Paratenic

Types of hosts

• Paratenic or transport host – an organism that harbors the sexually immature parasite but is not necessary for the parasite's development cycle to progress. Paratenic hosts serve as "dumps" for non-mature stages of a parasite in which they can accumulate in high numbers. The trematode Alaria americana is an example: the so-called mesocercarial stages of this parasite reside in tadpoles, which are rarely eaten by the definitive canine host. The tadpoles (or the frogs, following metamorphosis) are more frequently preyed on by snakes, which then function as paratenic hosts: the mesocercariae do not undergo further development there, but may accumulate, and infect the definitive host once the snake is consumed by a canid. The nematode Skrjabingylus nasicola is another example, with slugs as the intermediate hosts, shrews and rodents as the paratenic hosts, and mustelids as the definitive hosts.
• Dead-end, incidental, or accidental host – an organism that generally does not allow transmission to the definitive host, thereby preventing the parasite from completing its development. For example, humans and horses are dead-end hosts for West Nile virus, whose life cycle is normally between culicinemosquitoes and birds. People and horses can become infected, but the level of virus in their blood does not become high enough to pass on the infection to mosquitoes that bite them.
• Reservoirhost – an organism that harbors a pathogen but suffers no ill effects. However, it serves as a source of infection to other species that are susceptible, with important implications for disease control. A reservoir host individual may be reinfected several times.