Description of Sarcocystis platyrhynchosi sp. nov. (Apicomplexa: Sarcocystidae) infection in domestic ducks Anas platyrhynchos (Anseriformes: Anatidae) in China

Abstract

Abstract Background: Data on the genus Sarcocystis in waterfowls are very limited. To the best of our knowledge, the species of Sarcocystis have previously never been recorded in ducks in China. Methods: Leg muscles were obtained from 26 domestic ducks Anas platyrhynchos in 2021 in China. Sarcocysts were observed using light microscopy (LM) and transmission electron microscopy (TEM). Individual sarcocysts from different hosts were selected for DNA extraction, and three genetic markers, namely, 18S ribosomal DNA (18S rDNA), 28S ribosomal DNA (28S rDNA), and mitochondrial cytochrome oxidase subunit 1 (cox1), were amplified, sequenced, and analyzed. Results: Sarcocysts were found in 3 of the 28 (10.7%) domestic ducks. Under LM, the sarcocysts were microscopic and had brush-like villar protrusions (vps), measuring 3.8–4.3 μm-long. Ultrastructurally, the sarcocyst wall contained numerous lancet- or leaf-like vp. Each vps narrowed in the stalk and contained bundled microtubules extended into the ground substance. Comparison of the newly obtained sequences with those previously deposited in GenBank indicated that the most similar sequences were those of S. halieti ex Phalacrocorax carbo or Sturnus vulgaris,and S. calchasi ex Columba livia, with an identity of 99.1% at 18S rDNA, S. wenzeli ex Gallus gallus, with an identity of 95.9–96.0% identity at the 28S rDNA, and S. speeri ex opossum, with an identity of 98.2% at the mitochondrial cox1. Additionally, at the three loci, the newly obtained sequences unambiguously differed from those of Sarcocystis spp. obtained from Anseriformes birds. Phylogenetic analysis based on the three loci placed the parasite within a group containing Sarcocystisspp. that utilize birds or dogs as intermediate hosts. The parasite was proposed as a new species, named Sarcocystis platyrhynchosi. Conclusions:Sarcocysts were recorded in domestic ducks in China for the first time. Morphologically and molecularly, the sarcocysts remarkably differed from those of Sarcocystis spp. previously reported in different intermediate hosts, and S. platyrhynchosi was proposed for the new species. Depending on the limited date provided for Sarcocystisspp. in Anseriformes birds, there is confusion concerning the relationships of the morphologically similar species of Sarcocystisin Anseriformes birds. Therefore, more research on these closely related species of Sarcocystis needs to be undertaken in the future.