A favorite horror flick with PARASITOLOGISTS

In the biological science of Parasitology, parasitologists have a sense of humor and rank SHIVERS (aka, They Came From Within) as one of their fave horror films. Too bad this movie didn't come out twenty years later which might have lent a huge boost to the science of parasites. Just in the last twenty, even ten years, the scientific biological knowledge of the world's parasites has phenomenally advanced.

What makes SHIVERS such a fave with parasitologists is more of an inadvertent inside joke. The science fiction parasites depicted in the movie inadvertently captured several of the primary characteristics of parasites.

1) Some parasites can diabolitically alter the behavior of their hosts. One
microworm forces its ant host to crawl up to the top of a grass stalk so
that a passing cow can eat the grass along with the ant. Inside the cow's
stomach, the microworm is free to infest the cow's liver.

2) Method of transmission or infestation of the host.

3) Biological effects on the host. Most parasites are harmful to their hosts
but at the same time can cause beneficial side effects to the host because
it ensures the survival of the parasite.

What was pure science fiction was that the parasite was ostensibly bio-engineered to displace a non-functioning human kidney, filter the blood of its human host while simply drinking a small amount of the host's blood. In actual current parasite theory, known as, parasite ecology or parasite balance, millions of years of evolution have resulted in an unintended symbiosis between host and some parasites, even though the internal parasite harms the host. Parasitologists claim that allergies occur far more often in children in healthier western nations. But in poorer nations with lower health standards, the children may be suffering from parasite infestation, but their incidence of allergies is astonishingly low. The premise is that internal parasites lower or 'tame' the human immune system while allowing the immune system to function more or less normally against typical dangerous pathogens like bacteria and viruses that cause infections and illnesses. Allergies are typically traced to hyperactive human immune system reactions. But the parasites, typically large, one-celled, or tiny organisms infesting the body, keep the immune system from developing allergies.
That said, many parasites offer no useful side effects and are totally and completely devastating to the human host, like the malaria one-celled pathogen.