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New forms of swine influenza pose tough but manageable challenges

29 January 2018

Poultry Health Today

New strains of the swine influenza virus continue to emerge, making it difficult for pork producers to manage, two experts who specialize in the disease of food animals said at a recent webinar organized by Farm Journal’s Pork.

The webinar, “Swine Influenza and what it means to you,” featured two panelists: Marie Culhane, DVM, an associate professor in the Department of Population Veterinary Medicine, University of Minnesota, and Micah Jansen, DVM, a swine technical services veterinarian for Zoetis who has worked extensively with the disease in the field.

In the hour-long session, the two experts said that despite the changing nature of this deadly virus, producers can work with veterinarians to prevent or manage outbreaks by monitoring influenza-surveillance data, vaccinating pigs, and stepping up and enforcing biosecurity protocols.

Looking back

Like many diseases, influenza has been around for centuries. However, it didn’t attract much global attention until the 1918 flu epidemic, which is estimated to have infected more than 500 million people, or one-third of the earth’s population at the time, and killed between 20 million and 50 million, according to the National Institutes of Health.

Using advanced techniques, Culhane said scientists have determined that the 1918 virus was of the H1N1 variety that got into humans and swine at the same time. That H1N1 virus evolved in swine and was stable for 70 years.

But over time, a strain of the influenza virus, known as the H3N2, was transmitted from humans to swine.

“What happened around 1997 was that H3N2 got into swine. What emerged was this triple re-assortment,” Culhane said, referring to the mixing of genetic material of one influenza genotype into new and distinct combinations. “Since then, the world of this virus has been interesting for swine.”

She added that another big outbreak occurred in 2003, but this transmission was from swine to swine.

Evolving virus

The experts say that this continuous emergence of new viruses is one of the biggest threats to pig farmers.

“It’s difficult for producers and even veterinarians to keep up with all the changes,” Jansen said. “So, I think the key thing for producers is to work continuously with their veterinarian to help them understand what is circulating within their herd, and figure out what’s best for their situation.”

Culhane added that there are no new vaccination tools to combat some of these emerging viruses in a timely manner. Furthermore, it can take 9 months or more for animal-health companies to add or substitute a strain without conducting full-scale efficacy and safety studies under USDA’s Expedited Strain Change guidelines.

The two offered a variety of suggestions for staying ahead of and containing the influenza virus in swine. Among them:

1) Make sure workers and others who come in contact with the animals understand the importance of following biosecurity measures.

“One of the factors that drives influenza change is continuous introduction of virus from humans into pigs and how that changes influenza viruses in pigs,” Culhane said. “We want to not just vaccinate pigs but have good biosecurity protocols, such as wearing gloves when working with pigs and wearing masks when working with pigs.”
Jansen said the key to getting caregivers to buy into these protocols fastidiously is getting them to understand why.

“There’s a good reason for what we ask them to do, but sometimes caregivers may not get the back story,” she said, referring to both the economic and pathogenic ramifications of lax biosecurity. “When you help them understand the why, they are more passionate about it and care more.”

2) Study the data on swine influenza scrupulously.

Although influenza poses a year-round threat to swine herds, peak season is in the winter, particularly in the months of January, February and March.
“It is important to look at multiple streams of surveillance data,” Culhane said. “You could have any one of these viruses at anytime in the US.”

The USDA maintains a National Swine Influenza Surveillance Program. The program compiles results quarterly. The influenza data is broken down by geographic regions. There are five regions in all and the data vary by region.

“The most common virus in 2017 was the human-like, seasonal H3 that is passed from pig to pig,” Culhane reported. “The next most common were 4a and 4b.”

3) Adopt smart vaccination strategies.

Vaccine use is still advantageous for sow farms. As of last October, there were only two fully licensed, commercial vaccines for swine influenza available to US pork producers. However, there are five companies that produce autogenous vaccines and three more that are looking to produce them.
Studies show that sow vaccination and the gilts’ influenza status at entry often determined the likelihood of influenza at weaning.

Vaccinating a sow stimulates maternal-derived antibodies, or MDAs, which help protect piglets.

Another strategy is to vaccinate growing pigs. MDAs wane by 4 weeks, Culhane said. Studies show that sow vaccination decreases the likelihood of influenza in piglets at weaning.

“Vaccinated sow farms are less likely to have influenza A-positive piglets at weaning,” Jansen said. “Influenza is unpredictable, so you need a vaccine that will give broad coverage.”

 



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