Which one of the following is an example of airborne disease?

Correct — A, Tuberculosis. Tuberculosis is caused by the bacterium Mycobacterium tuberculosis, and WHO's own description of it is that it spreads through the air when people with TB cough, sneeze or spit. Those acts throw out tiny droplets that dry into droplet nuclei light enough to stay suspended in a room for hours; anyone breathing that air can inhale them, which is why crowding and poor ventilation drive transmission and why the disease usually settles first in the lungs. That is the definition of an airborne disease: no insect, no water, no contact needed, just shared air. The other three diseases each travel by a different route, and the item is really testing whether you can sort diseases by route rather than by name. TB remains an enormous burden — WHO estimated 10.7 million people fell ill with it worldwide and 1.23 million died in 2024, the most recent year reported around this exam — and India carries the largest share of the world's cases.

• (b)Malaria — Malaria is vector-borne. The Plasmodium parasite is injected by the bite of an infected female Anopheles mosquito; it does not pass from person to person through the air, which is why control works through nets, drainage and larval source management.
• (c)Dengue — Dengue is also vector-borne, spread by the day-biting Aedes mosquito. The virus needs the mosquito to complete its journey between people, so preventing dengue is a matter of removing standing water rather than of ventilating rooms.
• (d)Cholera — Cholera is water-borne. Vibrio cholerae is swallowed in water or food contaminated with faeces, and outbreaks follow the failure of sanitation and safe water supply, especially after floods.

Communicable diseases are classified by their route of transmission, and the route decides how they are prevented. Airborne diseases travel in droplets and droplet nuclei exhaled by an infected person — tuberculosis, measles, influenza, chickenpox and COVID-19 among them. Vector-borne diseases need a living carrier, usually an insect: malaria and filariasis through Anopheles and Culex mosquitoes, dengue and chikungunya through Aedes. Water-borne and food-borne diseases are swallowed: cholera, typhoid, hepatitis A and most diarrhoeal illness. Contact and blood-borne diseases, such as HIV and hepatitis B, need a still more direct exchange.

Sorting the four names by route is the whole task, and it is easiest done by asking what would prevent each. Nets and drained puddles prevent malaria and dengue, so those are mosquito diseases. Clean water and a working sewer prevent cholera, so that is a water disease. Nothing but ventilation, distance and treating infectious cases prevents tuberculosis, which places it in the air. The one distinction worth adding is that airborne strictly means the pathogen survives in droplet nuclei small enough to remain suspended and travel across a room, whereas droplet spread means larger droplets that fall within a metre or two. TB belongs to the first group, which is precisely why it spreads so readily in crowded, poorly ventilated housing.

• Tuberculosis is caused by Mycobacterium tuberculosis and, in WHO's words, spreads through the air when people with TB cough, sneeze or spit.
• TB usually affects the lungs, though it can also involve the kidneys, brain, spine and other organs.
• WHO estimated 10.7 million people fell ill with TB worldwide in 2024 and 1.23 million died of it.
• Malaria is carried by the female Anopheles mosquito and dengue by the Aedes mosquito; both are vector-borne, not airborne.
• Cholera, caused by Vibrio cholerae, is water-borne and follows contamination of drinking water with faecal matter.

• Grouping malaria with airborne diseases because it is common and severe; severity has nothing to do with route.
• Assuming a bacterial disease must be water-borne; both cholera and TB are bacterial, and they travel by different routes entirely.
• Confusing droplet spread over a metre or two with true airborne spread in suspended droplet nuclei; tuberculosis is the second kind.

Usually as an odd-one-out among diseases of different routes, or as a match between a disease and its causative organism or its vector.

• practice — not a real PYQ

  The causative organism of tuberculosis is

  • (a)a virus
  • (b)a bacterium
  • (c)a protozoan
  • (d)a fungus

  Answer(b) a bacterium — Mycobacterium tuberculosis. Malaria is caused by a protozoan, Plasmodium, and dengue by a virus.

• practice — not a real PYQ

  Which one of the following diseases is water-borne?

  • (a)Tuberculosis
  • (b)Chickenpox
  • (c)Cholera
  • (d)Dengue

  Answer(c) Cholera — Vibrio cholerae is swallowed in faecally contaminated water or food. Tuberculosis and chickenpox travel through the air and dengue through a mosquito.