Stability of different influenza subtypes: How can high hydrostatic pressure be a useful tool for vaccine development?

Molecular identification and virological characteristics of highly pathogenic avian influenza A/H5N5 virus in wild birds in Egypt

Multiple incursions of different subtypes of highly pathogenic avian influenza (HPAI) A/H5NX viruses have caused widely considerable outbreaks in poultry and hundreds of human infections. Extensive reassortment events associated with currently circulating clade 2.3.4.4b of A/H5NX viruses have been widely recorded. Wild migratory birds contribute to the spillover of diverse viruses throughout their migration flyways. During our active surveillance of avian influenza in Egypt, we successfully isolated and fully characterized HPAI A/H5N5 virus of clade 2.3.4.4b that was detected in a healthy purple heron. The Egyptian H5N5 virus is genotypically similar with the same subtype that was detected in the far east of Russia and several European countries. The antigenic analysis showed that the Egyptian H5N5 virus is distinct from HPAI A(H5N8) viruses in Egypt. The virus preferentially binds to avian-like receptors rather than human-like receptors. Our results showed that the virus caused 100% and 60% lethality in chicken and mice respectively. Increasing active surveillance efforts, monitoring the dynamics of emerging AIVs, and risk assessment implementation should be globally applied especially in hot spot regions like Egypt.

Inactivation of avian influenza viruses by hydrostatic pressure as a potential vaccine development approach

Vaccines are a recommended strategy for controlling influenza A infections in humans and animals. Here, we describe the effects of hydrostatic pressure on the structure, morphology and functional characteristics of avian influenza A H3N8 virus. The effect of hydrostatic pressure for 3 h on H3N8 virus revealed that the particles were resistant to this condition, and the virus displayed only a discrete conformational change. We found that pressure of 3 kbar applied for 6 h was able to inhibit haemagglutination and infectivity while virus replication was no longer observed, suggesting that full virus inactivation occurred at this point. However, the neuraminidase activity was not affected at this approach suggesting the maintenance of neutralizing antibody epitopes in this key antigen. Our data bring important information for the area of structural virology of enveloped particles and support the idea of applying pressure-induced inactivation as a tool for vaccine production.

Energy Requirements for Loss of Viral Infectivity

Outside the host, viruses will eventually lose their ability to infect cells due to conformational changes that occur to proteins on the viral capsid. In order to undergo a conformational change, these proteins require energy to activate the chemical reaction that leads to the conformational change. In this study, data from the literature is used to calculate the energy required for viral inactivation for a variety of different viruses by means of the Arrhenius equation. We find that some viruses (rhinovirus, poliovirus, human immunodeficiency virus, Alkhumra hemorrhagic fever virus, and hepatitis A virus) have high inactivation energies, indicative of breaking of a chemical double bond. We also find that several viruses (respiratory syncytial virus, poliovirus, and norovirus) have nonlinear Arrhenius plots, suggesting that there is more than a single pathway for inactivation of these viruses.