Bovine Mastitis due to Prototheca zopfi II

The occurrence of protothecosis in a dairy herd quarantined under the National Brucellosis Eradication Program is reported. Infection was detected by milk culture and the presence of serum precipitins to a culture filtrate antigen preparation of Prototheca zopfi. The alga was always cultured from the milk when serum precipitins were present. Whey antibodies were demonstrated in infected quarters. Consumption of colostrum from an infected cow may have accounted for the brief appearance of serum precipitins in young calves. A naturally infected cow was monitored for 20 months. Serum antibodies disappeared six months after lactation ended but reappeared following parturition, with both algal cells and antibodies in the colostrum. Prototheca zopfi survived a 13 month dry period. There was no spread of infection to the calf. An experimental infection of a healthy cow was short lived but the presence of both serum and whey antibodies was demonstrated. Cross-reactions between Prototheca and Brucella abortus antigens were not observed, and the association between the diseases was found to be coincidental.