Experimental transmission of Enteromyxum leei to freshwater fish

Abstract

The myxosporean Enteromyxum leei is known to infect a wide range of marine fish hosts. The objective of the present study was to determine whether freshwater fish species are also receptive hosts to this parasite. Seventeen species of freshwater fish were experimentally fed E. leeiinfected gut tissue from donor gilthead sea bream Sparus aurata obtained from a commercial sea bream cage farm. Four of the tested species, tiger barb Puntius tetrazona, zebra danio Danio rerio, oscar Astronotus ocellatus and Mozambique tilapia Oreochromis mossambicus, were found to be susceptible with prevalences ranging from 53 to 90%. The course of infection and pathology was limited to the gut mucosa epithelium and was similar to that observed in marine hosts. Little is known of the differences in physiological conditions encountered by a parasite in the alimentary tract of freshwater vs. marine teleost hosts, but we assume that a similar osmotic environment is maintained in both. Parasite infectivity may be influenced by differences in the presence or absence of a true stomach, acidic gastric pH and digestive enzyme activity both in the stomach and intestine. Variability in susceptibility among species may also stem from differences in innate immunity. Dimensions of spores produced in the donor sea bream and recipient freshwater species are variable in size, as previously observed in other captive marine host species. KEY WORDS: Direct transmission · Myxosporea · Sparus aurata · Danio · Oreochromis · Puntius · AstronotusResale or republication not permitted without written consent of the publisher

Novel horizontal transmission route for Enteromyxum leei (Myxozoa) by anal intubation of gilthead sea bream Sparus aurata

“…The histopathological damage caused by the parasite and the inflammatory host reaction were very similar to those described by other authors for different Enteromyxum leei-infected hosts (Diamant et al 2006, Alvarez-Pellitero et al 2008, Fleurance et al 2008. The disruption of the integrity of the mucosa, desquamation and detachment of the epithelium, which correspond to advanced, chronic infections, was observed earlier than in cohabitation and effluent transmission trials.…”

“…In previous studies, oral transmission of Enteromyxum leei to gilthead sea bream produced very variable results ranging from 0 to 86.7% prevalence of infection (Diamant 1997, Sitjà-Bobadilla et al 2007). E. leei was also orally transmitted to red sea bream Pagrus major, the tiger puffer (Yasuda et al 2002, Yanagida et al 2004) and several fresh water species (Diamant et al 2006). Similarly, a high prevalence of infection by E. scophthalmi was obtained orally for turbot (100%, 22 d p.i.)…”

“…Since the first description of Enteromyxum leei as Myxidium leei in cultured gilthead sea bream Sparus aurata from southern Cyprus (Diamant et al 1994), the parasite has been reported along the entire Mediterranean basin, the Red Sea and Japan, to date having been recorded in > 46 fish species (Diamant 1995, Le Breton & Marques 1995, Sakiti et al 1996, Paperna 1998, Zrn<ić et al 1998, Padrós et al 2001, Marino et al 2004, Yanagida et al 2004, 2006, Yasuda et al 2005, Diamant et al 2006, Sitjà-Bobadilla et al 2007). This myxosporean produces severe enteritis and is one of the most threatening parasites in Mediterranean fish culture.…”

Transmission Biology of the Myxozoa

“…This route of transmission may occur only in intensive culture systems, where it facilitates rapid spread of the parasite. Broad host range of E. leei also appears to assist the parasite's dispersion (Diamant et al, 2006). Indeed, an episode of enteromyxosis in 25 different fish species in an exhibition aquarium was reported (Padrós et al, 2001).…”

Fish immune response to Myxozoan parasites

“…Data obtained from proliferative kidney disease (PKD) experimental infections indicate that the development of the parasite and the severity of the disease may vary with host salmonid species (Arkush & Hedrick, 1990). For E. leei, some aquarium (Padrós et al, 2001) and fresh water (Diamant et al, 2006) fish are refractory to infection, and among susceptible species, a range of pathogenic effect has also been documented. Thus, in gilthead sea bream this enteromyxosis can be considered a slow-progressing disease, as external symptoms and mortality usually begin two months or later on after exposure to the pathogen .…”