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Can a pathogenic organism be totally resistant to the human immune system? For the purpose of this question, the organism in question must cause a disease.

Examples of organisms that would qualify as totally resistant:

Pathogenic organisms that are completely undetected by the immune system while the disease that they cause runs its course.

Pathogenic organisms that, even if detected, are completely invulnerable the immune system. For instance, macrophages and other immune cells would not be able to destroy even one cell of such an organism.

Is it possible for such a pathogen to exist? Are there any such pathogens? (For the purpose of this question, the HIV and diseases that only manifest in immuno-compromised individuals do not count)

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  • $\begingroup$ [1 of 2] One interesting organism that can evade the immune system (but not in the way you imagine) is Trypansoma brucei, the causative agent of sleeping sickness. T.brucei expresses a single protein on its coat, the VSG, which elicits a massive immune response. BUT the coat can switch to a new VSG with a totally different amino acid sequence (but with a virtually identical crystal structure), and if the immune response wipes out 99.999% of the VSG-1 organism, if even one cell with a different coat exists this will proliferate (and so on). $\endgroup$ – user1136 Jun 3 at 14:16
  • $\begingroup$ [2 of 2] Coat switching is though to be a stochastic event (by some!). An infection 'in the wild' with T.brucei will result in variants with many different VSGs being presented to the immune system, but because of 'coat switching' the infection if virtually impossible to wipe out by immune response. $\endgroup$ – user1136 Jun 3 at 14:18
  • $\begingroup$ The problem is much of the immune system is passive, that is it resists everything equally. $\endgroup$ – John Jul 3 at 13:46
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I can't think of any pathogenic organisms that are completely resistant to the immune system. Some bacteria that cause chronic diseases (e.g. tuberculosis) are relatively resistant, and a handful of viruses (e.g. spumaviruses) are relatively invisible, but the nature of pathogen transmission would mean that completely resistant organisms would spread through a population pretty fast and we'd know about it.

Pathogenic prion agents, like scrapie and Creutzfeld-Jacob disease, are essentially invisible to the immune system, and can be transmitted; but they aren't pathogenic organisms. They might be the closest to your description though.

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