Localization of porcine reproductive and respiratory syndrome virus in mammary glands of experimentally infected sows

We investigated the localization of porcine reproductive and respiratory syndrome virus (PRRSV) in the mammary glands of experimentally infected sows using reverse transcription PCR and immunohistochemistry. Six pregnant sows were inoculated intranasally with PRRSV three weeks prior to the predicted farrowing date. The six PRRSV-infected sows and two uninfected negative control sows remained clinically healthy and farrowed normally. Milk samples were collected from all sows on lactation days 1, 2, and 3. PRRSV was detected in milk as early as lactation day 1 in all of the PRRSV-infected sows, but not in the uninfected sows. PRRSV antigen was detected by immunohistochemistry in macrophage-like cells in the alveolar lumina of the mammary glands and in other tissues. Our results show that PRRSV is shed in the milk of infected sows, and that PRRSV antigen is present in the mammary glands of experimentally infected sows.