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Food Animal Matters – October CVJ 2023

September 27, 2023

Food Animal Matters

What is it like when the diagnosis of a disease means that you are no
longer in control of your farm?
Robert Tremblay

Introduction
Several diseases of terrestrial and aquatic animals are classified as “reportable” in Canada (1,2). Many of these reportable diseases are exotic and have never been reported in Canada; others were once present but have been controlled or eradicated. In this column, Brad Osadczuk and Dr. Blake Balog share their experiences during and after an outbreak of bovine tuberculosis (bTB) that started in 2016. Also, Dr. Teryn Girard shares her and her clients’ experiences in dealing with highly pathogenic avian influenza (HPAI) in 2022.

And then there were none…
Bovine tuberculosis (bTB) is a reportable and potentially zoonotic disease. After decades of work, Canada was declared free from bTB in cattle, but there are still sporadic, isolated occurrences. Since 2012, there have been 3 outbreaks, all in beef herds: 1 each in Alberta (2016), British Columbia (2018), and Saskatchewan (2023). The investigations of the first 2 have been completed and summarized by the Canadian Food Inspection Agency (CFIA) (3). The investigation into the most recent outbreak is ongoing. The official reports contain summaries of the investigations and give an idea of the effort required to complete even one of these investigations. For example, the outbreak in 2016 involved tracing and testing approximately 34 000 animals on 145 farms (4). As part of the investigation, almost 12 000 cattle were destroyed. Those numbers alone do not describe the impact of the outbreak on the cattle producers involved. During an outbreak of a reportable disease, most conditions imposed on affected farms are mandatory. The conditions usually include halting animal movement from premises that are suspected to be part of the outbreak. In the 2016 outbreak, quarantines were imposed on beef farms starting in September — the time when most ranchers would be weaning and selling that year’s calf crop. Those calf sales could not happen; ranchers had to find some way to keep those calves on the home ranches instead.

When the CFIA investigates an outbreak of bTB, at least 4 different types of farms or ranches will be involved in addition to the farm where the first, or “index,” case is identified. In 2016, the index case was a mature cow from a ranch in southern Alberta that was discovered to be infected at a slaughter plant in the United States. The first type of herds to be investigated were those whose cattle had had contact with cattle from the index herd. There were 2 subgroups of these herds. The first subgroup included herds where cattle had close, direct contact with cattle from the index farm. There were 15 farms that fell into this category. Those farms were also quarantined and not allowed to remove cattle from their properties. All the cattle on those properties (just like all the cattle on the index farm) were destroyed and examined postmortem for evidence of infection with bTB. Any areas on those premises that might have been contaminated by cattle were then ordered to be cleaned and disinfected before restocking could occur (5). After restocking, all the restocked cattle were monitored for evidence of bTB using follow-up testing.

There was another subgroup of 13 herds that also had contact with the index herd, but where contact was less direct. Cattle movements from those herds were also restricted. All the cattle on those herds had to be tested — a procedure that requires all cattle to be handled twice within 72 h. Any cattle that did not test negative were slaughtered and examined postmortem. After it was determined that none of the cattle from those 13 herds showed evidence of bTB at postmortem, the herds were released from quarantine without the need for cleaning and disinfection.

There were 68 herds in the second group of herds that required investigation. Those herds had supplied cattle to the index herd in the 5 y before the diagnosis of the index cow. These are termed “trace-in herds.” In those herds, any cattle older than 12 mo were tested for bTB. Any cattle that were non-negative on that test were subject to additional tests. If they were also non-negative on the second test, then they were ordered destroyed and examined postmortem. Herds with no evidence of bTB after testing and postmortem examination were also released from quarantine without further actions.

In addition, there were about 2700 cattle that had been removed from the index herd to other herds in the 5 y before the index case was identified. All those cattle had to be followed to the herds where they went. Herds of this third type are called “trace-out herds.” Many of these individuals were calves that had already been slaughtered. Calves that were still in feedlots were ordered slaughtered and examined postmortem. Any herds that had received breeding animals from the index herd were handled in the same manner as the trace-in herds: movement restrictions and testing, with slaughter and postmortem examination of non-negative reactors followed by release from quarantine if there were no infected cattle.

