Introduction of Direct and Indirect Transmission
The spreading of any pathogen from one body to another body is termed transmission. Moreover, the transmission of infections and diseases take place in various ways, like it may get transmitted directly or through means of specific bacteria, protozoa, fungi or virus. However, primarily two modes of disease transmission are there; direct transmission and indirect transmission.
Direct Transmission
When the pathogens are directly transmitted from a person suffering from an infection, it is called direct transmission. For instance, if an open wound somehow contaminates the blood of a person who has Hepatitis B, the person with the injury may get infected with the disease too.
Individual to Individual
In this scenario, transmission occurs when an infection-free person gets in touch or exchanges bodily fluids with an individual with an infection. For instance, a pregnant woman can transfer the infection to her unborn baby through her placenta. Moreover, gonorrhoea is a sexually transferred disease that is an example of direct transmission.
Transfer Through Droplets
During sneezing, coughing, or speaking, droplets can come out from the mouth and nose and infect a healthy person. Also, infections can spread if an infected person touches another person with his/her hands which are contaminated with the droplets. Furthermore, these droplets move a small distance as they are very minute. Hence, nearby people are prone to infections.
Transmission Through Skin
Here, when the skin of a person suffering from any disease touches another individual, it may infect him/her. For example, conjunctivitis, chickenpox, ringworm and head lice are some infections transmitted by skin.
Transfer by Fluids and Blood
As per the phrase, it is understandable that this transmission occurs when blood or body fluids make contact with the bloodstream or mucous membrane of a healthy person. The examples of such modes of transmission are cytomegalovirus, hepatitis, HIV, etc. These infections transfer via urine, semen, saliva, vaginal fluids, breastmilk, etc.
Indirect Transmission
Reversely, when pathogens are not directly transmitted from an individual suffering from an infection, it is called indirect transmission. Here, methods of disease transmission are vectors like flies, ticks, mosquitoes, dogs, etc.
Transmission Through Air
Sometimes, few infections stay in the air for a considerable amount of time. As a result, it may affect a person’s immune system who comes in contact with those infections. For instance, if a healthy man/woman goes into a room where a person suffering from measles used to stay, that uninfected man/woman may catch measles.
Transmission Through Contaminated Substances
Various objects and usable items can carry pathogens. Touching those infected items which were previously utilised by an infected individual may cause infection in a healthy human being. Its common sources are contaminated medical issues and blood transfer infections.
Transfer of Disease Through Vector
Various insects and flies can transmit infections. These flies and insects sit and feed on multiple animals, humans, birds and bring along disease-causing agents. Further, when they go and sit on some uninfected person, the infection may get transferred. Lyme and malaria are two examples of vector-borne diseases.
Drinking-Water and Food
Foods that are not appropriately canned or undercooked are one of the primary sources of disease-causing infections. Moreover, drinking water is also a mode of transmission of infection. Hence, individuals must boil or filter water before drinking and using it for cooking. Bacteria named E.coli get transmitted via contaminated food items that create stomach issues.
Transfer Via Animals
Infection through animals takes place when a diseased animal scratches or bites an individual. Examples of diseases caused by animals are anthrax, plague and rabies.
Transmission Through Certain Environmental Factors
Several infectious modes of disease transmission are available in water, plants and soil. They may come in contact with people who can cause diseases. For example, hookworm and legionnaires’ disease.
Do it Yourself
1. Which disease is caused by transmission via dog?
(a) Cholera (b) Rabies (c) Anthrax (d) Malaria
FAQs on Modes of Transmission of Diseases
1. What are the two primary categories of disease transmission?
The two primary categories are Direct Transmission and Indirect Transmission. Direct transmission occurs when a pathogen is transferred directly from an infected person to another. Indirect transmission happens when the pathogen is spread through an intermediate agent or vehicle, such as contaminated objects, air, water, or living creatures.
2. How does direct transmission of diseases occur? Provide examples.
Direct transmission occurs through immediate contact between an infected individual and a healthy one. The main ways this happens are:
- Person-to-Person Contact: This includes touching, kissing, or sexual contact. Examples are chickenpox and ringworm.
- Droplet Spread: When an infected person coughs or sneezes, spreading droplets that are inhaled by someone nearby. The common cold and influenza are spread this way.
