Vaccines, biosecurity, management keys to keeping IBH in check
Inclusion body hepatitis (IBH) can be a challenging disease, as the clinical signs are non-specific and there is no direct treatment. Consequently, producers rely on interventions such as vaccinations, not just for IBH but also for other immunosuppressive diseases.
Specific to IBH, autogenous vaccines are the go-to option for most farms, but diligence is necessary to ensure the vaccine is prepared and administered correctly. It takes time to “get it all ramped up,” said Suzanne Dougherty, DVM, with Pilgrim’s. For more than 16 months, Pilgrim’s has used an autogenous vaccine in all of its complexes, starting with the most severely affected units.
“We combined [IBH] with our infectious bursal disease (IBD) and reovirus vaccine antigens so it took a little extra time just to get that coordinated,” she added. Pilgrim’s started by vaccinating birds at move-in; any that were already past the 12-week handling period were then vaccinated at 18 weeks.
Discussions about vaccination protocols and interventions were part of a roundtable organized by Zoetis — “IBH: Managing an emerging immunosuppressive disease of broilers” — involving poultry-company veterinarians and academicians.
Vaccine dosage and formulations
The vaccination approach at Wayne Farms is similar to Pilgrim’s, noted Joel Cline, DVM, for the company. Wayne Farms had used an autogenous reovirus vaccine since 2015, and in September 2020, initiated an autogenous IBH vaccine companywide. “We started in south Alabama where we were seeing an [IBH] issue. We put it in with our 12-week handling,” he said. Any birds past that point received the vaccine at 18 weeks.
Simmons Foods also includes IBH into its autogenous reovirus vaccine but administers it at 18 weeks, said Sara Throne, DVM, Simmons Foods.
Administering one dose is the most common practice, with two doses sometimes given to complexes with the most severe IBH.
“We can’t really tell if it [two doses] has helped or not,” Dougherty said. “One dose seemed to significantly reduce vertical shedding from the hens.”
For perspective, Guillermo Zavala, DVM, PhD, Avian Health International, cited a Georgia 2021 breeder-vaccination survey that showed 38% of companies vaccinated against fowl adenovirus (FAdV), which causes IBH, and the vast majority administered one dose.
Worldwide, producers generally follow a one-dose IBH vaccination protocol, he said. However, it does vary by geographic area, depending on the serotype. “For those areas affected by serotype 4, we might vaccinate with one dose and then add a second dose of the newer vaccines that would not include serotype 4 but only 8b, 9 or 11 as autogenous,” Zavala added.
Although there are some live-attenuated vaccines available, for example in Australia, “most of the world uses killed products,” he said.
The FAdV 8b serotype predominant is worldwide, so it makes up most of the autogenous vaccines. Both Dougherty and Throne have encountered bouts of serotype 11 and added it to their IBH vaccine until the serotype could no longer be isolated.
A lingering question is, with 8a and 8b being semi-related, how much cross-protection exists? The research is limited. “There was some work done years ago indicating cross-protection between the two,” said Holly Sellers, PhD, University of Georgia Poultry Diagnostics and Research Center, “but we have not looked at that any further.”
Pullet-vaccination programs, of course, need to protect against immunosuppressive diseases for both the pullet and the progeny. The roundtable panelists shared their vaccination priorities to equip the birds to fight off FAdV 8b challenges in the field.
“The essential one that we all think about is Marek’s disease,” Zavala said. “If Marek’s disease protection is deficient, that bird or flock is not going to be able to mount an immune response.”
IBD is another priority, Zavala said, adding, “it’s probably the most important component in the whole picture of IBH.”
Industry practice is to use an IBD recombinant vaccine and/or live-attenuated vaccines, with two or three doses given during rearing, followed by one or two doses of a killed vaccine.
“You want to make sure your killed vaccine represents the relevant viruses that circulate in the broiler,” Zavala said. “The better you prepare that pullet to transfer sufficient immunity to protect broilers during the first 2 to 3 weeks of age, the less susceptible broilers will be to IBH problems.”
The third vaccination to consider is chicken anemia virus (CAV). CAV is not commonly associated with IBH, Zavala noted. However, it does affect the bird systemically, reducing its ability to fight off bacterial and viral infections.
Equally important to ensuring the right combination of vaccines is the proper execution of those programs. Wayne Farms implemented a program to track IBD titers, worked with vaccination crews and conducted internal and external audits.
Broilers also receive IBD vaccinations as part of IBH-control programs, particularly in repeat farms or certain geographical areas. These are typically live-IBD vaccines given between 10 and 14 days, depending on the company’s program, in an effort to extend maternal-antibody protection. Recombinant vaccines have also been used in complexes struggling with IBH.
“It’s only in a handful of complexes where we’re still fighting IBH, mainly in small-bird complexes,” Dougherty said. “It does not completely eliminate IBH, but it reduces the incidence and the severity.”
Throne agreed that IBD vaccination is a beneficial option to offer broiler growers. “We didn’t have to save a lot of birds to be able to pay for that program,” she said. “We’re also trying things such as litter amendments and disinfection.”
House management, such as cleanout and disinfection, needs to be part of IBH-intervention protocols. Because IBH is a very hardy virus it is hard to eliminate once it’s on a farm, and downtime alone won’t eliminate the virus. “You’re going to need some type of disinfection, cleanout [and] litter treatment…to try to reduce the viral load in houses,” Dougherty added. “Even then, it takes several flocks to dilute that virus.”
Adding to the challenge is that on repeat farms, it’s not always the same broiler house that breaks with IBH. “Sometimes it jumps between houses,” Throne noted. “We utilize windrowing…poultry-litter treatments…different disinfection schemes and organic acids.
“I don’t think we’ve found a silver bullet,” she added. “We’re trying to see if there is a combination that is both cost-effective and that reduces disease incidence.”
The veterinarians acknowledged the challenges of securing litter supplies and the expense. But when it comes to litter management, “you’re not only managing it for this disease [IBH] but also for coccidiosis and everything else,” Throne added.
Cline noted that Wayne Farms strongly encouraged cleanout and disinfection for houses experiencing a second IBH break that wasn’t attributed to vertical transmission. “That’s been very helpful for us and tends to take care of the problem in that house,” he said.
The veterinarians reported limited experience with water acidification to address IBH. For Pilgrim’s, “It was hit or miss; sometimes it would help, sometimes it wouldn’t,” Dougherty said.
“I’m not sure that changing the pH to acidified — maybe from 8 or 7 to 7 or 6, for example — is really going to help,” Zavala said.
For hardy viruses like IBH, “you can apply some interventions to try to reduce the concentration of infectious agents, but it’s probably not enough when you’re dealing with dirt floors and used litter,” Zavala said.
Poultry Health Today editors have developed a booklet with highlights of the roundtable discussion. To download a free copy, click here.
Posted on October 28, 2022