Infections with Sarcocystis wenzeli are prevalent in the chickens of Yunnan Province, China, but not in the flocks of domesticated pigeons or ducks.

The distribution and prevalence of infections with species of Sarcocystis in domestic fowl in Asia are poorly known. Here, ducks, pigeons, and chickens from Yunnan Province, China were examined for evidence of parasitic infection with Sarcocystis spp. One hundred and ninety one chickens, 514 ducks, and nine pigeons were investigated. Whereas the ducks and pigeons lacked tissue cysts in their muscle, brain or peripheral nervous system, cysts of Sarcocystis wenzeli were identified in 17 of 191 chickens (8.9%). Morphologically, the cysts were thread-like, ranging in size from 334-3169 × 41-117 μm (mean 1093 × 65 μm). Cysts were septate with dense, short finger-like protrusions which appeared radially striated. The cyst wall was 1.4-3.5 μm (mean 2.4 μm) thick. The bradyzoites were lancet shaped and measured 12.2-17.7 × 1.8-2.9 μm (mean 14.6 × 2.5 μm). Ultrastucturally, the primary sarcocyst wall had stubby villar protrusions, corresponding to the 'type 9' class previously designated. The protrusions measured 0.87-1.89 × 0.47-0.91 μm (mean 1.27 × 0.59 μm; n = 57). These findings confirm previous work from the vicinity of Kunming concerning the occurrence of S. wenzeli in chickens, and its use of both cats and dogs as definitive hosts, but indicate that corresponding infections may not occur in the regional domestic flocks of other types of fowl.