<unk> s are parasites with two or more hosts, capable of causing changes in the<unk>  of one of their hosts to enhance their transmission, sometimes directly affecting the hosts' decision-making and<unk>  control mechanisms. They do this by making the intermediate host, where they may reproduce asexually, more likely to be eaten by a predator at a higher trophic level which becomes the definitive host where the parasite reproduces sexually; the mechanism is therefore sometimes called parasite increased trophic facilitation or parasite increased trophic transmission. Examples can be found in bacteria, protozoa, viruses, and animals. Parasites may also alter the host<unk> r to increase protection of the parasites or their offspring. The term bodyguard manipulation is used for such mechanisms. Among the<unk> al changes caused by parasites is carelessness, making their hosts easier prey. The protozoan Toxoplasma gondii, for example, infects small rodents and causes them to become careless and may even cause them to become attracted to the smell of feline urine, both of which increase their risk of predation and the parasite's chance of infecting a cat, its definitive host. Parasites may alter the host's<unk>  by infecting the host's central nervous system, or by<unk>  its neurochemical communication, studied in neuro-parasitology.
Behavior-altering parasite
Carcinogenic parasite
Parasitic worm
Soil-transmitted helminthiasis
Food contaminant
Human parasite
Tick infestation
Clonally transmissible cancer