s0ssos

As another poster mentioned, you haven't made the leap to this actual causing illness. "Disease vector" is just a term for bacteria, viruses, etc. Almost all humans have immune systems. People usually don't die from ingesting some dirt (otherwise that would be classified as a weapon of mass destruction and bioterrorism. Though maybe in your book it already is. Someone running around throwing dirt at people!!!)

As to why it is a "leap": your logic is that transferred germs can make ill people, and thus transferred germs cause ill people. A can lead to B, and thus A causes B. Except we don't know whether B actually happens.
If you substitute A for carbon products, B for life, most people agree that carbon products can lead to life. But does just having carbon products cause life? Obviously not.