AASV: Managing influenza A virus in swine

May 20, 2024

During the 2024 American Association of Swine Veterinarians annual conference, two veterinarians explained how they deal with the ever-present threat of swine influenza.

Emily McDowell, DVM, Pipestone Veterinary Services in Minnesota, explained that a whole herd approach is needed to control and eliminate swine influenza A (IAV). The two common populations where IAV circulates in a sow farm are: gilt developer and piglets in farrowing.

It is recommended that an influenza vaccine be used routinely on sows and gilts regardless of their flu status and that the vaccine be administered as a mass vaccination, she said.

Killed vaccines are used; multivalent autogenous vaccines are made up of IAV strains from replacement gilt sources supplying the management company farms. These vaccines are updated annually, McDowell noted. In an IAV elimination effort, two whole-herd vaccinations are given two to three weeks apart to all sows and gilts. After the mass vaccinations are completed, internal biosecurity practices and piglet and sow movement restrictions start, she added.

The ideal is to bring in IAV negative gilts whenever possible. In situations where this is not possible and there is no IAV circulating in the farrowing house piglet population, an aggressive vaccination and internal biosecurity (extended quarantine) area is set up in the gilt developer unit, McDowell said.

Internal biosecurity
She noted that the goal of an extended quarantine in the gilt developer unit is to prevent IAV exposure to negative populations (piglets in farrowing, for example). IAV positive gilts that arrive in the gilt developer will receive multiple influenza vaccinations two weeks apart. These gilts will be quarantined from the remainder of the farm for 8-10+ weeks.

Caretakers must wear dedicated clothing, boots and gloves in these quarantined rooms after arrival. In addition, extra PCR testing may be done to validate a negative IAV status prior to allowing contact with other populations of animals at the farm. The extended quarantine plan utilized in gilts works well on farms that operate under aerosol filtration, she noted.

When pursuing an IAV elimination in the piglets, farrowing house biosecurity practices are vital. The farrowing house restrictions are enforced for a minimum of 12 weeks of time. Farrowing house rooms are strictly run all-in all-out. Partial washing of farrowing rooms is prohibited, McDowell emphasized.

Farrowing house personnel are blocked to rooms by age of the piglets. Individuals are allowed to move from younger to older rooms without any change of clothes or washing of hands. However, if personnel help with activities such as weaning in the morning, a change of clothes and washing of hands is required before going to help with the younger pigs (front end or processing, for example), she said.

The farrowing house is organized into three blocks of rooms: youngest block is front end (less than 3 days of age); the middle block is processing (3 to 7 days of age); and the final block is processing to wean (7 days of age to weaning). Farrowing house personnel within each block can go in and out of the rooms in that block without a change of clothes. If going from an older block to a younger block, a change of clothes and washing of hands is required, McDowell noted.

Sow and piglet movements between farrowing rooms must be highly restricted in an IAV elimination effort, she said. No nurse sows are allowed to be used routinely. If a sow dies or needs to be nursed off, a newly farrowed sow (less than 24 hours) is the only sow allowed to replace her. Piglets can be moved only on the day they are born to even out litters. No piglet movements are allowed after 24 hours of being born.

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