The fourth group of herds included any herds within a 5-kilometer zone around the index farm that had not already been considered as contact herds. Those were called “buffer zone herds” and were subjected to the same procedures as the trace-in herds.

In addition to the investigation of the cattle herds by the CFIA, the province of Alberta maintains bTB monitoring in wildlife.

Any description of this investigation cannot possibly relate the impact of this outbreak and subsequent investigation on the farmers and farm families who owned those herds or on the people whose livelihoods depended on those farms (6–8). A unique feature of being swept up in an outbreak of a reportable disease is that there is an almost complete loss of control over your business operations and over much of your day-to-day life, because the procedures for dealing with reportable diseases do not leave much room for flexibility.

Equally frustrating is the fact that nobody really knows how long the disruption will last. So much depends on the results of the animal testing, which is the most basic element of the investigation. It just takes time and the efforts of many people to complete the testing, and then to remove, slaughter, and necropsy animals ordered destroyed. In this particular outbreak, an additional complication was that the cattle that needed to be tested were range cattle that were not accustomed to being handled very often.

This outbreak started just as farmers were expecting to receive income from calf sales — income that would not be coming quickly. Because of movement restrictions, farmers also needed to find space, feed, and facilities to manage calves and cows that were not allowed to move off the property.

The impact of being involved in this sort of outbreak is enduring. When restocking is finally permitted, there will remain the uncertainty associated with waiting for the results of ongoing monitoring of the restocked cattle. Provided that there is no evidence of bTB among the restocked cattle, a beef farm is still not likely to generate income through calf sales for quite some time, since cow-calf producers need to wait for calves to be born and then grow to weaning weight before they can be sold. That might take 1 y or more, depending on when restocking can occur. If producers restock with unbred heifers, they will need to wait an additional year before having a calf crop to sell.

Restocking sounds so simple, but it is itself complex. The cattle that were lost in the depopulation will have adapted to local management styles and local conditions — in this case, the ability to thrive on shortgrass prairie. It may not be so easy to find replacements that will thrive in those conditions. Even if they do, that will take time to determine. In addition, the loss of a herd that had been built up over years might leave one haunted by thoughts of “What if…” for years to come.

A recent study conducted on farms affected by bTB eradication in the United Kingdom clarified some of the economic impact of bTB control on farmers that extends beyond the purchase price of the replacement cattle (7). It is important to have these costs acknowledged and included in the calculation of compensation that affected farmers will receive.

Fortunately, in this case, only 5 additional cattle were determined to be infected with bTB. All of those were in the index herd. Genetic testing determined that the Mycobacterium bovis found in the infected cattle had been first identified in Mexico some years before the outbreak in Canada. There was no conclusion as to how the index herd had been exposed to bTB.

A poultry veterinarian’s perspective on a highly pathogenic avian influenza outbreak
Dr. Teryn Girard recounts the next story

In April 2022, I was at a poultry conference in Vancouver. I was just 3 yr into my career as a poultry veterinarian when highly pathogenic avian influenza (HPAI) suddenly became a looming threat. Although I knew it was spreading throughout North America, I had trouble envisioning myself reacting to cases in barns where I worked.

Unfortunately, while at the conference, I received a call from a broiler farmer back home in Alberta reporting high mortality in the barn. I hoped that the high mortality was due to something else; however, I knew the list of differential diagnoses had to include HPAI. Diagnostic swabs from some of the deceased birds were submitted for immediate testing. That evening, I reviewed the procedures for reporting and responding to the diagnosis of a federally reportable disease.

The next morning, the broiler farmer called again, reporting even higher mortality. Within 30 min, an HPAI “non-negative” diagnosis was presented to him. Fifteen minutes later, I received a phone call from a turkey grower whose farm was located further north from the first barn. It was a call I will never forget.

Me: “Hi Bob.” [name has been changed] … Silence.
Me: “Bob, are you there?” … Silence.
Me: “Bob?”
Bob: “You better get out here, something is really wrong with
the birds. I don’t know what I’ve done.”
Me: “What are you seeing?”
Bob: “They’re so sick. They are dying fast. I don’t know what
I’ve done wrong.”
Me: “Bob, there has been a diagnosis of avian influenza in the
province and I think that may be what we are dealing with. I’m
sending someone right now.”

Bob became emotional and exited the call quickly.

