ملخص

INFECTIOUS DISEASES

Infection and the disease that results from it remain the greatest killer of human
The main characters of infectious diseases:
1. They are caused by living organism.
2. Communicability
3. Cure can occur either spontaneously or by giving antibiotics
4. Many of them are preventable
5. Permanent immunity can be resulted in some of them after exposure to the disease.

the causative agents of infection in man

1.Prions: These are the simplest infectious agents. They are causing a group of diseases in human like Creutzfeldt-Jakob disease (CJD).
2.Viruses
3.Bacteria
4.Others: include fungi ( e. g.candidia), protozoa (e. g. malaria, amoebiasis)

INFLUENCES ON PATTERNS OF INFECTION IN DEVELOPED COUNTRIES

1. Vaccines
2. Animal husbandry and preparation of food
3. Microbial resistance
4. Sexual behaviour: Increase in HIV infection and other sexually transmitted diseases
5. International travel: Importation of malaria
6. Resurgence of infections: Tuberculosis-world-wide, especially in association with HIV infection,
7. Immunosuppression
8. Injection drug addiction
9. 'New' and emerging infections


PATTERNS OF INFECTION IN DEVELOPING COUNTRIES

1. Killers of children, preventable but variably prevalent

2. Chronic disabling infections, widely prevalent:
3. Epidemic diseases, actual and potential
4. Infections liable to focal outbreaks (zoonotic or vector-borne)

FACTORS AFFECTING THE PATTERN OF INFECTIOUS DISEASES IN DEVELOPING COUNTRIES

1. Widespread poverty:
most developing countries cannot buy vaccines and drugs inaddition to malnutrition
2. Poor sanitation
e. g. cholera spread, in which the infecting agent is transmitted through contaminated sewage
3. Climate
Indirectly reducing agricultural production, which increases the risk of malnutrition.
hot weather and humid forests favor growth of the flies and mosquitoes that transmit malaria, yellow fever, ……..
4. Finally, in developing countries (including tropical areas), infectious diseases are often associated with natural disasters

Viruses, bacteria, fungi and protozoa all interact with the human body and do so in a relationship that is
- Symbiotic
- Saprophytic
- Parasitic
Symbiotic: e. g. colonising . Often the human body benefits from this type of colonisation, as in the prevention of supervening infection .

Saprophytic: e.g.fungal skin infections with minimal local damage and little or no systemic upset.


Parasitic: True infection only occurs when microorganisms upset normal physiology or breach skin and/or mucous membranes and enter the blood stream or normally sterile environments such as connective tissue, bones, muscles and joints or the central nervous .

Sources of infecting MO
1. Human reservoirs (sources)
Infection may originate from the patient himself (endogenous) or From outside sources i. e from other human (exogenous), often another person who may be either suffering from an infection or carrying a pathogenic microorganism. Carriers are usually healthy and may harbour the organism in the throat bowel or blood
2. Animal reservoirs (zoonoses) or sources
Examples are: contaminated meat/poultry (food poisoning organisms)
Milk from infected animals (tuberculosis, brucellosis)
body fluids of animals
3. Environmental reservoirs (sources)
examples
Legionella in air-conditioning or domestic water pipes,

METHODS OF TRANSMISSION OF INFECTION FROM ITS SOURCES:

1. From Human sourse
--Faecal/oral
--Direct contact Skin organisms,
--Sexually transmitted infections.
----Aerosol/droplet spread
--Water aerosol
--Sharps injury/needlestick


2. Animal (zoonoses
--Direct contact
--Faecal/oral (ingestion)
--Aerosol/droplet
--Penetration of skin
--Arthropod

3. From Environment:

--Direct/skin penetration: Tetanus, wound botulism
--Ingestion: Toxoplasma

MICROBIOLOGICAL INVESTIGATION OF INFECTION

3. IMMUNODIAGNOSIS
Enzyme-linked immunosorbent assay (ELISA)
Rapid immunochromatographic test
Western blot (immunoblot) test
Immunofluorescence (direct and indirect)

2. MOLECULAR DIAGNOSTIC METHODS

the polymerase chain reaction (PCR) has become the standard and most sensitive for the detection of pathogens in body fluids.
Two major disadvantages prevent its universal acceptance:
1. Expensive 2. False positive results.


1. DIRECT DEMONSTRATION
A. Microscopic examination of biological fluids or tissue slides with appropriate stains. B. In vitro culture.
C. Animal inoculation.