Biology of Alaria spp. and human exposition risk to Alaria mesocercariae—a review

Abstract

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.

Helminth parasites of the red foxVulpes vulpes(L., 1758) and the wolfCanis lupus italicusAltobello, 1921 in Emilia-Romagna, Italy

“…Definitive hosts, usually members of the family Canidae, become infected after ingesting mesocercariae in amphibians or paratenic hosts. A. alata is regarded as a potential zoonotic agent, especially considering the contamination of wild boar meat with viable mesocercariae (Möhl et al 2009;Széll et al 2013). Interestingly, we found another digenean trematode, Brachylaima spp., in three foxes ( (Urquhart et al 1996;Lahmar et al 2014).…”

“…Alaria alata (Goeze, 1782) ( Figure 1) is a common intestinal trematode of red foxes in European countries (Möhl et al 2009). Conversely, the presence of A. alata in Italy has been rarely reported.…”

“…The complex life cycle of A. alata requires a freshwater snail as the first intermediate host and an amphibian as the second one. Reptiles, rodents, wild boars and other vertebrates can act as paratenic hosts after feeding on infected amphibians (Möhl et al 2009). Definitive hosts, usually members of the family Canidae, become infected after ingesting mesocercariae in amphibians or paratenic hosts.…”

Free-living snakes as a source and possible vector of Salmonella spp. and parasites

“…The obtained data suggest that free-living snakes may act as vectors of parasites for wild scavengers and omnivores, i.e., wild boars. High numbers of DMS reported in freeliving snakes (Mohl et al 2009;Shimalov and Shimalov 2000) might be related with their prey on amphibians. Noteworthy, both the prevalence and enumeration of parasites might have been reduced by several factors.…”

“…One might presume them as paratenic hosts (Duscher et al 2015;Halajian et al 2013;Mohl et al 2009), although public health consequences of direct contact with carrier reptile itself or its' contaminated environment shall not be neglected (Mohl et al 2009;Zając et al 2013).…”