Recurrent mastitis–persistent or new infections?

Recurrent clinical mastitis contributes to around half of all infections having an economic impact in the dairy industry. It leads to milk yield reduction, increased risk of mortality, and culling, and may be caused by new infections or a persistent infection after previous treatment. Disease management is dependent on the infecting species, necessitating accurate identification of the pathogen in the range of persistent and reinfection cases amongrecurrentinfectionsusingcultureandmolecularbiologicalanalysis.Milksamplesfromdiagnosedclinical mastitis cases were collected from three Northern German dairy farms between 2011 and 2015. Totally, 2043 diagnosed mastitiscases were examined at quarter level(1598 (78.2 %) first and 445 (21.8 %) recurrentmastitis casesinlactation).Amongtherecurrentcases,145(32.6%)caseswereconfirmedtoharborthesamepathogenic species as previous infections. RAPD PCR confirmed the same species strain in 49 (11 %) of the recurrent infections. The contribution of new infections as compared to persistent infections in cases of clinical mastitis is clear from the data. Future studies in recurrent clinical mastitis control should be focused on influencing factors to prevent new infections in addition to therapeutic intervention and bacteriological cure.