Well, Giardia is a protozoal infection and thus is a far more complicated creature. Let's say that the microbial universe is like a zoo. In terms of complexity, viruses are like slugs (not too much to them), bacteria are the equivalent of lizards or frogs, and protozoa are like elephants, antelopes, or hippos.
The way that this infection escapes your immune system is quite elegant.
This protozoa has a population that multiplies in your intestines by making copies of itself. Your immune system does recognize the little parasite and is able to kill off the majority. There is enough difference in the outer surface proteins of a couple of these critters that they escape detection. Once the majority of the prior population is killed off, the new population grows. Your immunity can't keep up as it never sees the same population twice.
This explains why the diarrhea occurs, then nearly resolves, then comes back, then resolves.
However, if you have been infected and then completely cured, then you are getting re-exposed. You have a source that keeps infecting you.
Do you drink water from streams? Do you have a contaminated well? Is your septic tank very close to your water lines?
Anyway, that's the story on Giardia.
· 1 decade ago