The industry has been battling porcine reproductive and respiratory syndrome (PRRS) virus sine the late 1980s. It ahs been called 'The Mystery Disease,' and I think all of us agree, it still is. PRRS is the only disease I have ever dealt with in total frustration. You can't stop an outbreak; it makes both producer and veterinarian feel helpless.

PRRS is the one disease you watch and then decide how you are going to control it based on several factors.

Clinical Signs The clinical signs of a PRRS outbreak, or re-break, vary tremendously depending on the virulence (relative capacity of a pathogen to overcome the body's defenses) of the strain and secondary pathogens on the farm.

The PRRS virus attacks macrophages (cells that fight off bacteria in the body) that suppress the immune system.

This allows other primary and secondary pathogens to invade the pig, resulting in high death loss and the need to cull animals of all ages.

Swine influenza virus, especially the H3N2 strain, can be devastating in PRRS-positive herds. Other disease interactions with PRRS may include Streptococcus suis, Haemophilus parasuis, Actinobacillus pleuropneumonia, salmonella, ileitis, Mycoplasmal pneumonia, Pasteurella multocida and others.

Treatment This is where the frustration begins. There is no treatment.

We use various antibiotics to control the secondary diseases with little success and a lot of extra cost. The end result is the same - high mortality and poor-doers, especially in the nursery. The key is long-term control and elimination of persistent infection.

Control A main goal in controlling persistent PRRS infection and clinical signs is to get the sow herd "quiet" and maintain that status.

Specific farm plans should be written by the veterinarian and producer. The plans are based on pig and people flow, management schemes, disease interactions, strain variances, biosecurity measures, isolation/acclimation (I/A) procedures and vaccination protocols.

The number one cause of a PRRS re-break is poor I/A of incoming breeding stock.

Regardless of the vaccine protocol, bringing in "hot" animals will dramatically increase the chances of a re-break. I/A often can be a hard concept to sell to producers. But it is an absolute must for disease control.

Facilities must be operated all-in, all-out (AIAO). We often fill them with two to three months worth of breeding herd replacements and acclimate for six weeks. Older animals are moved into the breeding barn first. Goal is to have the isolation facility empty and ready for refill two to three months after the first fill. These facilities don't have to be fancy. Pigs need to be comfortable with access to food and water.

Single site, continuous flow systems are also a challenge in preventing re-breaks. These systems create so many subpopulations, and immune status varies so widely within each age group that virus cycling is inevitable.

Control measures are more easily implemented with multiple site, AIAO systems.

Case Study One of my clients built a 1,200-sow, breed-to-wean unit three years ago. It is a state-of- the-art facility with a tunnel-ventilated, totally slotted breeding-gestation barn and farrowing rooms with crates over pull-plug pits.

Due to the substantial investment in the sow unit, I couldn't convince this pork producer to build an isolation facility. Instead, all incoming stock went directly into the breeding-gestation barn. He also refused to implement a PRRS vaccination protocol.

Breeding and gestation systems worked well for the first three months. However, a group of incoming gilts were found to be cycling and shedding PRRS virus. Several gilts were off feed and lethargic, and a 40% abortion rate occurred in the pregnant gilts. Six boars died from secondary Strep suis and Hemophilus parasuis bacterial infections.

This proved to be a very costly mistake. Immediately following this outbreak, this producer constructed an I/A facility. An appropriate vaccination protocol has now been developed, and the herd has experienced an 86% average farrowing rate with sows producing 24 pigs/sow/year for the past year.

Summary PRRS continues to not only plague us, but also confuse us. A lot of controversy over vaccines continues, whether to use modified-live-virus vaccine or killed bacterins. Several producers incorporate both into their vaccine protocols. Your veterinarian can help in deciding what is best. Regardless, remember that proper I/A along with strict biosecurity measures are the main keys to controlling this disease.