Johne’s disease or Paratuberculosis is caused by Mycobacterium avium subspecies paratuberculosis (MAP). The disease is characterised by chronic, debilitating enteric inflammation in ruminants and causes significant economic losses to livestock industries worldwide. Eradication efforts have been hampered by the fact that it is very difficult to detect the presence of MAP during early infection.
Progression of the disease is usually very slow so the subclinical early phase of the disease can last for years. During this time, however, MAP continues to be shed in the faecal matter of the animal and can therefore readily contaminate the environment. Nursing young stock is at very high risk to become infected, either through contaminated faecal matter on the teats or through MAP being shed in the milk.
During the early phases of the disease, production losses include decreased milk production, decreased fertility, and higher premature cull rates. The most prominent signs of Johne’s Disease (incurable diarrhoea and weight loss up to emaciation and death) do not occur until later in the progress of the disease. In that stage, more MAP bacteria are being shed through the faeces into the environment and infected animals start to develop antibodies in the blood to fight the bacteria.
Neogen® offers two different tests to detect the presence of MAP on the premises:
- Detection of MAP. This test uses the polymerase chain reaction (PCR) methodology. Detection of MAP can be done on the individual animal's faecal sample or a faecal composite sample from the environment when MAP is suspected. The PCR method is currently considered the most sensitive detection method available that can achieve a diagnostic sensitivity up to 96%. The PCR method is much faster than the alternative detection method by culture.
- Detection of the antibodies against MAP. This test is an ELISA test (Enzyme-linked immunosorbent assay). Detection of the presence of antibodies means that the animal has been exposed to MAP for a while. Usually, the more advanced the disease is, the more readily and confidently the antibodies can be detected. The ELISA test is a very useful and affordable screening tool to assess the MAP antibody status in a herd. Once antibody titers have been found, either in the blood or in the milk, follow up testing by PCR is recommended to identify the individual animals that are actually shedding MAP.
Both the MAP detection and the antibody detection test that Neogen offers are certified by the National Veterinary Services Laboratory (NVSL), the federal reference laboratory for animal disease testing. Since only about 10% of infected animals progress to the most advanced stages of the disease, with heavy MAP shedding and high antibody levels, it can be assumed that for each animal that MAP was detected in, there are many more animals on the premises that are already subclinically infected but do not show any overt signs yet.
The NVSL check test is administered as part of the National Johne’s Disease Control Program. Individual states may have a voluntary Johne’s Disease control programs, with some able to subsidise the testing. A very valuable part of these programs are the "test negative herds." This program includes various status levels, which represent levels of certainty that the herd is free of Johne’s Disease. While this is not a guarantee, the highest status comes with a high degree of certainty and represents a significant addition of value to the herd.
Acceptable sample types:
For MAP detection by PCR
The sample type needed for testing is faecal matter. Several grams of sample are requested, equivalent to about half a cup. If samples are very liquid, make sure to include the liquid. Leak-proof sample containers are required. Wear gloves for sample collection. If possible, collect samples directly from the animal’s rectum.
If individual animal testing is desired, make sure gloves are changed between samplings so cross-contamination is minimised.
The Neogen laboratory is certified to pool five samples into one test sample. If a pool of animals is to be tested, collect the faecal samples from each animal into separate containers and request the samples to be pooled by the laboratory (on the submission form). Do not pool samples on the farm!
If environmental sampling is desired, collect faecal material from up to five areas most heavily travelled by the animals. Collect about equal amounts of faecal material per sampling site, either into one large container and indicate the sample is pre-pooled, or collect into several small containers and request pooling by the laboratory (on the submission form).
For detection of antibodies
The sample type needed is serum, plasma, or milk. Whole blood (about 2 ml) can be collected in a red top or red/gray top tube, or a purple top tube. Make sure tubes are labelled with the animal IDs and the consecutive number.
Requirements for shipping:
In order to maintain optimal sample quality for optimal test performance, it is recommended to send the samples by next day air in a Styrofoam box with an ice pack. Avoid freezing the samples.