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Please forgive the obviously silly appearance of this question, and/or of the tenor which may come across as flippant or dismissive of real world suffering. My intention is none of the above.

As a layperson, I have always understood that the expression of our various colds/flus etc, while frequently mis-understood as being caused by the virus, are actually just manifestations of our own immunity fighting same. In other words, all the snot, and fever and inflammation are not caused *by the virus, they are a reaction *to the virus, as we fight it off.

My question then is why do people with AIDS (or similar immunity destroying affliction) appear sick? If they have weak or non-existent immune systems, following the above logic, would one expect to see them passing away while looking entirely healthy?

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  • $\begingroup$ Let me see if I understand you correctly. You are asking why people suffering from AIDS show symptoms of being sick, when the body doesn't formulate any response to the virus? $\endgroup$
    – Gabriel Fair
    Commented Apr 3, 2012 at 3:45
  • $\begingroup$ @Gabriel Fair, yes, that's my question. What brings on the "sick", given that what we experience as illness (the simptoms) is entirely the effect of our auto-immune response, and not the virus' effects, themselves. $\endgroup$
    – Yevgeny Simkin
    Commented Apr 3, 2012 at 7:09
  • $\begingroup$ This is arguing semantics. Viruses cause flu symptoms. That they cause them indirectly by way of several body reactions, some of them from the immune system, is just a way of viewing this. All actions and reactions in our body are mediated in some way or other. This doesn’t make them less real or causal. $\endgroup$
    – Konrad Rudolph
    Commented Apr 3, 2012 at 10:24
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    $\begingroup$ @Kondrad, I beg to differ. If a person gets shot, it is not semantical to investigate what actually killed them. "The bullet" is a useless answer, though clearly semantically correct; Did they bleed to death? Did some specific organ get destroyed? etc. It is *more useful to say that a person died of blood loss, following a bullet wound. So, similarly, to say "the virus is causing the sickness" is meaningless. The virus is provoking a reaction, but the mucous is being created by the immune response. My question is what symptoms do patients exhibit who have no immune response. $\endgroup$
    – Yevgeny Simkin
    Commented Apr 3, 2012 at 19:39

2 Answers 2

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Many of the symptoms of disease are indeed related to inflammation, but inflammation depends heavily (though not solely) on the innate immune response. Patients with AIDS and some of the other immunodeficiencies lose their adaptive immune response, not their innate response. Therefore they are capable of mounting an inflammatory response that is not effective in clearing pathogens (because it doesn't have help from the adaptive immune system) but can still cause symptoms.

More importantly, many symptoms of disease are not caused by the inflammatory response, but are related to organ and tissue damage caused by the infection. A patient with pneumonia may have a reduced inflammatory response but will still have difficulty breathing and signs of reduced oxygen supply simply because the lung tissue has been damaged by the pathogen.

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  • $\begingroup$ that's a much better answer than the one that had originally been given the green check mark... I'm switching to yours. $\endgroup$
    – Yevgeny Simkin
    Commented Jan 11, 2016 at 17:18
  • $\begingroup$ @iayork good answer. But i think a citation or two would be appropriate and appreciated. $\endgroup$
    – theforestecologist ♦
    Commented Feb 5, 2016 at 7:12
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They appear sick because they are sick, but with other, opportunistic infections. The "immune deficiency" part of AIDS means that the immune system is not functioning normally and, thus, is unable to protect them. Typical illnesses that are more found more frequently in AIDS patients are pneumocystis pneumonia and Kaposi's sarcoma.

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    $\begingroup$ I'm sorry, but that's not really an answer. You don't appear sick because you are sick, you appear sick because as a response to the presence of a virus, the body starts to do all sorts of things which manifest themselves as symptoms. You develop a fever, you produce mucous, you cough, etc. But people afflicted with immune deficiency wouldn't have such a response, right? That's the nature of their illness. So, what symptoms do patients suffering from such illness exhibit? And why? $\endgroup$
    – Yevgeny Simkin
    Commented Apr 3, 2012 at 7:13
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    $\begingroup$ @Dr.Dredel: Kaposi's Sarcoma gives cutaneous lesions, Pneumocystis Pneumonia gives fever, tachypnea, and respiratory distress in immunodeficient people. $\endgroup$
    – nico
    Commented Apr 3, 2012 at 8:02
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    $\begingroup$ @nico, So, are you saying that these illnesses have their own (non immune related) symptoms that the patient experiences, and that all the while they are *not coughing and sneezing and all the other stuff we get when we are fighting off a cold? $\endgroup$
    – Yevgeny Simkin
    Commented Apr 3, 2012 at 19:42
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    $\begingroup$ @Dr.Dredel: Kaposi's sarcoma is a type of cancer, one can get it even without having an HIV infection. What you may be missing is that AIDS patients have a compromised immune system, but they still have an immune system. $\endgroup$
    – nico
    Commented Apr 4, 2012 at 7:11

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