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.