This PPT contains the source, mode and factors causing infections in humans. RESERVOIRS AND SOURCES OF INFECTION, MODE OF TRANSMISSION, SUSCEPTIBLE HOST Depending on the duration of carriage, carriers are classified as : temporary carrier, chronic carrier types of vectors: mechanical vector, biological vector, mode of transmission of infection- vertical transmissiom, horizontal transmission

1. INFECTION– SOURCE, MODE, FACTORS,TYPES
GENERALCONCEPTOF INFECTIOUS DISEASE &
TYPES OF INFECTION

2. INFECTION–
SOURCE,MODE,
FACTORS,TYPE
ANITMARYJOSELIN

3. INFECTION
DEFINITION :- Infection is defined as the lodgement and
multiplication of microorganisms in host tissue.

4. TYPES OF INFECTION DESCRIPTION
1. Primary infection Initial infection with an organism in a host
2. Reinfection Second infection by the same pathogen
3. Secondary infection Infection occurs in a person who already suffering from disease due to the
reduced host resistance
4. Cross infection A new infection acquired by a person who is already suffering from a disease
5. Nosocomial infection Infection acquired in hospital
6. Iatrogenic infection A physician induced infection
7. Subclinical infection Infection without clinical symptoms
8. Latent infection Some parasites, following an infection may remains in tissue as latent form,
which proliferate and cause infection when host resistance is lowered.
9. Atypical infection Infection without typical clinical manifestations
10. Endogenous infection source of infection is from the patients own body.
11. Exogenous infection Infection from external sources
12. Opportunistic infection Infection caused by normal flora when host defences are lowered
13. Localised infection Infection confined to a small area of the body
14. Generalised infection Spread of the infection in many system of the body

5. STEPS OF INFECTION :-
1. RESERVOIRS AND SOURCES OF INFECTION
2. MODE OF TRANSMISSION
3. SUSCEPTIBLE HOST

6. 1. RESERVOIRS AND SOURCES OF
INFECTION
Reservoir may be humans, animals, plants, soil or inanimate matters
where pathogens can survive and maintained as a source of infection.
e.g. Reservoir of Clostridium botulinum
is the soil but the source of infection is
contaminated food.

7. SOURCES OF INFECTION can be :-
1. Endogenous
e.g. E. coli which are normal flora of the intestine may cause
urinary tract infection in same host.
2. Exogenous
a. Animate sources :- includes humans ,animals and insects.
b. Inanimate sources :- includes food , soil, water and air.

8. A. HUMANS SOURCES
1. PATIENTS - Patients suffering from an active infection is an important source
of infection to others.
2. CARRIERS - A carrier is a person who harbours the pathogenic microorganism
without showing any signs and symptoms of the disease.

9. TYPES OF CARRIERS:-
1. Healthy carrier : is the host who harbours the microorganism without
ever suffering from the disease caused by the microorganism.
2. Convalescent carrier : is the host who continues to harbour the
microorganism even after recovering from the clinical disease caused
by the same pathogen.
3. Paradoxical carrier : It refers to a carrier who acquires the pathogen
from another carrier.
4. Contact carrier : The term contact carrier is applied to a person who
acquires the pathogen from a patient.

10. Depending on the duration of carriage, carriers are classified as :-
a. Temporary carrier : Where the Carrier state lasts less than 6 months
b. Chronic carrier : Where the carrier state last for several years and
sometimes even for the rest of one’s life

11. B. ANIMALS :
 Animal are also important sources
of infection for humans.
 Infections transmitted from animals to
humans are called as zoonotic infections.
e.g :- Bacterial : Bovine tuberculosis, Anthrax from domestic livestock
Viral : Rabies from dog
Protozoal : Toxoplasmosis from cat
Helminthic : Hydatid disease from dog
Fungal : Dermatophyte infection from cat and dog

12. C. INSECTS :
 Blood sucking insects such as mosquitoes, ticks, mites, flies, fleas and lice may
transmit a number of pathogen to man.
 Diseases transmitted by insects are called arthropod borne disease, and the
insects transmitting this pathogens are called as vectors.

