Infection

Published on 30/06/2015 by admin

Filed under Pathology

Last modified 30/06/2015

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 1773 times

Chapter 4 Infection

Infection

There are very many infections: the chapter will deal only with principles and a few examples.

Type of Infecting Agent Example Example of Disease
BACTERIA (a very wide range) STAPHYLOCOCCUS ABSCESS
VIRUSES (a wide range) HERPES ZOSTER CHICKENPOX and SHINGLES
FUNGI (a limited range) CANDIDA BUCCAL and VAGINAL THRUSH
PROTOZOA PLASMODIUM MALARIA
Infestation with PARASITES WORMS and FLUKES ECHINOCOCCUS GRANULOSIS HYDATID DISEASE

Infection and Infectious Disease

infection occurs when microorganisms invade the sterile internal body tissues. (Multiplication usually follows invasion.)

An infectious disease occurs when infection is associated with clinically manifest tissue damage.

Factors Influencing the Course of Infection

Once infection has occurred, important defence mechanisms operate:

1. Inflammation in the acute local reaction (see p.33) tends to limit the spread of organisms. In some important diseases, there is no acute local inflammatory response at the site of entry, e.g. Brucellosis (undulant fever) and many virus infections. In the chronic inflammatory reaction (see p.41), the formation of fibrous tissue also helps to localise infection.
2. Phagocytosis (see p.36) Note: some organisms may survive or multiply within phagocytes – usually associated with chronic infection. Good examples are tuberculosis, brucellosis, leprosy.

Bacteria

1. Production of toxins (poisons)

Exotoxins Endotoxins
Secreted by living bacteria Integral part of bactrial cell wall
Release on death of organism (usually Gram-negative)
Simple proteins Lipid-polysaccharide complexes
Neutralised by specific antibody (antitoxin) Do not stimulate antibody production
Many actions
– Enzymes, e.g. S. aureus protease
– Action on intracellular signalling, e.g. V. cholerae
– Neurotoxins, e.g. C. botulinum
– Superantigens, e.g. S. pyogenes
Beneficialeffects:Inlowdosestimulatesprotectiveimmunity Harmful effects: In high dose ENDOTOXIC
SHOCK – due to massive release of cytokines with activation of coagulation,fibrinolytic and complement cascades
LPS binds cell surface receptor CD14 and is delivered to TLR4 that starts intracellular signalling cascade