Mode of Transmission

Mode of Transmission

Infectious diseases are transmitted from person to person by direct or indirect contact. Certain types of viruses, bacteria, parasites, and fungi can cause infectious disease. Malaria, measles, and respiratory illnesses are examples of infectious diseases.

Susceptible Host - A person who lacks resistance to a particular pathogenic agent to prevent disease if or when exposed.

I.  Direct Transmission

1.  Direct Contact - Infection may be transmitted directly from skin to skin, mucosa to mucosa, mucosa to skin of others or same person. Example: skin-to-skin contact as by touching, kissing or sexual intercourse. Diseases transmitted - STD and AIDS, leprosy, leptospirosis, skin and eye infections.

2.  Droplet infection -This is direct projection of a spray of droplets of salaiva and nasopharyngeal secretions (airborne droplets of saliva or sputum) containing infectious organisms. The spray of droplets during coughing and sneezing can spread an infectious disease.

3.  Contact with soil - The disease agent may be acquired by direct exposure of susceptible tissue to the disease agent in soil, compost or decaying vegetable matter. Examples: hookworm larvae, tetanus, mycosis etc.

4.  Inoculation into skin or mucosa - Rabies virus by dog bite, Hep. B virus through contaminated needles and syringes etc.

5.  Transplacental (or vertical) transmission - TORCH agents - (Toxoplasma Gondii, Rubella virus, Cytomegalo virus, and Herpes virus). Varicella virus, Syphilis, Hepatitis B, Coxsackie B and AIDS. Some of the non-living agents (e.g., thalidomide, diethylstilbestrol) can also be transmitted vertically (mother to child) which will affect the embryo and causes malformations in the foetus.

2. Indirect Transmission

This embraces a variety of mechanisms including the traditional 5 F's, such as

1. Vehicle-borne - An indirect transmission of an infectious agent that occurs when a vehicle. (or formites) touches a persons body or is ingested

2. Vector - borne - Vector is defined as an arthropod or any living carrier that transports an infectious agent to a susceptible individual. Infectious agents are transmitted by insects, especially those that suck blood. These include mosquitoes, fleas, and ticks. The insects become infected when they feed on infected hosts, such as birds, animals, and humans. The disease is transmitted when the insect bites a new host. Eg. Malaria, West Nile virus, and Lyme disease are all spread this way.

3. Airborne - An airborne disease is any disease that is caused by pathogens that can be transmitted through air. Some infectious agents can travel long distances and remain suspended in the air for an extended period of time. Diseases spread by droplet include tuberculosis, measles, Q fever, and Respiratory infections.

4. Fomite - borne - Fomites are inanimate articles or substances other than water or food contaminated by the infectious discharges from a patient and capable of harbouring and transferring infectious agent to a healthy person. Fomites includes soiled clothes, toys, towels, linen, cups, spoons, pencils, books, surgical dressing, etc., Diseases transmitted by fomites are typhoid, diphtheria, and skin infections.

5. Unclean hands and fingers - Hands are the most common medium by whichpathogenic agents are transferred to food from the skin, nose, bowel, etc., as well as from other food.

Chain of Disease Transmission

The six factors involved in the chain of disease transmission are