Elimination of Influenza A Virus in multiple breed to wean herds

Influenza A virus (IAV) is an important infectious agent because of its impact on production and zoonotic potential. Vaccination effectiveness to control the disease is debatable in part due to the constant genetic change of this RNA virus. The goal of this case report is to summarize the protocol and results of herd closure, autogenous whole-herd vaccination and nursery depopulation to eliminate IAV from three 5.000-sows herds.

The entire sow herd and gilt developer unit (GDU) beyond the nursery phase were vaccinated twice, three weeks apart, using an autogenous product containing the hemagglutinin (H) antigen(s) isolated from the herd. Gilts received two vaccinations when moved from the on-site nursery to the GDU. Following the initial whole-herd vaccination replacement gilts were weaned to an off-site location until the on-site nursery was depopulated, washed and disinfected. During the time of off-site weaning McRebel management in the farrowing rooms was implemented to reduce transmission. Thirty nasal swabs from each of the two oldest rooms in farrowing were collected 6 and 8 weeks following the initial whole-herd vaccination, and tested in pools of 5 by IAV-PCR to evaluate shedding. Approximately 10 weeks after the initial vaccination, replacement gilts were weaned into the onsite nursery. At this time, the off-site facility was closed to new entries and PCR on oral fluid (OF) samples was used to monitor virus circulation. Seven weeks after closing the off-site facility two mass vaccinations three weeks apart were given with the same autogenous product. At the time of the second vaccination in the off-site facility a third whole-herd vaccination was given at the sow farm to all females. Two weeks later the off-site replacement gilts were brought back into the sow farm. Monitor of clinical signs and PCR testing were performed on the negative gilts in the on-site nursery.

IAV-PCR results at 6 and 8 weeks post whole-herd vaccination were negative in all herds. The off-site weaned gilts tested PCR positive on OF for several weeks but after the mass vaccination IAV RNA was no longer detected. No clinical signs suggestive of influenza or PCR-positive samples have been detected in the herd.

The use of whole-herd autogenous vaccination along with herd closure and partial depopulation is an effective method to eliminate circulating IAV in a sow herd. In two farms the vaccine contained a single antigen and in the most recent farm two different subtypes were included. Although results are encouraging, additional replicates with different strains and farm conditions are necessary to evaluate the repeatibility and feasibility of the protocol.

Disclosure of Interest: None Declared.