Recent incidental background findings of Alaria alata mesocercariae ["Distomum muscularis suis," Duncker, 1896] in meat of wild boars during official Trichinella inspection initiated a re-assessment of the potential human health risk as posed by this parasite. The present review of the literature on Alaria biology shows that the human exposition risk should no longer be accepted to be negligible, as it demonstrates a general lack of knowledge in relevant areas of Alaria biology confounding any risk analysis. Sound risk assessment needs future studies which should concentrate on the most pressing questions of (1) the optimization and/or development of methods for reliable Alaria mesocercariae detection, (2) the distribution of the mesocercariae within their paratenic hosts, i.e., identification of potential predilection sites, particularly in wild boars, and (3) their prevalence in sylvatic populations of animals with respect to their introduction into the human food chain. Further, the degree and possibly also the species specificity of Alaria mesocercariae tenacity within the paratenic hosts and respective meat as pertaining to food technological treatments need to be elucidated. While these questions remain unanswered, it is an incontrovertible fact that Alaria mesocercariae have a potentially high human pathogenicity by both occupational and alimentary exposition.

Distomum musculorum suis (DMS), the mesocercarial stage of the trematode Alaria alata, can cause severe damages within their hosts, and since several reports about cases of human larval alariosis have been published, it became apparent that infected game animals and in particular wild boars are a potential source of infection for both humans and animals. 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. Our studies concentrate on (1) the verification of suitability of the official digestion methods for Trichinella spp. for DMS detection in wild boars, (2) development, optimization, and validation of methods, and (3) the distribution of the parasites within their paratenic hosts. A total of 868 individual samples/digests from 48 wild boars were analyzed by the reference method for Trichinella detection in meat samples according to regulation (EC) No. 2075/2005. In addition to the official protocol, a method modification with Pankreatin(c) and bile acid was applied for analysis of adipose tissue samples (n = 89). On the basis of our results, a new detection method based on a larvae migration technique was developed and used for detection of DMS in 574 single samples. Furthermore, the distribution patterns of DMS in wild boars in a total of 1377 single sample migrations/digestions from 35 positive animals were analyzed by application of all three methods. The official digestion method for Trichinella spp. in wild boars meat is inapplicable for the detection of A. alata mesocercariae as it shows shortcomings in both digestion and sampling. A direct comparison between the newly developed A. alata mesocercariae migration technique and the official digestion method for Trichinella spp. based on 574 single samples from 18 animals clearly shows that the sensitivity to detect A. alata developmental stages in tissues of wild boars of the new method is nearly 60% higher compared with the magnetic stirrer method for pooled sample digestion as laid down in regulation (EC) No. 2075/2005. Among other advantages, this method offers a simple, highly applicable, fast, and cost effective way to detect DMS in wild boars which is already applicable in routine veterinary inspection.

Over the last decade, incidental findings of Alaria alata in stocks of German wild boar during the official Trichinella inspection have been increased. As early as 2006, the German Federal Institute for Risk Assessment pointed out the possible health risk to the consumer posed by this trematode. However, at that time, reliable data concerning the prevalence of the parasite in German wild boars and feral pigs were lacking especially because no appropriate detection method was available. The development of the A. alata mesocercariae technique (Riehn et al., Parasitol Res 107(1):213-220, 2010) now makes it possible to close the remaining gaps in knowledge in this field. Over a 2-year period, 286 retained samples of fresh meat from wild boars originating from different hunting areas in Brandenburg and Saxony-Anhalt, which were tested negative for A. alata during the official Trichinella inspection in the competent veterinary inspection offices, were reexamined with the A. alata mesocercariae migration technique (AMT). In 33 out of 286 retained meat samples (11.5%) with a preliminary negative report, the trematode was demonstrated during the follow-up examination using AMT. This result especially in connection with the highly heterogeneous distribution of the parasite within the hosts' body (Riehn et al., Parasitol Res 107(1):213-220, 2010; Moehl et al., Parasitol Res 105(1):1-15, 2009) shows clearly that a high number of unreported cases of alariosis in wild boars have to be assumed.

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