Zoonotic infectious diseases — ailments that jump from one species to another — have plagued human beings for a long time. Bubonic plague, smallpox, tuberculosis and rabies are all examples of diseases that started in other animals, and then made the leap to infect human beings. For much of human history, low population densities and little direct contact with other animals kept such diseases in check. Starting in the 18th century, humans began concocting vaccines to train human immune systems to attack viral and microbial agents. But as human and domestic animal populations have continued to expand, aand wildlife populations come into more frequent contact with humans, more and more microbial parasites have evolved the ability to exploit human hosts. Conservation biologist George Wittemyer spends most of his time working with animals at the other end of the size scale from microbes. He specializes in African elephants. But he is certainly no stranger to the international wildlife trade, which he thinks contributes to outbreaks like the current COVID-19 pandemic. Wittemeyer joined Monday Buzz host Brian Standing on April , 2020.