Is there a best time for collecting samples?
The likelihood of MAP shedding increases at times when infected animals are stressed. For cows, this occurs regularly during the late stages of pregnancy and during freshening. Testing of cows by fecal PCR at those times will enhance the ability to find MAP if it is present. Remember to include bulls in the testing. Even though they do not get stressed as predictably as cows, their breeding activities can be stressful as well, increasing the likelihood of finding MAP if it is present.
Can the PCR test tell me how much MAP is present?
Yes, to some degree. The strength of the positive signal is proportional to the number of MAP present, so the stronger the signal, the more MAP in the sample. This is how the animals shedding the highest numbers of MAP can be identified.
What other test methods for the diagnosis of Johne’s disease are there?
There is currently only one alternative MAP detection method available. That method is to try to selectively culture the MAP bacteria. Since MAP bacteria are very slow growing organisms, the culture can take weeks to conduct.
What does a certification of testing through NVSL mean?
NVSL sends out proficiency tests to participating laboratories. The PCR proficiency test consists of several fecal samples from known-positive and known-negative animals. The laboratories do not know the status, however. In order to be awarded a proficiency certificate, the participating labs have to identify the samples correctly. Correct identification means that the staff in the lab has the knowledge and the resources available to provide accurate testing. There are different certificates — one for the individual animal MAP detection PCR, one for the pooled MAP detection PCR (combination of five samples into one), and one for the antibody ELISA test.
Why is it so difficult to detect the presence of MAP in early infected animals?
During the early phase of infection (subclinical, without any noticeable signs of disease) MAP bacteria are either not shed at all, or are shed only intermittently. There are simply not enough MAP bacteria contained in samples taken during that time for the test to be able to detect.
Are there vaccines available to protect my animals against Johne’s disease?
Yes, there is one, licensed for use in the U.S., but the protective effect is limited. The vaccine can prolong the subclinical phase of the infection so the progression into clinical disease is slowed. It may reduce shedding of MAP and clinical disease but it cannot prevent shedding and infection of youngstock altogether. The vacine can, however be a part of a comprehensive test-and-cull control program. Since vaccinated animals also tend to test positive in the bovine tuberculosis test, the use of the vaccine is only possible under strict control by state veterinary officials. Vaccination may also have potentially significant side effects, including strong granulomatous reaction at the injection site. Vaccinated animals will also react positive in the MAP antibody ELISA test, so the ELISA can no longer be used as a screening test.
Two animals in my herd tested positive. Do I have to, or does my veterinarian have to, report that to the state veterinarian?
No, there is no mandatory reporting of Johne’s disease test results. Producers can voluntarily participate in an eradication program and results obtained under that program have to be reported to the program administrator. Different states will have different programs and program requirements may vary slightly. There will be no quarantine on farms because of the Johne’s disease status.