Symbiosis and attenuation.
Parasitic protozoa and bacteria transmitted by vector insects and ticks resist destruction in the intermediate host, possibly through the possession of antigens similar to those of the host. There is no evidence that symbiotic microorganisms have evolved similar eclipsed antigens. Symbiotes are protected from destruction by the natural lytic agents in the host, because they remain for the most part inside special cells that have lost the ability to recognize the symbiotes as "nonself." Metallic ions may play an important role in attenuation through their effect on cell membranes and on the release of lytic agents. The symbiotes of insects are useful and interesting subjects for studying attenuation.
Animals↗