Two-year longitudinal study of and oocyst shedding in Japanese rock ptarmigans ().

The Japanese rock ptarmigan () is a cold-adapted bird that inhabits only alpine areas of Japan. The birds have been reported to be highly infected with two species; however, these species including long-term infection dynamics have not yet been well documented. Since surveys requiring access into the mountain areas of the Japanese Alps are prohibited from November to April (winter), the prevalences of eimerian parasites and details on their transmission routes among the wild birds in the habitat in winter remain unknown. As part of conservation programs for Japanese rock ptarmigans, two families, including the female parent and chicks, were transported to two zoos for breeding in 2021. To examine fluctuations in the infection status of species in Japanese rock ptarmigans, we conducted a 2-year longitudinal study of oocyst shedding. We found that all examined birds were continuously infected with two species, although oocysts were sometimes not detected in feces. On average, the oocysts per gram (OPG) values were <100; however, those of female parent birds that successfully laid fertilized eggs and/or cared their chicks increased by more than 100 to 1000 before or when the chicks hatched. Subsequently, all of the chicks became infected with the species. The OPG values did not drastically change in the female birds that were not paired for breeding or had laid unfertilized eggs, and in the male birds. Although further studies are needed, our findings indicated that the parasites are transmitted from female parents to chicks after hatching, and that the birds may be continuously infected, showing low OPG levels.