Sarcocystis rileyi in UK free-living wildfowl (Anatidae): surveillance, histopathology and first molecular characterisation

The Distribution of Sarcocsytis Species Described by Ungulates-Canids Life Cycle in Intestines of Small Predators of the Family Mustelidae

PURPOSE

Using molecular techniques, we have previously shown that carnivorous mammals of the family Mustelidae might be common definitive hosts for various protozoan Sarcocystis species. In the present study we aimed to unravel whether Sarcocystis species using ungulates as intermediate hosts and canids or felids as definitive hosts can be found in intestine of mustelids.

METHODS

Small intestine samples of 93 individual mustelids of five different species from Lithuania were examined. Sarcocystis species were identified based on species-specific PCR and subsequent cox1 sequencing.

RESULTS

Six Sarcocystis species (S. arieticanis, S. bertrami, S. capracanis, S. capreolicanis, S. linearis and S. morae) defined by ungulate-canid life cycle were detected for the first time in small intestines of mustelids. By contrast, the prevalence of Sarcocystis characterised by ungulate-felid life cycle was low (3.2%). Overall, 76% of the examined animals were positive for at least one of the studied Sarcocystis species. Four species, S. arieticanis, S. bertrami, S. capracanis and S. morae were most commonly found, with the detection rate of about 40%.

CONCLUSIONS

The current finding, in addition to our previous studies, suggests that mustelids play an important role in the spread of various Sarcocystis species.

Sarcocystis spp. Macrocysts Infection in Wildfowl Species in Eastern Baltic Region: Trends in Prevalence in 2011-2022

Wildfowl meat infected with S. rileyi macrocysts is not suitable for human consumption. Ducks are among the main game birds in Europe, and S. rileyi infections cause significant economic losses. In 2011-2022, a total of 2649 anseriforms collected in Lithuania and 619 Mallards (Anas platyrhynchos) hunted in the Kaliningrad region of Russia, Belarus, and Latvia were tested for macrocysts. In Lithuania, macrocysts were detected in 206 of 2362 Mallards (8.7%) and in two of 88 (2.3%) Eurasian Teals (Anas crecca). The prevalence of macrocysts in the other three countries, Belarus (5.9%), Russia (5.0%), and Latvia (3.1%), was similar. For species identification, macrocysts isolated from 37 Mallards (21 from Lithuania, 8 from Russia, 6 from Belarus, and 2 from Latvia) were subjected to sequencing of the ITS1 region. Based on DNA analysis, S. rileyi was confirmed in all tested birds. By comparing the infection rates of macrocysts in Mallards in Lithuania, significant differences were observed in different years (p = 0.036), and a significantly higher prevalence of infection was established in November-December than in September-October (p = 0.028). Given the amount of data per decade on the prevalence of S. rileyi, awareness of infection needs to be increased.

Molecular Identification of Sarcocystis rileyi and Sarcocystis sp. (Closely Related to Sarcocystis wenzeli) in Intestines of Mustelids from Lithuania

The genus Sarcocystis is a group of numerous protozoan parasites having a two-host life cycle. Based on laboratory experiments and/or phylogenetic analysis results it was shown that seven Sarcocystis spp. producing sarcocsyts in bird tissues are transmitted via predatory placental mammals. To date the role of small mammals of the family Mustelidae in the distribution of avian Sarcocystis spp. have not been studied. During the current investigation, intestinal mucosa scrapings of 115 mustelids belonging to five species were tested for S. albifronsi, S. anasi, S. rileyi, and S. wenzeli infecting anseriforms and chickens. Microscopically, free sporocysts, sporulating oocysts, and loose oocysts were found in 61 samples (53.0%). Using nested PCR targeting the ITS1 region and sequencing, S. rileyi was confirmed in eight American minks, two European polecats and single European badger. Sarcocystis sp. was identified in one American mink and one European pine marten. Based on the partial ITS1 region this parasite showed that 100% identity to pathogenic Sarcocystis sp. caused a fatal infection in backyard chickens from Brazil. Phylogenetically, the Sarcocystis sp. identified in our study was most closely related to S. wenzeli parasitising domestic fowl (Gallus domesticus).

Sarcocystis rileyi (Apicomplexa) in Anas platyrhynchos in Europe with a potential for spread

Four specimens of mallard (Anas platyrhynchos) shot by local hunters (December 2020 to January 2021 along the eastern coastline of the island of Bornholm in the Baltic Sea) were diagnosed with a heavy load of sarcocysts in the musculature. Morphometric and molecular diagnosis based on rDNA (18 S, ITS1, 28 S) of parasites recovered from two of the birds revealed the causative pathogen to be Sarcocystis rileyi. We further present novel sequences for the entire 5.8 S and ITS2 for this species. Elongate cysts (mean length 5.25 (SD 0.6) mm, width 1.37 (SD 0.2) mm) were recorded in all parts of the striated skeletal musculature of the birds. The main part (72%) of the 2585 cysts in one female mallard was located in the outer superficial pectoral musculature, with 11% in the inner pectoral musculature. Minor but significant parts were found in the dorsal, ventral abdominal, neck and head, legs, hand and arm (wing) musculature. No cysts were found in the smooth musculature. Each cyst contained a median of 3.2 mio bradyzoites indicating that more than 8 billion bradyzoites are available for infection of one or more predators/scavengers ingesting the bird. Bradyzoites (median length 13.5 μm (range 12.1–14.5) and median width 2.66 μm (range 2.1–3.3)) were highly resistant to proteinase treatment, which secures the passage through the stomach of the predator to its intestine where wall penetration takes place. One of the birds was ringed (tagged) in Sweden Island Øland in the Baltic Sea two years before being shot. This is documenting immigration of mallards from northern locations. The parasite species was originally described in North America in 1893 and was commonly reported in this region during the 20th century but not in Europe. Recent cases from Norway, Finland, Lithuania, Poland, UK and Hungary suggest that the species may be spreading geographically. Experienced duck hunters with a 40 years record of hunting on the island reported that this type of infection unprecedented. The final host is reported to be canines (fox, raccoon dog), skunk and mustelids, including ermines and American mink. Presence of these hosts in Europe may allow establishment of the life cycle and further colonization of the local duck populations which calls for implementation of a survey program in Europe.

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Heavy loads of the apicomplexan Sarcocystis riley are described from mallards.

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Sarcocysts occurred in all parts of the striated musculature.

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Sarcocysts dominated in the superficial pectoral muscle.

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The number of bradyzoites in one single mallard was estimated to more than 10 billion.

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Sarcocystis rileyi is a new species record for Denmark.