Introduction

Distomum musculorum suis (DMS), Duncker, 1896 (syn. Agamodistomum suis, Stiles, 1898) is the mesocercarial stage of the trematode Alaria alata, an intestinal parasite of some carnivores. The adult and metacercarial stages of these trematodes have little relevance as pathogens, whereas its mesocercarial stage is known to cause lesions in its paratenic hosts, in particular, in wild boars (Hiepe 1985, Odening 1963). Ljubaschenko and Petrov (1962) report about serious damages in fox, dogs, and arctic fox caused by DMS. The authors distinguish between two different disease patterns: the metacercarial alariosis manifests itself in the lungs, pleura, and the lymphatic vessels of the bronchia, while the adult parasites can cause inflammation of the bowel and a general intoxication (Ljubaschenko and Petrov 1962). Danijarow (1968) mentions high economic losses in fur farms caused by A. alata. Several human infections have been reported since Odening (1961a) recovered A. alata mesocercariae from an experimentally infected primate. Nevertheless, the risk for humans was generally ignored or at least postulated to be negligible until after about four decades this issue re-emerged in Europe: Jakšić et al. (2002) and Große and Wüste (2004, 2006) published results on repeated incidental findings of DMS in meat of wild boars during routine Trichinella inspection in certain areas of Croatia and Germany, respectively. In view of their findings, deficiencies in methodology, lack of data on prevalence, and the human DMS cases which were reported, they were the first to point out that the human DMS exposition risk is not negligible and would merit increased scientific attention. The Federal Office for the Environment (FOEN, Switzerland) categorized A. alata as a stage 2 risk (Z) for parasites with zoonotic potential (Anonymous 2003) as pertaining to occupational health risks. The Federal Institute of Risk Assessment (BfR 2007) finally concluded in its risk assessment that meat which contains A. alata mesocercariae should be regarded as unfit for human consumption. A final statement concerning the health risks for consumers could not be given due to the lack of information about both the prevalence of DMS and the suitability of Trichinella inspection methods to detect this parasite in wild boar meat (BfR 2007).

In the present paper, a review of the relevant knowledge on Alaria biology is given in order to further our understanding of potential consumer health risks which might be associated with this parasite.

History and taxonomy

The original description of the adult stage of A. alata in its definitive host was given by Goeze in 1782. Gestaldi (1854) first described the larval stage of the trematode (“Distoma tetracystis”) in frogs, and upon trichinellosis control in Saxony, sexually immature trematodes were found in swine muscles, which were studied and described by Duncker in a number of communications (Duncker 1881a, b, 1884, 1896, 1897). It took nearly 50 years to show that there is a link between the appearance of the mesocercarial stage of the parasite in frogs and in pigs (Bugge 1942a). Stefansky and Tarczynski (1953) finally demonstrated the relation between Alaria alata and Distomum musculorum suis, Duncker, 1896.

A. alata (Diplosomatidea, Strigeata) is a parasitic trematode of carnivores in Europe and the former Soviet republics (Schnieder 2006). Further Alaria species can be found in North and South America: A. mustelae (Bosma 1931), A. intermedia (Olivier and Odlaug 1938), A. marcianae (La Rue 1917), Alaria arisaemoides (Augustine and Uribe 1927), Alaria canis (La Rue and Falis 1934) (Paerson 1956), Alaria taxideae (Swanson and Erickson 1946). According to Sudarikov (1960) A. mustelae was also found in Europe; however, only in imported cases from America.

