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

SIMPLE SUMMARY: Macrocysts of the protozoan Sarcocystis rileyi, resembling rice grains, are found in the muscles of numerous duck species. Meat from ducks contaminated with S. rileyi is not suitable for consumption, and severe S. rileyi infections are harmful to infected birds. This Sarcocystis species was reported only in North America for a long time. However, recently, the number of reports of S. rileyi infection in European wild ducks has increased. The present research is the first long-term surveillance study on macrocysts in wildfowl species. Overall, 3268 individuals of wildfowl species collected in Lithuania, Latvia, Russia, and Belarus were tested for macrocysts of Sarcocystis. The examined parasite was detected in 237 Mallards and in two Eurasian Teals. Macrocysts isolated from 37 Mallards were examined by DNA methods and identified as S. rileyi. The infection rates of macrocysts in Mallards in the examined region ranged from 3.1% to 8.7%. The fluctuations in infection rates were observed in different years, months, and studied countries. Based on the results of the current research and previous studies, the prevalence of macrocysts depends on the duck species, age of the bird, year, geographical region, and hunting season but is not related to the sex of the bird. ABSTRACT: 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.