Infection, Non specific host mechanisms

1. INFECTION
MSc IV SEMESTER
Immunology and toxicology

2. INFECTION
An infection is the invasion of an organisms body tissue
by disease causing agents, their multiplication and the
reaction of host tissues to the infectious agents and the
toxins produced.
An infectious disease also known as transmissible
disease or communicable disease is an illness resulting
from an infection.
Infections are caused by different infectious agents like-
Virus, bacteria, fungi, parasites, arthropods, etc.
They vary in their size, shape, function genetic content
and how they act on the body.

3. TYPES OF INFECTIONS
VIRAL INFECTION
Viral infections are caused by a virus. Million
types of virus are thought to exist but only 5000 types
have been identified. Viruses contain a small piece of
genetic code. They are protected by a coat of protein
and fat.
Viruses invade a host and attach themselves to a
cell. As they enter the cell they release genetic
material. The genetic material forces the cell to
replicate and the virus multiplies. When the cell dies ,
it releases new viruses and these go on to infect new
cells.

4. VIRAL INFECTION
Some examples for viruses
HPV- Human Papilloma Virus
EBV- Epstein Barr Virus can leads to cancer.
Common cold, mainly caused by the rhinovirus,
coronavirus and adeno virus.
Encephalitis and menengitis caused by enterovirus and
herpes virus.
Gastroenteritis- caused by Nova virus.
Zika, HIV, Hepatitis C, Polio, Influenza, Dengue,
H1N1, Swine flue, Ebola etc.

5. BACTERIAL INFECTIONS:
Bacteria is single celled micro organism.
Some Bacterial diseases are deadly like
cholera, diphtheria, dysentery, pneumonia,
tuberculosis, typhoid, bacterial meningitis,
pneumonia, gastritis, eye infections, skin
infection etc..

6. FUNGAL INFECTIONS
A fungal is an multi cellular parasite that can
decompose and then absorb organic matter using an
enzyme. They are approximately 51 millions species of
fungus.
Examples are- valley fever, ring worm, eye infection,
skin diseases, prion diseases etc.
OTHER INFECTIONS
Protozoan infection
Helminths infection. etc

7. Non Specific Host defenses
Resistance: It is a ability towards diseases. The
capability of an organism to defend itself against a
disease. The capacity of an organism or a tissue to
withstand the effect of a harmful environmental agents.
Non specific resistance: Defenses that protect
against all pathogens.
Specific resistance: Protect against specific
pathogens.

8. Three lines of defense against
infection.
NON SPECIFIC DEFENSE MECHANISM SPECIFIC DEFENSE
1 st line of Defense 2nd lines of Defense 3rd Line of Defense
Skin
Mucosa Membrane
Secretions of skin,
Mucous membrane
Phagocytic cell
WBC
Antimicrobial Protein
The inflammatory
response
Lymphocytes
Antibodies

10. 1. Mechanical Defenses
A) SKIN: It has two layers-
i) Epidermis- thin outer layer of epithelial tissue.
ii) Dermis- Thick inner layer of connective tissue.
B) MUCOUS MEMBRANE: A line of gastrointestinal,
genitourinary and respiratory tracts.
C) LACRIMAL APPARATUS: Continual washing and blinking
prevents microbes from setting in the eye surface.
D) SALIVA: Washes microbes from teeth and mouth.
E) NOSE HAIR & CILIA: Coated with mucus filter dust, pollen
and microbes in respiratory tract.
F)COUGHING AND SNEEZING; Expel foreign objects.

11. 2. Chemical Defenses:
i) SEBUM: Oily substances produced by sebaceous glands that
forms a protective layer over skin contains unsaturated fatty acids
which inhibit growth of certain pathogens like bacterial and
fungi.
ii)Gastric Juice: Mixture of HCl, Enzymes and mucus. pH
between 2-3 kills many microbes and destroys most toxins.
iii) Cellular Elements of Blood: WBC- 5000-10000

12. 2nd Line of Defense:
Phagocytosis: - Chemotaxis.
Inflammation- Destroy and remove pathogens.
Antimicrobial Substances:
i) Complement System- large group of serum
proteins that participate in the lysis of foreign
cells, inflammation and phagocytosis.
ii) Interferons- Small proteins, Heat stable and
antiviral protein.
iii) Monocytes:
iv) Macrophages: