Pathogenesis of infectious disease

• Path means disease• Pathogens refer to microorganism capable to

cause a disease.• Pathology : the study of structural and

functional manifestation of disease.• Pathologist : a physician who has specialized in

pathology.• Pathogenicity : the ability to cause a disease • Pathogenesis : is the step or mechanisms

involved in development of a disease

• Phs in the corse of an infectious disease:1. Incubation period: is the time that elapses between

arrival of the pathogens and the onset of symptoms. And it is varies by many factor as health state-virulence of the pathogens- number of pathogens that enter the body.

2. Prodormal period: is the time during which patient feels out of sorts but not yet experiencing actual symptoms of the disease.

3. Period of illness: is the time during which the patient experiences the typical symptoms associated with that particular disease .(headache – sore throat-sinus congestion)

• The convalescent period: is the time during which the patient recover.

• Localized infection • Systemic infection • Acute infection : rapid infection followed out by rapid

recovery (measles-mumps-influenza)• Chronic infection : slow insidious and last for long time• Symptoms of a disease: define as some evidence of a

disease that is experienced by the patients. ( headache-fever-pain-itching)• Asymptomatic disease • Sign of a disease: define as some objective evidence of

a disease that is experienced by the patients. (skin rash-enlargment of the spleen)

Latent infection : an old infection that was contained by the body but may re-activate at any time as ( ?)

Primary infection: is the infection that the body get exposed to for the first time .

Secondary infection : is an infection that follows a primary infection.

• Step in the pathogenesis of infections disease:

1. Entry: of the pathogen into the body by: (Penetration, inhalation, ingestion and introduction of the pathogens directly into the blood. [shades needles]

2. Attachment: of the pathogen to some tissues within the body.

3. Multiplication: with local or system4. Invasive / spread of the pathogens5. Evasion of a host defenses.6. Damage to host tissue (s). extensive or death.

• Virulence: • is measure or degree of pathogenecitiy.

different organism vary in their ability to cause disease some strain virulence some is a virulence.

• Virulence factor: are the phenotypic characteristics of a microorganism that enable it to cause disease.

1. Structural features as pili ,capsule, flagella. It help adhesion: which is molecule on the surface of the pathogens that able to recognize the reception on the host cell: that is glycoprotein molecule on the surface of the host cell that the adhesion on the pathogen attach to it.

2. Obligate intracellular pathogens.3. Facultative intracellular pathogens.4. Capsules: antiphagocytic by WBC. (No receptor).5. Flagella: move and invade the aqueous area in

the body it avoid phagocytosis.

6. Exoenzymes : is the two major virulence factors by which bacteria cause disease the exoenzyme as

(a) coagulase as in staphaurus: clot plasma → sticky coat → protect it from phagocytes.

(b) kinases: → streptococcus & stophausus: body produce fibricolt → kinases → lysis.

(c) hyaluronidase: enable organism to spread through connective tissue by breaking down hyaluronic acid.

(d) collagenase: Break down the collagen to invade tissue.

(e) hemolysins: damage RBC. (f) lecithinase: damage extensive area of tissue.

7. Toxins: there are endotoxins that is integral part of the cell wall of the gram-negative bacteria can cause a number of adverse physiologic effect.

Exotoxins are the toxins that produced within the cells and then releases from the cell example: – Neurotoxins= that cause paralysis.– Enterotoxins = gastro intestinal disease.

• Mechanisms by which pathogens escape immune responses:

• The pathogens change their surface antigens example: influenze virus, HIV and nisseria.

• The pathogen's surface antigens closely resemble host antigens and therefore not recognized by immune system = molecular mimicry.

• Destruction of the host antibodies by producing enzyme as (IgA protease) that destroy IgA.