coccidial

Coccidial refers to coccidia, a group of single-celled protozoan parasites in the subclass Coccidia within the phylum Apicomplexa. Coccidia include several genera such as Eimeria, Isospora (now often called Cystoisospora in some classifications), Cyclospora, and Sarcocystis. The term is commonly used in veterinary medicine to describe infections known as coccidiosis, which affect the intestinal tract of many animals.

The life cycle of coccidia typically begins with oocysts excreted in the feces of an infected host. In the environment, oocysts sporulate and become infectious. When a new host ingests sporulated oocysts, sporozoites invade intestinal epithelial cells and undergo multiple rounds of asexual replication (schizogony) followed by sexual development (gametogony) to produce new oocysts that are shed in feces. Different coccidia species have specific tissue tropisms and may infect the intestinal tract or other organs.

In animals, coccidiosis is a major problem in poultry, where species of Eimeria cause intestinal lesions, diarrhea, reduced feed efficiency, weight loss, and sometimes death. Other livestock, such as cattle, sheep, and goats, can also be affected by various Eimeria species. In humans, coccidia such as Cyclospora cayetanensis and Cystoisospora belli can cause gastrointestinal illness, particularly in immunocompromised individuals or through contaminated food or water.

Diagnosis is typically by microscopic identification of oocysts in fecal samples, often aided by flotation methods or molecular tests. Treatment depends on the host and parasite; anticoccidial drugs (such as ionophores or sulfamides) are used in animals, and trimethoprim–sulfamethoxazole is commonly used for certain human coccidial infections. Prevention relies on hygiene, sanitary management, litter or housing controls in livestock, vaccination in poultry, and, for humans, safe water and food handling.