Ichthyophthiriasis in carp Cyprinus carpio: infectivity of trophonts prematurely exiting both the immune and non-immune host.
Ichthyophthirius multifiliis exposed to naturally immunised carp established short-term infections, the majority of parasites actively emerging within 2 h of entering the epidermis. A small, but significant, number of these expelled parasites were shown to retain theront-like properties with the capacity to directly re-invade a further fish host. Infectivity fell rapidly with time in the host and was comparable to that of trophonts of a similar age artificially induced to emerge from non-immune hosts with the aid of MEM (minimal essential medium). Trophonts recovered with MEM from immune carp 2 to 8 h post infection rarely established infections upon exposure to susceptible new hosts and no infections resulted from older trophonts recovered after 8 to 24 h exposure; older trophonts, however, represented only a small percentage of the original parasite population. A low level of infectivity was recorded in trophonts collected with the aid of MEM from non-immune carp after up to 24 h of infection. The results are discussed in relation to theront transformation and evasion of the host immune response.
Centre for Fish and Wildlife Health, University of Berne, Switzerland. thomas.wahli@itpa.unibe.ch
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D000818:Animals; D002347:Carps / Q000276:immunology* / Q000469:parasitology; D016770:Ciliophora Infections / Q000276:immunology / Q000662:veterinary*; D004198:Disease Susceptibility / Q000276:immunology; D005393:Fish Diseases / Q000276:immunology* / Q000469:parasitology; D005398:Fisheries; D016803:Hymenostomatida / Q000276:immunology / Q000472:pathogenicity*; D011529:Protozoan Infections, Animal / Q000276:immunology*