MAKE Podcast
MAKE Podcast
A discussion on airborne diseases in the swine industry
In Manitoba, the pig industry makes a significant contribution to the local economy and the Province’s GDP. A threat to the pig industry is disease outbreaks, which can be economically and emotionally devastating. In this podcast, we talk about important pig diseases in Manitoba and their routes of transmission, with a focus on airborne transmission. The processes of airborne transmission, various factors affecting transmission possibility and distance, and strategies to protect against airborne transmission are discussed. Hosted by Van Doan of Manitoba Agriculture and Resource Development, with guest speakers Dr. Qiang Zhang and PhD student Amy La, from the Department of Biosystems Engineering at the University of Manitoba.
The way we grow and produce food is ever-changing, shaped by consumers and the climate in which we live and farm, research at all points of our food system is essential for continuously improving food's journey from farm to table. The Manitoba Agriculture and Food Knowledge Exchange explores timely research innovations and applications that make our food system better than ever- join us for today's podcast.
Van Doan:Over half million pigs culled this winter due to deadly disease, highly contagious virus popping up and show pigs, the deadly pig virus that's proving difficult to beat. These are just some of the headlines we are seeing around the world with pig production alone worth approximately 1 billion to Manitoba. The potential of disease outbreaks in the swine industry is a big concern. This got me thinking, what do we really know about disease transmission in pigs, anyways? My name is Van Doan and I'll be your host for today's podcast. I'm an agro-resource engineer with Manitoba Agriculture and Resource Development. And today I have a couple of people who will shed some light on the transmission of disease in the swine industry, specifically airborne diseases. I have with me, Dr. Zhang, who is a professor in the department of Biosystems Engineering. He focuses on animal environments. Hi, Dr. Zhang.
Dr. Qiang Zhang:Hi Van. Nice talking to you.
Van Doan:It's nice to see you, Dr. Zang for those listeners out there. Dr. Zhang was actually one of my profs when I did my engineering degree- way back when. I also have with me Amy La, she is a PhD candidate doing her research on airborne transmission of animal diseases. Hi, Amy. Welcome to the show.
Amy La:Hi, Van. Nice to see you today.
Van Doan:It's good to have you both here. So why don't we just dive into it? There appears to be a plethora of diseases in the swine industry, which types of diseases are we most concerned with in Manitoba?
Amy La:So there were a few pig diseases that we are concerned about, here in Manitoba. One of them is Porcine Reproductive and Respiratory Syndrome Virus, or PRRS. Which has been around since the early 90s. It is associated with both reproductive failure and respiratory disease with more severe disease occurring in younger pigs. Because of this, it causes annual profit losses due to reduced performance of herds. Another important disease is Porcine Epidemic Diarrhea Virus or PED, which arrived in Canada around 2015. So this disease causes vomiting, watery, diarrhea, dehydration, and reduce growth. It is also more severe in nursing pigs and less so in grower finisher, pigs. Lastly, there's another important disease that's been spreading across Europe and Asia. It is called African Swine Fever virus or ASF, and it has not yet entered North America, but we are definitely on the watch for it. So what it does is it causes fever, internal bleeding, and can lead to very high death rates. Dr. Zhang, do you have anything to add?
Dr. Qiang Zhang:I like to add 1 more disease to your list that is the Foot and Mouth Disease or MFD. Although Canada has been MFD free since the last outbreak in 1952, MFD is still considered one of the most important animal diseases globally. They MFD virus could spread as far as 250 kilometers by winds under certain weather conditions. I guess we never know when it's going to knock on our door again.
Van Doan:Thanks for clarifying the- what, the types of diseases. Let's move on to the how, how can these diseases be transmitted?
Dr. Qiang Zhang:There are 3 routes of animal disease transmission that is- direct contact, indirect contact and airborne. Direct contact is the most possible route of transmission within the herd, when pigs are in direct contact with each other.
Van Doan:Okay. So let's pretend I'm a pig and you're a pig and we're both in a pen together and we rubbed shoulders. Would that be considered direct contact?
Dr. Qiang Zhang:Absolutely right. Uh, pigs do rub shoulders, literally with each other in a pen when indirect contact viruses can be transmitted through, uh, excretions and the secretions such as saliva, urine, blood and milk. Indirect contact transmission occurs when healthy animals touch contaminated surfaces or objects such as a feeder, your clothes or transport trucks, or through vectors such as flies.
