Cancer plague

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Cancer plague
Cancer plague

Cancer plague

Systematics
Subdivision : Heteroconta
Class : Egg mushrooms (Oomycetes)
Order : Saprolegniales
Family : Leptolegniaceae
Genre : Aphanomyces
Type : Cancer plague
Scientific name
Aphanomyces astaci
Schikora 1906

The crab plague ( Aphanomyces astaci ) is a species within the order of the egg fungus . Aphanomyces astaci affects crayfish and is considered one of the most invasive species (on the list of 100 of the World's Worst Invasive Alien Species ). Aphanomyces astaci does not attack vertebrates and is not pathogenic to humans.

At the same time, cancer plague is the name given to the usually fatal fungal disease of cancers. The pathogen was brought into Europe through the introduction of American crayfish species. The invasive fungus is in the process of largely exterminating the native crustaceans, especially the noble crayfish , in their ancestral habitat, as the disease, which has been spread by humans through the naturalization of the much more resistant representatives, especially the Cambaridae group, is spread as alien species ( neozoon ) easily spread in crayfish species of non-American origin. As an animal disease, the crayfish plague represents a general hazard potential for crabs, especially outside of America, both in aquariums and in public waters.

Chronological sequence of the occurrence of cancer plague in Europe

The spread of crayfish plague has led to a dramatic decline and even extinction of native cancers in some bodies of water , such as the jackdaw crab ( Austropotamobius pallipes (Lereboullet)) in Lough Lene , County Westmeath , Ireland in 1987.

Description of the disease

infection

The infection occurs via zoospores , which can move from the carrier to the host with the help of two flagella . After the zoospore reaches a crustacean, it sheds the two flagella and forms a cyst on the surface of the host . This is an intermediate station from there to overcome the barrier of the exoskeleton and penetrate the host's body. It is less the matrix of chitin and calcium carbonate that inhibits it than the non-chitinous proteolipids (complexes of proteins and lipids ) of the epicuticle, which is a hydrophobic coating. If the penetration fails, the life expectancy of a zoospore without ingestion of food from the host is about five days and the process of scourge shedding is possible up to three times through regeneration. Penetration is easier in previously damaged areas (micro-cracks).

Different susceptibility of different cancers

West American crabs are generally more resistant to the symptoms of cancer plague.

In West American crabs, penetration through the cuticle of their exoskeleton is very rarely successful, even with a concentration of 1000 virulent spores per milliliter in the water. After previous damage to their epicuticula, West American crabs fell victim to crayfish plague just as frequently as European crayfish.

In signal crayfish ( Pacifastacus leniusculus ), a North American crayfish of the Astacidae family, which also occurs as a neozoon in Europe, a large number of circulating blood cells also seem to be able to protect against infectious pathogens.

The body's own enzymes can also prevent the spread of the disease in American cancers.

At least three of the invasive North American species can harbor the cancer plague as benign parasites : signal cancer ( Pacifastacus leniusculus Dana), crayfish ( Orconectes limosus Rafinesque) and red American marsh crayfish ( Procambarus clarkii Girard).

In addition to the noble crayfish ( Astacus astacus ), stone crayfish ( Austropotamobius torrentium ) and jackdaw crayfish ( Austropotamobius pallipes ), as well as species such as the Galician crayfish ( Astacus leptodactylus ), are often fatally infested . In addition to the European species, the infectiousness of Australian and East Asian crayfish has also been proven.

transmission

Cancer plague spreads after leaving a (dead) host in the water by attaching the self-moving zoospores. In addition, there is direct infection. As omnivores, crayfish are also typically carrion users , even of their own species, and even cannibalize smaller specimens of their own species while molting. A transmission between water bodies requires the vectors .

In Europe, North American crabs are considered the main reservoir . With the molt or death of an infected cancer, the fungus enters the water and starts producing the spores. For example, the American red marsh crayfish was described as a vector in Louisiana that can carry Aphanomyces astaci schikora in its cuticula as a benign parasite and release it into the water after its death.

Crustaceans that are transferred from infected aquariums to clean aquariums or that are released into water bodies as infected animals can serve as vectors. Also plankton - or Bachflohkrebse must apply as an intermediary, especially Aphanomyces irregularis could be found in all of the studied small cancers. Aphanomyces astaci was determined to be adherent to the water louse ( Asellus aquaticus ), the river flea shrimp ( Gammarus fossarum ) and Pallasiola quadrispinosa , but there was no common flea shrimp ( Gammarus pulex ) and Gammarus lacustris .