Still in Vancouver, I made the call to our clinic’s poultry team. They sprang into action collecting samples quicker than I could have asked. In the midst of catching a flight back to Alberta and prepping and organizing the clinic team, I received another phone call. It had been 14 min since I had gotten off the phone with Bob. This call was from an industry representative. “Hi Teryn. I think Sarah [name has been changed] has something really wrong at her barn. There are dead birds everywhere.” Again, our team assembled and got ready to sample another site for the presence of a disease I never thought I’d see in Alberta.

As my poultry clients waited for their HPAI results, they called me numerous times to discuss any other possible differential diagnoses. What else could they do while they waited? Would all their barns have to be depopulated? Were there any treatments we could get the birds while we waited? Could we get new feed or vitamins for the birds in case there had been some feeding errors? Would I be able to continue to support and advocate for them if it was HPAI and the CFIA took over their
cases? Looking back, we all knew this was the beginning of the provincial outbreak, but at the time we held onto hope that it wasn’t. The Chief Provincial Veterinarian of Alberta called to advise me that both Bob’s and Sarah’s birds were indeed positive for HPAI. The farmers sobbed as I gave them their results. I felt so incredibly sad for them.

As the spring of 2022 continued, there was an onslaught of cases as more farms throughout the province became positive for HPAI. During this time, Alberta had the highest number of cases and a cloud of quiet fear crept through the industry. My routine days of regular barn visits and postmortem submissions came to a halt. Some poultry farmers became reluctant to call me and our team. In turn, we became reluctant to visit anywhere for fear of spreading the virus. Although we began to find our rhythm and work through the cases with clear protocols, the emotional toll of HPAI cases never waned. There were still sleepless nights, new levels of frustration, and — often — many, many tears.

When I tell people that I am a poultry vet, I often catch the look of surprise. They ask what my job entails. I state that it’s population medicine with a specific focus on bird welfare. Being a population medicine vet means that we become part of the farmer’s “team.” Our team works towards optimal animal production. The roles of the veterinarian are to maintain a high level of animal welfare, prevent disease, treat disease, and optimize health in hopes of a consequential production improvement. However, the 2022 Alberta HPAI outbreak forced me to realize this career is so much more. My relationship with poultry farmers extends beyond what I offer as a veterinarian. I am the point of contact if production decreases and the farmer can’t figure out why. I am the first person a distraught farmer will call when she discovers a hidden camera, planted by animal rights activists, in her barn. I am also the first person called when a farmer suspects avian influenza. Through this relationship built on trust, I can easily become a confidant about the new grandbabies, the death of a family member, welcoming a new puppy, or sometimes more, if the emotional weight of avian influenza becomes too much…

It is clear to me that poultry farmers affected by the 2022 HPAI outbreak suffered immensely. Our veterinary team, the veterinary community, and the entirety of the poultry industry were also severely affected. However, what is less often discussed is the aftermath of HPAI. From my observations, farmers who experienced avian influenza directly appear to have experienced
something akin to post-traumatic stress disorder. For example, during any production cycle, there will be deaths of a small number of birds; but now, those losses bring back harsh reminders of HPAI.

I’ve also noted that poultry farmers on farms that remained HPAI-negative during the outbreak seemed to be affected, too. These farmers often found opening the barn door to be traumatic, as they were unsure if they were about to find sick or deceased birds inside the barn. The anxiety of previously routine tasks, coupled with reluctance to contact the veterinary team with concerns, often left them feeling anxious and isolated.

Tragic events affect individuals in different ways. During the HPAI outbreak, what I saw as a poultry veterinarian was a coming-together of those affected, to mourn, take action, care for their flocks, and help each other get through trauma. I have come to realize that poultry production is not for the faint of heart. The 2022 HPAI outbreak is a testament to the inner strength of farmers and farm families. I felt deeply saddened, and still do to this day, for the farmers both directly and indirectly affected by HPAI; but I am also proud to be part of a community that united to tackle this devastating experience as a team.

Conclusion
Both of these situations took substantial tolls on the farmers, veterinarians, and members of the animal health teams involved in the reportable disease outbreaks. It was likely equally stressful
for the regulatory personnel who had to complete the investigations (6). Even so, everyone agreed that it is critical to control diseases that are so important that they are classified as “reportable” either nationally or internationally.