Which of the following is a viral disease?

Step 1: Analyze the question We need to identify which disease is caused by a virus. The other options are caused by different types of pathogens.

Step 2: Explain the concept Diseases are grouped by the type of organism that causes them:

• Bacteria: single-celled prokaryotes with no true nucleus. They cause many common diseases.
• Viruses: tiny, non-cellular particles that can only reproduce inside host cells.
• Protozoa, fungi, worms: cause other diseases such as malaria (protozoan) and ringworm (fungal).

Step 3: Go through the options

| Option | Disease | Causative agent | Type | |---|---|---|---| | A | Syphilis | Treponema pallidum | Bacterium | | B | Measles | Measles virus (a paramyxovirus, genus Morbillivirus) | Virus | | C | Cholera | Vibrio cholerae | Bacterium | | D | Typhoid | Salmonella typhi | Bacterium |

Syphilis, cholera and typhoid are all bacterial infections, and antibiotics can treat them. Measles is the only viral disease in the list. It spreads through airborne droplets and causes fever, a rash and a cough. It is prevented by vaccination, which is why children in Nigeria receive the measles vaccine at 9 months.

Step 4: Answer The correct option is B. Measles.

Exam tip: Memorise these in groups.

• Viral: measles, polio, chickenpox, mumps, HIV/AIDS, rabies, yellow fever, Lassa fever, influenza, hepatitis
• Bacterial: cholera, typhoid, tuberculosis, syphilis, gonorrhoea, tetanus, leprosy
• Protozoan: malaria, sleeping sickness, amoebic dysentery

A good memory trick is that "-oid" and "-ra" diseases like typhoid and cholera come from contaminated food and water and are bacterial. Diseases that cause a rash in childhood (measles, chickenpox) are usually viral.