In order to infect a host, parasites first have to find it in their environment, and for this, they develop what we call transmission strategies, or ways of finding and successfully infecting a host. Sometimes, parasites can be transmitted when an infected host is consumed by a predator that just happens to be the next host for the parasite. Then, the parasite infects this host and the life cycle continues. On other occasions, more than just luck is involved, and parasites actively increase their chances of transmission in various ways. One common strategy is by influencing the host's behavior, to make contact with the next host easier. For example, the parasite Gyrodactylus bullatarudis uses the colorful guppy fish as a host, infecting its gills and changing how the fish swim. Healthy guppies meet with the infected ones because they are attracted to their strange swimming behavior, which is caused by the infection with the parasite. In this way, the parasite infection spreads among the healthy fish.

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