Zoologists have known for decades that some of the most virulent viral infections are animal in origin.

Here, the simian immunodeficiency virus successfully transitioned to humans - through contact with animal blood or meat - to become the human immunodeficiency virus or HIV, causing AIDS.

Since the first record of HIV-1 in humans, this virus has mutated several times.

Very little is known about the coronavirus - SARS-CoV-2 - that causes COVID-19, even though it isn't the first time that a member of the coronavirus family has jumped from its natural animal host to humans.

This is important because to fully understand the properties of the virus, we need to know the animal host (so called patient zero).