Question

What are the different means by which infectious diseases are spread?

Answer 1

Infectious diseases are those which are caused by an infectious agent such as a bacterium, virus, protozoan or fungus that can be passed on to others. Infection occurs when an infectious agent enters the body and begins to reproduce. An infectious agent that causes the disease is called a pathogen and a host is an organism infected by another organism.

Complete answer:
Germs can enter the human body through-
Mouth, respiratory tract, eyes, genitals, broken skin.

Different means by which an infection can spread-

1. Spread through the air by droplets:
When an infected person talks, coughs or sneezes small droplets containing infectious agents spread into the air, due to their size, these droplets in the air travel only a short distance (around a metre) from the infected person before falling, these droplets in the air may be breathed in by those nearby. Spreading can also occur by touching the nose or mouth with droplet contaminated hands.
Example- Spread of common cold, flu.

2. Spread through the air by aerosol:
When an infected person talks, breathes, coughs or sneezes tiny particles containing infectious agents spread into the air, these are called small particle aerosols. Due to their tiny size, they can travel long distances on air current and remain suspended in the air for minutes or hours, these small particles of aerosols may be breathed in by another person.
Examples- Spread of chickenpox, measles etc.

3. Faecal-oral spread of disease:
Some infections are spread when microscopic amounts of faeces from an infected person with symptoms or an infected person without symptoms (a carrier) are taken in by another person by mouth. The faeces may be passed:
directly from soiled hands to the mouth indirectly by objects, surfaces, food or water soiled with faeces.
Example- Giardia infection causes giardiasis, Salmonella typhi infection causes typhoid etc

4. By skin and mucous membrane-
Some infections are spread directly when skin or mucous membrane comes into contact with another person’s skin or mucous membrane. Infections can spread indirectly also when skin or mucous membrane comes in contact with contaminated objects or surfaces.
Example- Chickenpox, herpes simplex infection.

5. By body fluids(eg blood):
Some infections are spread when blood or other body fluids, for example, urine, saliva, breastmilk, semen and vaginal secretions, from an infected person, comes into contact with the mucous membranes through kissing, breast-feeding or sexual contact or the bloodstream of an uninfected person, such as through a needle stick injury or a break in the skin.
Examples- Hepatitis B ( spread through blood, saliva, semen and vaginal fluid),
Human immunodeficiency virus (HIV) infection (spread through blood, semen, vaginal fluid, breast milk).

6. Spread through contaminated food or water:
These diseases spread through the ingestion of water or a wide variety of foods contaminated with disease-causing germs or their toxins. Often these infections are also spread by the faecal-oral route.
Examples- Campylobacter infection, salmonella infection.

7. Spread through vector:
Some infectious agents need vectors to reach their host.
Example- Malaria is caused by protozoa of the genus Plasmodium , Plasmodium travel by female anopheles mosquitoes (vector) to their host (human).

8. Spread from mother to unborn child:
Some infections can be spread through the placenta from a mother to her unborn child in the womb or during delivery, or both.
Example- chickenpox, Hepatitis B

Note:
The spread of infectious diseases can be reduced by giving vaccines to the people before the actual infection so that body produces enough antibodies to fight the infection, antimicrobial drugs can be administered after the infection, good personal hygiene and sanitation, protection against vectors(eg mosquitoes) by applying mosquito repellent creams, wire mesh etc, quarantine for few days to few weeks to avoid any social contact to prevent the mass spread of disease.