Trollpanosoma prawnzi

Trypanosoma cruzi is the parasite responsible for Chaga's disease.
Transmission is via the bite of the 'kissing bug' which defecates
ingesting a blood meal. The parasites are in the feces. Often, a
will scratch the site of the bite, expanding and deepening the initial
wound of the bite and so provide a pathway for the parasite
to enter the host. The bite is annoying and moderately painful.
disease is much worse.

A similar creature infects usenet. It also likes to take a bite on a
and defecates in the process. When scratched, an entire life cycle of
parasitic infection is induced, sapping the energy of the group and
undeniably reducing its viability.

Reflexive and thoughtless scratching at annoying pests has its

Refusing to scratch has a separate affect. It appears that the whole
blood sucking behavior of the vector for Trollpanosoma prawnzi is
induced by the infecting parasite that has consumed its brain. By not
scratching, one interrupts the parasites life-cycle. Robbed of a mode
reproduction the parasite dies out. The vector may be noticed to cast
about wildly, biting in a vane attempt to get a scratch. Desperate
will likely occur, including means of making the bites more painful
but if
robbed of the necessary scratch the cycle will not continue. The
dies, consumed by the parasite that induced its pathological behavior
and no new parasites are born.