Morphology

The adult and mesocercarial stages of Alaria spp. are depicted in Fig. 1. The adult stage of A. alata measures approximately 3–6 × 1–2 mm (Schnieder 2006, Hiepe 1985, Wojcik et al., 2002). The body is clearly divided into two sections. The anterior end has a wing-like shape (alata, “winged”) and contains four clavate cells, with granular cytoplasm and spherical nuclei, within the oral sucker. They are glandular in appearance, but ducts were not observed (Pearson 1956). The posterior end is short and cylindric with a typical short intestine. The tribocystic organ shows a tongue-like shape (Hiepe 1985). The muscular ventral sucker, or acetabulum, measures approximately 0.04–0.1 × 0.04–0.09 mm and is therefore slightly smaller than the oral sucker (0.06–0.07 × 0.06–0.08 mm) (Andreas 2006). In order to receive nutrients, the ventral sucker is used for digestion and absorption of mucus and tissue from the wall of the host intestine (Roberts and Janovy, 2000).The lobed testicles of the male individuals are located one after the other in the rear body section. Anterior to them, the germarium is situated in the transient area of both body sections. The gonads of the female parasites lie in pairs in the anterior body region. Alaria species from North and South America differ morphologically in some aspects (Marshall 1972; Roberts and Janovy, 2000).

Fig. 1
figure 1

Fully developed adult (a) and mesocercarial (b) stage of Alaria spp. 1 remnant of penetration gland duct, 2 caecum (elonged), OE oesophagus, FBG forebody glands and their ducts, AC acetabulum, EF edge of fold over anterior and of holdfast organ, HF holdfast organ, VF ventral lip of spathiform forebody, GP genital primordium, a oral opening and oral sucker, b gland cells, c penetration glands, d caecum, DPG duct of penetration gland

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The eggs measure 110–140 × 70–80 μm (Hiepe 1985, Lucius et al., 1988). Development from egg to full-grown individual takes 92–114 days (Lucius et al., 1988).

The mesocercariae of A. alata are morphologically similar to the mesocercariae of american Alaria species (Odening 1961a). In the front body, anterior to the ventral sucker, lie two pairs of characteristic finely granular penetration glands which measure 300–500 μm and show a typical leaf-shaped appearance (Wirkerhauser 1980). According to Odening (1961a) the excretory bladder is V-shaped with dilatations at the posterior ends. Its branches lead in twisted attachments. These attachments are connected with the primary excretion system. The junction starts at the area approximately between the ventral sucker and the intestine, and the vessels bend laterally and to the rear, meandering until they reach the main excretory vessels. The reserve bladder system is developed within the larvae only in the form of a small anteromedial arranged tap (Odening 1961a). A ciliar trimming of the attachments, as shown in the respective larvae of A. intermedia, is missing (Olivier and Odlaug, 1938). In the rhesus monkey (scarpula region) the mesocercarial stage of A. alata is fully developed and enclosed by host tissue within 38 days (Odening 1963). The mesocercarial stage is characterized intra vitam by a unique motion sequence. In the stereomicroscopical examination for Trichinella, one “cannot but recognize it” (Große and Wüste 2006). This is illustrated by a sequence of single shots taken from a film of a DMS in typical motion in Fig. 2.

Fig. 2
figure 2

Alaria alata from a film of A. alata mesocercaria in motion after HCL/Pepsin digestion

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The metacercarial stage of Alaria spp. is a roundish, thin-walled, almost transparent vesicle of 0.4–0.7 mm length and 0.2 mm breadth with fine parallel lines on it (Hiepe 1985). In these cysts, one can recognize the whitish larva with a magnifying glass (Odening 1961b, 1963). The reserve bladder system is, as within most Strigeata larvae, strongly developed and covers large parts of the primary excretion system (Komiya 1938, Odening 1961a, Savinov 1954).

