Eimeria tenella is a single-celled parasite that primarily infects the intestines of chickens. It belongs to the genus Eimeria, which includes several species that cause coccidiosis, a disease characterized by diarrhea, weight loss, and poor growth in poultry. This parasite is transmitted through contaminated feed or water, leading to outbreaks in flocks. Infection with Eimeria tenella can result in significant economic losses for poultry farmers due to decreased productivity and increased veterinary costs. Control measures include proper sanitation, vaccination, and the use of anticoccidial medications to manage and prevent the spread of the parasite in chicken populations.