Review of Biological Factors Relevant to Import Risk Assessments for Epizootic Ulcerative Syndrome (Aphanomyces invadans)

Abstract

Summary Epizootic ulcerative syndrome (EUS) is a disease affecting both wild and farmed fish in freshwater and estuarine environments. After it was first described in Japan in 1971, the disease has spread widely across Asia and to some regions of Australia, North America and Africa. In Asia and Africa, the spread of the disease has substantially affected livelihoods of fish farmers and fishermen. No reports are yet published showing the presence of the disease in Europe or South America. Given its epizootic nature and its broad susceptible fish species range, it would appear that the disease has the potential for further spread. This study provides a review of the scientific literature on several biological factors of the pathogen, Aphanomyces invadans, associated with the disease EUS and aspects of the disease that are relevant to undertaking import risk assessments (IRA) covering (i) Life cycle and routes of transmission; (ii) Minimum infectious dose; (iii) Tissue localization and pathogen load; (iv) Predisposing factors for infection and factors influencing expression of disease; (v) Carrier state in fish; (vi) Diagnostic methods; (vii) Survival in the environment; (viii) Permissive temperature range; (ix) Stability of the agent in aquatic animal products; (x) Prevalence of infection; and (xi) Affected life stages. Much of the biological information presented is relevant to a broad range of risk questions. Areas where data are lacking were identified, and the information provided is put into context with other aspects that need to be addressed in an IRA.

Deciphering microbial landscapes of fish eggs to mitigate emerging diseases

“…Achlya species have been described for diseased fish in natural environments (Jeney and Jeney, 1995;Kales et al, 2007;Sosa et al, 2007), and A. invadans is a notorious pathogen of different natural and farmed fish species worldwide, except in Europe and South America (Oidtmann, 2012). Both Achlya and Aphanomyces spp.…”

Scientific Opinion on Epizootic Ulcerative Syndrome

“…Information on the agent, characteristics of the disease and the range of susceptible species has been reviewed in a number of recent publications or reports (Lilley et al, 2001b;Baldock et al, 2005;EFSA, 2007EFSA, , 2008OIE, 2009;Oidtmann, 2011).…”

“…How A. invadans survives outside the host is still unclear. It is assumed that motile zoospores (the infective stage), which are released from infected fish, can encyst when they have been unsuccessful in finding a suitable substrate to grow on (Oidtmann, 2011). A. invadans isolates have been shown to produce one additional generation of motile zoospores from artificially encysted secondary zoospores, but no further generations could be induced .…”

“…In a cross-sectional study, the disease was confirmed (by histology) at within country level ( Bangladesh) in fish farms in nearly half of all districts (30 of 64) and in wild fisheries in three quarters of all districts (Sarker and Chowdhury, 2001). Further prevalence data are summarised in Oidtmann (2011). In experimental bath challenge, cumulative incidence and mortality over a 4 week period reached 64% in net stressed fish and 14 and 11%, respectively, in fish not exposed to skin damage (Kiryu et al, 2003).…”

Emergence of the Epizootic Ulcerative Syndrome in Pond Reared Carp Fish (Cyprinids) and It's Control Measure in Chitwan, Central Nepal

“…EUS has been reported in more than 94 fish species spread across 26 countries (Lilley et al, 1998;Andrew et al 2008;Saylor et al 2010;Boys et al 2012;Huchzermeyer et al 2012;Oidtmann, 2012). EUS was spread across Asia from Japan and Australia to Pakistan in 1996 and to southern Africa in 2006 (Baldock et al, 2005).…”