Perspectives
The circulation of PEDV has caused huge economic damages to the pig
industry in the world, while the emergence of its variant strains
aggravates the challenge. An increased prevalence of PEDV has been
witnessed in those years. For example, an outbreak of PEDV caused PED in
China in 2010 was characterized by high mortality in suckling pigs (RQ
et al., 2012). Though progress in the understanding of PEDV including
its genome, viral structure, has been made by the efforts of numerous
investigations during the past years, it seems we still stand a little
far away from completely revealing the pathogenic mechanisms of PEDV. In
addition, the development of effective and preventive measures like
medicines and vaccines remains on the way.
To establish a productive infection, invading viruses need to overcome
their host’s first line of defense, the innate immune response. Although
this reaction can largely protect the host from attacking by most
microorganisms, it is still susceptible to antagonism and destruction of
pathogenic viruses. As an important porcine pathogen emerging in recent
years, PEDV has evolved strategies to overcome host innate immunity,
including avoiding recognition by PRRs, inhibiting IFN production,
and/or antagonizing IFN signal transduction and antiviral action
mechanism of the host. Relative to extensive studies and in-depth
information on other coronaviruses like SARS-CoV, the host-PEDV
interactions just receive increased attention recently. One typical
example is that PEDV targets intestinal epithelial cells (IECs) in the
intestinal villi of pigs, while the most common in vitro cell culture
system used to study PEDV does not derive from IECs of pigs. The
development of new pig IEC derived cell lines will undoubtedly provide
an alternative, more physiologically relevant model for future studies
of the PEDV-host interactions.
After an outbreak of PED in the United States in 2014, Zoetis has
developed PEDV inactivated whole virus vaccine, which can provide
passive immunity to piglets by immunizing sows before delivery. Before
the new PED outbreak, the attenuated virus vaccine has played an
effective role in the prevention and control of PED (CH, BJ, JG, GO, &
YB, 1999; DS et al., 2007). Besides this, PEDV genetic engineering
vaccines based on the S protein which can induce the body to produce
neutralizing antibodies, also display broad prospects. As the most ideal
vaccine for oral immunization, transgenic plant vaccine similarly have
great development space (TJ, SC, MS, & YS, 2006). The numerous
properties of nanoparticles, including possessing immunoadjuvant
activity, generating natural immune response of antigens, easily
reaching antigen-presenting cells to regulate the immune response
through a variety of ways, targeting to present antigen, and releasing
slowly, allow it to be an ideal candidate for preparing new vaccines
against the occurrence of PED (DM, JK, & JR, 2013; T et al., 2020).
Notably, although vaccine immunization is an effective way to prevent
and control PED, for piglets infected with PEDV, it often cannot solve
all of the issues. Therefore, some therapeutic drugs are urgently needed
as well. In this regard, the validly inhibitory effect of IFN-L on the
proliferation of PEDV in pig intestinal epithelial cells together with
better action than type I interferon, empowers it to receive more
attention (L. L et al., 2017). Likewise, PEDV specific yolk antibody has
also been reported to increase the survival rate of infected piglets (DH
et al., 2015). Besides these, prokaryotic expression of single stranded
variable region of PEDV monoclonal antibody or small peptides identified
by phage screening, which is able to bind to PEDV receptor, can also
prevent PEDV from invading host cells (M. F et al., 2014). Additionally,
the key role of proteases in virus release from cell surface and
enhancement of PEDV infection, render them to be important drug targets.
Therefore, protease inhibitors may also be good candidates for
developing anti-PEDV compounds to fight this infectious disease (S. K et
al., 2011). Similarly, some Chinese herbal extracts, such as quercetin
and ginkgo peel extract, can effectively suppress the infection process
of PEDV in vitro (HJ et al., 2009; L. JH et al., 2015; S. JH, JK, & HJ,
2011; T et al., 2020). Although some drugs have been proved to have
anti-PEDV activity, they have not been used in clinical treatment due to
its cost and safety. Therefore, it is of far-reaching significance to
deeply study the pathogenesis of PEDV, identify PEDV receptors and
related host factors, thereby providing more druggable targets for the
prevention and treatment of PEDV.