Life cycle

The complete life cycle of Alaria species, as schematically depicted in Fig. 3, had been worked out in the middle of the twentieth century (Petrov et al., 1950a, 1950b, Potekhina 1950, Savinov 1953a, b, Savinov 1954). The role of DMS in connection with the cycle of A. alata was recognized only at this time (Dollfus and Chabaud 1953, Stefański and Tarczyński 1953). While the members of the genus Strigea have an obligatory four-host life cycle, Alaria spp. develop in a three-host life cycle with an interjectional mesocercarial stage between the cercarial and the metacercarial stage. This life cycle can be extended by paratenic hosts. The term “hôtes d´attente” was first characterized by Joyeux and Baer (1934). The original description of this kind of life-cycle as well as the term “mesocercaria” was given by Bosma (1934). The mesocercarial stage is a kind of “resting stage” which is characterized morphologically by persistence of penetrating glands and a cyst which is solely formed by the host’s connecting tissue. The mesocercaria can survive several host transitions unharmed. After breaking through the intestine wall of the new host, it behaves as in the preceding host (Bosma 1934, Hiepe 1985, Lutz 1933a, b, Lutz 1921, Odening 1963, Pearson 1958, Pearson 1956, Schnieder 2006). Adult flukes, residing in the intestines of the definitive hosts, pass unembryonated eggs through the feces of the host. After two weeks, these eggs hatch in water, releasing the miracidium. They actively penetrate and develop further in a snail host (Planorbis-, Heliosoma-, Lymnea- and Anisus species) (Bosma 1934, Cort and Brooks 1928, Nikitina 1986, Odlaug 1940, Pearson 1956, Potekhina 1951, Ruszkowski 1922, Wójcik 2001). In this first intermediate host the miracidiae reproduction starts and after nearly a year of maturation, daughter sporocysts release cercariae provided with a fork tail (furcocercariae). They show a high motility in the water until an appropriate second intermediate host is exposed to them. This host might be a tadpole, an adult frog or other amphibian in which the furcocercariae develop into mesocercariae. The spectrum of snails, frogs, and amphibians and their preference vary depending upon Alaria species as shown in Table 1.

Fig. 3
figure 3

Life cycle of Alaria species: developmental stages

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Table 1 Second intermediate hosts of Mesocercariae of Alaria species according to literature
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In addition to the amphibian intermediate hosts, specified in Table 1, there are also paratenic hosts in the developmental cycle of Alaria spp., as already mentioned above. In this potential intermediate hosts, the larval parasites can survive when ingested, but they do not undergo any further development. They are also called “transport” or “auxillary intermediate” hosts (Wallace 1939, Baer 1951). These hosts may accumulate the mesocercariae with each transition, and they may also serve to pass over the infection from the aquatic to the terrestrial environment (Dönges 1969). While such hosts are not essential for the development of the parasite, they may be necessary for the completion of the life cycle for ecological reasons. For example, the intermediate host in which the larval stage develops obligatorily may not be included in the diet of the definitive host, whereas a paratenic host may be included. On the other hand, a paratenic host may be excluded from the diet of the definitive host in which case this host would be a “cul-de-sac” (Pearson 1956). The infection of these paratenic hosts takes place via the uptake of obligatory second intermediate hosts. Then the mesocercaria migrates through the intestine wall into the musculature of the anterior body section and/or settles at or in the different organs. The further development of the mesocercariae takes place in the body of the definitive hosts. According to Odening (1963), only members of the canidae can act as definitive hosts for A. alata. More recent studies point to the fact, however, that other carnivores (felidae, mustelidae) can also serve as definitive hosts for the parasite (cf. following chapter). After the oral uptake of an infected auxiliary or obligatory second intermediate host by a definitive host, the metacercariae perform a somatic migration. After reaching the lungs, the mesocercariae change into the metacercarial stage, are swallowed, and develop into adult worms in the host’s small intestines (Cuckler 1940, 1949, Odening 1963, Pearson, 1956, Schnieder 2006). Migration and reorganization of the mesocercariae through the metacercarial stage (syn.: Diplostomulum) to the adult worm are continuous processes with no intermediary stationary phase.

With the excretion of eggs into the intestine of the definitive host by adult trematodes and the entry of the eggs in the environment, the infection cycle starts again.

Hosts

The mesocercarial stage is particularly nonspecific toward its hosts. All Alaria species have a broad spectrum of paratenic hosts and almost all representatives of vertebrate animal classes may act as a carrier for the mesocercariae. Within the paratenic host, the parasite does not lose its infectivity toward the definitive host (Odening 1960, 1961a, 1963). The wide range of potential paratenic hosts of Alaria species is demonstrated in Table 2.

