Long before the Oct. 29 H5N1 avian influenza detection in pigs in Oregon, researchers across the U.S. swine industry have been working to prevent and prepare for cases happening in commercial swine operations. However, as Montse Torremorell, department chair and professor, University of Minnesota, noted during a recent Swine Health Information Center/American Association of Swine Veterinarians webinar, knowledge gaps surrounding this influenza strain still exist.

“We know the traditional swine influenza spreads very well through the air. So, would this happen the same way with some of these new H5N1 genotypes? We do need to have that answer,” Torremorell says. “When we think in terms of commercial pigs, things change when you have so many pigs in an enclosed population. The role of aerosol transmission, or even just transmission via fomites, might play or take a different dimension, so it's very important to understand that.”

The experimental infections that have been conducted so far have happened in healthy pigs. Torremorell notes it would be a much different scenario if this virus appeared under field conditions where infections with other pathogens are common.

“The question is whether we would be able to recognize the disease or would it be actually present in a different way? That's something that we have to pay attention to as well, and we will have to rely on testing to be able to address that question,” she says.

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It’s important to first understand the source of the virus, as each introduction could have a different epidemiological outcome. Then it comes down to knowing the risk the virus could have on different pig populations, such as feral pigs versus, outdoor pigs vs. commercial swine operations, Torremorell says.

The other area the swine industry needs to be very conscious of is the fact that influenza viruses like to reassort in pigs.

“If we have some of these H5N1 viruses introduced into pigs, it is very likely that  they would reassort with endemic swine influenza viruses, resulting in new viruses ,” Torremorell says. “Would those new reassorted viruses have increased virulence, increased transmissibility among pigs, across other species, or represent a higher risk to the people? That’s really something that we will have to keep an eye on.”

Another knowledge gap is targeted surveillance. Early identification is key to preventing transmission of viruses across the industry, however there are interfaces, whether that be feral swine and backyard pigs or birds and other species, that need to be considered as well.

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“I think we have to have a good understanding of what's the risk in those populations including peri-domestic species such as mice, and them transmitting the virus, bringing it, in this case inside the farm. There will be changes as well in migration patterns, seasonal patterns, winter is coming up. Many of these species will look for shelter inside swine facilities,” Torremorell says. “If they are located in an area where there are outbreaks in poultry or in dairy, would that be another risk for swine that we have to keep in mind? When it comes down to agricultural seasons, is there a risk of getting the virus into exhibition swine, agricultural fairs? All those are areas in which we should be thinking in terms of establishing surveillance programs.”

Field investigation follow-ups also need to occur, to understand how the virus is transmitted within the herd and the role of asymptomatic pigs.

“We see that all the time with influenza infections. Silent infections are very common, and it's also how we spread common endemic influenza. So, would it be the same here?” Torremorell questions.

Under field conditions, it’s also important to understand the duration of the infection at the population level. The duration can be different in small versus large populations, and even though at the individual animal level it might be limited, animals can get reinfected resulting in prolonged infections at the population level.

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Another knowledge gap is the epidemiological links. For example, is there shared labor that are taking care of pigs in the morning and working at a dairy in the afternoon?

What role immunity plays is another unanswered question thus far. Vaccination against H5N1 in pigs would also need to be robust to limit viral mammal adaptations and mutations.   

As for prevention through biosecurity, the question surrounding H5N1 is whether most of the standard biosecurity practices would work against this virus. Torremorell says the answer is most likely, yes, but there needs to be some validation

“In particular, when you think access to water, that could be water treatments or recirculating water in those systems, and in particular if the water comes from surface water that could be exposed to fecal material from avian species … there are areas on the biosecurity side that I think would be important to do some additional research to make sure that we keep this virus out, or at least would make us feel more comfortable with the biosecurity measures that we do have are also effective against this virus,” she says.

For traditional or endemic swine influenzas, aerosol transmission is a concern. Torremorell says it’s important to understand what role that plays when H5N1 happens within the farm, and between farms as well. Knowing the viral load in aerosols, the particle size distribution and whether those viruses are viable when they are in the air is essential. Also, when these particles land on surfaces, what’s the risk of contamination from fomites and surfaces?

“We've learned the last few years, when we think about controlling endemic influenza, the need to work at both ends, the immunity side of things, but then also management practices. If we had an incurrence of H5N1 in commercial farms, could we apply some of the same principles of how we manage the immunity and how we decrease the risk of exposure that then would also be effective to control and eliminate H5N1 from swine farms,” Torremorell says. “I think it would be very good to make sure that those same practices that we use for endemic influenza would also work for H5N1.”