SARS-CoV-2 has been evolving for at least 7 years

By Dr. Liji Thomas, MD

The current COVID-19 pandemic demonstrates the vast unknown of virology, which continues to challenge the ability of humanity to remain healthy when faced with pathogens. While most known microbes have restricted affinity for specific species, continuing to adapt with the host species, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has crossed over from an unknown animal reservoir, like the preceding SARS and MERS coronaviruses, to infect human cells. Such viruses are typically more readily infective and cause more severe disease, as they have not yet adapted fully to the target host.

The burning question is how novel viruses acquire the ability to recognize, bind to and enter human cells for the first time – whether this is dependent only on viral proteins recognizing host cell proteins, or adaptations in other viral processes that allow replication in a human host.

This issue is discussed by researchers at the University of Calgary in a new study published on the preprint server bioRxiv* in June 2020. The spike protein is the most well known of the SARS-CoV-2 proteins, and its binding to ACE2 receptors on the host cell is responsible for viral entry into the target cell. The human ACE2 (hACE2) has some rare variants which make the host more vulnerable to infection. Similarly, the spike protein of this virus has a greater affinity for the receptor than the previous SARS virus, which is another possible explanation for the increased infective potential of the current virus.

The implications are that firstly, the binding affinity of the spike-RBD to hACE2 is not the primary driver of the highly infectious nature of the current virus since the ancestral virus was capable of doing this too. Secondly, the researchers suggest that this virus was, even then, able to bind tightly to the receptor. Therefore, this was not sufficient to produce the currently observed ability to spread rapidly and widely among humans. Instead, this must be due to another set of mutations in the viral genome.

Yet another implication is that the current virus may not have jumped to humans from an animal origin at all because its affinity for hACE2 was not a recently acquired molecular trait. This may mean that the ability to infect human cells was present over a more extended period in the past, but produced less obvious or fewer clinical symptoms which passed unnoticed. Another alternative was that it affected only a small number of people, allowing it to remain under the public health radar.

2. Brain Activity During Sleep. By Yolanda Smith.

Although it was historically believed that sleep was a passive but necessary process for healthy bodily functions, it is now known that brain activity continues during sleep. In fact, this brain activity is thought to play several important roles in the maintenance of physical, emotional and mental health.

Brainwaves in Sleep Stages. There are different stages of sleep, each of which is characterized by unique brain activity. Stage 1 sleep is the lightest stage of sleep that occurs as an individual is falling asleep. There is slow movement of the eyes and activity of the voluntary muscles in the body is reduced. The brainwaves in stage 1 sleep are smaller and more uniform than in the awake state, what are referred to as alpha and theta waves.

In stage 2 sleep, the movement of the eyes ceases and the brain waves become slower than in stage 1. There are also occasional bursts of waves that are more rapid, which are referred to as sleep spindles.

Stage 3 of sleep is characterized by slow, rhythmical brain waves called delta waves. This stage of sleep is very heavy with no movement of the eyes or voluntary muscles, and it is difficult to wake a person in this stage.

During REM sleep, an individual usually breathes more rapidly and there are quick movements of the eyes that characterize the state. In this stage, the brain activity is very similar to that of a person who is awake, suggesting that there are significant processes taking place in the central nervous system.

REM Brain Activity. It is believed that dreaming occurs for at least 2 hours each night during REM sleep and this activity plays an important role in the processing of information and creation of memory. During this stage of sleep, heart rate and blood pressure increase and the activity of the brain is markedly more dynamic. Sleep research with EEG monitoring has established that infants spend a greater proportion of sleep time (up to 50%) in comparison to adults, leading to the hypothesis that the brain activity helps in the development of the memory and learning.

The signals initiate at the base of the brain, in an area referred to as the pons, and then expand to the thalamus and cerebral cortex. The cerebral cortex is responsible for processes of learning, thinking and organizing information.

Sleep Stage Cycles. Over time, an individual progresses through the different stages of sleep and the activity of the brain changes accordingly. It begins with stage 1 for about 5-10 minutes, then stage 2 for about 10 minutes, then stage 3 for about 30 minutes, before reaching REM sleep more than an hour after first falling asleep.

Shortly after, the individual returns to stage 2 sleep, then stage 3 sleep and then REM sleep once again, repeating this cycle approximately five times before awakening.

It is unclear why this cycling through the stages of sleep and continual changes in the brain activity is required for the healthy function of humans and other mammals. Further research in this area is currently being undertaken to understand this area more comprehensively, particularly for the function of the brain activity.

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