Virus Infections - Is There a Defective Particle?

In the context of viral infections, it's a bit easier to at least schematize what defective means because you may package half your genome. There is almost no understanding for why bacteria would be able to successfully execute the virulence plans or unsuccessfully do so. We don't know why salmonella, which has the same problem as Legionella, why Eucinia, why Listeria, why these pathogens sometimes are able tosuccessfully execute their plans. The interesting thing for me is that our immune system, once a pattern recognition receptor is executed or activated, the downstream consequence is systemic.