominantly affects ruminants, although it has been reported in rabbits, hares and camelids. Johne’s disease occurs worldwide and is endemic in most European countries, including the UK.
Johne’s disease is a significant welfare issue. Animals in the clinical stages of the disease become progressively emaciated and die. Johne’s disease is responsible for significant financial losses to the livestock industries. The true losses are difficult to quantify as Johne’s disease is so difficult to diagnose but they include decreased productivity, increased wastage of adult animals, increased sensitivity to other diseases, infertility and the cost of diagnosis, monitoring and control programmes. If no control measures are implemented on a farm with affected animals, the problem will only get worse and the losses incurred will increase.
- Johne’s disease (paratuberculosis) is a chronic intestinal disease caused by infection with a bacterium called Mycobacterium avium subspecies paratuberculosis (referred to as Map).
- Clinical signs are severe weight loss, reduced body condition and diarrhoea (in cattle) culminating in death.
- Johne’s disease is spread by the ingestion of faeces from an infected animal. Infected animals can also pass on the infection in colostrum or milk and across the placenta to unborn animals. The organism can be found in the semen of infected bulls, but it is thought that this is of negligible importance in the spread of the disease.
- Young animals are more susceptible to infection than adults.
- Johne’s disease usually has a long incubation period of 2 to 4 years during which time the animal may appear healthy but may shed Map intermittently. Animals in this stage of the disease are said to be subclinically infected and act as carriers of the disease.
- Different strains of Map can infect a broad range of hosts but cause disease predominantly in ruminants, camelids, rabbits and hares.
- The diagnosis of Johne’s disease is problematic and there is no single diagnostic test that can detect all stages of the disease. Subclinically infected animals are particularly difficult to diagnose and will test negative for a variable period.
- Johne’s disease may be diagnosed by detecting antibody in the blood or milk using the enzyme-linked immunosorbent assay (ELISA) or by detecting the organism (Map) in faeces or milk using culture and molecular techniques such as polymerase chain reaction (PCR).
- There are biosecurity and management solutions that can reduce the spread of Map and thereby the impact of Johne’s disease. These will depend on the type of farm and species farmed. Your veterinary surgeon will be able to advise you on the best control strategy for your situation.
Current interests and future aims:
- Development of novel diagnostic tests for Map infection
- Evaluation of the efficacy of different diagnostic tests and their utilisation for disease control
- Investigation of early host immune responses to Map infection
- Identification of genes and proteins associated with virulence and pathogenesis
- Development of a live attenuated vaccine for Johne’s disease using Map knock-out mutants
- Identification of Map genotypes and phylogenomics
- The effect of concurrent nematode and Map infections on the intestinal microbiota of commercially farmed sheep
- Assessing environmental contamination by studying the microbiomes of marine mammals (as surrogates for sea water quality), soil and water