Coronaviruses are a large family of viruses that are known to infect animals and humans. They are largely categorised into four genera — alpha, beta, gamma and delta. Broadly speaking, alpha and beta coronaviruses commonly infect mammals such as bats and humans, while Gamma and Delta mainly infect birds. While animals, including bats, are generally considered as the reservoirs of coronaviruses, rarely spillover events could occur. It is possible for viruses that infect animals to jump to humans, a process which is known as zoonotic spillover. Many major infectious diseases, including COVID-19, is widely thought to be a result of spillover.
A number of human coronaviruses have been identified previously, including OC43, HKU1, 229E, and NL63 which cause mild and seasonal infections in humans and SARS-CoV and MERS-CoV which cause severe disease. SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic, belongs to the genus of beta coronavirus and is in fact the 7th type of coronavirus known to infect and cause severe disease in humans.
Also read: NeoCoV coronavirus found in bats may pose threat to humans in future, scientists caution
Identified in 2012, the Middle East respiratory syndrome coronavirus (MERS-CoV) was transferred to humans through infected dromedary camels through zoonosis. Since its identification, MERS-CoV has infected over 2000 people, specifically in several countries in the Middle East, Africa and South Asia. The case fatality rate for MERS is estimated by WHO to be 35%, but the number may be overestimated since disease surveillance systems could have missed milder cases of MERS-CoV.
How a coronavirus latches onto special receptors on host cells depends on a key part of the virus known as its receptor-binding domain. The differences in the receptor-binding domain of coronaviruses are therefore what determine the type of host receptor the virus will use and thus the host that it will be able to infect. There are currently 4 well-characterised receptors for coronaviruses, including ACE2, which is used by SARS-CoV and SARS-CoV-2, and DPP4 used by MERS-CoV.
In a recent preprint, researchers in China explore how coronaviruses that are similar to MERS-CoV interact with different receptors in different host cells. The not yet peer-reviewed work has been deposited in biorxiv, which describes the NeoCoV coronavirus.
What is NeoCoV?
NeoCoV is a bat coronavirus that was first identified in 2011. It was identified in a species of bats known as Neoromicia, which is where the name NeoCoV was derived from. Commonly known as aloe bats, this species is distributed in the Afro-Malagasy region. NeoCoV shares an 85% similarity to MERS-CoV in the genome sequence, making it the closest known relative of MERS-CoV.
Does NeoCoV infect humans and cause high mortality?
It is important to note that inherently, NeoCoV cannot interact with human receptors, implying that in its current form the virus cannot infect humans. NeoCoV does not infect humans yet and has thus not caused any deaths.
What does the preprint say, and why is it important?
The study reports that despite their similarity, MERS-CoV and NeoCoV use different receptors to infect cells. The bat coronavirus NeoCoV was found to use bat ACE2 receptors for efficiently entering cells and the interaction between NeoCoV and bat ACE2 receptors is different from what is seen in other coronaviruses that utilise ACE2. The preprint also reports that although NeoCoV does not have the potential to use human ACE2 receptors and infect humans, specific mutations artificially created in the receptor-binding domain of NeoCoV can enhance its efficiency to interact with human ACE2 receptors. These mutations have not yet been seen in NeoCov isolates from natural settings.
SARS-CoV-2 is not the first coronavirus to infect humans and cause large disease outbreaks, nor is it likely to be the last. The study highlights that through further adaptation, coronaviruses like NeoCoV or other related viruses could potentially gain the ability to infect humans. The interactions between humans and animals continue to increase, given the expanding human population and encroachment of animal habitats. While the likelihood of spillover events are rare, an increased interaction can potentially accelerate such events. To prevent future outbreaks, it will thus be important to monitor this family of viruses for potential zoonosis while continuing research efforts on understanding the complex receptor usage of different coronaviruses. Genomic surveillance of human and animal viruses is therefore the key to understanding the spectrum of viruses, and possibly provide early warning to potential spillover events.
(The authors are researchers at the CSIR Institute of Genomics and Integrative Biology in Delhi. Opinions are personal.)