In a flock of broiler chickens with sudden diarrhea, which organism is most likely the cause?

The presence of sudden diarrhea in a flock of broiler chickens is most characteristic of an outbreak involving Eimeria spp., which are protozoan parasites responsible for coccidiosis. Coccidiosis is a common intestinal disease in chickens, particularly broilers, and can lead to significant digestive disturbances including diarrhea that may be bloody or watery, depending on the severity of the infection.

Eimeria spp. invade and damage the intestinal lining, leading to malabsorption of nutrients and loss of fluids, which manifests as diarrhea. In broiler production, coccidiosis can spread rapidly, especially in young birds, causing extensive economic losses due to decreased weight gain and increased feed conversion ratios, alongside mortality in severe cases.

The other organisms listed, such as Capillaria spp., Heterakis spp., and Syngamus spp., are also parasitic infections in poultry but are less commonly associated with sudden diarrhea. Capillaria affects the gastrointestinal tract but typically presents with less severe symptoms. Heterakis and Syngamus infections can lead to respiratory and digestive issues, but they are unlikely to cause the rapid onset of diarrhea observed in this scenario. Thus, Eimeria spp. is the most plausible cause of sudden diarrhea in the affected flock