Corona viral disease (Covid-19) is caused by the severe acute respiratory syndrome coronavirus-2 (Sars-CoV-2) from the coronavirus family. This virus family consists of over 200 different viruses that can infect mammals, birds and even fish.

In general, infections with these viruses are mild and even asymptomatic, with most people not even seeking medical care. In humans it is mostly a respiratory disease, affecting the upper respiratory tract (sinuses, nose, and throat) or lower respiratory tract (windpipe and lungs).

This is in contrast with infections in animals that are mostly gastrointestinal. Coronaviruses spread most efficiently by droplet transmission when a sick person coughs or sneezes and droplets containing the virus can spray as far as six feet.

If you breathe them in or swallow them, the virus can get into your body. You can also get the virus from touching a surface or object that the live virus is on and then touching your mouth, nose, or eyes. Coronaviruses can live for several hours on a surface they land on. This is why social distancing and hand washing helps prevent infection.

The first known human coronaviruses were HCoV-OC43 and HCoV-229E that cause common colds every year worldwide. Except in high-risk groups such as the elderly and infants, infections are mild with infected people probably unaware it is a coronavirus infection. Until the severe acute respiratory syndrome (Sars) outbreak in 2002 and Middle East respiratory syndrome (Mers) outbreak 10 years later, coronaviruses were not considered important disease-causing organisms.

However, these two viruses were both new in the human population, originating from animals, with a 10% and 30% mortality rate respectively. Sars-CoV originated in China and spread to four continents infecting 8,096 individuals and claiming 774 victims before it was contained and has since vanished.

Mers infections is still continuing in the Middle East. Other coronaviruses have also spilt over from animals but with less severe outcomes including OC43, a transmission from cattle to humans, and 229E, a potential spillover from bats. Two new human respiratory coronaviruses, HCoV-HKU1 and HCoV-NL63 have also been identified in the past decade with no proven animal link.

The most devastating coronavirus is by far the current global Covid-19 outbreak with infections ranging from asymptomatic, mild to serious and a mortality rate of around 3%. The effective viral transmission rate and high percentage of mild and potentially asymptomatic cases, make control of the outbreak extremely difficult.

As Sars-CoV-2 infects new people, it will change (mutate) and this is normal, especially in viruses that have RNA as genetic material. These changes are, however, so small and there is no evidence it is changing into a more "aggressive" virus.

Several changes need to happen to cause more severe disease and the probability for this is very low, especially in a short time period. Covid-19 causes a low mortality with the majority of people recovering.

Studies have shown that in recovered patients a protective immunity does develop but it is not sure how long it will last and it is also very variable between individuals. We simply don't know yet if you will be protected against reinfection of Covid-19 and the same recommendations to prevent infection apply for recovered patients.

*Markotter is a director in the Centre for Viral Zoonoses in the Faculty of Health Sciences, University of Pretoria