In December 2019, the Chinese authorities notified the world that a virus was spreading through their communities. In the following months it spread to other countries with cases doubling within days. It has triggered lockdowns in dozens of nations, and the disease continues to spread. This disease is called COVID-19 (most commonly known as coronavirus). COVID-19 is caused by SARS-COV-2 or “severely acute respiratory syndrome coronavirus 2” (because it’s genetically similar to the SARS CORONAVIRUS which was responsible for the SARS outbreak in 2002).
The whole family of coronaviruses are named like that because corona means crown and this refers to the way that the virus looks under the microscope (crown like spikes on its surface). There are many kinds of coronaviruses. Those that circulate among humans are typically benign and they cause about a quarter of all common cold illnesses. But there are others that are zoonotic viral diseases, which means they are passed from animals to humans. Although COVID-19 is thought to have originated in bats, this doesn't necessarily mean it was directly passed from bats to humans. The distinct ecological differences between bats and humans means it is likely that the novel coronavirus needed to pass through another mammal and further mutate, so that it could be transmitted to humans.
What happens in the body when it contracts the coronavirus?
The coronavirus must infect living cells in order to reproduce. Inside the virus, genetic material contains the information to make more copies of itself. A protein cell provides a hard protective enclosure for the genetic material as the virus travels between the people it infects. An outer envelope allows the virus to infect cells by merging with the outer membrane of the cell. Projecting from the envelope are spikes of protein molecules. Both a typical influenza virus and the new coronavirus use their spikes like a key to get inside a cell in the body, where they take over the internal machinery of the cell, repurposing it to build the components of new viruses. When an infected person talks, sneezes or coughs droplets carrying the virus may land in another person’s mouth or nose and then move into the lungs. Once inside the body the virus comes in contact with cells in the throat, nose or lungs. One spike on the virus inserts into a receptor molecule on the healthy cell membrane. This action allows the virus to get inside the cell. A typical flu virus would travel to the cell’s nucleus (that houses all its genetic material) inside a sac that is made from cell membrane. The corona virus on the other hand doesn’t need to enter the host cell nucleus. It can directly access parts of the host cell called ribosomes. These use genetic information from the virus to make viral proteins such as the spikes on the virus’s surface. A packaging structure in the cell then carries the spikes in vesicles which merge with the outer layer of the cell. All the parts needed to create a new virus gather just beneath the cell membrane. Then a new virus is released through the cell membrane.
What is the mode of transmission for COVID-19?
As it was previously said, while animals are believed to be the original source, the virus can now spread from person to person. There is not enough epidemiological information right now to help determine how easily this virus spreads between people, but it is currently estimated that, on average, one infected person will infect between two and three other people.
It seems to be transmitted mainly via small respiratory droplets through sneezing, coughing, or when people interact with each other for some time in close proximity (less than one meter). These droplets can then be inhaled, or they can land on surfaces that others may come into contact with, who can then get infected when they touch their nose, mouth or eyes. The virus can survive on different surfaces from several hours (copper, cardboard) up to a few days (plastic and stainless steel). However, the amount of viable virus declines over time and may not always be present in sufficient numbers to cause an infection.
The incubation period for COVID-19 (which is the time between exposure to the virus and onset of symptoms) is currently estimated to be between one and 14 days.
It is known that the virus can be transmitted when people who are infected show symptoms such as coughing. But, there is also some evidence suggesting that transmission can occur from a person that is infected even two days before showing symptoms. However there are still uncertainties about the effect of transmission by people who are non-symptomatic.
When is a person infectious?
The infectious period may begin as early as one to two days before symptoms appear, but people are mostly infectious during the symptomatic period, even if symptoms are very mild. The infectious period is estimated to last for 7-12 days in moderate cases and up to two weeks in severe cases.
What are the symptoms?
Symptoms vary in severity from having no symptoms at all (asymptomatic) to having fever, cough, sore throat, general weakness, fatigue and muscular pain and in the most severe cases, severe pneumonia, acute respiratory distress syndrome, sepsis and septic shock, all potentially leading to death. Reports show that clinical deterioration can occur rapidly, often during the second week of disease.
How can you develop pneumonia symptoms?
The airways in the human body catch most germs in the mucus that lines the trachea, bronchi and bronchioles. In a healthy body, hair-like cilia lining the tubes constantly push the mucus and germs out of the airways where they might be expelled by coughing. Normally cells of the immune system attack viruses and germs that make it past the mucus and cilia and enter the alveoli. However if the immune system is weakened like in the case of coronavirus infection, the virus can overwhelm the immune cells and the bronchioles and alveoli become inflamed as the immune system attacks multiplying viruses. The inflammation can cause the alveoli to fill with fluid making it difficult for the body to get the oxygen it needs. A person could develop lobar pneumonia or bronchopneumonia. These can cause difficulty breathing, chest pain, coughing, fever and chills, headache, muscle pain and fatigue.
Are some people more at risk of getting infected than others?
The answer is yes. Elderly people above 70 years of age and those with underlying health conditions (such as hypertension, diabetes, cardiovascular disease, chronic respiratory disease and cancer) are considered to be more at risk of developing severe symptoms. Men in these groups also appear to be at a slightly higher risk than females.
Are children also at risk?
Children actually make up a very small proportion of reported COVID-19 cases. They appear as likely to be infected as adults, but they have a much lower risk of developing symptoms or severe disease.
Diagnosis and treatment
To confirm the diagnosis a reverse transcription polymerase chain reaction or RT-PCR test can be done. This can detect very small amounts of viral RNA. However early in the disease the RT-PCR can often miss the infection altogether. If severe pulmonary disease is suspected a chest CT can be done to help detect the presence of a viral pneumonia. There are also newer rapid testing methods for COVID-19 which can get the results within minutes. One of these is Isothermal Amplification which also checks for viral RNA. The other is Rapid Serological testing which checks for the antibodies created by the immune system to fight the virus. Since it is checking for the antibodies made by the body it can detect previous infections even after the virus is gone.
There is no specific treatment for this disease yet. If the infection is mild individuals should isolate themselves at home so they improve with plenty of rest and fluids. In more severe cases, healthcare providers mostly try to treat the symptoms rather than target the virus, and provide supportive care (oxygen therapy and fluid management) for infected people. There is some early data showing that Remdesivir, an antiviral drug previously used against ebola may be helpful. Other medications that have been used include a combination of Lopinavir and Ritonavir both of which are antiretroviral drugs.
As this is a new virus, no vaccine is currently available either. Although work on it has already started by several research groups and pharmaceutical companies worldwide, it may take from months to more than a year before a vaccine has been tested and is ready for use in humans.
How to avoid getting infected?
The virus enters the body through the eyes, nose and/or mouth, so it is important to avoid touching the face with unwashed hands.
Washing of hands with soap and water for at least 20 seconds, or cleaning hands thoroughly with alcohol-based solutions, gels or tissues is recommended in all settings. It is also recommended to stay at least one meter away from people infected with COVID-19 who are showing symptoms, to reduce the risk of getting infected through respiratory droplets.
So, for individuals the best strategy is prevention.