Notes

We may not be absolutely certain about the origin of COVID-19, but, what we know for a fact is that most human disease-causing pathogens came from animals. And when I say most, I mean over 60% of them. This transference of a disease from an animal to human beings is called Zoonoses, and all such diseases collectively are called zoonotic diseases.

All recent epidemics have their origin in animals. For example, the extremely fatal ebolavirus, which had killed 11,323 people between 2014-2016 in west Africa, was transmitted either from bats or non-human primates. The Severe Acute Respiratory Syndrome or the SARS epidemic of 2002-03 was caused by civet cats, and the Middle Eastern Respiratory Syndrome or MERS came from camels. Even the roots of influenza or the common flu can be found in birds and pigs. And, HIV came from monkeys. The list goes on and on.

Yet zoonotic differ in the way they are transmitted. Dog owners are conscious that their pets need vaccination against rabies. Rabies is spread among humans through a bite of an infected dog. This is called direct transmission. Similarly, influenza which can be transmitted through air or SARS which may have been acquired by meat handlers directly from the animal are examples of direct transmission. Direct transmission is when a human acquires an animal disease straight from the infected animal.

In contrast, diseases can also be delivered to humans through an intermediary or a vector. Here the vector, like a mosquito, is just transporting the pathogen. But the mosquito does not get infected instead it transfers it to a human. The Zika fever is one such example, where mosquitos may have first introduced the virus to humans from monkeys. Or the African sleeping sickness, the microbe of which is transported by the Tse Tse fly from wild and domesticated animals to infect humans