Alveolar echinococcosis

The alveolar echinococcosis is a Zoonose caused by (Cestode) which is worms parasitic (Echinococcus multilocularis in Europe, but there exists other parasitic echinococci, in almost all the areas of the world).

Human contamination

The man is famous to contaminate himself accidentally by introducing microscopic eggs of the parasite:
  • by soiled hands;
    • - with the direct contact with parasitized animals (Dog and Cat mainly, and possibly field vole, Fox or others Canidé S)
    • - by handling soiled ground, itself (gardening)
  • by the consumption of plants and soiled fruits

Pathogenesis

The introduced eggs are transformed into larvae which will colonize the liver and will form a false tumor at the end of several years. The larvae can exceptionally also reach other bodies like the lungs or the brain. Curiously the children seems saved by this disease whereas it is those which carry more the hands to the mouth and is made lick by the dogs and cats. (Or they were in an immunizing state of deficiency). their immune system easily seems to get rid of the echinococci.

Clinical signs

Alveolar echinococcosis is a grave disease which develops slowly and in an asymptomatic way, formerly often confused with Cirrhose or Cancer of the liver: abdominal pains, jaundice, fever, with increase in the volume of the liver. The only existing treatment can be an surgical operation with a possible clerk's office of the liver, but the disease remains extremely serious for contaminated.

Prevention

The parasite resists congelation but is killed by heat.

It can be advised to put a protection mask if for example you have with " manipuler" ground, to use a mower or " manipuler" hay (apart from the fact that it is advised to use a mask if one regularly handles hay to avoid lung diseases specifically related to the hay).

Zones at the risk

The modes of transmission of Echinococcus multilocularis remain badly included/understood even if the food chain and deposit them coming from the contaminated animals seem to be the most probable source of the contagion. It is not known if the epidemic extends quickly or if the prevalence of the echinococcus before had been underestimated. It is possible that certain stocks of echinococcus more virulent or are recognized by certain immune systems.
On seeks to more finely determine the zones at the risks. In France it is a priori: Franche-Comté, Lorraine, the Alps, Massif Central, the Ardennes. with some cases brought back out of these areas. It is currently estimated that there is a dozen cases treated surgically in France per annum.
Au Japan, the meadow field voles do not exist. There, it is C. rufocanus , a forest rodent, is the principal intermediate host of the echinococcus. Elsewhere in the world, they are always meadow field voles or rodents which seem to be the tank of the parasite, but dogs and cats, with the fox and others are canidés (fennecs.) vectors towards the man.

Mr. agrestis and/or Mr. arvalis?

In Europe, these two species are difficult to differentiate without having of the jaw or a means of genetic analysis (expensive).
En 2006, one did not know yet in Europe so forest rodents can maintain the cycle also there echinococcosis. (prevalence of the parasite is generally lower than 1%).
Le field vole is a sometimes discrete underground animal (in forest) and difficult to study. One does not know the percentage of the rural field voles within the kind Microtus (impossible cf determination within sight of the only evidence (traces, droppings.)

Without analysis (expensive) of the bond between space distribution, parasitic load and genetic polymorphism of the found echinococci, one does not know if a parasite discovered in an area considered saved before means that it was absent (but not detected because nonrequired) or if it is about a real emergence, or of a simple increase in prevalence in the field voles. (Romig and Al, 1999a). Moreover displacements by the Man of game and dogs from one area to another could have already disturbed the charts by diffusing parasites. One already found genotypes parasitic different within the same population from fox, without one to date being able to measure their differences of virulence, contagiousness or prevalence according to polymorphisms.

Tracks of research

To define zones at the risk: For that, one seeks possible correlations between densities of field voles ( Microtus ), their degree of Prédation by the foxes and other carnivores (of which dogs and cats) and the real prevalence of echinococci.

to better detect: It is possible that many zones of prevalence atlow rate of infection were not detected fault of having sought the parasite there.
Thus, a thesis (2006) has it showed a strong prevalence of E. multilocularis in the foxes of the French Ardennes (Microtus being the probable tank) in a zone before considered as saved by the endémie and where one forever announced Pullulation of field voles. Two Génotype S of the parasite were found there, identical to those of other French areas, of Poland, Slovakia, Austria, Switzerland and Germany historically found endemic.

ecoepidemiologic Approach: the university of Franche-Comté for a long time noted - with regional scales - strong local variations of prevalence and parasitic load, according to altitude, the ecology of the landscape and, within the landscapes, according to the “ grain écopaysager ” which characterize the structure and éco-landscape heterogeneity, variations confirmed in other areas of the world (of which in the canton of Zhang (Sichuan, China) where a strong prevalence of the disease exists at the Man).

