Strange as it may sound, while at university, I spent a great deal of my spare time in the library researching parasites. This is partly because my friend had returned from India with a couple of nasty intestinal bugs and they pretty much defined his life for the next couple of years.
I recall that there is a parasite – a small worm - bearing an unpronounceable Latin name, that migrates from the gut to the brain of a human host. This journey takes about a year. Having reached the brain, the worm lays its eggs.
Anything that can colonise the brain is likely to cause physical damage that could upset the personality, although the type of changes would depend on which parts of the brain were infected.
That worm was a tropical parasite and so it is unlikely that it would have infected an entire English village. The most likely candidate for causing mass personality change in the UK would be Toxoplasma gondii. By the way, you may not want to read this if you are a cat lover.
Toxoplasma gondii is endemic in cats and it is estimated that around half of the UK human population is also host to the parasite. In France and Germany 80-90% of the population are thought to be infected. Once infected there is no cure and the parasite will continue to multiply throughout the life of its host.
In rats, the toxoplasma appears to undermine natural behaviour. They become less fearful of cats and even seek them out. Obviously, this isn’t very good news for the rat, but it does benefit the parasite.
Although research into the effects on human behaviour is still in the early stages, it appears that infected men become more prone to fits of aggression and anti-social behaviour. They also take less care over their personal appearance. Infected women show a tendency towards promiscuity and become more fun loving and easy going.
There is also an unfortunate increase in the incidence of schizophrenia and depression, as well as a decrease in reaction times and a drop in IQ.
It is unlikely that Toxoplasma gondii alone would be enough to make an entire village vanish off the face of the earth, but I wonder if an outbreak of the parasite taken in conjunction with another catastrophic event might explain the disappearance of Oldton. Perhaps an environmental or industrial disaster damaged the immune systems of Oldton residents, which allowed the Toxoplasma gondii parasite to produce more dramatic effects than is normal.
It is strange that in the other Oldton thread, we have recently been discussing dogs and now, all of a sudden, we learn about this parasite, whose main gateway into the human species is through the domestic cat.