1. INTRODUCTION TO INFECTIOUS DISEASES

2. Infection and the disease that results from it remain the greatest killer of human

3. The concept of an infectious agent emerged in the mid-19th century and was defined by a German physician, Robert Koch (1843-1910), When he isolated Bacillus anthracis,(Kocks postultes).

4. The main characters of infectious diseases : 1. They are caused by living organism. 2. Communicability: Can be transmitted from human to human or from animals to human (zoonosis). 3. Cure can occur either spontaneously or by giving antibiotics (except for some viruses). 4. Many of them are preventable through different methods of prevention including vaccination. 5. Permanent immunity can be resulted in some of them after exposure to the disease.

5. The causative agents of infection in man Prions: These are the simplest infectious agents, and consist of an altered form of normally occurring protein. They are causing a group of diseases in human being called spongiform encephalopathy like Creutzfeldt-Jakob disease (CJD). Viruses: Viruses contain two types of macromolecule: proteins and nucleic acids, (either DNA or RNA). They cannot reproduce by theirselves, but needing to enter a cell. Bacteria: They contain both RNA and DNA, have facilities for protein metabolism and are generally free living, although some (e.g. Chlamydia and rickettsiae) are intracellular parasites. Bacteria have no nuclei but reproduce autonomously. They include mycoplasmas, spirochaetes, Actinomyces, bacilli and cocci. Others: include fungi ( e. g.candidia), protozoa (e. g. malaria, amoebiasis) and parasitic worms like ascars, scistosoma (helminths).

6. INFLUENCES ON PATTERNS OF INFECTION IN DEVELOPED COUNTRIES 1. Vaccines: 2. Animal husbandry and preparation of food: Salmonella originating in poultry and eggs. 3. Microbial resistance: Staphylococcus aureus (meticillin-resistant, MRSA. 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:Avian/pandemic 'flu

7. Infections in developing countries infection remains one of the most common causes of disease and death, particularly in children

8. PATTERNS OF INFECTION IN DEVELOPING COUNTRIES 1. Killers of children, preventable but variably prevalent (Measles, Diphtheria, Pertussis, Poliomyelitis, Tetanus, Hepatitis B, Gastroenteritis, Malaria, Meningococcal diseas, Acute diarrhoeal illness). 2. Chronic disabling infections, widely prevalent : (Leprosy, Tuberculosis, Trachoma, Malaria, Trypanosomiasis cruzi, Amoebiasis, Intestinal helminthes, Schistosomiasis, Filarial infection 3. Epidemic diseases, actual and potential (Louse-borne typhus and relapsing fever, Cholera, Malaria, Visceral leishmaniasis HIV infection, Tuberculosis in association with HIV epidemic, Influenza, Enteric fevers 4. Infections liable to focal outbreaks (zoonotic or vector-borne ) Dengue fever, Cutaneous leishmaniasis, African trypanosomiasis, Plague, Anthrax, And Yellow fever).

9. FACTORS AFFECTING THE PATTERN OF INFECTIOUS DISEASES IN DEVELOPING COUNTRIES 1. Widespread poverty: most developing countries cannot buy vaccines and drugs inaddition to malnutrition, which makes people more susceptible to disease,.Vector control (e.g. malaria, African trypanosomiasis) remains imperfect. 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 such as drought, flooding and earthquakes as well as with war and political strife.

10. MO and Host interaction Viruses, bacteria, fungi and protozoa all interact with the human body and do so in a relationship that is - Symbiotic - Saprophytic - Parasitic

11. Symbiotic : The symbiotic e. g. colonising bacteria in the human gut, upper respiratory tract and lower genital tract, and on the skin and superficial mucous membranes. Often the human body benefits from this type of colonisation, as in the prevention of supervening infection with Clostridium difficile by normal gut flora or Candida albicans by vaginal lactobacilli. 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 system. Subsequent illness is produced in the individual by the interaction of the host immune mechanisms and the infecting organism and its toxic effects