Reservoirs and proposed transmission routes of Staphylococcus aureus related to intramammary infections in dairy goats: A scoping review.

Mastitis is an important health and welfare issue in dairy ruminants, including dairy goats. Staphylococcus aureus is one of the major contagious pathogens causing mastitis in dairy goats and is generally believed to be transmitted between goats in the milking parlor via contaminated teat cup liners. It is, however, also found on other body sites in dairy goats. Genotypes of S. aureus isolates from milk were often the same as those on dairy goats' extramammary body sites. We therefore hypothesize that extramammary sites may play a role in the transmission of S. aureus to the mammary gland. In this paper, we reviewed the literature on intramammary and extramammary S. aureus reservoirs. We found 71 studies that investigated the occurrence of S. aureus intramammary infections in dairy goats showing no signs of clinical mastitis. In most of the studies (67.6%: 48 out of 71), the reported proportion of dairy goat udder halves with an S. aureus intramammary infection was below 10%. We found 9 studies that took samples of extramammary body sites of clinically healthy dairy goats. The nose had the highest proportion of positive samples for S. aureus, followed by feces and the rectum, and then the vulva, hock, groin, udder cleft, and teat skin, in that order. The prevalence estimates reported in this review are descriptive if nature, and substantial heterogeneity across studies in study design and diagnostic tools used was found. In addition, we show that the transmission routes from extramammary body sites to intramammary infections in dairy goats are not well understood. The possible transmission routes are described to identify the knowledge gaps in the management of S. aureus intramammary infection prevention in dairy goats. In future research, whole genome sequencing could to help understand the relationships between the extramammary and intramammary reservoirs.