Question

Which virus is NOT sensitive to disinfection of water by chlorination?

• A. Rotavirus
• B. Norwalk virus
• C. Poliovirus
• D. None

Hint:

Think of the non-enveloped enteric viruses that survive routine chlorine, the same group as hepatitis A and E.

Answer 1

The Correct Option is C

Step 1: Chlorination is one of the most important advances in water purification. It reliably kills most pathogenic bacteria, but in the usual doses it does NOT inactivate bacterial spores, cysts of Entamoeba histolytica, and certain resistant viruses.

Step 2: The classically chlorine-resistant viruses are poliovirus and the viral hepatitis (hepatitis A and E) viruses. These survive routine chlorination because of their compact, stable capsid structure. Hence poliovirus is the correct answer.

Step 3: Mechanism: when chlorine is added to water it forms hypochlorous acid, which ionises into hydrogen and hypochlorite ions. The disinfecting action is mainly due to hypochlorous acid, which is about 70 to 80 times more effective than the hypochlorite ion.

Step 4: Rotavirus and Norwalk virus are comparatively more susceptible than the enteroviruses, so among the options poliovirus is the one resistant to chlorination.