Table 2 Paratenic hosts of Alaria spp. mesocercariae following natural (N) and experimental infection (E) according to literature
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There was a long-standing controversy whether fish could act as paratenic hosts for Alaria spp. Leiper (1920) maintained that encysted larvae as recovered from naturally infected fish (African butter catfish, lat. Schilbe mystus) developed into A. alata when fed to wolves. Pearson (1956) fed mesocercariae of A. canis to six goldfish to see whether this fish could act as a paratenic host. Three days p.i., all mesocercariae were found on the viscera in the body cavity in various stages of encapsulation. None was found within the viscera or musculature. Pearson concluded that the mesocercariae made their way into the body cavity of goldfish, where some survived for 2 days, but where all were dead and encapsulated by 3 days. So the observations of Pearson (1956) suggest that, at least, goldfish are unsuitable as paratenic hosts for the mesocercariae of A. canis.

Riis et al. (2006) found living encapsulated mesocerariae in the periocular tissues, cornea, sclera, and occasionally the iris of an oyster toadfish (Opsanus tau). Unfortunately, they could not identify the mesocercariae properly. It is, however, well-known, that larvae of the Diplostomatidae occasionally infest the lens and the vitreous body of fish eye (Ashton et al., 1969, Hoffmann 1976, Leibovitz et al., 1980). Whether this infestation of the eye can be due to an oral intake of the parasites is contentious.

Moreover, the spectrum of definitive hosts is very broad and includes, depending upon the Alaria species, a wide range of carnivores in the respective geographic range. In the literature, numerous descriptions of A. alata infections in different canides, felides, and mustelides can be found as summarized in Table 3.

Table 3 Prevalence (Prev. %) of carnivore hosts of Alaria alata as reported in literature
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Foster et al. (2008) demonstrated A. marcianae mesocercariae in the lungs of three freshly dead Florida panther neonates. The 11-, 12-, and 17-day-old neonates were presumably fed only on milk from the dam since birth. Milk was the only item found in the gastrointestinal tract of these whelps. Mesocercariae and diplostomula of A. marcianae were collected from the lungs of the three neonates, indicating a transmammary route of infection. No mesocercariae, diplostomula, or mature A. marcianae were seen in the stomach or the small intestine. So the dam was assumed to be the definitive host. The probable paratenic host for the A. marcianae infection in the adult Florida panther is the raccoon (Procyon lotor). Several authors already reported about the possibility of a vertical transmission of Alaria mesocercarial stages (Pence et al., 1988, Shoop and Corkum 1983, 1984a, b, 1987, Shoop et al., 1990). Shoop and Corkum (1987) assume not-lactating and male cats to serve as definitive hosts for Alaria spp., whereas lactating dams would usually act as a paratenic host (Shoop and Corkum 1987). Yastrebov et al. (2005) demonstrated A. alata mesocercariae in the blood of stray cats and dogs. The results of these studies indicate a hematogenous spread of the mesocercarial stage of the parasite and simultaneously point to the fact that even definitive hosts can act as carriers of Alaria spp. mesocercarial stages.

Prevalence

As stated above, A. alata is reported to be the species of European carnivores. However, recent studies revealed that DMS can also be found in South American carnivores (Castro et al., 2008, Ruas et al., 2008). Alaria species are distributed worldwide (Danijarow 1968, Ljubaschenko and Petrov 1962, Mehlhorn 2008, Schnieder 2006). Mehlhorn (2008) estimated that about 30% of the wild canides in Europe are carriers of A. alata. The results of various field studies are listed in Table 3. Variability of prevalence data is high, ranging, for example, in the red fox from 0.1% to 88% as shown in Table 3. A. alata is the most frequently described trematode of the raccoon dog (Thiess 2006) with prevalence data ranging from <10 to nearly 70% (Schuster et al., 1993). Moreover, the number of parasites that were found per individual animal varied strongly and ranged from 1 to 1.533 adult helminthes (e.g., Borgsteede 1984, Castro et al., 2008, Moks et al., 2006, Shimalov et al., 2000a, 2001a, b, c, 2002, 2003, Wolfe et al., 2001).

