In parasitology, the term paratenic describes a host that is not necessary for the development of a particular species of parasite, but nonetheless may happen to serve to maintain the life cycle of that parasite. In contrast to its development in a secondary host, a parasite in a paratenic host does not undergo any changes into the following stages of its development.
Alaria americana may serve as an example: the so-called mesocercarial stages of this parasite reside in tadpoles, which are rarely eaten by the definitive canine host. The tadpoles are more frequently preyed on by snakes, in which the mesocercariae may not undergo further development. However, the parasites may accumulate in the snake paratenic host and infect the definitive host once the snake is consumed by a canid.
See also 
- Biological life cycle
- Intermediate host
- Parasitic life cycles
- Foundations of Parasitology, 6th Ed. (Schmidt & Roberts, 2000) ISBN 0-07-234898-4