By Dr. Maha M.Abuhashim

Means invasion of the body by pathogenic micro-organisms which may be - Bacteria - Viruses - Fungi - protozoa

The body has both non-specific (e.g. inflammation) and specific (immunity) defense mechanisms to protect against infection.

Pathogenecity = capacity of the organism to cause disease.

Pathogenic bacteria can cause disease by many mechanisms e.g. 1- Toxin production …endo or exotoxins.. Which cause cell injury (reversible or irreversible) or inflammatory reaction. 2- Direct induction of inflammation (acute or chronic) or direct cell death.

3- Stimulation of hypersensitivity reactions (especially types III and IV).

4- Usually there’s overlap between these factors and one organism can cause the disease by many mechanisms.

Local spread….this route is facilitated by local tissue destruction especially if exotoxins are produced by the organism .

Natural passages …trachea, ureters,…etc

Lymphatic spread …organism is taken by macrophages to lymph nodes or may gain access in lymphatic fluid. Enlargement of the draining lymph node may be due to immune response or infection by the micro-organism.

Spread in tissue fluids …takes place in the pleural and peritoneal cavities leading to pleurisy and peritonitis.

Neural spread …Rabies virus and varicella zoster virus produce infection by traveling along nerves.

Hematogenous spread …organism may travel in plasma (bacteria and hepatitis B virus) or within cells as monocytes (herpes virus, cytomegalovirus, HIV).

There are several terms used to describe blood spread of an infecting agent…

Viremia and bactremia….passive carriage of small numbers of viruses and bacteria without growth in the blood stream.

Toxemia…means circulation of bacterial toxins in blood with clinical and pathological manifestations

Septicemia…Is the circulation of large number of virulent micro-organism with multiplication and toxin production in the circulation. This commonly leads to septic shock.

Pyemia…Is the circulation of septic emboli (detached septic thrombi) with their localization in different organs. -It may be pulmonary, systemic or portal. - It results in the formation of multiple, uniform small abscesses in many organs. -It is usually fatal.

T.B bacilli are - Aerobic - Acid fast - Non motile - Do not produce toxins

- It is an infective bacterial granuloma which is widely spread all over the world. - It is caused by bacteria called mycobacterium tuberculosis. - It may be primary or secondary. - It can affect almost all organs in the body

Mode of infection - Human type…by droplet infection from an open, active pulmonary disease.

Bovine type of bacilli …. lead to oropharyngeal and intestinal lesions acquired by drinking raw contaminated milk. This type of infection is greatly reduced by pasteurization of milk.

Organism is phagocytosed by macrophage which is not able to destroy virulent micro-organism.

In the early phase of primary tuberculosis, (in the non immunized person), there's uncontrolled proliferation of bacilli within pulmonary alveolar macrophages with resulting bactremia and seeding of multiple sites.

After 3 weeks of infection, cell mediated immunity develops. Macrophages process mycobacterial antigen and present it to unstimulated CD4+Tн0 cells.

Under effect of IL-12 secreted by macrophages, CD4+Tн0 cells mature into CD4+Tн1 cells which secrete IFN-γ .

IFN-γ activates macrophages to secrete a group of mediators that induce lymphocyte and macrophage activation ending in granuloma formation

The reaction ends by the formation of epithelioid granulomas with giant cells , central caseation and peripheral fibrosis.

Primary tuberculosis 1st infection

Secondary tuberculosis

Age & previous infection

Young ages (childhood type) non immunized persons

middle age (adulthood type) 2ry infection in patient taking 1ry infection or B.C.G vaccine

Methods of infection

Inhalation & Ingestion Direct contact

Endogenous due to reactivation. Exogenous due to reinfection

Site 1) Lung 2) Intestine 3) Tonsils 4) Skin 5) Nose

Any site but mainly lung & intestine are affected

Reaction of the body against bacilli

* Proliferative reaction : Primary complex formed of :Parenchymatous lesion; tubercles with minimal caseation T.B. lymphadenitis T.B. lymphangitis

* Proliferative reaction in solid organs, tubercles with marked caseation * Exudative reaction in serous covering

Spread Spread : mainly lymphatic and blood

-Spread: mainly local and natural passages.

-Infective granuloma, - Caused by a spirochete (Treponema pallidum). - One of the venereal diseases. -May be congenital or acquired - Acquired has 3 stages *Primary. chancre *Secondary *Tertiary

Characterized by:- 1- End arteritis obliterans of small blood vessels. 2- Perivascular infiltrate of chronic inflammatory cell with predominant plasma cells. 3- Granulation tissue and fibrosis. 4- Variable degrees of necrosis.

1

4

2

3

Chancre - Appears after an incubation period 2-4 weeks of exposure.

Sites a. Genital - (penis, vulva or cervix). b. Extra genital - Tongue, lips, nipples.

Lymph nodes are enlarged.

Patient is highly infectious during this stage

Occurs 1-3 months after the onset of infection in untreated patients.

Characterized by muco-cutaneous lesions and painless enlargement of the lymph nodes.

Patient is also infective during this stage.

Affects about 1/3 of patients with untreated syphilis.

It occurs after a latent period of 3-30 years.

Affects mainly the cardiovascular system (80-85%) and the central nervous system (5-10%).

-Lymph nodes are not affected in this stage and the patient is not infective.

it is an infective parasitic granuloma.

There are three species:

- S. haematobium (urogenital system).

- S. Mansoni (LI)

- S. Japonicum (SI).

- Endemic in Egypt

Tissue reaction to living ova

Inflammatory reaction ( lymphoctes, esinophils, macrophages and may be giant cells) that may be arranged in either……….

1. Granulomatous reaction. - focal inflammatory reaction forming a bilharzial nodule. - More common in the colon ( S. Mansoni). - Moderate amount of ova.

2. Diffuse reaction - In which inflammatory cells are diffusely dispersed. - More common in the urinary bladder. - Dense ova deposition.

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S.M

S.H

Diffuse bilharzial reaction Bilharzial granuloma

Intestine Urinary bladder

Hypochromic anemia…. Due to repeated blood loss

Stone formation. Obstructive uropathy… due to inflammation and fibrosis.

Carcinoma….of the urinary bladder

Bilharzial hepatic fibrosis Microcytic hypochromic anemia Fibrotic stenosis is rare. Bilharzial desentry. No relation to malignancy.

Diffuse hepatic fibrosis.

Results from emboli of ova and worms from the intestine that reach the portal tracts where they induce an inflammatory reaction that ends with fibrosis.

Portal tracts are the main site of affection.

It leads to portal hypertension.

Not related to HCC.

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Splenomegaly.

Ascites.

Congestion of GIT.

opening of porto-systemic anastomosis.

Piles.

Caput Medusa.

Esophageal varices

Splenomegaly

Intestinal Bilharzial hepatic fibrosis Splenomegaly Anemia, Leucopenia Irregular fever.

Effects of Splenomegaly

Compression. Hypersplenism Irregular fever.

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