Exploring Coronaviruses: From Animals to Humans

24/06/2024

In our previous article, we discussed some easy ways to protect yourself from zoonotic disease. Now we will take a dive into the world of coronaviruses, which have once again received worldwide attention following the COVID-19 pandemic.

Non-Human Coronaviruses

Many animal species, besides humans, can contract coronavirus…from cats and dogs to cattle. When an animal contracts coronavirus, gastrointestinal upset is a very common result, although it is also possible to be carrying coronavirus without showing any signs at all. One of the more scientifically interesting aspects of coronavirus is the occurrence of mutation in a small, but not unimportant, percentage of cat and dog (feline and canine) cases, by a mechanism which is still somewhat of a mystery. Until the recent discovery of therapeutic intervention, this mutation in feline coronavirus was considered deadly in 100% of cases, causing a disease state known as Feline Infectious Peritonitis (FIP). The canine coronavirus mutation is a relatively novel discovery and has not attracted the same attention as feline and human coronaviruses—at least for now. But case reports on the deadly mutation for canines and other animals in the genetic family of canines are becoming more numerous.

Human Coronaviruses

Humans have experienced several types of coronaviruses since their discovery in the 1960s, including SARS-CoV (Sudden acute respiratory syndrome coronavirus) in 2003, MERS (Middle Eastern respiratory syndrome) in 2012, and SARS-CoV-2 (Sudden acute respiratory syndrome coronavirus from group 2B) in 2019, which we commonly refer to just as COVID-19. Fortunately, SARS and MERS didn’t proliferate to a great extent, but we all know how COVID-19 was transmitted widely, causing a global pandemic.

Interestingly, these human coronaviruses tend to cause respiratory symptoms as opposed to the gastrointestinal signs seen in other mammalian (non-human) variants. When human coronaviruses infect cats, however, the clinical signs tend toward those seen in humans: respiratory and cardiac abnormalities. Human coronaviruses may also result in cases without clinical signs or symptoms, another feature in common with their non-human counterparts. Effective vaccines were developed for the prevention of COVID-19 as an emergency public health response to the pandemic, and it helped save countless lives. In comparison, less effective vaccines have existed for non-human coronavirus for a long time.

Can we learn from one to prevent the other?

Even though these different coronaviruses belong to the same overall virus family, the genera (plural of the biological classification called “genus”) and species, which dictate each virus’s unique qualities and effects, contain quite a large amount of variation. This means there may be some lessons to be learned from one another but the lessons are not necessarily widely applicable. For example, we may have been able to expect the emergence of variants and asymptomatic infection in human coronaviruses having seen the high incidence of variants and asymptomatic cases caused by other mammalian coronaviruses. The most common route of infection, however, differs. Human coronavirus is commonly spread via respiratory droplets, which makes sense given that it causes respiratory symptoms such as coughing and sneezing. Non-human coronavirus is commonly spread via the faecal-oral route—if only animals could abide by our previous biosecurity article and regularly wash their paws or hooves! Isolation and frequent cleaning surrounding both human and non-human cases have proven to be effective in the control of the virus, and the vaccines recently developed for the mutated feline coronavirus are being studied as a potential therapeutic intervention for human coronavirus. This may give scientists a head-start in developing more effective vaccines for both humans and companion animals in the future.

What’s the bottom line?

Coronaviruses have been in existence for a very long time and will likely be with us forever. Animals have proven to be an important reservoir for novel human infections, and while the mechanisms or clinical signs may not always be similar, we can apply some of the same principles across the various variants of coronavirus. An important note on this is that in order to learn about a virus and offer insight into its prevention and control, the virus needs to run its course for a while. Recommendations are based on good quality data, and the more data that can be gathered gives scientists a better chance to find trends and understand transmission. Additionally, we can learn from previous human AND non-human cases to widen our knowledge base and gain an advantage on the next zoonotic disease outbreak.

The fascinating story of coronaviruses illustrates very well why ‘One Health’ (as we described at the beginning of the series of articles) is such an important topic. We must observe and take note of coronavirus infections in both animals and humans. One cannot draw a line between the animal and human worlds because they are inextricably linked.

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