2020-21 Rapid Ag: Development of a Novel Vaccine to Protect Turkeys from Hemorrhagic Enteritis Virus Infection (renewal)
Veterinary Biomedical Sciences
In addition to generating over $800 million in economic activity, the turkey industry in Minnesota and its related businesses support 26,000 jobs in the state, 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, enlarged spleen, and sudden and rapid death of the affected animals. Flock mortality may reach 60% through the course of the disease that can incur significant economic losses to the turkey producers and can negatively impact the state economy. This application aims to develop new and effective vaccines to prevent HEV infection of turkeys.
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 . Previous studies have 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, 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 and an adjacent 34 aa of the shaft domain of the HEV fiber protein (called knob-h) 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 have produced a new generation of HE vaccines based on the Pichinde virus (PICV) that has recently been shown to efficiently express foreign protein antigens to induce strong and long-lasting humoral and cell-mediated immunity in both rodents and avian species (see our published and unpublished data described below). We, therefore, 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 planned studies outlined below were developed in consultation with an industry partner.
Goals and Objectives
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 (please see Dr. Wileman’s letter attached for more details). 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 . PICV is a virus found only in rice rats in Colombia, South America, and therefore is not known to induce pre-existing immunity or cause disease in humans or livestock. Using the PICV-based vaccine vector to express the influenza viral hemagglutination protein (HA) and nucleoprotein (NP), we have shown that animals (mice, chickens, turkeys, 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. During the initial cycle of funding support from the RARF, we have successfully constructed and tested a representative PICV-based vaccine that expressed the HEV fiber knob protein as the antigen to show this new PICV-HE-Fiber vaccine was able to infect turkeys, which was cleared by the vaccinated animals while generating good levels of protection against the HEV challenge, and that this PICV viral vector platform was safe to administer to turkeys as a vaccine (details provided in the attached Summary of Progress page toward the end of the document). Encouraged by these exciting results, in the remaining 6-8 months of the currently funded period, we plan to generate an additional PICV-based vaccine to express the HEV hexon protein antigen as originally proposed (PICV-HE-hexon vaccines) and will test this new HE vaccine in turkeys as described below. In the current proposal, we seek additional funding support in the next cycle to test the two aforementioned PICV-based versions of the new HE vaccines in order to:
- Determine the most convenient and effective routes of vaccinating turkeys with these new HE vaccines (i.e., via intramuscular, oral, and areosol/spray cabinet inoculation) that would protect vaccinated animals against virulent HEV infection (challenge)
- Determine the proper timing of vaccination in order to optimize the duration and breath of immune responses against HEV infection in turkeys
- Determine whether the new PICV-based HEV vaccines can overcome the known immunosuppressive effect associated with vaccination of turkeys with the tissue culture-attenuated HEV vaccine . These studies, which were described in the “future studies” section of our original application, are logical extensions to our currently funded work and are aimed at determining the potential practical applications of the new HE vaccines in the poultry industry.
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