Persian Cat

　　1. Pathogen: The pathogen is Toxoplasma gondii, a protozoan and an intracellular parasite. The trophozoite stage of its life cycle is bow-shaped, hence the name, also called "Toxoplasma." Toxoplasma has two hosts: an intermediate host and a definitive host. Its life cycle includes five stages: trophozoite, cyst, schizont, gametocyte, and oocyst. Trophozoites and cysts mainly appear in the intermediate hosts (mammals other than cats, birds, and some poikilotherms). Trophozoites are mostly found in body fluids and tissue fluids during acute cases and exhibit pleomorphism such as bow-shaped, crescent-shaped, banana-shaped forms. The cyst form is common in chronic or asymptomatic cases, residing in brain, retina, muscle, and internal organs tissues. Cysts are typically round with a thick cyst wall, representing a relatively dormant stage of Toxoplasma. Schizonts, gametocytes, and oocysts only appear in the definitive host (cats). When a cat ingests meat containing trophozoites, cysts, or mature oocysts, the parasites enter the intestinal mucosal epithelial cells to reproduce asexually, producing schizonts. Some schizonts develop into gametocytes; male and female gametocytes combine for sexual reproduction, forming oocysts that are excreted with feces. Under suitable environmental conditions, within 2–4 days, the oocysts develop into infectious forms. Parasites ingested by cats can also penetrate the intestinal epithelium to enter lymph and blood, spreading to various organs and tissues, invading cells where they reproduce asexually by budding or binary fission, producing large numbers of parasites. When parasite virulence is high, cats can suffer acute illness. Alternatively, immune responses or other factors in cats can slow parasite reproduction; some parasites are eliminated while others form cysts in the host’s brain, skeletal muscles, etc., surviving for years. Animals and humans other than felines are intermediate hosts. Infection in intermediate hosts generally occurs through trophozoites or cysts via various routes. Parasites enter tissue cells via blood and lymph, reproducing asexually. Depending on host resistance, infection may cause acute illness or only mild or asymptomatic infections. Toxoplasma’s resistance varies greatly by life stage; trophozoites are least resistant and can be killed by most disinfectants, e.g., 1% Lysol solution kills them within one minute. Cyst forms have stronger resistance, remaining infectious for up to 1.5 years at room temperature, withstanding many acid and alkaline disinfectants, but are sensitive to heat: 80°C for 1 minute kills them, and 100°C causes immediate death.