As scientists across the world scramble to identify the source of the novel coronavirus, a new study points to stray dogs as possible intermediary hosts of Covid-19.The study was conducted by Professor Xuhua Xia, a full-time Professor of Biology at the University of Ottawa, Ontario, and has published two books on bioinformatics and molecular evolution. In an email interview with Outlook, Professor Xia spoke about the significance of his study and how it can help in finding a vaccine for the pandemic.
Here are the edited excerpts.
Q) How significant is this study in arriving at a cure or vaccine for SARS-CoV-2?
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There are two implications from my study which are relevant to vaccine development. First, SARS-CoV-2 is likely to depend on its reduced genomic CpG to evade ZAP-mediated host defense. Second, the remaining CpG in the genome are likely to be functionally important, given the benefit of reducing CpG. Thus, either increasing genomic CpG in SARS-CoV-2 or modifying the remaining CpG is likely to result in an attenuated virus, which may be used as a vaccine.
Q) Your study suggests that stray dogs may have acted as the possible intermediary hosts between bats and humans. How do you think the virus spread, consumption or animal bite?
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What you are referring to is called zoonotic transmission and little information is available on this subject so far.
Q) Is there a possibility of the virus changing its characteristic even in canines?
I did speculate on this based on the results from canine coronaviruses (belonging to a different genus, Alpha coronavirus, in viral taxonomy). In short, one clade of canine coronavirus (including one highly virulent strain) has much lower CpG than all other known alpha coronaviruses. One of these low-CpG strains, when cultured in cells, with minimal immune response, quickly regained CpG dinucleotides in the genome. This suggests that some selection pushes down CpG in canine coronavirus in their natural cellular environment. I believe that the selection is ZAP-mediated degradation against viral RNA genome.
Q) Does this also raise the necessity of culling stray dogs?
No. One should test rectal swabs of stray dogs for the presence of SARS-CoV-2 before taking measures against them. If we decide to exterminate stray dogs, we not only miss an opportunity of detecting various viruses in stray dogs, but also commit unjustified brutality against these animals.
Q) Are domesticated pets, which have been vaccinated, susceptible to the virus?
If they are vaccinated with a certain coronavirus vaccine, then there might be heterologous immunity against SARS-CoV-2. If the pets are vaccinated with vaccines totally unrelated to coronavirus, then they are most likely not protected against SARS-CoV-2.
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Q) Some researchers have suggested that the virus could become less deadly over time. Others have argued that it could mutate to become more lethal. What do you think?
In a crowded environment, where SARS-CoV-2 can easily transmit from person to person, then efficiently enter into the cell, develop rapid viral proliferation in the infected host tissue, and consequently, rapidly build-up virions that can go on to infect others, are the key contributors to viral fitness. In this case, being deadly does not reduce viral fitness. In contrast, when people practice self-isolation, a SARS-CoV-2 strain, that is immediately deadly, will effectively stop its own transmission and consequently reduces its fitness. In this context, viral fitness is increased by carriers not exhibiting obvious symptoms to facilitate its transmission. In other words, viral fitness is context-dependent, but being cautions with self-isolation typically discourages the origin of deadly viral strains.
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Q) What will be the impact of your study on the animal food chain?
My study is not really on animal food chain.
Q) There are news reports which state that snakes also act as intermediaries in spreading the virus?
These reports were not substantiated.
Q) Is there a need to change consumption patterns?
I can bet that over 90% of Chinese people have never tasted dog meat during their lifetime, and hardly anyone regularly eats dog meat.
Q) What’s your forecast for India?
Self-isolation has always been the most effective against viral outbreaks. As long as people are cautious, with strictly observed self-isolation, the viral outbreak will be under control.
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Q) Does this study also negate the theory that the virus is a human engineered one?
The study has no bearing on this issue.
Q) What’s the way forward from here?
More extensive monitoring of viral reservoir in nature, so we can act proactively against emerging viral pathogens.