Van Doan:Pretending I'm still a pig here. If I'm a healthy pig and a worker comes into my pen with contaminated boots and I end up touching their boot, can I potentially become infected?
Dr. Qiang Zhang:Yes, absolutely. This is often called fomite transmission.
Van Doan:I've never heard of fomite transmission. So in this case, the boot would be considered the fomite because it's the object that could be contaminated with the infectious agents and serve in their transmission.
Dr. Qiang Zhang:That's right.
Van Doan:Okay. So now we know direct, we know indirect, let's move on to the third route of transmission mentioned- what is airborne transmission?
Dr. Qiang Zhang:Airborne transmission is the situation where the disease pathogens become airborne and move with air currents and inhaled by healthy animals. Disease pathogens rarely float in air by themselves, they attach themselves to aerosols, which are tiny solid and liquid particles suspended in the air typically, with a size smaller than 5 micrometres.
Van Doan:5 micrometres. Hmm. Uh, can you describe to our listeners what that even looks like?
Dr. Qiang Zhang:Uh, it's about 1/10th of the diameter of a human hair. Uh, not visible to the naked eye.
Van Doan:Looking at my hair right now, and that's pretty tiny.
Dr. Qiang Zhang:Yes. Very tiny. You can see you hair with your eyes, but not the small aerosols attached to your hair. The simplest examples of aerosols are fine dust particles and very small water particles from a sneeze.
Van Doan:We're talking about water particles. Does that include water droplets? Is there a difference?
Dr. Qiang Zhang:Uh, yes and no, both droplets and aerosols are particles. Droplets are large in size and do not stay in the air for a long time. While aerosols are smaller and can be suspended in air for long time. Aerosols in pig barns are typically from a wasted feed, shedding of the dead skin cells, dry feces and animals sneeze and coughs.
Van Doan:Thanks for that. I do have an understanding of the aerosols now, but I'm still a little fuzzy on how exactly airborne transmission occurs.
Dr. Qiang Zhang:Airborne transmission involves 3 steps. Step 1, aerosols carry disease pathogens are directly expelled from the respiratory systems of animals or from dried fecal materials or from accumulated dust on various surfaces. Step 2, aerosolized pathogens move with air currents and Step 3, aerosolized pathogens may be inhaled by healthy animals to cause infection or settle on surfaces objects, which may be touched or licked by healthy animals to cause infection.
Van Doan:Okay. Last scenario here with me being a pig, I'm a pig I'm still in my pen here. If a feed truck drives into the yard and has some contaminated dust on it, and the wind blows this dust from the truck into the barn, and I breathe in this dusty air, I could possibly get infected by an aerosol transmission?
Amy La:That's correct.
Van Doan:What if this contaminated dust that was carried into the barn landed on my waterer and I licked it. Would this also be transmission by aerosol?
Amy La:Yeah. So since it is difficult to differentiate between infection caused by direct inhalation of aerosols or from infection caused by contacting objects that were contaminated with settled aerosols, we will refer to both causes of infection as airborne transmission in this podcast.
Van Doan:Thinking about where we are today COVID is a disease that most of us know something about just to put things into context. Can you explain to us if COVID is transmitted directly, indirectly or airborne?
Amy La:So COVID, it is caused by the SARS COV 2 virus or the SARS Corona 2 virus. And it can be transmitted by all 3 routes. So at the beginning of the pandemic, most people thought that COVID was transmitted only by direct or indirect contact.
Van Doan:Uh. Okay. So that's why there is so much focus on washing your hands.
Amy La:Yeah, so in the beginning, we were very focused on washing our hands using hand sanitizers and using cleaners, but new evidence has shown that the virus is also airborne transmissible. So while washing our hands reduces a chance of indirect transmission through contaminated objects, wearing masks protects us from inhaling aerosolized viruses and from airborne transmission or COVID.
Dr. Qiang Zhang:I also would like to add off the 3 routes of disease transmission, airborne transmission is mostly under appreciated. Largely because we do not fully understand the airborne transmission processes. Even for many human diseases that has been studied extensively, airborne transmission is still elusive, in the context of a pig operations. Few current biosecurity measures are specific for preventing airborne transmission, as solutions are generally expensive.
Van Doan:Which diseases in the swine industry are considered transmissible by aerosol, then.
