Which disease is caused by a virus?

Step 1: Analyze the question You're asked to find the one disease caused by a virus. The other options are caused by other types of pathogens, so you need to know the causative agent of each disease.

Step 2: The concept Diseases are caused by different types of microorganisms:

• Bacteria: single-celled organisms with no true nucleus
• Viruses: tiny non-cellular particles that can only reproduce inside living host cells

Step 3: Check each option

| Option | Disease | Causative agent | Type | |---|---|---|---| | A | Cholera | Vibrio cholerae | Bacterium | | B | Measles | Measles virus (a paramyxovirus) | Virus | | C | Tetanus | Clostridium tetani | Bacterium | | D | Typhoid | Salmonella typhi | Bacterium | | E | Tuberculosis | Mycobacterium tuberculosis | Bacterium |

Step 4: Answer Measles is the only viral disease in the list. It spreads through droplets from coughing and sneezing, and it causes fever, a rash and red eyes. It is prevented by vaccination (the measles vaccine is given at about 9 months in Nigeria's immunisation schedule).

The correct answer is B. Measles.

Tip to remember: Common viral diseases for exams: measles, polio, chickenpox, mumps, HIV/AIDS, influenza, rabies, yellow fever, hepatitis, Ebola, Lassa fever. Most "-osis" or bacteria-named diseases, such as cholera, typhoid, tetanus, TB and leprosy, are bacterial. A quick way to remember is that bacterial diseases are usually treated with antibiotics, while viral diseases are prevented with vaccines and are not cured by antibiotics.