Ebola and Its Travels Among Species

I read a very interesting article in the NYT which touched on the biology of Ebola. Something they said really got me thinking about viruses in general and their raison d'etre. Ebola, it seems, lives a peaceful life in the Fruit Bat; reproducing at such a rate that the bat is unaffected. As we know, when Ebola crosses species, all hell breaks loose. Why is this? Why cause havoc in one species but yet co-exist in another?

To make sense of this, I thought of the first predator. There was one, you know--there had to be a first. Now, whether this "predator" first feasted on other living things or first feasted on inorganic matter--still making it a predator of sorts--and then went on to prey on plants is something we may never know. But what we do know, instinctively, is that life blossomed on this planet as a result of the invention of photosynthesis, and, afterwards, the "first" predator had ample food available.* Fortunately, for us anyway, evolution does not sit still, the predator found itself being attacked by another predator.

Before we go on, we must bring out the violins and feel sorry for predator vis-a-vis the self-sufficient plant. Putting food on the table is the top concern of any organism. The plant has to find a way to get sunshine, water, and air but, for the plant, that's not that hard to do. The plant, of course, has to contend with the predator but not having to worry about food that much, it can utilize its genome to come up with defenses in the form of tough fiber, pointed fiber, and a vast assortment of poisons. But, as with everything, there is a fine line and the plant came to its senses and realized that it could employ the animal to disperse its seeds and provide fertilizer. What wonderful efficiency and frugality. The plant has chosen to give up making its own fertilizer (a few still do) and utilize the freely available animal dung. Can you say win-win?

There is wonderful cooperation between plants and their main predator, the herbivore. Unfortunately for those two bosom buddies (fortunately for us), there soon developed the kind of predator which forms the main focus of this post: the predator of the predator of which we are top banana or so we like to think. Now, the plant has poisons but what does the first predator (the herbivore) have? I submit for your consideration that it has infectious agents just like the Fruit Bat has Ebola. If a second or higher tier predator eats a Fruit Bat, it risks getting a serious infection if it has not developed immunity. I once developed the theory that viruses were a means of population control** but what I now have to add is that it is a means of population control of the 2nd or higher tier predator in order to protect the first tier predator. The first tier predator does not want to be wiped out but what defenses does it have? It is, after all, the staple for a higher-tier predator.

It is pure speculation on my part but I believe that these infectious agents surface as a result of first tier predators succumbing to stresses imposed by higher-tier predators. The zebra that relaxes after a lion has eaten one of its own can no longer do so because lions have overpopulated (a lion somewhere has found the means of outrunning the zebra, for instance) and are a constant non-stop day after day stressor.*** As a result of this stress, the zebra's immunity gets impaired and the zebra is more likely to become host to a virus. The zebra, of course, has to be lucky enough to not be so adversely affected by the virus that it dies from the infection. But the Fruit Bat did it and so, why not the zebra or any other vertebrate whose immune system is disabled from stress.**** Once our hypothetical zebra regains tranquility as a result of fewer lions, its immune system picks up and  mounts a great defense against future viral invasion. Is the Fruit Bat under stress? I don't know but wherever man goes, there goes another species' habitat.

The take-away (you can thank me later, PETA) is that we need to become or stay a first tier predator--we need to go vegan (I'm almost there but can't seem to go 100%, and, as such, I live in fear of Mad Cow, liver flukes, trichinosis, bird flu, etc. but not Ebola as I do not eat Fruit Bats or monkeys that eat Fruit Bats. The other take-away is that nothing in biology is as simple as we would like it to be but, nevertheless, there is much food for thought therein.


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*This freed the organism to plop down nearly anywhere and make itself a home. It was no longer constrained to hot vents on the ocean floor. Previously, it may have enjoyed frolicking in a hot ocean but its inorganic energy source was not readily replenished and, luckily, it found a way to harness the Sun.

**This seems obvious because epidemics surface and are at their worst when population densities increase.

***You'd be very hard-pressed indeed to find an organism that cannot be infected by viruses and that includes plants. However, I do not see how a plant population would eliminate--through viruses--another organism that was encroaching on its "territory" or harming it in some way. For one thing, plant viruses stay within their kingdom. Indeed the vectors that they often need to disseminate a virus usually only infect members of the same species. Viruses vis-a-vis the plant kingdom seem to be just plain old parasites. Let's also remember that plants do not want to harm the main source of their fertilizer. What about a plant encroaching on the territory of some other plant species? Would the one plant get stressed and by then succumbing to a virus cause an invading plant to also get the infection? First, I don't think there is much cross-species contamination and second, would an insect (the primary vector of most plant viruses) find a stressed out plant appetizing?

**** (I'm assuming that the Fruit Bat was stressed out from monkeys trying to eat them--otherwise, it's all just happenstance that Ebola works that way. That is, harms monkeys and humans but not Fruit Bats)