Although only the definitive host of the parasite excretes its contagious eggs, transition of mesocercariae between paratenic hosts is quite common (Odening 1963, Hiepe 1985). High infestation rates can therefore be found particularly in omnivores such as wild boars, which live in areas with high Alaria prevalence in the definitive hosts. This is because these animals, besides the obligatory second intermediate hosts, also feed on paratenic hosts such as rodents, reptiles, and amphibians (Dönges 1969).

Generally, a significant prevalence of A. alata mesocercariae in wild animal populations can be expected in water-rich areas in which the suitable host species (snails, amphibians, and definitive hosts) are present. Wojcik et al. (2001) demonstrated the dependency between the occurrence of suitable snail and amphibian hosts and the prevalence of A. alata mesocercariae in wild boars. The studies were conducted between 1999 and 2001 in two hunting regions. Larval alariosis was only revealed in the boars from one of the studied regions. In this region, the results of the parasitological studies revealed definitive (domestic dogs) and intermediate hosts (snails, Planorbis planorbis and Anisus vortex as well as frogs: Rana temporaria and Rana terrestris) to be carriers of A. alata. The lack of snail hosts in the other region was interpreted as a possible reason for the absence of the parasite in the boar (Wójcik et al. 2001).

In 2002, first incidental findings of A. alata during Trichinella inspection in the Perleberg abattoir (Brandenburg, Germany) were reported to one of the authors (KG). The parasite was found in carcasses of two wild boars which were finally judged fit for human consumption (personal communication to KG). Jakšić et al. (2002) demonstrated that 1.8% of 210 wild boar samples from Croatia were positive for A. alata mesocercariae. Positive carcasses were judged unfit for human consumption (Jakšić et al., 2002). Große and Wüste (2004, 2006) were the first to publish results on incidental findings of DMS in meat of wild boars during routine Trichinella inspection in certain areas of Germany (Brandenburg), indicating a potential health risk to consumers. Whereas the first finding of a mesocercarial stage (April 7, 2003) could not be confirmed by the BfR, the second finding of eight highly motile mesocercariae (October 12, 2003) was clearly identified as A. alata by the BfR. The carcasses were declared unfit for human consumption. In 2007, DMS was demonstrated in 0.24% of all Trichinella samples in Brandenburg. However, as samples were then pooled, the correct prevalence could not be exactly stated (Große and Wüste 2008). During the examination of other wild animals (reptiles, amphibians, birds, mammals) in Brandenburg, A. alata mesocercariae could be demonstrated in a badger (personal communication to KG). The isolated parasite is depicted in Fig. 4.

Fig. 4
figure 4

Four motile Alaria mesocercariae and two unspecified nematodes after HCL/pepsin digestion from muscle tissue of a badger (bar conforms 200 μm)

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Detection

In the following, we will concentrate on the methods for detection of mesocercariae in paratenic hosts with respect to the human exposition risk.

All detections of Alaria mesocercariae in wild boar meat were incidental background findings during official Trichinella inspection, which was and is obligatory for meat of all potential Trichinella carriers to be introduced into the human food chain (64/433/EEC, 854/2004/EC). Only official methods for Trichinella detection which have been standardized and officially published may be applied (77/96/EEC, 2075/2005/EC). Currently, one reference method and three alternative methods exist which are all based in principal on (a) pepsin/HCl-digestion of muscle tissue, (b) concentration of the digest by sedimentation or filtration, and (c) microscopic examination (2075/2005/EC). A fourth method, the traditional compression method (“trichinoscopy”), where a small muscle sample compressed between to glass slides is directly examined under the microscope, may still be applied in an exceptional case s (2075/2005/EC). It is of some interest that this method, which has shown to be of significantly less sensitivity then the digestion methods, is apparently applied with relatively high frequency in some countries/areas of the European Union for Trichinella inspection of the meat of wild boars.