Amy La:That's a really great question. So there's a lot of scientific evidence showing that Foot and Mouth Disease virus and Porcine Reproductive and Respiratory Syndrome virus can transmit by aerosol or by aerosol transmission over long distances from building to building or from herd to herd. There is some scientific evidence showing that PED or Porcine Epidemic Diarrhea, virus and African Swine Fever virus can be transmitted by aerosol within a room, from infected pigs to uninfected pigs that were physically distanced from one another. But we are still in need of more research about whether or not PED and ASF can be transmitted over long distances from herd to herd or building to building.
Dr. Qiang Zhang:Yes, we still need to do more research to find out any other bacterial or virus pathogens can be transmitted by aerosol.
Van Doan:Amy, you mentioned transmission by aerosol over long distances. Can you clarify how far the pathogen can travel?
Amy La:That really depends. So one of the important factors that affects the distance that pathogens can travel is weather. And so this includes wind, temperature and humidity. So in terms of how far it can travel, it can also affect how concentrated it'll be after it travels. So for example, if it moves as a very concentrated plume or whether it spreads and scatters over a large area downwind.
Van Doan:How far exactly are we talking though? Is it a 100 meters? Is it a kilometer? Is it 50 kilometers?
Amy La:It also depends. So let me name some studies to kind of provide some context. So for example, Foot and Mouth Disease was introduced into a new region because it carried in the wind over a very long distance, but this is considered a very rare event. There was also another study in which air samples were collected downwind of an infected farm and PRR was found in these air samples up to 9 kilometers downwind of that farm. There was also another study in which air samples were collected in 4 different swine dense regions with 2,299 neighbouring farms within a 10 kilometer area. And the researchers were able to capture 8 to 14 different PRRS types per location. So it really depends on case by case and how far these viruses can travel in the wind.
Van Doan:So we talked about the wind factor, what about temperature? Does temperature affect aerosol transmission?
Amy La:That's a really great question. So temperature is very important and generally viruses tend to survive for shorter periods of time the warmer it is. For example, a virus is more likely to survive at 0 degrees Celsius than at room temperature.
Van Doan:How high does of a temperature can viruses survive in?
Amy La:Generally viruses survive for less time as the temperature gets warmer, but I'll give a specific example. So in one study, PRRS aerosols were sampled in the air and it showed that at 41 degrees Celsius, it had a half-life of 5 minutes. And by half-life, I mean the amount of time that it took for half of that virus to die. So 5 minutes, isn't very long at 41 degrees Celsius.
Van Doan:No, it isn't very long. You did mention warm temperatures. What about cold temperatures? We know Manitoba, it gets quite frigid. Are viruses able to survive extreme cold?
Amy La:There hasn't been much research on the survival of animal viruses in cold air, in aerosols, but I would imagine that they would stay alive for longer periods of time than they would in the summer. Another thing is that winter air tends to be very dry as well. And survival of viruses is also linked to the humidity of air. For example, PRRS virus, PED and ASF are all known as Envelope Viruses and generally Envelope Viruses survive better in low humidity conditions. Another example is Foot and Mouth Disease virus, it is a Non-envelope Virus and generally Non-envelope Viruses survive better in higher humidity conditions.
Van Doan:Thanks, Amy. I feel I have a general understanding of disease transmission in the swine industry. Are there any practical methods or biosecurity measures that could be used to decrease airborne transmission? For example, humans with the COVID, right? We can wear a mask, but I think it would pretty hard to get pigs to wear a mask.
Dr. Qiang Zhang:I totally agree. Pigs are not small enough to wear masks or we can spend a lot of time to train them to wear masks. They probably would enjoy chewing masks instead of wearing them. However, we can actually put a big mask on a facility, which is called a filter. Many studies have shown that installing air filtration system can reduce the risk of new introduction of diseases. When you use air filters, keep in mind the filter efficiency is critical. Similar to choosing a face mask for COVID 19. You can use an N95 mask, which has a 95% efficiency for 0.3 micron particles. Or you can actually put the bandana over your nose, which is going to give you probably up to 50% of efficiency. So the filter efficiency is important, but it's also changes or decreases with the smaller particles. Filters used in animal facilities typically have, uh, efficiency between 75% and 95% for particles in a range of, uh, 0.3 to 1 micro-metres. If high efficiency are required, HEPA photos can be used, which can remove 99.97% particles as small as 0.03 micro-metres. It should also be noted. Generally speaking, the higher, the filtration efficiency, the more powerful fans are needed to put air through the filter.
Van Doan:Right? So when we're talking about HEPA filters, HEPA stands for...
Dr. Qiang Zhang:High Efficiency Particulate Air filter, it is defined by the US Department of Energy.
