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INFECTIOUS DISEASES Dr Noha

INFECTIOUS DISEASES Dr Noha. INFECTIOUS DISEASES. Definition: Infection is the Invasion of a living tissue by pathogenic organisms and development of pathological changes. INFECTIOUS DISEASES. Mode of Infection: (1) Exogenous infection: - From the environment, a patient or a carrier.

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INFECTIOUS DISEASES Dr Noha

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  1. INFECTIOUS DISEASES Dr Noha

  2. INFECTIOUS DISEASES • Definition:Infection is the Invasion of a living tissue by pathogenic organisms and development of pathological changes.

  3. INFECTIOUS DISEASES • Mode of Infection: (1) Exogenous infection: - From the environment, a patient or a carrier. - The routes of exogenous infection are: (a) Direct contact (through skin & mucous membrane). (b) Inhalation. (c) Ingestion. (2) Endogenous infection: When commensals become pathogenic (e.g. E. coli in the intestine). - Infection occurs when defensive mechanisms of the body are overcomed (if immunity is lowered).

  4. INFECTIOUS DISEASES • Types of infectious diseases: Bacterial, Viral, Parasitic, & Fungal infections

  5. BACTERIAL INFECTIONS I - Acute bacterial infections II - Chronic bacterial infections.

  6. Effects of acute bacterial infections: 1- Cell injury 2- Inflammation 3- Immunity &/ hypersensitivity 4- Bacterial invasion of the blood &/ its products: A- Toxemia B- Bacteraemia C- Septiceamia D- Pyaemia

  7. TOXAEMIA • Definition: Circulation of bacterial toxins in the blood causing pathological and clinical manifestations.

  8. Bacterial toxins may be: - Exotoxins: Produced by gram positive bacteria as diphtheria bacilli, shigella organisms and some types of streptococci and staphylococci. - Endotoxins: Released from the bodies of dead gram negative bacteria as typhoid bacilli. - Sapremia: Toxemia occuring in cases of gangrene due to action of saprophytes on dead tissues.

  9. TOXAEMIA • Types: (1) Acute toxaemia: Occurs in acute infections as abscess, pneumonia, and diphtheria. (2) Chronic toxaemia: Occurs in chronic infections as tuberculosis

  10. TOXAEMIA • Clinical manifestations of Toxaemia:Fever, headache, general aching, and anaemia (due to bone marrow depression by the toxins).

  11. TOXAEMIA • Pathological manifestations of Toxaemia: The pathologic effects vary: - from mild effects such as degeneration & focal necrosis in parenchymatous organs (e.g. liver, kidney, heart, …), - to fatal changes that may cause death of the patient.

  12. TOXAEMIA • Severe toxaemia may kill the patient by:- toxic myocarditis → acute heart failure- acute tubular necrosis → acute renal failure. - necrosis and haemorrhage of the adrenal cortex → acute adrenal cortical insufficiency. - septic endotoxic shock.

  13. TOXAEMIA • Some bacterial toxins may show a selective involvement of living tissues:- Diphtheria toxins→ affection of peripheral nerves. - Clostridium tetani toxins→ affection of motor end plate → tetanic muscular spasm. - V. cholera enterotoxin→ massive, watery diarrhea

  14. BACTERAEMIA • Definition: Transient presence of small number of bacteria in the blood stream without toxic manifestations.

  15. BACTERAEMIA • Pathogenesis: Bacteraemia can occur in the following conditions: - After tooth extraction (Strept. viridans bacteria). - Blood spread of small number of bacteria derived from a septic focus (e.g. tonsillitis, sinusitis..). - During the course of some bacterial infections (e.g. in typhoid fever).

  16. BACTERAEMIA • Effects of Bacteraemia:(1) In most cases: the bacteria are rapidly eliminated by immune mechanisms, causing no pathological effects. (2) In some cases: the bacteria may localize in the tissues causing a pathological lesion. This is usually predisposed by an underlying cause (e.g. streptococcal viridans bacteraemia → endocarditis on top of diseased cardiac valves).