Samples for Trichinella inspection have to be “free of all fat and fascia” as stated expressis verbis in Annex I, Chapter I, No 2 b) and c) of the respective regulation, (EC/2075/2005). However, Alaria mesocerariae show “apparently a high affinity to the host’s adipose tissue” (Odening 1961b). This high affinity to the adipose tissue was first described by Bugge (1942a). As can be seen from Table 4, Alaria mesocercariae were detected in all paratenic hosts—in most cases, exclusively (North American river otter, Kimber and Kollias (2000), raccoon and opossum, Shoop and Corkum (1981), hedgehog and wild canides, Sudarikov (1960), snakes (e.g. Cort 1918, Dick and Leonard 1979, Odening 1961b, Pearson 1956, Shoop and Corkum 1981, Shoop at al. 1990)—in adipose tissue.

Table 4 Anatomic localization of and detection methods for mesocercariae of Alaria spp. in several paratenic host species as described in literature
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It is highly questionable if a method as optimized for the detection of Trichinella in pure muscle tissue can reliably detect Alaria mesocercariae which obviously distributes quite differently in its host as shown in Table 4.

Up to 2005, Trichinella inspection was by way of derogation from the obligatory ruling—until a common harmonizing rule would be created for so-called “Trichinella-free areas”—not necessary in member states which applied for non-inspection on a national level (92/120/EEC). The extent of this derogation from Trichinella inspection of fattening pigs reached substantial orders of magnitudes in some member states (Lücker and Hartung 2006). It might be concluded that also a substantial number of wild boars remained unexamined for Trichinella and thus for DMS in some European member states. Today, derogation from the obligatory Trichinella inspection is possible in the context of so-called “Trichinella-freedom” which is under strict official control (i.e., “Trichinella-free” farms and “Trichinella-free” regions) and only applicable to fattening pigs (2075/2005/EC). For wild animal populations, derogation from obligatory Trichinella inspection will be possible, where “the competent authority has ascertained by risk assessment that the risk of Trichinella infestation of a particular farmed or wild species is negligible.” Moreover, Trichinella inspection of wild game or wild game meat directly supplied to the final consumer or to local retail establishments directly supplying the final consumer falls within the responsibility of the member state s (2075/2005/EC). Thus, future development in Trichinella inspection might also contribute to a further increased underestimation of DMS in wild animal populations.

Pathogenicity

For a long time, it was assumed that DMS in wild boars would not imply any risk to consumers (Beutling 2004, Lerche et al., 1957, Ostertag and Schönberg 1955).

In contrast, Odening (1961b) demonstrated by experimentally infecting a primate that Alaria mesocercariae can cause severe damages within a paratenic host closely related to humans. Overall pathogenicity is correlated to high infestation densities, in particular, after repetitive intake of mesocercariae. The transition of the mesocercariae from one paratenic host to another fails to decrease infectivity of the parasite (Bosma 1934, Dönges 1969, Hiepe 1985, Lutz 1933a, b, Lutz 1921, Odening 1963, Pearson 1958, Pearson 1956, Schnieder 2006). Since 1973, several reports about human larval alariosis have been published as summarized in Table 5.

Table 5 Cases of human larval alariosis according to literature
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It is important that most infections with trematodes are found to be associated with eosinophilia and an increase of IgE (Löscher and Sonnenburg 2005), which means that a general anaphylactic reaction may arise from a repetitive oral intake of infected material. The symptoms of an anaphylactic shock range from tachycardia and drop in blood pressure to vasomotoric collapse and unconsciousness (Bork 1985, Egger 2005).

