From drinking hot water to eating garlic, “cures” for Covid-19 abound on the Internet.

Like the two mentioned, most of these health tips are just myths. It will take more than just hot water to kill the virus in an infected person.

This is because the virus in an infected person triggers a cascade of molecular activity, which eventually results in the respiratory symptoms experienced by Covid-19 patients.

The Straits Times speaks to medical experts to understand the science behind a viral invasion.

HOW A VIRUS INFECTS A CELL

Outside a living host, viruses are not able to replicate and spread.

In fact, many scientists would not even consider a virus outside a host as being alive.

But a virus sheds its innocuous nature once it enters a living host, such as an animal or a human.

In the body, the virus is a parasite. It begins its invasion by first hijacking a healthy cell.

Professor Subhash Vasudevan from the Emerging Infectious Diseases Programme at Duke-NUS Medical School explained: “On its surface, the virus has proteins coated with sugars that can latch on to receptors on the host cell.”

This is similar to how a key (the virus) fits into a lock (the receptor on the human cell).

While research is ongoing to understand how the genome of Sars-CoV-2 determines the way the virus affects humans, scientists have already discovered some important proteins made by this viral recipe. For example, a non-structural protein which slows down the infected cell’s production of its own proteins has been identified, The New York Times reported earlier this month.

Under a microscope, the virus that causes Covid-19 appears spherical. In the centre is its genome – comprising a single-strand genetic material called RNA – which is surrounded by an oily membrane that has a “crown” of sugar-coated spike proteins protruding from it.

When the spikes latch on to a healthy human cell, the virus gets internalised by normal cellular processes and injects its RNA into its new host cell.

Genetic material such as RNA contains a set of instructions that is often decoded by protein-making “factories” in the cell.

A healthy human host cell, for example, would take its cue from its own genetic material. But when the virus latches on to a human cell, the viral RNA “hacks” the system.

This hijacking causes the cellular machinery of the host to produce more viral genetic material in addition to the molecules that cells usually produce to keep the organism healthy and alive.

Microbiologist Ong Siew Hwa, director and chief scientist at home-grown biotech company Acumen Research Laboratories, said: “The viral genetic material will further ‘hack’ the human cell to produce the full set of viral proteins which are assembled into new infectious viral particles – this is how the virus replicates.”

This process of the human cell decoding the “instructions” from the viral RNA is known as translation, said Prof Vasudevan.

He added: “The viral genes in its genome are translated in the human cell, where more viral proteins are formed and these proteins drive the replication of the viral genome to make more viral particles.”

Examples of viral proteins include structural proteins, which make up the viral membrane and spikes, for instance; or non-structural proteins, which can manipulate cellular activity.

For example, certain non-structural proteins can camouflage the presence of the virus so it passes undetected by the body’s immune system, while others help to multiply the virus in the human cell using the resources of its host.

RECEIVING INSTRUCTIONS

The RNA genome of Sars-CoV-2 – the virus which causes Covid-19 – is made up of an “alphabet” of molecules known as nucleotides.

It has four different nucleotide bases that function as the basic building blocks – adenine (a), cytosine (c), guanine (g) and uracil (u).

Said Prof Vasudevan: “These four bases are universal, found in the RNA of micro-organisms and man.”

But the way in which these four nucleotide bases are arranged is unique to the specific virus, similar to how human fingerprints can help to differentiate one person from another.

The genome of the virus causing Covid-19 has about 30,000 “letters” in all. In comparison, the human genome is about three billion “letters” long.

But, other than serving as an identifier for the virus, the unique arrangement of nucleotides along the genome is important for another reason: genes.

In humans, genes determine how we look and how we behave, as genes direct the type of protein – an important building block of cells, tissue and organs – being produced.

This is also the same for viruses.

Genes refer to a specific sequence of nucleotides, so essentially, the genome is made up of a code for many different genes.

But not all genes are activated at the same time. Some genes are activated only when they receive “signals”, such as when they come into contact with another cell.

While research is ongoing to understand how the genome of Sars-CoV-2 determines the way the virus affects humans, scientists have already discovered some important proteins made by this viral recipe.

For example, a non-structural protein which slows down the infected cell’s production of its own proteins has been identified, The New York Times reported earlier this month.

“This sabotage forces the cell to make more virus proteins and prevents it from assembling antiviral proteins that could stop the virus,” said the report.

Research has also shown that an overactive immune system could be the cause of respiratory distress.

If the immune system kicks into overdrive, for instance, it could stimulate the overproduction of proteins called cytokines, which can cause inflammation in the lungs.

Cytokines are molecular messengers of the immune system. For Covid-19 patients, this cytokine storm can lead to symptoms such as breathlessness or respiratory distress.

Prof Vasudevan said scientists from all over the world have, over the years, built up a database of what genes can translate into various proteins.

“It is a little like checking the meaning of a word in the dictionary,” he said.

“You search for a certain gene, and the database would return with the answers on what are the possible proteins that can be translated.”

Having a better idea of what various genes can do could help in the development of therapeutics, said Prof Vasudevan.

For instance, identifying the gene responsible for the production of the enzyme that can produce more copies of the viral genome would allow medication to be developed to stop the spread of the virus in the host body, he said.

But more studies need to be done to get highly specific drugs that will make their way to the cells that are affected, he said.

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