Passive carriers of adherent zoospores are:

  • Shell of molluscs and plumage of waterfowl
  • Fish, amphibians and insects
  • Anglers and athletes and their equipment
  • Boats, flotsam and other things

Symptoms, course of the disease

After a non-American crayfish is infected, the flight reflex stops. He scratches his eyes, the underside of the abdomen and the limbs with his striding legs. He shows increased daytime activity and increasing signs of paralysis. The limbs fall off, the cancer tips over on its side and then dies. The death of the infected crabs is foreseeable with the breakout of the egg fungus as a white coating on the eyes and scissor joints.

Cancer plague is usually incurable after the onset of the disease symptoms and ends with the death of the infected cancer.

The severity of the disease depends on various criteria:

treatment

A therapy for infected cancers is unknown.

Natural or artificial bodies of water or aquariums must sensibly be sterilized before they are reoccupied or a waiting period must be observed, which depends in particular on the size of the body of water and the density of the host population. If live hosts remain, restocking with European cancers is usually disappointing.

Evidence of the disease

Dead crabs in otherwise intact water are a first indication of a possible infection with crayfish plague. Various PCR techniques are used today for detection . An additional culture attempt is usually also tried, but not always successful. The isolation of A. astaci from American cancers is particularly difficult. A positive result in the culture should also be confirmed by genetic identification of the isolate. There is an EU reference laboratory (European Union Reference Laboratory (EURL) for Fish and Crustacean Diseases) for diseases of the crustacean . In some European countries there are national reference laboratories that should carry out the tests on the samples in the event of crayfish deaths.

literature

  • B. Oidtmann, RW Hoffmann: The cancer plague. In: Stapfia 58 (= catalogs of the Upper Austrian State Museum , New Series No. 137), 1998, pp. 187–196, PDF on ZOBODAT

Web links

Individual evidence

  1. ^ William W. Scott: A monograph of the genus Aphanomyces. In: Technical Bulletin. Virginia Agricultural Experiment Station , 151, 1961.
  2. ^ Paul Kirk: Aphanomyces astaci Schikora, 1906 . World Register of Marine Species . 2010. Retrieved June 29, 2011.
  3. ↑ a b c Lit. Oidtmann, Hoffmann: Die Krebspest. 1998, p. 188 (pdf p. 2).
  4. ↑ Milton Matthews, Julian D. Reynolds: Ecological impact of crayfish plague in Ireland . In: Hydrobiologica , Volume 234, No. 1, May 1992, pp. 1-6, doi : 10.1007 / BF00010773 .
  5. ↑ a b T. Unestam, DW Weiss: The host-parasite relationship between freshwater crayfish and the crayfish disease fungus Aphanomyces astaci: Response to infection by a susceptible and a resistant species. In: J. gen. Microbiol. Volume 60, pp. 77-90, 1970 ( PDF) .
  6. ↑ M. Persson, L. Cerenius, K. Söderhäll: The influence of haemocyte number on the resistance of the freshwater crayfish, Pacifastacus leniusculus Dana, to the parasitic fungus Aphanomyces astaci. In: Journal of Fish Diseases , Volume 10, No. 6, November 1987, pp. 471-477, doi : 10.1111 / j.1365-2761.1987.tb01098.x .
  7. ↑ a b J. Diéguez-Uribeondo, K. Söderhäll: Procambarus clarkii Girard as a vector for the crayfish plague fungus, Aphanomyces astaci Schikora . In: Aquaculture Research , Vol. 74, No. 6, 1993, pp. 761-765, doi : 10.1111 / j.1365-2109.1993.tb00655.x .
  8. ↑ T. Unestam: Defense reactions in and susceptibility of Australian and New Guinean freshwater crayfish to European crayfish-plague fungus. In: AJEBAK 53 (1975), pp. 349-359; and other works by the author (1970, 1972); According to Lit. Oidtmann, Hoffmann: Die Krebspest. 1998, p. 188, col. 2 (pdf p. 2).
  9. ↑ B. Czeczuga, M. Kozłowska, A. Godlewska: Zoosporic fungus species growing on dead benthos crustaceans . In: Polish Journal of Environmental Studies , Volume 8, No. 6, 1999, pp. 377-382 ( PDF ).
  10. ↑ Information page on cancer plague at www.wirbellose.de
  11. ↑ List of national reference laboratories ( Memento from January 12, 2011 in the Internet Archive )