From the NMC Newsletter "Udder Topics", April-May, 2003
Sources of Arcanobacterium pyogenes (formerly Actinomyces pyogenes) include wound infections, teat injuries, udder infections, abscesses, and genital tracts.
Means of spread
Spread may be due to contact of teats with a contaminated environment, such as calving areas and dry cow housing. Arcanobacterium pyogenes may be transmitted by flies.
Prevention and control measures
Control measures include fly control programs, maintaining cows in clean and dry calving areas, drying up ("killing") affected quarters to reduce the risk of spreading the infection to other cows, and removing the affected cow from the herd.
Arcanobacterium pyogenes often cause an acute, purulent form of mastitis. Prognosis is poor once an infection is established. Cows usually lose the function of the affected quarter. Infections occur most frequently in dry cows or heifers before calving. Intramammary infections may occur in lactating cows after teat injuries or the use of cannulas or dilators. Mastitis caused by A. pyogenes is more common in humid weather. Arcanobacterium pyogenes are involved in the etiology of "summer mastitis" in Europe.
Source: NMC Publication "Laboratory and Field Handbook on Bovine Mastitis" (1999) pg. 139.