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Report: The infectious process, levels of infectious process. Features of infectious diseases, their characterization. Sajid Mehmood

Adnan Akram

Aftab Ahmed

Accident & Emergency Department. Royal Infirmary Liverpool. United Kingdom

Department of Infectious Diseases. University Hospital Riga. Latvia

Department of Infectious Diseases. Kaunas Medical University Hospital. Kaunas. Lithuania

The infectious process is a unity of physiological defensive reactions and pathological reactions that develop in definite conditions of outer world (environment) as a response to the impact of the initiator. In other words -: Infectious process is the interaction between micro and macro – organisms in the conditions of the outer world. Infectious disease – terminal stage of infectious process who’s manifestations are different. +/physiological, clinical, etc. Infectology – science of infectious process. Infectious disease are that which are initiated by pathogenic or conditioned pathogenic microorganisms. Characteristics: 1. contagiousness 2. incubation 3. cycle of clinical symptoms development 4. development of specific immunity Classification of infectious diseases: In the international classification infectious and parasitic diseases are included in the 1 st class. The 1st class can be subdivided into: - Intestinal infections - Tuberculosis - Other viral infections- Bacterial zoonosis - Syphilis and other venereal - Other bacterial infections diseases - Poliomyelitis and other enteroviral diseases of the CNS - Other diseases caused by - Viral infections with rash spirochetes - Viral infections carried by arthropods - Mycoses - Helminthiases - Other infectious and parasitic diseases -Rickettsiosis and other diseases carried by arthropods Classification according to carrying mechanism of causative agent - Intestinal infections : the intestines are the main localization of the disease,

e.g. shigellosis, cholera, poliomyelitis - Respiratory infections : causative agent is localized in the respiratory tract, in the mucous membrane of the oral cavity, trachea, bronchi, and teeth ridge (gums and jaw) e.g. influenza, diphtheria, meningococcal, TB - Transmissive infections (blood borne) : the causative agent is localized mainly in the blood and lymph, e.g. typhus, hemorrhagic fever, rabbit fever - Integument infections : the causative agent uses to localize in the integuments, e.g. erysipelas, rabies, tetanus, listeriosis General Clinical Characteristics A cyclic course interchanging in periodically defined succession. 1. Incubation – from entrance/ingression of disease initiator into the organism till occurrence of symptoms prior to disease. It lasts from some minutes till many months. 2. Prodromal or precursory period – occurrence of the first, usually general symptoms. Commonly it lasts for several days. 3. Meridian of peak period of disease – non-specific symptoms manifest to the utmost, specific symptoms appear. 4. Period of convalescence or recovery period – clinical symptoms gradually disappear, function and structure of injured organs are restored. Type of disease course 1. Typical course – the disease has the main symptoms and syndromes that are characteristic to it. 2. Atypical course – the disease has the main symptoms and syndromes characteristic to it but they are effaced (unmanifested), unapparent (subclinical form). 3. Carrying of infection – in spite of the presence of initiator in organism clinical symptoms of the disease are not present, completely missing. Obligatory steps for infection of microorganism 1. Attachment +/- entry into body 2. Local or general spread in the body – evade immediate local defense 3. Multiplication – typical clinical signs 4. Evasion of host defenses (microbial answer to host defense) 5. Shedding from body – leave body at a site and on a scale that ensures spread in new organisms (transmission) Causes damage to host (pathology, disease) Types of transmission – horizontal, vertical Vertical can be pre-natal, peri-natal, post-natal, and germ line

Host defense 1st line  skin and mucous membrane, few bacteria are found below larynx due to cough reflex Non-specific immune response factors  phagocytic cells Specific immune response factors  antibodies Tissue reactions 1. Multiplication of microorganisms, production of toxins, decreased host defense, host dies or, 2. Equilibrium between microorganism and host – latent period 3. Host > Microorganism Pathogenesis of infections 1. Toxin – can interact with adjacent or far situated cells (distant cells) 2. Virulence factors 3. Microbial adherence – microorganisms bind to surface of host, that adhere by fibrilla, specific adherence organ cells – fimbria (can attach to all cells) Viral infections – neurotropic virus grow in blood and then cross blood brain barrier. After viremia invades cerebral capsule etc. Manifestation of infection Fever > 37.8C orally 38.2C rectally Pyrogens cause fever. They may be exogens – microorganisms, microbial products, LPS of Gram negative bacteria on endogens cause fever by affecting metabolism in hypothalamic thermoregulation center. Systemic response Hematological manifestations – a) Leucocytosis -  Neu :  immature circulatory neu b) Anemia – acute bleeding, chronic c) DIC d) Thrombocytopenia Cardiopulmonary Manifestation – a) Tachycardia / bradycardia (dengue, plague) b) Hypotension c) Hyperventilation with marked respiratory alkalosis d) Adult respiratory distress syndrome Renal Manifestations – proteinuria, oliguria, azotemia Hepatic Manifestations – liver dysfunction GIT Manifestations – upper GIT bleeding caused by sepsis CNS Manifestations – confusion, coma, stupor

Endocrine and Metabolic Manifestations – Hypoglycemia, not common in sepsis Major pathogens can be: 1. Viruses, DNA or RNA 4. Protozoa 2. Bacteria 5. Worms 3. Fungi 6. Rickettsia Most common diseases 1. Diarrhea, 2. TB, 3. Helminthiasis, 4. Malaria, etc… Newly identified infectious agent – 1999, Napah virus Guidelines for health provision Education – what is infectious diseases, how to avoid them Control – epidemiological surveillance, vaccination

Report: The infectious process, levels of