Polio or poliomyelitis is a disease caused by a virus. It primarily affects the nervous system and can lead to paralysis or even death. The virus responsible for polio is called the poliovirus, which belongs to the family Picornaviridae.

1. Poliomyelitis:
Poliomyelitis, commonly known as polio, is a highly contagious disease caused by the poliovirus. It mainly affects children under the age of 5. Polio is transmitted through contaminated water or food, as well as through direct contact with an infected person. The virus enters the body through the mouth and multiplies in the throat and intestines. From there, it can invade the nervous system, leading to paralysis.

2. Malaria:
Malaria is not caused by a virus. It is a mosquito-borne infectious disease caused by the Plasmodium parasite. The parasite is transmitted through the bite of infected female Anopheles mosquitoes. Malaria affects millions of people worldwide, primarily in tropical and subtropical regions.

3. Whooping Cough:
Whooping cough, also known as pertussis, is caused by the bacterium Bordetella pertussis. It is a highly contagious respiratory infection characterized by severe coughing fits. While whooping cough is not caused by a virus, it is important to note that viral infections can sometimes lead to similar symptoms.

4. Ringworm:
Contrary to its name, ringworm is not caused by a worm but by a group of fungi known as dermatophytes. It is a common fungal infection that affects the skin, scalp, and nails. Ringworm is highly contagious and can be transmitted through direct contact with an infected person or animal, as well as through contaminated objects.

In conclusion, among the diseases mentioned, poliomyelitis (polio) is caused by a virus (poliovirus), making option A the correct answer. Malaria is caused by a parasite, whooping cough is caused by a bacterium, and ringworm is caused by fungi.