Which protozoan parasite is a key target in modern drinking water treatment due to resistance to disinfection methods?

• A. Giardia lamblia
• B. Entamoeba histolytica
• C. Cryptosporidium
• D. Microsporidia

Answer: (C)

Some protozoa form hardy cysts or oocysts that survive standard disinfection, so modern drinking water treatment emphasizes not just chemical disinfection but also physical removal and alternative disinfectants. Cryptosporidium is a key target because its oocysts are highly resistant to chlorine, the common disinfectant used in many water systems, and can pass through untreated or inadequately treated water. This resilience means treatment plants rely on a multi‑barrier approach: effective filtration to physically remove oocysts (often using fine pore sizes or membrane filtration) combined with disinfection methods like UV light or ozone that inactivate Cryptosporidium more reliably than chlorine alone. The importance of this parasite was highlighted by major outbreaks that led to tighter filtration standards and overall water safety practices. While Giardia lamblia cysts also pose a disinfection challenge, Cryptosporidium’s greater resistance to chlorine makes it the primary focus of modern treatment strategies. Entamoeba histolytica and Microsporidia can be concerns in certain contexts, but Crypto’s robust chlorine resistance makes it the standout target in routine drinking water protection.