Human alariosis manifests in various clinical signs which range from low-grade respiratory and cutaneous symptoms to a diffuse unilateral subacute neuroretinitis (DUSN) (Bialasiewicz 2000, Hedges 2000) and to an anaphylactic shock with lethal consequence as mentioned above. Freeman et al. (1976) report on a 24-year-old Canadian male who complained of tightness in the chest and abdominal symptoms after several long hikes across eastern Ontario (Canada). Within 2 days of the initial illness, the patient developed flu-like symptoms like headaches, fever, faintness, and cough, and on the third day, showing severe dyspnea and hemoptysis, he was admitted to a local hospital. On the fourth day, the patient became comatose, and skin petechiae were evident. The tentative diagnosis was viral pneumonia, and he was treated with broad-spectrum antibiotics. After the treatment failed, biopsy of a skin lesion and an open-lung biopsy were performed. The tissue sections of fixed lung tissue contained lengthwise sections of a fluke which was tentatively identified as Alaria spp. mesocercaria. By the ninth day, after initial symptoms, the patient died in the hospital. At autopsy, practically all viscera showed extensive local or diffuse hemorrhage. Several thousand mesocercariae were estimated to have been present within the viscera and nearly all organs. The cause of death was asphyxiation from extensive pulmonary hemorrhage, probably due to immune-mediated mechanisms, after repetitive oral intake of Alaria Americana mesocercariae. The possibility that the infective dose of mesocercariae might have been ingested with drinking water was investigated and ruled out. The authors concluded that the victim ate uncooked or more likely inadequately cooked frog legs heavily infected with mesocercariae; however, relatives denied that.

Risk assessment and conclusion

In accordance with the recent assessment of the BfR (2007), which concluded that current methodology and data are insufficient, a sound analysis of consumer exposition risk to Alaria mesocercariae is impossible for the time being. However, there is no question about the high potential pathogenicity of this parasite as shown in the previous chapter. Jakšić et al. (2002) and Große and Wüste (2004, 2006) pointed out, that the parasite represents a potential source of infection for both humans and animals and that consumption of wild boar meat can be an important factor for the epidemiology of this zoonosis.

Both alimentary and occupational exposition must be taken into account. As to the latter, the Swiss Federal Office for the Environment (FOEN) categorized A. alata as a stage 2 risk (Z) for parasites with zoonotic potential (Anonymous 2003) as pertaining to occupational health risks.

Up to now, only few reports on human larval alariosis exist, and none have been reported in Germany. Keeping the possibly high non-inspection rate of wild boars for Trichinella as well as the methodological deficiencies in mind, we must balance this against a presumably low level of awareness of this zoonosis in general and particularly against more or less uncharacteristic symptoms of low level infections. A tendency can be noted for European official meat inspection to treat DMS positive meat of wild boars as unfit for human consumption, at least on a provisional basis and in favor of consumer protection (BfR 2007, Jakšić et al. 2002).

In conclusion, we can state that the high potential pathogenicity of Alaria spp. mesocercariae and their presence in wild game should initiate further studies. They must concentrate on (1) the optimization and/or development of methods of DMS detection, (2) the distribution of the mesocerariae within paratenic hosts (so-called predilection sites), (3) their prevalence in sylvatic populations of wild animals and in the food chain. Further, their tenacity within the paratenic host and meat as pertaining to food technological treatments has to be elucidated. Moreover and in close connection with the parasites’ pathogenicity and tenacity, the question whether Alaria alata might split up into different species should be elucidated.

Following the publications of incidental findings of Alaria mesocercariae in wild boar meat (Große and Wüste 2006) and the statement on the DMS problem by the BfR, the Federal Ministry of Nutrition, Agriculture and Consumer Protection (BMELV, Germany) consequently initiated and funded a study on the detection and prevalence of Alaria mesocercariae in wild animal populations. We will present first results of this study in a following paper. They support the conclusions of this review strongly and will supply further prevalence data as well as first results of a preliminary method for the detection of Alaria mesocercariae in adipose tissue.