First case of fatal leucocytozoonosis in domestic ducks in a zoological garden in Japan.

Leucocytozoon spp. are common avian haemosporidian parasites that can cause clinical symptoms with lethal cases in poultry worldwide. However, leucocytozoonosis has not been reported in domestic ducks (Anas platyrhynchos domesticus) in Japan. Two adult domestic ducks maintained in a zoological garden in Japan became lethargic, exhibited labored breathing, and died in July 2024. These ducks had hemorrhages in the visceral organs with splenomegaly and hepatomegaly. Megaloschizonts of haemosporidia were histologically observed in the spleen and other organs. Partial sequences of Leucocytozoon mitochondrial cytochrome b gene DNA were determined and classified as lineages known to infect wild waterfowl (Anseriformes). To the best of our knowledge, this is the first known fatal case of leucocytozoonosis in domestic ducks in Japan.