For Smithfield veterinarian Jeremy Pittman, influenza is one of the “Big Four” of swine diseases, falling in the same category as porcine reproductive and respiratory syndrome, porcine circovirus type 2 and Mycoplasma hyopneumonaie.

Speaking at the All-Star Interactive Symposium hosted by Boehringer Ingelheim he says, “Influenza is significantly costly for hog producers. It is estimated from $3 to $10 a pig. Based on experience, I believe that is underestimating what the true cost of influenza within the production system, set of farms or flow because what you are not considering all the time and energy that goes into controlling the disease.”

For Pittman, influenza is more frustrating than PRRS. Comparing the diseases, the information and research on influenza have only been available within 10 years. Also, it’s constantly changing nature similar to PRRS but more complex. “It is a complex disease, and we work in complex systems. When you put those two things together, it is very difficult to deal with on a day-to-day basis,” he notes.

Diverging opinions from producers to veterinarians on influenza exist. He says, “There is a general misunderstanding of influenza and unfortunately oversimplification of flu as it exists today in swine production. That is at the producers, management and veterinarian level.”

It is a complex disease. New information on the disease and epidemiology is being learned every day. “One revolution that I had a couple of years ago is Influenza is a pig flow problem as it is a lateral and horizontal introduction into a growing pig population,” Pittman says.

From sow down
The sow herd is an essential component to controlling the disease. Pittman says we need to look at influenza the same way that we look at PPRS and that starts with the sow.  

Historically, influenza was a seasonal nuisance. H1N1 hit a herd in the winter. The pigs got sick for a couple of days. It was high morbidity, but low mortality. It lasted about five to seven days, and pig farmers did not have to worry about it again until the next winter.

However, in 1998 with the emergence of H3N2 the whole story changes. “It is where we are today. We have multiple isolates circulating in the field. It is year round with seasonal influence,” explains Pittman.

Influenza builds gradually in the barn with a slow spread from pig to pig. It can be almost under the radar in many pig flows if pig caretakers are not looking for it. Pittman says, today you can have influenza in barns up to 60 days.

“Morbidity can be variable to low in these cases where you may not see influenza clinically significantly, but the resulting component of that is you get variable to high mortality usually not as a single entity,” he states.  “We have to give credit to PRRS and other bacteria pneumonia because we do not live in a single disease world.”

Influenza is an RNA disease and can mutate. Different strains, isolates and pathogens coupled with the human seasonal N3s that come in and out of populations along with avian population in dense swine areas make it a challenging disease for pig farmers.

Previously, tissue testing sick pig leads to the discovery of influenza on the farm. “The problem with that is you only know you have a problem when you have a problem,” notes Pittman.

Hog farmers need an active routine monitoring system to understand what’s there and where it is. It can start with the gilt pool or the wean pigs leaving the sow farm. It also must be done in growing pigs.

Farms need to decide what is out there on all levels.

• Farm level or pig flow level to understand the transmission of flow with wean pigs coming off the sow farms and moved to grow-finishing units
• System levels with multiple systems layered on top of each other
• Regional level
• National level

Monitoring for influenza starts with admitting you have a flu problem. Monitoring does cost, so you can quantify that the problem is big enough to justify the cost of monitoring.

Once a farm decides to monitor, it needs to answer the following questions before beginning the process.

• What methodology?
• What are the questions you are asking for a system?
• Are you going to monitor sow farms? Gilts? Grow-finishing sites?
• What are you going to do with that data?

At Smithfield, the sows are monitored once a month for influenza and PRRS. It is reported to the team. The veterinarian service team uses the data to isolate influenza to get it under control.

“The reason we do surveillance to understand what is out there, how is it changing and how it relates to our current vaccine,” explains Pittman. “The cost of surveillance that we put forward is helping us drive decisions off that information. Hopefully, it is making an economic impact on our business by helping us predict new isolates, understand the prevalence of isolates across the systems and number of piglets it effects.”

Routine monitoring shows the sow farm is a reservoir for influenza and disseminators of the isolate downstream for farms across the United States. Pittman says, “it is important to understand the sow herd is a reservoir and the weaned pig is a vector for disease.”

