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Aphanomyces Astaci Prepared by the IUCN SSC Invasive Species Specialist Group

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Aphanomyces Astaci Prepared by the IUCN SSC Invasive Species Specialist Group Management information: Aphanomyces astaci Prepared by the IUCN SSC Invasive Species Specialist Group Preventative measures: Once a watershed is infected, the control of the spread of infection is very difficult if not impossible; therefore only preventative measures are mainly effective. Spread of the disease occurs due to movement of infected crayfish which are the only known carriers of the disease. Investigations of other possible means of transmission via contaminated water, infected fish and other crustaceans have been carried out (Unestam 1972; Alderman et al. 1987; Oidtmann et al. 2002). They found that the oomycete could not survive in these hosts or environments and that transmission only occurred while zoospores were viable, i.e. a few days. Oidtmann et al. (2002) investigated two possible means of transmission of crayfish plague. The first was through fish as vectors, and the second through other crayfish as hosts or vectors when deceased. The authors state that, that A. astaci remains viable for 5 days, and possibly longer in crayfish kept in water at 21 degree C after dying of crayfish plague. It was also found that A. astaci is unlikely to survive passage of the gastrointestinal tract of either mammals or birds. When pure mycelium or spores were fed to fish there was no indication of viable forms of A. astaci after passage through the gastrointestinal tract. However, if A. astaci was fed to fish as infected abdominal cuticle, it was still viable after passage through the gastrointestinal tract. This shows there is a risk of transmission of crayfish plague via fish faeces of fish. The investigation of crayfish as vectors delivers methods that could be used for treatment of crayfish imported for human consumption into crayfish plaguefree areas. This application is particularly important for the importation of American crayfish, which are carriers of A. astaci in their cuticle. Physical: Bower (2002) believes that, "Prevention of all introductions of crayfish to natural waters and into enclosed waters from which they may escape to natural waters can be effective. The possibility of transmission via movement of contaminated water or boots and fishing gear between watersheds is small but should be still considered. Disinfection of water and equipment with bleach or drying of equipment (>24 hours) is effective because the Oomycetes are not resistant to desiccation. A. astaci does not survive at 5°C and below for more than 24 hours. Taugbøl (1994), Diéguez Uribeondo et al. (1997) and Holdich (2003) state that, "The restocking of rivers previously infected by plague is a possibility, as long as the source of infection, i.e. North American crayfish, is no longer present. Recent research has shown that plague may persist in a river system for over a year." CEFAS (UNDATED) conducted a study and found that, "The crayfish plague, A. astaci has a limited thermal range. Even when potentially "protected" in crayfish tissue rather than "exposed" in in vitro conditions, A. astaci will not survive 1 minute at 100°C or 3h at 20°C." Chemical: Lilley and Inglis (1997) conducted a study among fifty four isolates of various fishpathogenic and saprophytic fungi which were characterized in terms of their susceptibility to three antibiotics (penicillin, streptomycin and oxolinic acid), three fungicides (malachite green, hydrogen peroxide and sodium chloride) and three disinfectants (an iodophore, sodium hypochlorite and a solution of peracetic acid and hydrogen peroxide)." The authors determined that A. astaci and two other Aphanomyces species were more sensitive to the majority of these treatments than the other fifty one studied. Rantamaki et al. (1992) found that, "Spore production of the fungus A. astaci was prevented in vitro by the addition of MgCl2 to a concentration of 20 mM or more into the lake water used as sporulation medium. When zoospores were used for infection at least 100 mM of MgCl2 was needed to protect the crayfish from infection. If crayfish were infected in lake water and then transferred to 25 mM or more of MgCl2, the oomycete still grew within the cuticle but no sporangia were produced and the disease was not transmitted to uninfected A. astacus." Cerenius et al. (1993) states that, "The effects on growth, asexual and sexual reproduction of different Aphanomyces species by the new fungicide ampropylfos ((RS)1aminopyropylphosphonic acid) were tested using highly synchronized cultures. Ampropylfos reduced mycelial growth in A. astaci along with two other Aphanomyces species. The authors also state that, "The fungicide was found to reduce zoospore numbers in all Aphanomyces species tested except A. euteiches." Bower (2002) reports that various chemicals (e.g., sodium hypochlorite and iodophores) are effective against removing surface contamination of A. astaci providing that surfaces are clean of mud or organic contamination in which the oomycete can survive for prolonged periods if kept moist." Biological: Diéguez-Uribeondo and Cerenius (1998) purified three different proteinase inhibitors from crayfish blood and tested for their inhibitory activities against extracellular proteinases from A. astaci, the saprotrophic A. laevis the plant parasitic A. chochlioides and A. euteiches. The authors found that, "It is possible that these proteinase inhibitors may reduce the proteolytic breakdown exerted by A. astaci proteinases during an infection. Cultural: Cerenius and Söderhäll (1993) found that P. leniusculus already infected with A. astaci was further challenged by a second pathogen that, “The crayfish could no longer protect themselves from the plague infection they carried and these animals died in acute plague. In contrast, if A. astacus, which are not carriers of chronic plague, were challenged likewise the animals survived. In conclusion, the chronic infection carried by P. leniusculus renders them susceptible to any kind of environmental changes or new pathogens which would have serious implications for the use of this species for stocking or aquaculture purposes." .
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