- Mother to Child (Vertical Transmission): A pathogen passes from a mother to her baby during pregnancy, birth, or breastfeeding. HIV is an example.
3. What are the different types of indirect disease transmission?
Indirect disease transmission involves an intermediary that carries the pathogen. The main types include:
- Airborne Transmission: Pathogens remain suspended in the air for long periods and can travel distances. Examples include measles and tuberculosis.
- Contaminated Objects (Fomites): This happens by touching a surface or object, like a doorknob or phone, that is contaminated with pathogens.
- Vector-Borne Transmission: An insect or animal (the vector) carries the disease. Mosquitoes spreading malaria is a classic example.
- Vehicle Transmission: Pathogens are spread through a medium like contaminated food, water, or blood. Cholera is a well-known water-borne disease.
4. Can you explain the difference between droplet and airborne transmission?
The key difference is the size and travel distance of the particles carrying the pathogen.
- Droplet transmission involves relatively large respiratory droplets expelled by coughing or sneezing. These heavy droplets travel only a short distance (typically less than 2 metres) before falling.
- Airborne transmission involves much smaller particles (droplet nuclei) that can remain suspended in the air for extended periods and travel much farther, infecting people who are not in close proximity to the source.
5. What is a 'vector' in disease transmission and why are they so effective at spreading illnesses?
A vector is a living organism, typically an insect like a mosquito, tick, or fly, that transmits an infectious agent from an infected host to a new one. Vectors are highly effective at spreading diseases because:
- They are mobile and can carry pathogens over large geographical areas, introducing diseases to new populations.
- Many vectors require a blood meal, which creates a direct pathway for pathogens to enter the bloodstream of a new host.
- Their life cycles are often linked to environmental factors, which can lead to predictable seasonal outbreaks of diseases like malaria and dengue.
6. How can contaminated food and water act as a major source of disease transmission in a community?
Contaminated food and water serve as common vehicles for pathogens, often causing widespread community outbreaks. This occurs when:
- Water sources are polluted with infectious agents, such as bacteria like Vibrio cholerae (causing cholera) or Salmonella typhi (causing typhoid).
- Food is improperly handled, undercooked, or stored at incorrect temperatures, allowing bacteria like E. coli or Listeria to multiply.
7. Give some examples of diseases spread by direct contact versus those spread by vectors.
- Diseases spread by direct contact: These require close physical interaction. Examples include the common cold, influenza (through droplets), chickenpox, measles, ringworm (skin-to-skin), and HIV (through bodily fluids).
- Diseases spread by vectors: These are transmitted by insects or animals. Examples include malaria (spread by Anopheles mosquitoes), dengue fever (spread by Aedes mosquitoes), Lyme disease (spread by ticks), and rabies (spread by infected animals).
8. Why is handwashing considered a critical step in preventing the spread of infectious diseases?
Handwashing is critical because hands are a primary vehicle for transferring pathogens via both direct and indirect contact. We frequently touch our faces (mouth, nose, and eyes), which are mucous membranes that serve as entry points for germs. By washing our hands with soap and water, we physically remove or inactivate pathogens picked up from contaminated surfaces (fomites) or other people, effectively breaking the chain of transmission before the germs can cause an infection.
9. Are all diseases communicable? Explain with respect to their modes of transmission.
No, not all diseases are communicable. Diseases are classified into two main types based on how they spread:
- Communicable (Infectious) Diseases: These are caused by pathogens and can be transmitted from one person to another through various modes like direct contact, airborne particles, or vectors. Examples include COVID-19, tuberculosis, and malaria.
- Non-Communicable Diseases (NCDs): These are not caused by infectious agents and cannot be transmitted between people. They are typically caused by a combination of genetic, physiological, environmental, and behavioural factors. Examples include most cancers, diabetes, and cardiovascular diseases.
10. What role do fomites play in the indirect transmission of pathogens?
Fomites are inanimate objects or surfaces that become contaminated with infectious agents and can transmit them to a new host. They are central to indirect contact transmission. For instance, if a person with the flu touches a doorknob, the virus can survive on that surface. When a healthy person later touches that same doorknob and then touches their own mouth or nose, they can become infected. Common fomites in daily life include cell phones, keyboards, toys, and utensils.
