Behavior-altering parasite

Behavior-altering parasites are parasites with two or more hosts, capable of causing changes in the behavior of one of their hosts to enhance their transmission, sometimes directly affecting the hosts' decision-making and behavior 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^[1][2] which becomes the definitive host where the parasite reproduces sexually; the mechanism is therefore sometimes called parasite increased trophic facilitation^[3] or parasite increased trophic transmission.^[4] Examples can be found in bacteria, protozoa, viruses, and animals. Parasites may also alter the host behavior to increase protection of the parasites or their offspring; the term bodyguard manipulation is used for such mechanisms.^[5]

Among the behavioral changes caused by parasites is carelessness, making their hosts easier prey.^[6][4] 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 behavior by infecting the host's central nervous system, or by altering its neurochemical communication (studied in neuroparasitology).^[7]