2018-2019 Rapid Ag: Development of a Novel Vaccine to Protect Turkeys from Hemorrhagic Enteritis Virus Infection
Veterinary Biomedical Sciences Department
- 2018 Fiscal Year: $120,041
- 2019 Fiscal Year: $127,042
Hemorrhagic enteritis (HE) is an economically important disease of commercial turkeys. The etiologic agent of HE is hemorrhagic enteritis virus (HEV), an avian adenovirus. The vaccines currently available to the commercial poultry producer are effective in preventing disease outbreaks; however, they are immunosuppressive creating opportunities for opportunistic infections and vaccine failures.
Minnesota (MN) is ranked #1 for both turkey production and processing in the U.S. In addition to generating over $800 million in economic activity, the turkey industry and its related businesses support 26,000 jobs in MN, according to the MN Dept of Employment and Economic Development. Turkeys consume annually $163 million of corn and $169 million of soybean meal, effectively adding another approximately $251 million to these agricultural industries in MN. Hemorrhagic enteritis (HE) of turkeys is an economically important disease of turkeys that are characterized by hemorrhagic and necrotic intestine (e.g., duodenum), enlarged spleen, and sudden and rapid death of the affected animals [2, 3]. Flock mortality may reach 60% through the course of the disease . In addition to this acute aspect of the disease, HE causes a long-lasting immunodepression [4, 5] that prevents turkeys from mounting effective immune responses against opportunistic infections [2, 6-10] and vaccine antigens . Hemorrhagic enteritis virus (HEV), a type II aviadenovirus, is the etiologic agent of HE and causes a contagious disease of young turkeys. A tissue culture-attenuated HEV has been used extensively as a vaccine  and has been shown to be highly effective in preventing HE, although it too is immunosuppressive . We have previously shown that turkeys vaccinated with a recombinant Fowl poxvirus (rFPV) expressing the native hexon protein of HEV (together with the 100 kDa folding protein), which is the main capsid protein of HEV (Fig. 1), can provide a good level of protection of turkeys from HE . However, HEV replication in the spleen was not prevented with this rFPV, suggesting that the anti-HEV antibody titer generated by vaccination wasn’t sufficient to prevent virus replication likely related to the fowl poxvirus expression system used, which might partly explain the observed immunodepression in some of the vaccinated animals. A subunit vaccine that includes the knob protein, together with an adjacent 34 aa of the shaft domain of HEV (herein referred to as knob-h protein) has also been used as a potential vaccine in turkeys . Partially purified fractions of E. coli expressing HEV knob-h protein have been used to vaccinate turkeys, which shows a good level of protection. It is important to note, however, that bacterially expressed knob-h protein might not be properly post-translationally modified and folded. Building on these earlier studies, we propose here to produce a new generation of HE vaccines based on the Pichinde virus (PICV) that we have recently shown to efficiently express dual foreign antigens to induce strong and long-lasting humoral and cell-mediated immunity and is ideal for a prime-and-boost vaccination strategy in both rodents and avian species (see our published and un-published data described below). We believe that this new viral vector can be exploited to express known HEV antigens to induce protective immunity against costly HE disease in commercial turkeys.
The main purpose of this project is to develop and test a new vaccine for HE that are based on a viral vaccine vector (Pichinde virus, PICV) recently developed and published by our laboratory . Using the PICV-based vaccine vector to express the influenza viral hemagglutination protein (HA) and nucleoprotein (NP), we have shown that animals (mice, chickens, and swine) vaccinated with these vaccines show protective levels of antibody and T-cell mediated responses, and when vaccinated mice were challenged with a lethal dose of the mouse-adapted influenza virus, they were 100% protected. Using this PICV-based vaccination strategy, we plan to:
- Generate various recombinant PICV (rP18tri) expressing different known immunogenic protein antigens of HEV (e.g., the hexon protein along with the 100 kDa folding protein and the fiber knob protein knob-h)
- Determine the safety of the virus-vectored vaccines and whether turkeys vaccinated with these PICV-based HEV vaccines will show high and persistent levels of neutralizing antibody responses that would protect vaccinated animals against virulent HEV infection (challenge)
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