Pathogenesis of infectious disease

1. Pathogenesis of infectious disease

2. 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

3. Phs in the corse of an infectious disease: • 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. • Prodormal period: is the time during which patient feels out of sorts but not yet experiencing actual symptoms of the disease. • Period of illness: is the time during which the patient experiences the typical symptoms associated with that particular disease .(headache – sore throat-sinus congestion)

4. 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)

5. 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.

6. Step in the pathogenesis of infections disease: • Entry: of the pathogen into the body by: (Penetration, inhalation, ingestion and introduction of the pathogens directly into the blood. [shades needles] • Attachment: of the pathogen to some tissues within the body. • Multiplication: with local or system • Invasive / spread of the pathogens • Evasion of a host defenses. • Damage to host tissue (s). extensive or death.

7. 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.

8. 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. • Obligate intracellular pathogens. • Facultative intracellular pathogens. • Capsules: antiphagocytic by WBC. (No receptor). • Flagella: move and invade the aqueous area in the body it avoid phagocytosis.

9. 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.

10. Toxins: there are endotoxins that is integral part ofthe cell wall of the gram-negative bacteria can cause a number of adverse physiologic effect. Exotoxinsarethe toxins that produced within the cells and then releases from the cell example: • Neurotoxins= that cause paralysis. • Enterotoxins = gastro intestinal disease.

11. 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.