Alaria alata mesocercariae prevalence and predilection sites in amphibians in Latvia

Alaria alata is known as a trematode with a complex life cycle. The trematode Alaria alata infects amphibians as second intermediate hosts. In the present study, we examined 390 amphibians-European water frogs Pelophylax esculentus complex (n = 335), common frogs Rana temporaria (n = 19), moor frogs Rana arvalis (n = 3), and common toads Bufo bufo (n = 30) collected from randomly selected wetland habitats in Latvia. Out of all examined specimens, 80 were tadpoles and 310 were adult amphibians. Mesocercariae of A. alata was detected in 108 specimens from all examined amphibian species, except the common toad, reaching the overall prevalence of 27.7%. Tadpoles were found to be more frequently infected with A. alata, when compared with adults, 58.8% and 22.4%, respectively. The results showed that mesocercariae accumulate in visceral membranes, different internal organs, and muscles in the head area. This is a comprehensive study to identify A. alata mesocercariae predilection sites in amphibians.

The wild boar (Sus scrofa, Linnaeus, 1758) as an important reservoir host for Alaria alata in the Baltic region and potential risk of infection in humans

Alaria alata trematode is widely distributed throughout Europe and has a complex life cycle in which wild boar serve as a reservoir host. The primary aims of the present study are to establish the occurrence of A. alata mesocercariae in naturally infected wild boar in Latvia and to assess the risk for humans to acquire A. alata infection via consumption of wild boar meat. By summarizing long-term data using the Trichinella inspection method from 2014 to 2019, the overall A. alata prevalence was 8.3%, of which significantly higher A. alata prevalence was observed during the summer seasons. Additionally, 43.9% (n = 485) of wild boar were found to be infected with A. alata using Alaria mesocercariae migration technique. The present study indicates that the probability for humans to acquire A. alata mesocercariae is possible, yet improbable and varies from 0.2% to 2.2%. Most likely, it depends on both frequency of A. alata presence in wild boar population and of a method of preparing wild boar meat for consumption that will allow for the parasite inactivation.

The occurrence of Alaria alata mesocercariae in wild boars (Sus scrofa) in north-eastern Poland

Various species of mammals, including humans and wild boars, can serve as paratenic hosts of Alaria alata mesocercariae – Distomum musculorum suis (DMS). Cases of DMS can be reliably detected by the recent introduction of the A. alata mesocercariae migration technique (AMT). The aim of this study is to present current data on the occurrence of DMS in wild boars in north-eastern Poland, and to compare the findings with those obtained in other European countries. A. alata was identified in 98 of 221 (44.3%) tissue samples of wild boar taken from five provinces in north-eastern Poland during the hunting seasons 2015–2016 and 2016–2017 based on AMT analysis. Positive results were found in all studied regions, but the percentage of infected individuals ranged from 26.3% in the Pomorskie province to 65.5% in the Warmińsko-Mazurskie province. The mean number of larvae exceeded seven larvae per 30 g sample for three provinces: Pomorskie, Mazowieckie and Lubelskie. In turn, lower values were found in the Warmińsko-Mazurskie province (3.3 larvae per 30 g), and the lowest in the Kujawsko-Pomorskie province (1.8 larvae per 30 g). The occurrence and intensity of A. alata infestation in wild boars was found to depend on the environment in which they live. Neither the sex or the age of the wild boar appeared to influence the occurrence nor the intensity of infestation.

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High percentage (44.3) of Alaria alata in samples of wild boars in Poland.

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High prevalence of A. alata infestation in wild boars compared to other reports.

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Sex does not affect the risk or intensity of infestation by A. alata in wild boars.

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Age does not affect the risk or intensity of A. alata infestation in wild boars.

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A. alata poses a potential risk for wild boar consumers in Poland.

First confirmed case of Alaria alata mesocercaria in Eurasian lynx (Lynx lynx) hunted in Latvia

Trematode Alaria spp. have a complex life cycle that includes canids, mustelids, and felids as definitive hosts. However, several mammal species, besides acting as definitive hosts, may also act as paratenic hosts. Alaria spp. life cycles are well studied. Still, there is a lack of knowledge on one host significance as both-the paratenic and definitive host, especially in the case of Eurasian lynx (Lynx lynx). Previous studies have described Eurasian lynx as a definitive host for A. alata although the prevalence has always been low. The aim of the present study was to analyze the occurrence of A. alata in Eurasian lynx in Latvia. The viscera (n = 231) and muscle samples (n = 234) from Eurasian lynx were collected during the hunting seasons from 2004/2005 to 2017/2018. The prevalence of the adult A. alata in Eurasian lynx was 1.7%. However, mesocercariae infection in Eurasian lynx was detected for the first time. These findings suggest that the Eurasian lynx may serve both as paratenic and definitive host for A. alata.

Alaria alata mesocercariae in domestic pigs and wild boars in South Banat, northern Serbia

Alaria alata (Diplostomidae, Trematoda), a potentially zoonotic pathogen, is the only Alaria species in Europe. In recent years, increasing reports of mesocercariae of A. alata in wild boars have been recorded in European countries; however there have been no described cases in domestic pigs over the past decades. Out of 272 diaphragm samples from wild boars (Sus scrofa) and domestic pigs (Sus scrofa), from Serbia, included in the present investigations, mesocercariae of A. alata were found in six (3%) samples from wild boars and in two (2.77%) samples from domestic pigs. Due to the lack of sensitivity of artificial digestion with a magnetic stirrer which was applied in the study, the true prevalence is estimated to be considerably higher in the area of investigation. Confirming the infection in domestic pigs and a wide distribution in wild boars in the area of investigation, the present paper should influence the growing awareness of alariosis as a potential human disease. The meat from free-range domestic pigs and game meat as a potential source of alariosis should always be adequately thermally treated before consumption.

Prevalence and intensity of Alaria alata (Goeze, 1792) in water frogs and brown frogs in natural conditions

In the last 15 years, the mesocercariae of Alaria alata have frequently been reported in the wild boar during routine Trichinella inspections made compulsory for the trade of venison meat in Europe. If these studies have focused primarily on mesocercariae isolated from meat, few works have been done so far to understand the circulation of the parasite in natural conditions especially in the intermediate hosts. This study focuses on the second intermediate hosts of this parasite assessing the suitability of two amphibian groups-brown frogs and water frogs sensu lato-for mesocercarial infection on an area where A. alata has already been identified in water snails and wild boars. During this study, both groups showed to be suitable for mesocercarial infection, with high prevalence and parasite burdens. Prevalence was higher in the brown frog group (56.9 versus 11.54 % for water frogs) which would indicate that it is a preferential group for infection on the study area, though reasons for this remain to be investigated. No significant difference among prevalences was observed between tadpoles and frogs. This study, the first focusing on A. alata in these amphibians in Europe, provides further information on circulation of this parasite in natura.