What the cat tells us about Covid-19

Jean-Marc Sabatier (DR)

The scientific community is distraught in the face of the new coronavirus which appeared a year and a half ago in China. For the first time, Jean-Marc Sabatier * draws an analogy between the coronavirus of feline infectious peritonitis or PIF (not transmissible to humans) and SARS-CoV-2 at the origin of Covid-19. A better understanding of physiological phenomena complexes common to both viruses will perhaps, tomorrow, provide a definitive medical response to the pandemic. Maintenance.

In collaboration with managers of the Wuhan State Virology Laboratory (China), Professors Zhijian Cao and Yingliang Wu, and Veterinary Doctors Pierre Petruzzi (Chambéry) and Pierre Durieux (Meaux), you have highlighted the strange similarities that exist between a cat disease and Covid-19. Can you explain to us?

Feline infectious peritonitis (FIP) is a viral disease of cats caused by an alpha-coronavirus, while the SARS-CoV-2 responsible for Covid-19 is a beta-coronavirus. These are related viruses. The FIP virus is contagious to cats, but does not spread to other species, including humans. FIP has been well known and documented since the 1980s. We know that FIP ​​viruses are enteric coronaviruses that have become pathogenic as a result of mutation (s), and concern either young cats (from 3 months to 3 years old), or older cats (10 to 15 years old). The pathologies associated with FIP are similar to the diseases of Covid-19.

That is to say ?

The clinical signs of FIP are very polymorphic, like Covid-19, and are divided into “dry” and “wet” forms. In the “dry” form, we find possible ocular damage, as well as granulomatous damage in the lungs, kidneys, liver, central nervous system, lymph nodes, intestines, accompanied by possible neurological disorders …
The “wet” form is manifested by effusions from the abdomen or thorax, inflammation of the pleura (pleurisy), inflammation of the peritoneum (peritonitis) which are also well defined in Covid-19.
There are other clinical manifestations common to both forms of the disease: organ inflammation, thrombosis, thrombocytopenia, coagulopathy, etc.
The “dry” and “wet” forms can coexist, or follow one another. FIP virus infection of macrophages is sometimes responsible for fatal granulomatous vasculitis in cats.

What do we still know about this cat disease?

The FIP virus can be dormant and harmless for years (up to 14 or 15 years) or multiply and become fatal in a short time. The progression to severe forms takes place on average over 2 to 5 weeks. Yes cats cannot transmit the FIP virus to humans, on the other hand, cats can be (exceptionally) infected with the SARS-CoV-2 responsible for Covid-19.

How is the virus transmitted to cats?

The virus is transmitted from mother to kittens. The virus is present in the stool and can easily infect other cats, especially in shelters and catteries.

What are the Similarities Between Cat Viruses and SARS-CoV-2?

Both PIF viruses and SARS-CoV-2 are enveloped, single-stranded, positive-sense RNA coronaviruses. This means that although one is from the alpha family and the other from the beta family, they are both very closely related and of zoonotic origin.
In fact, these two viruses attack the renin-angiotensin system (RAS) host, and over-activation of this system triggers comparable disorders and pathologies, although the two viruses act on separate cell receptors.
The cell receptor of the FIP virus is a molecule called “Amino-peptidase N” (APN). It is a surface receptor found in the intestines, kidneys, lungs, epithelial and endothelial cells, etc. APN transforms angiotensin 3 into angiotensin 4. However, angiotensin 3 targets the AT1R receptor, responsible for Covid-19.

What about the other virus, SARS-CoV-2?

SARS-CoV-2 binds to the ECA2 receptor and leads to an increase in angiotensin 2 which again causes over-activation of the very deleterious AT1R receptor since it is responsible for Covid-19.
In other words, the two viruses will target the AT1R receptor (cat or human) by going through different paths.
What must be understood is that APN and ECA2 are compounds of the ARS which is a major physiological system for the functioning of the organism, be it kidney, cardiovascular or pulmonary functions. It is also involved in the intestinal microbiota and innate immunity, both in cats and in humans.

What do you deduce from this?

Cat diseases caused by the FIP virus are comparable to those caused by SARS-CoV-2. There is no specific treatment for cats except comfort medication. We need ARS inhibitors.

There is no vaccine for FIP?

There have been trials of vaccination using inactivated FIP viruses. Young cats were vaccinated with an avirulent strain of the virus. But this vaccination did not protect them against inoculation of the virulent virus by the oro-nasal route. In contrast, vaccinated animals were more easily infected than unvaccinated cats.
This lack of protection suggests the existence of a phenomenon called ADE for “antibody-dependent enhancement”. ADE generates a succession of events that can be found in several viral diseases (HIV, dengue, Ebola, etc.). Viruses infect cells by a mechanism that relies on the interaction between so-called “facilitating” antibodies (as opposed to protective “neutralizing” antibodies), and the virus.

It’s unexpected. Can the vaccine promote disease?

Indeed, the “facilitating” antibodies allow the virus to penetrate better into the target cells. This mechanism favoring the infection of cells by the virus would prove to be problematic if it were found during the vaccination against SARS-CoV-2. The remedy would then be worse than the disease. It is nevertheless possible to circumvent the problem posed by ADE during vaccination.

* Jean-Marc Sabatier, Research Director at CNRS and Doctor in Cell Biology and Microbiology, affiliated to the Institute of NeuroPhysiopathology (INP), at the University of Aix-Marseilles. Editor-in-Chief of international scientific journals: “Coronaviruses” and “Infectious Disorders – Drug Targets” (DR)

Next article: A lead for one vaccine effective against Covid-19

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