One health, multiple challenges: The inter-species transmission of influenza A virus

Abstract

Influenza A viruses are amongst the most challenging viruses that threaten both human and animal health. Influenza A viruses are unique in many ways. Firstly, they are unique in the diversity of host species that they infect. This includes waterfowl (the original reservoir), terrestrial and aquatic poultry, swine, humans, horses, dog, cats, whales, seals and several other mammalian species. Secondly, they are unique in their capacity to evolve and adapt, following crossing the species barrier, in order to replicate and spread to other individuals within the new species. Finally, they are unique in the frequency of inter-species transmission events that occur. Indeed, the consequences of novel influenza virus strain in an immunologically naïve population can be devastating. The problems that influenza A viruses present for human and animal health are numerous. For example, influenza A viruses in humans represent a major economic and disease burden, whilst the poultry industry has suffered colossal damage due to repeated outbreaks of highly pathogenic avian influenza viruses. This review aims to provide a comprehensive overview of influenza A viruses by shedding light on interspecies virus transmission and summarising the current knowledge regarding how influenza viruses can adapt to a new host.

H1N1 Swine Influenza Viruses Differ from Avian Precursors by a Higher pH Optimum of Membrane Fusion

“…To compare requirements of the viruses for the acidic pH during cell entry, we studied inhibition of viral single-cycle infection in MDCK cells by the lysosomotropic agent ammonium chloride, which counteracts acidification of endosomes (46,47). Concentrations of NH 4 Cl that reduced infection by 50% were determined from the dose-response curves, as illustrated in Fig. 2a 4 Cl and values of pH treatments that caused 50% effect were determined from the curve by interpolation.…”

“…Concentrations of NH 4 Cl that reduced infection by 50% were determined from the dose-response curves, as illustrated in Fig. 2a 4 Cl and values of pH treatments that caused 50% effect were determined from the curve by interpolation. All individual values were averaged (Table 1). similarly to EAsw viruses, were less sensitive to ammonium chloride than avian H1 viruses.…”

“…After the cultures were incubated for 16 h at 37°C, the cells were fixed, and virus-infected cells were detected by immunostaining for viral nucleoprotein (NP) as described previously (31). Numbers of infected cells per culture were counted under the microscope and expressed in percentages with respect to the control cultures that were infected in the absence of NH 4 Cl. The dose-response curves were plotted, and concentrations of NH 4 Cl that inhibited infection by 50% (IC 50 ) were determined for each replicate curve by linear interpolation as illustrated in Fig.…”

“…Numbers of infected cells per culture were counted under the microscope and expressed in percentages with respect to the control cultures that were infected in the absence of NH 4 Cl. The dose-response curves were plotted, and concentrations of NH 4 Cl that inhibited infection by 50% (IC 50 ) were determined for each replicate curve by linear interpolation as illustrated in Fig. 2a.…”

Multiple Natural Substitutions in Avian Influenza A Virus PB2 Facilitate Efficient Replication in Human Cells

“…Another substitution in PB2, known to have a role in host adaptation, is the exchange of aspartic acid with asparagine at position 701 (PB2-D701N). Several other sub-stitutions in PB2, PB1, PA, NP, and NEP have been suggested to enhance polymerase activity in mammalian cells (22)(23)(24)(25). However, productive-and sometimes fatal-viral infections of humans with avian viruses of the H5N1 and H7N9 subtypes lacking any previously identified adaptive substitutions have been frequently reported (26).…”