Coronavirus: ferrets 'candidate animal' for testing treatments for COVID-19 © Getty Images

Ferrets potential ally in the search for coronavirus vaccine

The virus replicates efficiently in ferrets, a study has found.

Ferrets could help in the race for treatments and vaccines for coronavirus, researchers say.

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Scientists looking for animal models for COVID-19 infections to support urgent development of drugs found that it replicates poorly in dogs, pigs, chickens and ducks but efficiently in ferrets and cats. They say their findings point to ferrets as a candidate animal model for evaluating antiviral drugs or vaccines.

Jianzhong Shi of State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, and colleagues, evaluated the susceptibility of different model laboratory animals to coronavirus. They also looked at companion and domestic animals.

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All experiments were performed in biosafety level 4 facilities, following protocols for animal welfare.

The researchers delivered viral samples to the animals through the nose or via the trachea (for ferrets), and then measured the extent of replication in various tissue sites. They found that COVID-19 replicated poorly in all the animals but the ferrets and cats. In ferrets and older cats, it replicated in the upper respiratory tract, not the lung.

In studies of airborne transmission, they found it was poorly transmissible in ferrets, but it transmitted via air in cats, particularly in juvenile cats.

Researchers say the fact that the virus replicates efficiently in the upper respiratory tract of ferrets makes them a candidate for evaluating antiviral drugs or vaccine candidates.

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In the study published in the Science journal, the authors write: “We found that SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and ducks, but ferrets and cats are permissive to infection. We found experimentally that cats are susceptible to airborne infection.

“Our study provides important insights into the animal models for SARS-CoV-2 and animal management for COVID-19 control.”

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They add: “The fact that SARS-CoV-2 replicates efficiently in the upper respiratory tract of ferrets makes them a candidate animal model for evaluating antiviral drugs or vaccine candidates against COVID-19.”

What is viral load and why is it important to coronavirus?

Viral load is simply the amount of virus in the body. This varies in different parts of the body, and can change over time. Recent studies have shown, for example, that the viral load in the lungs of COVID-19 patients is greater than that in the nose.

A patient’s viral load increases as the virus replicates and disease symptoms get worse, and then decreases as the patient recovers. So monitoring the viral load can give us a useful indication of how a patient’s infection is progressing.

The amount of virus that you’re exposed to at the beginning of an infection is something different, and this is called the ‘infectious dose’. Studies on other viruses such as the flu and SARS have shown that the higher the infectious dose (the more virus you breathe in), the greater your chances of having more severe symptoms.

With one small exposure, your immune system may be able to fight off the virus before you get sick, but with repeated small exposures (such as touching your face throughout the day) or one large exposure (an infected person coughing in your face), the virus may grow faster than your body can control.

We don’t yet know if this link between infectious dose and disease severity holds for COVID-19, but it may do, and that’s why it’s so important to maintain physical distancing and keep the initial exposure as low as possible.

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