What is Inclusion Body Hepatitis?
Inclusion body hepatitis (IBH) can cause severe mortality in 2 to 5 week old broiler chickens. It is caused by a virus called Fowl Adenovirus (FAdV). There are many “types” of FAdVs. Different types of FAdVs can cause different diseases such as gizzard erosion and ulceration (FAdV1) or hydropericardium hepatitis syndrome or HHS (FAdV4). The FAdVs that cause IBH are FAdV2, 8a, 8b and 11. In Saskatchewan, we have found that FAdV8b and 11 are the most predominant in IBH cases. These “types” of FAdVs can be grouped into families – FAdV2 and 11 in one family and FAdV8a and 8b in another. A FAdV within a family can cross-protect against other FAdVs within the same family. This is an important concept when developing a vaccine as only one FAdV per family is required to obtain broad spectrum protection. Typically IBH in broilers is controlled by vaccination of broiler breeders. This allows maternal antibodies from broiler breeders to be transferred to the broilers. There is no commercial IBH broiler breeder vaccine in Canada, only autogenous vaccines. Therefore, the objectives of our research program was to develop an IBH vaccine for broiler breeders.
Our Research
Develop a live-virus broiler breeder vaccine containing FAdVs from two different families, and determine the appropriate dose per broiler breeder
We were able to develop a live-virus broiler breeder vaccine containing FAdV8a and FAdV11. Research broiler breeders were vaccinated orally at 16 weeks of age with this vaccine – one group with a low dose and another group with a high dose. We collected blood and hatched broilers to analyse the efficacy of the vaccine. We found that the efficacy of the low and high dose was exactly the same, therefore suggesting only a low dose of this specific vaccine is necessary. Additionally, we challenged the broilers from the vaccinated broiler breeders with high levels of FAdVs. We found that broilers from these vaccinated breeders were protected against an FAdV challenge, no matter which “type” of FAdV we gave. Additionally, we housed both live-vaccinated broiler breeders together with unvaccinated broiler breeders. We found that the unvaccinated broiler breeders ended up having the same antibody levels as the vaccinated ones. This is due to the vaccinated broiler breeders shedding the live-virus in feces for up to 21 days after we vaccinated them. To test if these antibodies protected the broilers, we again challenged the broilers with different FAdVs and found all were protected against IBH. This may be an effective immunization technique for our live-virus vaccine.
Compare the live-virus vaccine to an inactivated vaccine
Since we were able to determine a live-virus vaccine was effective in preventing IBH in broilers, we also needed to determine if an inactivated vaccine would work just as well. An inactivated vaccine is sometimes more preferable to use as it is safer than introducing live-viruses into a barn, even though more labor is required in administering it to birds. In this experiment, we gave a live-vaccine containing FAdV8b and FAdV11 orally to one group of broiler breeders and in the other group we injected inactivated FAdV8b and FAdV11. We did the same as in objective 1 – collected blood and hatched broilers from these groups. We found that both the live-virus and inactivated vaccines worked exactly the same. This means that the safer option – the inactivated vaccine - protects broilers from IBH just as well as the live vaccine.
Develop an alternative vaccine to live-virus and inactivated vaccines
Finally, we wanted to determine if there was an alternative to our live and/or inactivated vaccines described above. Even though we found that both the live-virus and inactivated vaccines protected broilers against IBH, actually making the vaccines was difficult! The process for making the live-virus and inactivated vaccines involves growing large amounts of the virus in a lab, then for the inactivated vaccine, having to actually kill the virus. For this objective, we studied subunit or virus-like particle (VLP) vaccines. These types of vaccines are good alternatives since they have been found to be safe and are easy to produce. Similarly to the other objectives, we injected either a fiber-vaccine, fiber-knob or a VLP vaccine to broiler breeders and collected blood and broilers. We found that the VLP and fiber-vaccines were the most effective. The fiber-knob vaccine unfortunately did not good levels of antibodies in broiler breeders and did not protect broilers against an IBH challenge.
These technologies are available to commercial vaccine companies through Innovation Enterprise, University of Saskatchewan.