What are the modes of transmission of diseases?

Diseases or infections are transmitted in many ways. It may be directly transmitted from one person to another, or by certain bacteria, viruses, protozoa, or fungi. There are two different modes of transmission of diseases:

A) Direct Transmission– This occurs when the pathogen is transmitted directly from an infected person. For eg., if an open wound comes in contact with the blood of a Hepatitis B infected patient, the wounded person might contract the disease.

B) Indirect Transmission- When the pathogens are not transmitted directly from the infected person but through vectors such as flies, mosquitoes, ticks, dogs, etc., it is known as indirect transmission.

Disease Transmission:
A) Direct Transmission
1. Person to Person: When an infected person comes in contact with or exchanges body fluids with a non-infected person. A mother can transmit infections to the unborn child via the placenta. A sexually transmitted disease such as gonorrhoea can be transmitted by direct transmission.

2. Droplet Transmission: The droplets spread during sneezing, speaking, and coughing by an infected person can spread infections. The infections can also spread by touching the nose and mouth with the hands contaminated with infectious droplets. The droplets are so minute that they travel only a short distance before falling. The people nearby might contract infections.

3. Spread by skin: There are a few infections such as chickenpox, conjunctivitis, head lice, ringworm, etc., which spread when the skin of an infected person comes in contact with the skin of the other person.

4. Spread through body fluids or blood: A few diseases spread when the body fluids or blood of an infected person come in contact with the mucous membrane or bloodstream of an uninfected person. Diseases such as hepatitis, HIV, cytomegalovirus infections, etc. spread through semen and vaginal fluids, saliva, breastmilk, urine, etc.

B) Indirect Transmission:
1. Airborne Transmission: Some infectious agents remain suspended in the air for a long period of time. These pathogens might attack the immune system of a person in contact. E.g. if you enter a room that was initially occupied by a patient of measles, you too might catch the infection.

2. Contaminated Objects: The objects around us carry pathogens. Touching the infected objects which were initially used by a diseased person might render us diseased. Contaminated blood and medical supplies can also spread infections.

3. Vector-Borne Diseases: Some infectious agents are transmitted by the blood-sucking insects. The insects feed on hosts such as birds, animals, and humans and carry infectious agents from them. These infections are transmitted to some new host. Malaria and Lyme disease are the two vector-borne diseases.

4.Food and Drinking Water: Improperly canned and undercooked food is the main source of infections. Water also carries various pathogens from rivers and lakes. It should be boiled or filtered before use. E.coli is transmitted through contaminated food which causes various stomach problems. Botulism is caused by the consumption of improperly canned food. Cholera is one water-borne disease which has affected millions of people consuming contaminated water.

5.Transmission through Animals: When an infected animal bites or scratches against a person, it transfers the infectious agents to the person. These agents can also be transmitted through animal waste. When diseases are transferred from animals to people, zoonosis occurs. Anthrax (sheep), rabies (dogs), plague (rodents) are some of the diseases transmitted from animals to humans. Pregnant women and people with weak immune systems are more prone to infections.

6.Environmental Factors: The infectious agents are present in soil, water and plants as well. These agents can be transmitted to people and may cause diseases. For eg., Hookworm is transmitted through contaminated soil. Legionnaires’ disease is spread by water supplied to condensers and cooling towers.