The characteristics écopaysagères influence the risk indeed;

- via the probability for the fox of consuming intermediate hosts,
- via the speed of decomposition of deposit
- via the survival of eggs of echinococci (cf moisture and condition of the ground which varies according to the hydromorphie, the drainage, Pâturage, Jachère S, zones attended by the man, etc.

The lifespan of deposit and eggs: this factor remains to be studied in situ. It must vary according to the medium and from the climatic conditions (activity of the coprophages, worms of ground, etc). Marie-Helene Guislain (see note of step of page) suggests studying the speed of decomposition of deposit of foxes (high in captivities with known food modes), under microclimatic conditions and environmental varied, for better identifying possible “zones with Risque, where these deposit would be more present or more " biodisponibles " ;

One is interested in the eggs present in deposit, but one badly measures the quantity excrêtée by the Canidé S, Félin S and other animals, and one does not know how much between them nor the viral attacks , fungic and survive how long bacterial or with the ingestion by animals Coprophage S and détritivores in the real environment.
Détecter the parasite where its prevalence is very low remains very difficult, but could be done thanks to the biomolecular techniques based on target microsatellitaire (EmsB). they would make it possible to better evaluate the genotypic variation of the worms, but also to evaluate that of eggs present in the environment, to detect possible genotype écoépidémiologiquement more “effective”.

to better evaluate the risk: the risk seems to depend on the possibility of contact between the intermediate vector-host and egg. In the “natural ”, it strongly varies according to the medium considered, and is a priori is higher when the density of deposit infected is high and when the number of rodents is also raised, in the same zone, generally on the Lisière S, in intermediate zone of vegetation between forest and meadow. In our landscapes, except at the time of the close-cropped cuts, the edges are fixed whereas they would move in time in the natural savage. The parasite could find favorable conditions there. Moreover the fragmentation of the landscapes (and in particular of the Forest S) strongly the number of these “fixed” edges increased .

Do the parasitic rates of transmission have to be estimated according to the mediums, which implies massive captures of meadow rodents (and forester?) to allow the diagnosis, the estimate of the density and to detect of it possible correlations with the presence and the rate of parasites in deposit or the ground.

The behavior of the fox itself is modified by the human frequentation, of the dogs and/or by hunting that one gives him, like by various anthropic modifications of the landscape, which can modify the distribution and localization of its deposit in the environment, and its consumption of intermediate hosts contaminated.

Éco-ethology : The eggs of echinococci are not mobile in the Environment. The meadow rodents move only on disances lower than a few hundred meters at most, and generally less few tens of meters. Dogs, cats and foxes to contaminate itself must thus come to eat a contaminated field vole, or to move in a site where a fox (or another carnivore) contaminated déféqué.
Or, their displacements are also influenced by the fixed artificial edges imposed by the man on the landscape (cf Private property), which one knows favourable with the rodents intermediate tank. The study of the hunting grounds and the places of defecation common to several foxes (Hen and Al, 1994; Henry and Al, 2005), or to foxes and dogs and cats are of éco-epidemiologic interest. Here still, of the detectable markers microsatellites in deposit permetraient to better measure the dispersion of deposit of very contaminated foxes little or, and would help to include/understand how the parasite disperses in the landscape. This method was already used to count badger ( Meles mix ) in England, the wombat common ( Vombatus ursinus ) in Australia or of the bearded bustards ( Otis delayed ) to the Morocco.

Lastly, the role of the dog and the cat as vector of the parasite towards the man could be underestimated.

See too

External bonds

  • Thesis: '' An emergent disease; alveolar echinococcosis '' (by Marie-Helene Guislain, University of Frank County, France, 2006,163 pages)
  • Site of the French ministry of health (see files alphabetically, Z, Zoonoses)
  • Laboratory of Environmental Biology Besancon-Montbeliard (INRA/University of Frank County)

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