Van Doan:Right. And then since aerosols carrying disease pathogens are within this range, we are actually able to filter them out and thus prevent transmission.
Dr. Qiang Zhang:Yes, you are right.
Amy La:I'd also like to add, that filtration using HEPA filters can be expensive to implement. So it is more worth it in a region that is very populated with pig barns. As these barns are more at risk of airborne transmission.
Van Doan:Amy, is it the cost of the filter that is expensive? Or is it the need to retrofit your existing ventilation?
Amy La:Both of them, the cost of HEPA filters is expensive and these filters need to be replaced from time to time.
Dr. Qiang Zhang:And also I want to add, you know, filtration system can affect your ventilation system.
Van Doan:In which way does it affect your ventilation system in a good way or a bad way?
Dr. Qiang Zhang:Uh, in a bad way. In particular, if you use the existing ventilation fans, adding filters could actually reduce your airflow rate, which is not a good thing. So you will make sure your ventilation fans are capable of overcoming the pressure drops through the filters. If not adding booster fans is option.
Van Doan:What about dust control measures? Are there any out there that would be helpful?
Dr. Qiang Zhang:Uh, yes, to some extent, because dust is a carrier of pathogens. When moving dust inside the barn, it can reduce the release of pathogens from infected facility, thus reducing the spread of the disease to the neighboring facilities in the area. Whatever the strategy or technology is used for dust control, removing small particle like less than 10 micro-metres is very critical. And it's also very expensive and challenging. So many strategies and technologies have been used in research for dust control in swine facilities. Such as good housekeeping to keep the barn clean, select the right feed, oil spray air ionization and filtration.
Van Doan:What if the premise was already affected, or if there was an outbreak? What measures should or could you take to prevent aerosol transmission?
Amy La:In this case outdoor dust control may help reduce the chance of airborne transmission of animal diseases. For example, animal and feed transport trucks can be sources of airborne pathogens. So during disease outbreaks, these trucks should plan their driving routes carefully to stay away from other animal facilities and not drive through areas with a high density of animal facilities. Also shelter belts, such as installation of trees around farms can help reduce dust spread.
Dr. Qiang Zhang:Also, this fundamental principle here is, once there's an outbreak, you have to follow the biosecurity or the emergency response protocol. But 1 proactive measure could be used is to filter or clean the exhaust air from an infected facility to actually protect the neighbouring facilities. Conceptually, this could be achieved by using a mobile bio-containment system.
Van Doan:What exactly is a bio-containment system? What does it look like?
Dr. Qiang Zhang:Uh, a conceptual picture. My mind, it's a, it's a modular filtration systems sitting in a truck, something similar to your home duct cleaning truck. So once you move the mobile unit to the site, you can use the ducts to connect to the ventilation system to the filtration system. And then you clean up all the aerosols before you discharge the ventilation air to the environment.
Van Doan:Oh, thanks for the picture Dr. Zhang, it helps us get a glimpse of your vision. With that, I think that's all the questions I have for today. I did learn a lot from the both of you. I learned about direct transmission, indirect transmission, airborne transmission, as well as, that weather plays a really big part in transmitting these diseases. Is there any last words or anything you want our listeners to know before we end the show?
Amy La:Oh yes. I would like to tell the listeners that there are many animal diseases that can be transmitted by aerosols or by airborne transmission, both in short and long distances. However, our understanding of aerosol and airborne transmission is still limited. We still need to do much more research in the area. However, the transmission distance and possibility of transmission is affected by many factors, such as the type of pathogens and also the environmental conditions such as wind temperature and humidity.
Dr. Qiang Zhang:I would like to add, although airborne transmission is not the main route of transmission of most animal diseases, it is a critical piece in managing disease spread. Airborne disease transmissions are difficult to manage and the very few current biosecurity measures for swine operation are specific for preventing airborne transmission.
Van Doan:Thank you for sharing with us, your wisdom on airborne transmission of diseases in the swine industry.
Dr. Qiang Zhang:Thank you Van for hosting the podcast.
Amy La:Thank you Van for having us. It was a great time.
Van Doan:Yeah, it was a great time. This is Dr. Zhang and Amy La from the department of Biosystems Engineering and myself Van Doan from Manitoba Agriculture and Resource Development. We want to thank you for joining us on this make podcast, for more information on this podcast or any other Manitoba Agriculture and Food Knowledge Exchange podcast, go to www.makemanitoba.ca.