Mimicking the passage of avian influenza viruses through the gastrointestinal tract of chickens

Abstract

In contrast to human influenza viruses that replicate in the respiratory tract and are airborne transmitted, avian viruses also replicate in gut epithelial cells and are transmitted via the fecal-oral route. On this route, the virus is exposed to destructive fluids of the digestive tract, which are acidic and contain the proteases pepsin (gizzard) or chymotrypsin and trypsin (intestine). Only the latter enzyme activates virus by cleaving hemagglutinin (HA) into HA 1 and HA 2 subunits.We mimicked the passage of viruses through the gastrointestinal tract by treating them with digestive fluids from chicken and determined titers and integrity of HA by western-blot. Gizzard fluid completely inactivated virions and degrades HA even at a high dilution, but only if the pH was kept acidic. If the fluid is diluted with neutral buffer (mimicking virus uptake with seawater) particles were more resistant. Virions containing an uncleaved HA were even activated suggesting that gastric juice contains a trypsin-like protease. Undiluted intestinal fluid inactivated particles and destroyed HA, but diluted fluid activated virions. A virus isolated from the duck´s intestine is more tolerant against intestinal fluid compared to fowl plague virus suggesting that the former is better adapted to grow in the intestine. We also demonstrate that influenza viruses replicate to high titers in a novel chicken epithelial gut cell line. While viruses with a monobasic HA cleavage site require addition of trypsin, these cells effectively process HA with a polybasic cleavage site, which could be blocked with an inhibitor of the cellular furin protease.

Delving deep into the structural aspects of a furin cleavage site inserted into the spike protein of SARS-CoV-2: A structural biophysical perspective

“…S protein contains two functional domains: a receptor binding domain (RBD) [2], and a second domain which contains sequences that mediate fusion of viral and cell membranes [3][4][5][6][7]. Recently, it was reported that S protein contains a potential cleavage site for furin protease [8], including four residues (Pro681 (P681), Arg682 (R682), Arg683 (R683) and Ala684 (A684)) [9][10][11][12][13]. Functionally, R682, R683, A684 and Arg685 (R685) constitute the minimal polybasic furin cleavage cite (FCS), i.e., RXYR, where X or Y is to be a positively charged arginine or lysine.…”

Molecular Analysis of the Avian H7 Influenza Viruses Circulating in South Korea during 2018–2019: Evolutionary Significance and Associated Zoonotic Threats

“…The major force guiding the evolution of AIVs is the adjustment with new hosts or the escape from the pre-existing host community [31]. This process of evolution is assisted by nucleotide substitutions involving amino acid mutations and reassortments [32].…”

Exploring the potential of foodborne transmission of respiratory viruses

“…In the appropriate conditions, AIV can remain infective for up to 6 months in surface waters ( Keeler et al, 2014 ). AIV are rapidly inactivated by low pH and bile acids ( Hirose et al, 2016 ; Scholtissek, 1985 ); although, evidence has shown that mucus can provide protection from inactivation in the gastrointestinal environment ( Hirose et al, 2016 ), and the possibility of water being a diluent to lower the pH of the stomach and allow AVI to pass has also been suggested ( Han et al, 2019 ).…”

“…There is growing evidence that specific enveloped respiratory viruses can endure low pH, enzymes, and bile in the upper GI tract and replicate in the intestinal epithelium ( Bertran and Swayne, 2014 ; de Wit et al, 2014 ; Zhou et al, 2017 ). The potential deleterious effect of low pH and digestive enzymes on viruses can also be mitigated if viruses are swallowed with water or food ( Han et al, 2019 ). Food and water can also decrease the activity of pepsin, which could otherwise degrade virus particles ( Witkowski et al, 2017 ).…”