1. Both authors contributed equally to this paper
2. Bavarian Health and Food Safety Authority, Oberschleißheim, Germany
3. National Consiliary Laboratory for Diphtheria, Oberschleißheim, Germany
4. Clinic for Swine, Ludwig-Maximilians-Universität München, Oberschleißheim, Germany
5. Max von Pettenkofer-Institut, Ludwig-Maximilians-Universität München, München, Germany