Prototheca is not a bacterium, but it is a colourless unicellular alga which occurs naturally in the environment especially where it is humid – in soil, water, manure, sewerage. Infections in animals are not common but spread globally; they occur even in the Czech Republic and their number is gradually increasing. Very rarely, the infection in humans can also be seen (infections of people with decreased immune functions – rarely very severe skin infections, diarrhoea).  

In most cases, mastitis in the dairy cows is caused by Prototheca zopfii (the Prototheca genus comprises of 6 other species). 

Prototheca causes both clinical and subclinical mastitis which can progress to a chronic form. The alga does not respond to the antibiotic treatment; it can be transferred to people by ingestion of contaminated milk or milk products because the usual pasteurization does not eliminate it. The cows affected do not heal spontaneously; early diagnosis and prevention are thus important.

Considerable gradual decrease in the milk yield in the affected quarter is the main consequence of the infection because the alga damages and irreversibly destroys the mammary gland tissue. The secretion may be serous with white flakes or greyish, but the infection can also proceed without visible signs. A somatic cell count in milk becomes significantly high.  

Occasionally, the alga can penetrate farther into the body, affect the lymph nodes and in some animals, swelling and painfulness of the udder can be present.

Prototheca is spread via contact of an opened or damaged teat canal with the contaminated environment, faeces or milking machines. It thrives in the warm and humid environment where it multiplies rapidly. It was even detected in faeces of rodents caught on milk farms. Research shows that protothecal infections in dairy cows herds are directly connected with the level of milking hygiene and stabling, with the quality of feeding and drinking water. The alga reproduces very well and persists in humidity on various flat surfaces – rubber, polypropylene and even glass and stainless steel.   

Prevention of the algal infection comprises of the high level of animal hygiene, proper technique of milking and especially correct care for teat canals; their ducts must always be dry and clean, even in the dry period. When the infection is diagnosed, it is essential to stop milking the affected quarter, pay more attention to pre- and post dip and never to feed milk from the Prototheca infected quarter to calves because the alga would then spread via their faeces. 

Regarding the fact that no specific treatment exists, elimination of cows infected with Prototheca is recommended.