  17. SEPTICAEMIA • Definition: The circulation and multiplication of large number of virulent bacteria and their toxins in the blood stream. The condition is highly fatal.

  18. SEPTICAEMIA • Aetiology:Causative organisms: (1) Pyogenic bacteria as streptococci, staphylococci, pneumococci and gonococci. The commonest is streptococcus haemolyticus. (2) Bacilli as bacillus proteus, bacillus anthrax and bacillus pestis.

  19. SEPTICAEMIA • Aetiology: Predisposing factors:Low immunity (e.g. immunosuppressed pts, uncontrolled diabetic pts, ..). Source of infection: infected septic wounds, puerperal sepsis, acute osteomyelitis, meningococcal meningitis…

  20. Pathological featuresof Streptococcus Haemolyticus Septicaemia: 1- Effects of acute toxaemia: - Fever, headache, general aching, …. - Degenerations & focal necrosis in parenchymatous organs (liver, kidney, heart, ..). - Bone marrow depression causing anaemia (Leucopenia may occur in severe cases) - fatal complications may occur (toxic myocarditis, acute adrenal insufficiency, septic shock, ..)

  21. Pathological featuresof Streptococcus Haemolyticus Septicaemia: 2- Vascular & Haematological disorders:- Red cell haemolysis by haemolysin: causing anaemia and red staining of the intima of the vessels by the liberated haemoglobin. - Capillary haemorrhages (due to capillary destruction by streptococcal toxins) → Petechial hges in different tissues as the skin, mucous membranes.

  22. Pathological featuresof Streptococcus Haemolyticus Septicaemia: 3- Serous membranes: Serofibrinous or suppurative inflammation in the serous sacs. 4- Heart, Liver & Kidney: toxic injury

  23. Pathological featuresof Streptococcus Haemolyticus Septicaemia: • 5- Spleen:Acute Splenic Swelling Grossly:The spleen is enlarged, soft and friable. Cut surface shows a dark red semi-fluid red pulp. Microscopically:The sinuses are dilated, congested and contain excess neutrophils and macrophages. - Littoral cells lining the sinuses show active phagocytosis. - The lymph follicles are early hyperplastic. Later on they show necrosis and atrophy.

  24. PYAEMIA • Definition: Pyaemia is the circulation of septic emboli in the blood stream and their arrest indifferent organs causing multiple small pyogenic abscesses. Pyaemia has a high mortalityrate.

  25. PYAEMIA • Pathogenesis: - When a septic focus involves a vein, septic thrombophlebitis occurs. - Proteolytic enzymes in the inflamed area break down fragments from the septic thrombus. These fragments circulate in the blood stream as septic emboli. - Next the septic emboli get impacted in the small vessels of different organs producing multiple small pyaemic abscesses.

  26. PYAEMIA • Types:(1) Systemic pyaemia. - The septic emboli circulate in the systemic venous blood. - They are derived from acute osteomyelitis, puerperal sepsis, suppurativeotitis media, cellulitis and acute bacterial endocarditis. - They get arrested in the lung forming multiple pyaemic abscesses. - Smaller emboli from the lung reach the kidney, liver, brain ... etc.

  27. PYAEMIA • Types: (2)Portal pyaemia: - The septic emboli circulate in the portal venous blood. - They are derived from acute suppurative appendicitis, infected piles, acute cholecystitis, diverticulitis and septic lesions in the colon. - The emboli get arrested in the liver forming multiple pyaemic abscesses.

  28. Types: :(3) Pulmonary pyemia - The presence of septic emboli in the pulmonary circulation. - They are derived from thrombi in the systemic veins.

  29. PYAEMIA • Pathological Features: (1) The affected organ shows multiple small abscesses. The abscesses are nearly of the same size, peripheral in position, rounded in shape, yellow in colour and surrounded by a dark red zone of congestion.

  30. PYAEMIA • Pathological Features: (2) Effects of toxaemia: e.g. Cloudy swelling and fatty change in the parenchymatous organs. (3) Leucocytosis may occur in pyaemia as it is a pyogenic infection, however leucopenia is more common due to bone marrow depression by the associated toxaemia.

  31. Thank you

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