Also, the surveillance program reveals the types of influenza present on farms, and it helps the communication process between veterinarians and farms. Tests reveal flu is not a single entity but four different types of influenzas. “So, we need to speak about them independently like they’re four different diseases when we try to manage them,” Pittman notes.

Any business must control inputs to control output. So, it is no surprise the vital role the gilt plays in controlling influenza. Pittman says every farm needs to know the flu status of gilts coming into the farm.

Do you know the gilts’ flu status?

• What is her history?
• Has she been exposed to influenza already?
• What strains of influenza has she been exposed to?
• What is your immune system walking into a door?

Most gilts are orally sampled for PRRS already. He advises checking the box for influenza. For protection, a farm must decide when to vaccinate that gilt and with what vaccination. Ideally, the gilt is vaccinated with the current isolates already present on the farm she is entering.

Building immunity
For farms wanting to focus on sow farm immunity, it is necessary to define the goal and decide who the farm is protecting — breeding population, sows, suckling piglets in the farrowing unit, weaning pigs leaving the sow farm or a combination.

Each farm needs to decide their individual influenza vaccination strategy: 1) do nothing 2) mass vaccination 3) batch vaccination — pre-farrowing or post-farrowing or 4) Combination of mass and batch vaccination.

“We know vaccination of pigs can affect the transmission of influenza among the population. Also, we know the vaccination of dams can affect the transmission and protect those animals. However, it needs to be homologous or cross-protection,” explains Pittman. “We know vaccination is beneficial. They are not always married in such that you can effectively change the transmission dynamics of the weaned pig in the farrowing house or post-weaning.”

Research has shown if there are no maternal antibodies present at the time of weaning then the epidemic is rather short and very quick. If you provide them with different levels of protection, then the epidemic stays longer, and there is more variation in that batch of pigs.

Protecting growing pigs can also be challenging. For growing pig strategy, it is essential to know the viral status of the weaning pig population. Weaning pigs can carry influenza from the sow farm but also be exposed in the grow-finish unit if flu is circulating as the pigs enter the barn. Knowing the viral status of the weaned pig population helps identify options for protecting the growing pigs.

Pittman says you need to ask the following questions when formulating a vaccination strategy for growing pigs.

• Can I even get in front of the circulation to vaccinate those pigs effectively?
• What is the maternal antibody status of the pigs? If maternal antibodies are present in the pigs then killed vaccines will not be effective.
• What is a source of the pigs? Do the pigs come from a single source or co-mingled from multiple sow sources. Co-mingling can only compound the problem.
• What is your flow — all-in/all-out or continuous? Continuous flow creates a disease control mess that will make it impossible to stay in front of influenza.
• Is the pig moving locally or across state lines?
• When will you give the vaccination? Some farms wait until 10 weeks of age. Most pigs will have influenza if you wait until 10 weeks of age.

Vaccines are not cheap. Careful planning and considering all the options can assist the farm to determine the right vaccine and the right procedure to ensure a return on investment. Furthermore, when implementing a program, especially in growing pigs, make sure the pig caretakers understand the why behind the vaccination strategy to guarantee compliance. 

Influenza stability
Like PRRS, a standard definition for influenza stability or classification for sow farms needs to be developed, states Pittman. It starts with a negative replacement breeding stock, or you should understand at a minimum the influenza status of the replacement breeding stock. 

Strategies have been presented on eliminating influenza in the sow herd. Again, a standard protocol needs to be established. If that protocol involves a certain vaccine then there needs to be an understanding what the characteristics need to be for those farms that want to eliminate or stabilize the herd for influenza.

More information and research need to be completed on biosecurity. “We do not understand the biosecurity of influenza. The challenge of influenza is the human component,” states Pittman.  

When it comes to influenza, diversity is the challenge and change is the only constant. It can be difficult to stay ahead of the disease. Vaccinations can be effective but also elusive. New platforms and technologies for vaccines are becoming available. The pork industry needs to keep supporting the research to understand the epidemiology, immunological influence of influenza and new technologies, he stresses.

Pig farmers along with their veterinarians need to access the information and design a vaccination program that best suits the hog operation and results in a smart economic decision for the farm. “I challenge everybody to challenge yourself on what you think you understand about influenza. And do not think about flu as a single entity anymore,” Pittman concludes.