ecology and medical research

Nature gives clues about where to find medicines. For example, one would expect the rainforest to have both natural pesticides as well as defenses against those pesticides. The many species of cordyceps fungi are natural laboratories for pesticides, as well as other useful chemicals. 

When we look at what a tree uses to defend itself from insects, bacteria, or fungi, that points the way to chemicals that could defend people and domesticated plants and animals.

Insects and rodents are useful for research because they can be bred cheaply and quickly in captivity, but still more useful would be to understand the mechanisms by which they resist the pathogens found in their natural environments. 

To put it another way, many infectious diseases only affect humans, because those germs and parasites are adapted to circumvent our immune systems. I have never heard of a case of tuberculosis among pigs or HIV/AIDS in chickens. Large wild animals appear healthier still. Whales that survive to adulthood rarely die of infections. Elephants don't get polio. 

Defeating a disease means augmenting the human immune system, as was done with vaccines and antibiotics. The way to forward is to carefully study the immune systems of many kinds of living things. 

Bats and other flying animals have high metabolisms. This gives them an edge against viruses but often leaves them vulnerable to fungi. Why is that? What might a study of a hummingbird's immune system reveal about cancer?

These questions perplex me, and I do what I can to answer them with what I can find online.