Generation and protective efficacy of a cold-adapted attenuated genotype 2b porcine epidemic diarrhea virus

Won, Hokeun; Lee, Dong-Uk; Jang, Guehwan; Noh, Yun-Hee; Lee, Seung-Chul; Choi, Hwan-Won; Yoon, In-Joong; Yoo, Han Sang; Lee, Changhee

In summary, this is the first report describing the development of a cold-adapted MLV vaccine based on a virulent G2b PEDV strain. The present study demonstrated the loss of virulence of a highly pathogenic PEDV strain, with 12 genetic mutations throughout the entire genome, after cold adaptation. Vaccination-challenge studies revealed that sows immunized with a homologous oral L/L maternal vaccination regimen provides protective lactogenic immunity to piglets, thereby reducing mortality, morbidity, and fecal shedding of the virus. In South Korea, multiple-dose vaccination programs including L/K/K at 2-or 3-week intervals before delivery have been recommended nationwide in pregnant sows for decades [1, 2] . Due to the absence of a new safe and effective G2b live vaccine, controlled oral exposure (feedback) for prime-boost vaccination strategies is mostly implemented as a countermeasure in the field since the 2013-2014 PED epidemics. Despite certain positive contributions of feedback to naïve herds, intentional infection using an undefined inoculum may cause undesirable negative consequences, which include insufficient immunity induction, unexpected virus transmission, amplified viral recombination and diversity; and more importantly, dissemination of other microbial pathogens conceivably evolving to develop into a new disease agent. Once the cold-adapted Aram-P29-CA-based MLV vaccine is supplied in the market, gradual withdrawal of the feedback practice will be imminent. Since oral administration does not have the capacity to ensure that all animals are immunized with a proper dose, this demerit should be ameliorated to easily use the live vaccine under field conditions. With the availability of inactivated G2b PEDV vaccines in the domestic market, customized vaccination programs, such as the application of heterologous oral prime-parenteral boost L/K/K or L/L/K schemes, could be established based on various herd circumstances, including naïve, epidemic, and endemic statuses. It is noteworthy that maternal vaccination has to be implemented in conjunction with additional intervention strategies involving intensive biosecurity, husbandry, and hygiene practices for PED prevention and eradication.