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1. MODE OF TRANSMISSION OF
DISEASES

3. MODE OF TRANSMISSION
 An infectious agent may be transmitted from its natural
reservoir to a susceptible host in different ways

4. MODE OF TRANSMISSION

5. CLASSIFICATIONS
DIRECT- infectious agent is transferred from a reservoir
to a susceptible host by direct contact or droplet spread
INDIRECT- transfer of an infectious agent from a
reservoir to a host by suspended particles, inanimate
objects (vehicles), animate intermediaries (vectors)

6. DIRECT TRANSMISSION
 Direct Contact
 Droplet Spread

7. DIRECT CONTACT
 Occurs through skin to skin contact, kissing or sexual
intercourse

8. DIRECT CONTACT
Direct contact transmission of pathogens can occur through
physical contact. Many pathogens require contact with a mucous
membrane to enter the body, but the host may transfer the
pathogen from another point of contact (e.g., hand) to a mucous
membrane (e.g., mouth or eye).

9. DIRECT CONTACT
When skin or mucus membrane (thin most lining of many parts of
the body comes into contact with the skin or mucus membrane of
infected person (cold sores, head lice, conjunctivitis)

10. DROPLET SPREAD
 To spray with relatively large, short range aerosols by
sneezing, coughing or even talking
 Classified direct because transmission is by direct spray
over a few feet

11. DROPLET SPREAD
When a person talks, coughs or sneezes, droplets
travel only a short distance from the infected
person before falling. The droplets in the air may be
breathed by those nearby (common colds,
influenza)

12. INDIRECT TRANSMISSION
 Airborne
 Vehicles
 Vector- mechanical or biologic

13. AIRBORNE
 Occurs when infectious agent are carried by dust or
droplet nuclei suspended in the air
 Airborne Dust includes material that has settled on
surfaces and become resuspended by air currents
 Droplet Nuclei are dried residue of less than 5 microns
in size

14. AIRBORNE
Airborne dust and Droplet Nuclei can travel long distances on air currents and
remain suspended in the air for minutes to hours. This particles may be
breathed by other persons. (Chickenpox, Tuberculosis, Measles)

15. VEHICLES
 Indirectly transmit an infectious agent include food,
water, biologic products, and fomites
 Fomites are inanimate objects such as handkerchiefs,
beddings, surgical scalpels

16. VEHICLES
Food is an important vehicle of transmission for
pathogens, especially of the gastrointestinal and upper
respiratory systems. Often these infections are also
spread by the fecal-oral route (Hepatitis A, E)

17. VEHICLES
Fomites are nonliving objects that facilitate the indirect transmission of
pathogens. Contaminated doorknobs, towels, and syringes are all common
examples of fomites.

18. VECTORS
 Diseases can also be transmitted by an animal
(anthropod) that carries the disease from host to
another

19. VECTORS
 Mechanical transmission- an animal that carries a
pathogen from one host to another without being
infected itself
 Biologic Transmission- when the pathogen reproduces
within the vector that transmits the pathogen from one
host to another

20. VECTOR- MECHANICAL TRANSMISSION
 A fly land on fecal matter and later transmit bacteria
from feces to food that it lands on; human eating the
food may then become infected by the bacteria
(diarrhea, dysentery)

21. VECTOR- BIOLOGIC TRANSMISSION
 Mosquitoes through biting the host create a wound
that transmits Malaria and other diseases
 Ticks can transmit Lyme Disease
 Rabid animals like Monkey, Dog and Cats may transmit
rabies virus by means of bite

22. VECTORS
(a) A mechanical vector carries a pathogen on its body from one
host to another, not as an infection. (b) A biological vector carries
a pathogen from one host to another after becoming infected
itself.