Dear Zahra,

It depends on the numerosità of the herds. I think that starting with 2 herds (with and without Johne's disease history) with at least 50 animals each would work.

Let me know

Leonardo

Thank You. I will

Dear Leonardo,

That is how a colleague of mine responded to this question:

1. Case definition A: where a herd was classified as positive if it contained at least one ELISA-positive animal; and,

2. Case definition B (more conservative): calculated by classifying a herd as positive only if it contained more than one ELISA-positive animal.

3. Healthy: where a herd was classified as negative if it does not contained any ELISA-positive animal.

"You can check at least 12 animals from each flock to do so," he said.

Thanks

I am sorry. I did not read your message until now because I am not closely following ResearchGate.

I do not understand your question. What do you want to do? To confirm paratuberculosis in herds with and without paratuberculosis history? or to run a survey in a region? for the first, obviously, you have to test a number of animals in those herds. If the goal is to compare seroprevalence with and without history you need to set a difference threshold, and the calculate the comparison statistical power with an application that you can find in the web if you look for sample size for comparison of prevalence.

For the case you want to survey a region, you can estimate that your are going to have 50% prevalence which is the situation at which you are going to have the greatest error (this will give you an estimate with a fixed error). If the infection is rare, then the problem is what is the number of herds you need to test to find, at least one positive herd. This can be a large number. Anyway, you have web applications that will make the calculations for you also for this. https://epitools.ausvet.com.au/samplesize is an option, but there are many others.

Regards,

Dear Prof. Justi,

I appreciate your answer. In one work package, it is planned that we test antigenicity of the recombinant proteins in goat flocks with paratuberculosis and in goats of unsuspicious flocks. To calculate the number of animals that should be included in our study for convincing statistics, we would like to know the in-herd prevalence in our goat flocks with paratuberculosis.

I have now the calculation of the minimal herd size needed for antigen testing.  Assuming 25% MAP positive animals in a positive herd  and considering a test sensitivity of 70% and specificity of 99% we need only 12 animals for the antigen testing to obtain specific results.

Regards

Zahra