13. Vectors are of 2 types :-
A. MECHANICAL VECTORS : Carry the organisms
on their legs, wings and body and transmit them to eatables.
e.g. Transmission of Dysentery bacilli to human through food by domestic
fly.
B. BIOLOGICAL VECTORS : Pathogens multiply
in the body of the vector, often undergoes
a part of a development cycle in it.
e.g. Malarial parasite in female anopheles mosquito , Filarial parasite in
culex mosquito .

14. D. FOOD
 Contaminated food may act as a source
of infection.
 The presence of pathogens in food may be due to
External
contamination
Pre-existing infection in
animal products
e.g. food poisoning
by Staphylococcus
e.g. Brucellosis

15. E. SOIL AND WATER:
 Soil may serve as a source of infection of microorganism which are
able to survive in soil for long periods.
e.g. C. tetani spores survive in soil for long period.
 Water may act as the source of infection either due to
Contamination Presence of aquatic vector
e.g. V. cholera
E.coli
e.g. Guinea worm

16. 2. MODE OF TRANSMISSION
A. HORIZONTAL TRANSMISSION :-
1). CONTACT : Contact transmission may be direct or indirect.
 Direct contact : Sexually transmitted disease such as
syphilis, Gonorrhoea and AIDS are acquired by direct
contact.
Indirect contact : Through the agency of fomites
e.g. Transmission of Diphtheria

17. 2). INHALATION :
 The organism in mouth and respiratory tract are expelled in
the form of droplet during coughing, sneezing or talking.
 Fate of droplets depends upon the size.
 Small droplets less than 0.1mm in diameter evaporate to form minute particles
called droplet nuclei(1 to 10 µm in diameter) remain in air for hours and act as a
source of infection, whereas large droplets fall down to the ground.
e.g. Measles, Influenza, Tuberculosis,

18. 3). INOCULATION :
Infections can be transmitted by inoculation
of microorganisms directly into the tissue of the host.
e.g. Rabies virus deposited subcutaneously
by dog bite
Arboviruses injected by insect vectors.
Infection by inoculation may be iatrogenic .
e.g. Hepatitis B and HIV may be transmitted through
the use of contaminated syringes and needles .

19. 4). INGESTION :
Gastrointestinal tract infection are generally transmitted by contaminated food or
water.
Infections transmitted by ingestion may be
a) Water borne: e.g. Cholera
b) Food borne: e.g. Food poisoning
5). Insects:
Insects may act as vectors and transmit infection from one person to another.
Transmission may be
a. Mechanical: e.g. Dysentery
b. Biological: e.g. Transmission of Malaria.

20. B. VERTICAL TRANSMISSION
where microorganisms are transmitted from mother to child.
Transplacental
Within birth canal or at the time of birth
Breast milk

21. 3. SUSCEPTIBLE HOST
 A person lacking effective resistance to a particular pathogenic
organism
 The infective agents enter the body of susceptible host by 4 main
portals of entry.
Respiratory tract
Gastrointestinal tract
Genital tract
 Skin

22. TYPES OF INFECTIOUS DISEASES
On the basis of spread of infection in community :-
1. Endemic diseases :- are those which are constantly present in a particular area.
e.g. Malaria.
2. Epidemic diseases :- Diseases that spread rapidly, involving many persons in an area at the
same time.
e.g. Cholera
3. Pandemic diseases :- Disease that spreads through many areas of the world involving very
large numbers of people affected within a short period.
e.g. Corona, Influenza and plague are pandemic diseases.

23. STAGES OF PATHOGENESIS OF AN
INFECTION
The infection process involves the following stages :-
 Transmission from an external source into portal of entry
 Evasion of primary host defence
 Adherence to the cell surface
 Growth and multiplication of the bacteria at the site of adherence
 Manifestations of the disease caused by toxin production or the invasion
 Host responses- both non-specific and specific
 Progression or resolution of disease.

24. REFERENCES :-
1. Text Book of Microbiology by Ananthanarayan and Paniker, 7th edition.
2. Review of Medical Microbiology and Immunology by Warren Levinson, 10th
edition
3. Text Book of Diagnostic Microbiology by Mahon, Lehman, Manuselis, 3rd
edition.
4. Clinical and Pathogenic Microbiology by Barbara. J. Howard, 2nd edition.
5. Internet sources