Spiroplasmas, are present in the hemolymph of almost all insects; there probably are several million strains. They can also cause diseases in plants but are usually associated with a vector. For example, a leaf hopper carries a spiroplasma that infects orange trees.

A common phenomenon among the mycoplasmas is that the organisms bind host proteins that often are of identical molecular weight to their surface proteins and, therefore, are looked at by the immune system as being the same as the host. The spiralin protein on the surface of spiroplasmas shows a migration pattern on gel electrophoresis with a molecular weight of 27,000 Da to 30,000 Da, similar to that of the prion protein. This biochemical similarity is compatible with spiroplasma etiology.