Coronaviruses in Veterinary Species

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Biomarker expression patterns in Bovine, Canine, Porcine and Avian.

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The 2020 COVID-19 pandemic, caused by SARS-CoV-2, was first noticed in Wuhan in China and spread around the world within weeks making coronaviruses a global risk to human health again. The last outbreak was SARS in 2002-2003. However, within the animal health field coronavirus mediated diseases have been a concern for decades.

Coronavirus Components

Coronaviruses are positive-sense single-stranded RNA viruses assembled with four structural proteins:

• S (spike)
• E (envelope)
• M (membrane)
• N (nucleocapsid)

The S, E, and M proteins make up the viral envelope, while the N protein stores the RNA genome. Additionally, up to 16 proteins make up the non-structural components responsible for regulatory and enzymatic functions.

Structural Proteins

The S protein (~150 kD) has probably received the most attention as it is the protein that facilitates cell entry of the virus by docking to the host cell. It forms homotrimers to construct the distinctive spike structures on the surface of the virus. During virus assembly, a host cell furin-like protease cleaves the S protein into two separate polypeptides, S1 and S2. S1 forms the receptor-binding domain and S2 is the stalk of the S protein spike. Different coronaviruses bind varying host cell receptors (see table below).

Table 1. Coronavirus receptors.

Spike Protein and Its Fascinating Role in the SARS-CoV-2 Infection Micro-Review.

Update your knowledge on how the S protein on SARS-CoV-2 is cleaved into S1 and S2 subdomains upon binding its cellular receptor, ACE2, and then arranges the juxta positioning of virus and host cell membrane to initiate viral fusion with the host cell leading to infection and COVID-19.

The E protein is a small (~8-12 kD) transmembrane protein with ion channel activity. It seems to have several functions related to virus assembly and release. For some coronavirus viruses, for example SARS-CoV, it is needed for infectivity but not replication.

The M protein (~25–30 kD) is the most abundant structural protein in the virion. It has three transmembrane domains with a short N-terminal glycosylated external sequence and a longer C-terminal chain inside the viral particle. It forms the distinctive shape of the virion.

The N protein makes up the nucleocapsid. It is functionally split into two separate domains; an N-terminal and a C-terminal domain, both able to bind RNA. During virion assembly, the N protein is extensively phosphorylated which has been suggested to facilitate preferential binding of the viral RNA. Finally, it also interacts with components of the replicase complex and the M protein (Perlman and Netland 2009).

Coronavirus Infection

The severe disease forming abilities of coronaviruses in humans became apparent first with SARS, then MERS, and now COVID-19. However, in animal species the lethal nature of coronaviruses is well known (Fehr and Perlman 2015).

Pigs

Pigs can be infected by Transmissible Gastroenteritis Virus (TGEV) and Porcine Epidemic Diarrhea Virus (PEDV). These infect the epithelial cells of the jejunum and ileum causing the destruction of the villi, leading to diarrhea and dehydration. In the case of TGEV, it is nearly always fatal for piglets less than a week old, however older pigs rarely die. PEDV has milder symptoms.

Cows

Bovine coronavirus (BCoV) is a significant problem for cattle health and causes production losses in the farming industry. It induces respiratory distress and diarrhea leading to weight loss, dehydration, and decreased milk production. While it generally spreads to the whole herd, the mortality rate is very low. Both the small and large intestine are affected, the latter showing general lesions and damage to the colonic glandular epithelium.

Cats

Cats are frequently infected with the feline enteric coronavirus (FCoV) resulting in a mild or asymptomatic infection with occasional diarrhea. FCoV, like other coronaviruses, replicates in the epithelial cells of the enteric tract. However, if the infection with FCoV becomes persistent, the virus mutates into the Feline Infectious Peritonitis Virus (FIPV) which causes feline infectious peritonitis (FIP). This version replicates in monocytes and macrophages and thus also spreads throughout the body causing dysregulated cytokine and chemokine expression and lymphocyte depletion resulting in high mortality (Rottier et al. 2005).

Veterinary Species as Intermediates

A further dimension seen with SARS-CoV-2 is the potential for its transmission to pets of infected humans. SARS-CoV-2 neutralizing antibodies were found in cats in Wuhan indicating transmission to cats from humans has occurred (Zhang et al. 2020). Several cases have been reported in the press of transmission to dogs and cats. Recent scientific work indicates that SARS-CoV-2 replicates at low efficiencies in dogs, pigs, chickens, and ducks, but more so in ferrets and cats. Moreover, the virus can spread from cat to cat. The authors suggest that cats should be under surveillance to aid the elimination of SARS-CoV-2 from humans (Shi et al. 2020).

Antibodies to Coronaviruses

Bio-Rad, the leading supplier of veterinary research antibodies, offers two antibodies reactive with feline coronavirus, both directed to the nucleocapsid protein. Clone FIPV3-70 is suitable for use in ELISA, flow cytometry, immunofluorescence, immunohistology on frozen and paraffin (with pre-treatment) sections, and western blotting. It is available in purified format. Clone CCV2-2 is suitable for use in ELISA and is biotinylated. A further monoclonal antibody, clone 5A4, for use in ELISA detects the S protein of the bovine coronavirus.

Discover an industry leading portfolio of species-specific antibodies for immune response research in our online veterinary product catalog.

To view Bio-Rad’s resources supporting research into COVID-19 visit our SARS-CoV-2 Antibody Research page.

References:

• Fehr AR and Perlman S (2015). Coronaviruses: an overview of their replication and pathogenesis. Methods in molecular biology (Clifton, N.J.) 1282, 1-23.
• Perlman S and Netland J (2009). Coronaviruses post-SARS: update on replication and pathogenesis. Nat. Rev. Microbiol. 7(6), 439–450.
• Rottier PJ et al. (2005). Acquisition of macrophage tropism during the pathogenesis of feline infectious peritonitis is determined by mutations in the feline coronavirus spike protein. J Virol. 79 (22), 14122-30.
• Shi J et al. (2020). Susceptibility of ferrets, cats, dogs, and different domestic animals to SARS-coronavirus-2. Preprint on bioRxiv https://doi.org/10.1101/2020.03.30.015347
• Zhang Q et al. (2020). SARS-CoV-2 neutralizing serum antibodies in cats: a serological investigation. Preprint on bioRxiv https://www.biorxiv.org/content/10.1101/2020.04.01.021196v1