Nocardia mastitis

Mastitis caused by N. asteroides may range from subclinical infection to severe acute infection with a 5-10% mortality rate. Milk samples from 18 dairy herds in Mississippi revealed Nocardia in 35 cows (1.3%) in ten of the herds. All 35 infected cows had single quarter infections. Of 293 quarters with clinical mastitis 4% yielded Nocardia. In vitro antibiotic sensitivity tests on 17 isolates showed erythromycin and miconazole to be active against all isolates, and neomycin against 13. Treatment with erythromycin, novobiocin and ampicillin for extended periods of 1-2 weeks during the lactating period reduced clinical signs but did not eliminate the infection. Cloxacillin and novobiocin did not eliminate infections in dry cows. Introduction of the organism into the udder is considered to be due to contamination during mastitis therapy. The prevalence of single quarter infections supports this view. Laboratories may miss nocardial infections if whole herds are not sampled or if cultures are not maintained for 72-96 hours.