Tilmicosin Reduces PRRSV Loads in Pigs in vivo

Porcine respiratory and reproductive syndrome virus (PRRSV) is an important pathogen having a significant economic impact on the swine industry worldwide. Tilmicosin is a new semi-synthetic macrolide antibiotic developed from tylosin B. Tilmicosin can enter pulmonary alveolar macrophages (PAMs) and inhibit the replication of PRRSV in PAMs in vitro. This study was conducted to evaluate the impact of tilmicosin in controlling the replication of PRRSV in vivo. Forty and 635 weaned piglets were randomly chosen from PRRSV-contaminated farrow-to-finish herds in Taiwan and China, respectively. The piglets were equally divided into two groups and housed in the same pen but separated into individual spaces. Tilmicosin (Tilmovet® 20% premix, 400 mg/kg) was administered after weaning for 21 days (treated group). The untreated group of piglets did not receive tilmicosin. Blood samples were collected at 4, 6, 8, 10 and 12 weeks of age to detect of the PRRSV load. At 8 and 10 weeks of age, the tilmicosin-treated piglets had a significantly lower PRRSV load than the untreated piglets (P < 0.05) in Taiwan. At 6, 8, 10, and 12 weeks of age, the tilmicosin-treated piglets had a significantly lower PRRSV load than the untreated piglets (P < 0.05) in China. These data indicates that animals treated with tilmicosin exhibited not only reduced PRRSV loads but also improved average daily weight gain during the study period.