The immunity arising from continuous low-level infection with <i>Eimeria maxima</i> and <i>Eimeria acervulina</i>

Abstract

Field observations at one site on brown trout (Salmo trutta) and three-spined sticklebacks (Gasterosteus aculeatus) concurrently infected with mature Neoechinorhynchus rutili, together with the knowledge that large trout can be piscivorous in habit led to the proposition that the post-cyclic transmission of N. rutili may occur between these fish species. This route of transmission has been suggested for a number of acanthocephalan species. A laboratory experiment was conducted and it was demonstrated that uninfected rainbow trout (Salmo gairdneri) can acquire a N. rutili infection as a result of feeding on sticklebacks already carrying established worms in their intestines. This finding may help to explain how N. rutili is found in a wide range of fish definitive hosts throughout the northern holarctic region. More generally this example provides further evidence of the flexibility within acanthocephalan life-history patterns.