Which of the following set represents communicable diseases?

Concept: A disease is classified as communicable (infectious) when it is caused by a pathogen — a bacterium, virus, protozoan parasite, or other microorganism — that can pass from an infected host to a new host through a mode of transmission such as direct contact, air, water, food, or a vector like a mosquito. A disease is non-communicable when it results from a nutritional deficiency, a metabolic or genetic disorder, or another non-infectious cause, and therefore cannot spread from person to person.

Application: Applying this test to the set Typhoid, Swine flu, Malaria, Polio: Typhoid is caused by the bacterium Salmonella typhi and spreads through contaminated food or water; Swine flu is caused by the H1N1 influenza virus and spreads through respiratory droplets; Malaria is caused by Plasmodium parasites transmitted by the bite of an infected Anopheles mosquito; Polio is caused by the poliovirus and spreads mainly through the faecal-oral route. Every member of this set is therefore pathogen-caused and transmissible between hosts, so the whole set qualifies as communicable diseases.

Contrast with the other sets:

• Anaemia and Scurvy are not caused by pathogens — Anaemia is an iron-deficiency blood disorder and Scurvy is a Vitamin C deficiency disorder — so a set containing either of them cannot be an all-communicable set, even if it also contains genuinely infectious diseases like Diarrhoea or Cholera.

• Anaemia, an iron-deficiency disorder, appearing alongside otherwise-infectious diseases such as Typhoid, Malaria, and Swine flu still breaks an all-communicable set, because Anaemia itself does not transmit from person to person.

• Diabetes is a metabolic/endocrine disorder linked to insulin function, not to any pathogen, and Anaemia is a nutritional deficiency — the presence of either alongside genuinely infectious diseases such as Typhoid and Malaria still disqualifies the set.

Cross-check: Reconfirming disease-by-disease: Typhoid — bacterial, faecal-oral spread; Swine flu — viral, airborne/droplet spread; Malaria — parasitic, mosquito-vector spread; Polio — viral, faecal-oral spread. All four are infectious in origin and transmissible, independently confirming the set as communicable.

Result: The set "Typhoid, Swine flu, Malaria, Polio" is the only offered set consisting entirely of communicable diseases, matching CBSE's official CTET 2019 Paper II answer key.