Porcine Reproductive and Respiratory Syndrome (PRRS) is one of the most devastating diseases in pigs and affects the pork industry globally. PRRS is caused by the PRRS virus (PRRSV) - an enveloped, single-stranded RNA virus (Figure 1).
Options to control PRRS outbreaks are limited and the efficacy of vaccines is thwarted by the high antigenic variability of PRRSV.
PRRSV replicates and multiplies in lung alveolar macrophages
Macrophages function as the first line of defense against bacterial and mycoplasmal infections, playing a crucial role in immune survelliance. Macrophages are the target of PRRS infection - initial replication of the PRRS virus takes place in alveolar macrophages before the virus is distributed to regional lymph nodes, lungs, and other tissues. PRRS disease severity is closely related to the ability of the virus to impair disease-fighting macrophages, increasing susceptibility to respiratory bacteria pathogens and the emergence of secondary infections.
Tilmovet®'s important accumulation in lung alveolar macrophages
One of Tilmovet®'s key abilities is to accumulate intracelluarly in lung macrophages (Figure 2). Macrophages serve as a vehicle for the transport of tilmicosin to the site of infection.
Tilmovet® accumulates in lung macrophages to a much higher extent (75:1) in comparison to other macrolides (erythromycin 6:1., tylvalosin 12:1, tulathromycin 28:1) and antibiotic groups. As a consequence, higher tilmicosin concentrations can be transported to the infection sites when Tilmovet® is administered.
Tilmovet®'s PRRSV replication and transmission effect
In an in vitro study, tilmicosin (Tilmovet®) was shown to inhibit the replication of PRRS virus inside porcine alveolar macrophages in a dose dependent manner (Figure 3). Maximum inhibition was achieved at the highest tilmicosin concentration (10 µg/ml tilmicosin).
The effect of Tilmovet® feed medication of PRRSV vertical transmission and circulation in nursery pigs suffering from PRRSV infection was determined in a field study. ELISA PRRSV antibody titers were determined before and after implementation of a Tilmovet® medication program in different age groups (Figure 4).
PRRSV antibody titers in Tilmovet® medicated gilts and sows decreased to lower levels vs. antibody values determined before medication. Disapperance of antibody titers in different age groups after medication verifies the reduction of PRRS prevalence and virus circulation in the pig herd.
The reduction of PRRSV transmission and prevalence post-farrowing and post-weaning after Tilmovet® medication results in marked improvements in clinical performance parameters in the pig herd as shown in Table 1.
Tilmovet®'s PRRS therapeutic approach
Based on the suppression of PRRS virus replication, the reduced risk of PRRSV vertical transmission and fewer complications from secondary bacterial infections, Tilmovet® represents an important element of a PRRS chemotherapy approach.
References are available on request.