High Prevalence of Prototheca bovis Infection in Dairy Cattle with Chronic Mastitis in Ecuador

Simple Summary Prototheca bovis is a non-photosynthetic alga ubiquitously distributed in water, sewage and soil. The alga appears to be responsible for a significant proportion of bovine mastitis cases in some countries, and occurs worldwide in tropical and temperate climatic areas. To date, no effective and economically favorable treatment is available, and control therefore requires culling of the infected animals. In the present study, we isolated P. bovis from 15.1% of cows with chronic mastitis from a tropical region in Ecuador. Species identification was carried out by nucleotide sequence analysis of the cytochrome b (cytB) gene. This is the first report that confirms the presence of P. bovis in cattle with mastitis in Ecuador. The genus Prototheca, a unicellular, non-photosynthetic, yeast-like microalgae, is a pathogen of concern for the dairy industry. It causes bovine mastitis that currently cannot be cured, and hence generates significant economic losses in milk production. In this study, for the first time in Ecuador, we identify Prototheca bovis as the etiologic agent of chronic mastitis in dairy cattle. Milk samples (n = 458) of cows with chronic mastitis were cultured on Sabouraud Dextrose Agar (SDA). Microscopy and cytB gene sequencing were used to identify Prototheca, whereby Prototheca bovis was isolated from 15.1% (n = 69) of the milk samples, one of the highest infection rates that can be found in the literature in a "non-outbreak" situation. No other Prototheca species were found. We were unable to isolate the alga from environmental samples. We showed that P. bovis was relatively resistant to disinfectants used to sterilize milking equipment on the cattle farms where it was isolated. We discuss how to avoid future infection and also hypothesize that the real prevalence of Prototheca infection in bovine mastitis is probably much higher than what was detected. We recommend a protocol to increase the diagnostic yield in the bacteriology laboratory.