The Brain Louse
The brain louse, Resistae cerebrali, unlike it's name suggests, is neither a louse, nor does it live exclusively in the brain. In fact, brain lice can be found along the entirety of the human nervous system, and possibly also in those of other animals.
The brain louse is, so far, the only member of the Resistae genus, a new branch of green algae with surprising characteristics, whose origin and evolution are as of yet poorly understood. The main difference between Resistae and other species of algae, or chlorophyllic lifeforms in general, is the way they get energy. Usually green algae, or plant cells, use the energy of the sunlight to power their cells, converting the electromagnetic waves that make up light into sugar, which can then be used by the rest of the organism. However, Resistae have a different, although similar, mechanism.
The cells of brain lice, instead of having photoreceptors, have electroreceptors which allow them to transform electrical surges into usable energy, and, subsequently, sugar. Which is why they have, so far, been found only on human nerve cells. They attach themselves to the “outer coating” (Schwann cells or similar) of neurons, and get energy off of the electric impulses from neural transmissions, while using nearby cells as construction materials. Of course, this is not without consequence for the infected host.
Although brain lice reproduce rather slowly (in comparison to most unicellular organisms), they can cover the whole nervous system in less than a year after the initial infection. If their host survives that long. The presence of brain lice can greatly reduce effectiveness of neural transmission, leading to loss of muscle control, and, when present in the cranium, brain function. If left untreated, the nervous system will ultimately be broken up, and the host will die.
Brain lice propagate mainly through sneezing, as well as sexual intercourse, but any close contact to important nerve centers (such as the genitalia, or buccal organs) can lead to contamination.
Although only discovered recently, it is believed that there are probably hundreds, if not thousands more species of Resistae, and OECD countries have recently founded the Insitute for the Research of Electric Parasites (IREP), who will focus mainly on the question of wheter or not Resistae species exist that use the electricity in modern tools or power plants, and what impact they have.
Your brain, it seems, will have to fend for itself for a little longer.