In the midst of the coronavirus pandemic with all the new rules and regulations it is easy to overlook why it started. We just pray that we will remain safe and that everything will return to ‘normal’ when it is over. When there is a vaccine against Covid-19 and we can go back to touching, hugging and kissing strangers we will, if we survive, look back on the disaster and it will become just another part of modern history. Where were you during the coronavirus outbreak? What was it like for you? we will ask.

But let’s recall once again that we are animals and that the constrictions on the behaviour of other mammals also apply to us. Viruses, like other parasitic organisms need certain conditions to survive and to multiply. If Virus A normally infects an individual animal of a certain species, it needs to infect another individual of the same species to be able to multiply before that animal’s immune system gets it under control. And to make the jump to a new ‘host’ there has to be another uninfected animal of the same species and close contact between them.

A second consideration is that viruses evolve, like all life forms. Sometimes by chance, they may change enough to be able to infect a different species of host. It seems likely that Covid-19, a virus that normally infects bats, changed so that it became also able to infect humans. This is not the first time that bat viruses have ‘jumped’ to humans or that we have become susceptible to the diseases affecting other animals.

The critical issue here, and in all epidemics, is closeness of contact between the hosts. And in our case, closeness with other humans and with the animal species we exploit. We live in densely populated cities: we interact daily with many other humans; we confine large populations of farm animals together; we are in close contact with pets and some wildlife species. Pandemics caused by new viruses are inevitable and unavoidable. And, of course, if you wish to greatly increase the chance of being infected with a new virus, take a trip on a cruise ship, calling at many ports around the world, thereby sampling all the local infectious agents, and be confined with a couple of thousand others while eating and socialising in close proximity!