Host Parasite Relationship 1446 (2024) PDF

Host Parasite Relationship Prof. Hanan Habib Department of Pathology ,Microbiology Unit College of Medicine 1446 (2024) OBJECTIVES  Define core terms related to host-parasite relationship.  Recall host response to parasite invasion (specific and non-spec...

Host Parasite Relationship Prof. Hanan Habib Department of Pathology ,Microbiology Unit College of Medicine 1446 (2024) OBJECTIVES  Define core terms related to host-parasite relationship.  Recall host response to parasite invasion (specific and non-specific responses).  Know important examples of primary and secondary pathogens.  Recognize the differences between virulence and pathogenicity and how virulence measured.  Recall the transmissibility of pathogens.  Describe the attributes of pathogenicity (including: adherence, survival, multiplication ,invasion & tissue destruction) and recall examples.  Know Koch’s postulates Host-Parasite Relationship Human host is normally in contact with many microorganisms (microbiota (normal flora)) Only a small number of these microorganism (primary and opportunistic pathogens) can cause disease. Host-parasite relationships (interaction) is characterized by fighting the organism to invade the body and the body defending itself by protective measures.  Host-parasite relationship is discussed under: Pathogenicity & Microbiota  A pathogen Definitions A Pathogen Parasite Pathogenicity Host The ability of the microorganism to cause Microorganism having diseases the capacity to cause Bacteria, viruses, fungi disease in a particular Human (or animal or or parasites which live host. others) that support the in or within the host Infection growth and survival and ,may cause disease or Invasion of cells and protection of the parasite A pathogen may infect one live mutually with the multiplication by body organ or multiple host. microorganisms without organs tissue destruction. Some pathogens enter into latent state ( infection but Disease no symptoms) eg. Is the end product of an Mycobacterium infectious process (signs & tuberculosis symptoms of infection)  Definitions ,cont, The ability of the host to prevent establishment of infection by using RESISTANCE its defense mechanisms Lack of resistance to the organism and establishment of SUSCEPTIBILITY disease The ability to spread from one host to another. This enables organism TRANSMISIBILITY to maintain continuity of species in case of death of original host. Mode of transmission by : airborne, contact ,vehicle or vector Virulence is the degree of pathogenicity , or the ability to invade and destroy tissue to produce disease. Virulence is measured by the Lethal dose 50 (LD50) which is the number of organisms or mg of toxins that will kill 50% of susceptible lab animals ( usually mice ) when injected into such animals. When the LD 50 virulent is low ,the organism is considered highly virulent but when LD 50 is high the organism is considered having low virulence. eg. Shigella species is more virulent than Salmonella spp.  Primary pathogens Pathogens Primary pathogens Opportunistic (secondary) An organism that is able to pathogens cause disease in an apparently healthy individual who is non- immune to that organism. Having low pathogenicity and infects people with e.g. - Bordetella species low immunity. - Mycobacterium tuberculosis eg. Pseudomonas & S. epidermidis  True pathogen vs opportunistic pathogen  True pathogen: cause disease in healthy individuals Associated with specific recognizable diseases  Opportunistic pathogen: Cause diseases in immunocompromised hosts Gain access to sterile regions (e.g. by injury)  Host resistance to parasite invasion Non-specific defense Specific defense Natural Acquired resistance to certain organism: e.g. Antibodies  Skin mechanical barrier  Ciliated epithelium of respiratory tract  Competition by normal flora  Low pH of the stomach  Cough  Peristalsis  Lysozymes  Neutrophils Determinants of pathogenicity Before causing disease, the microorganism should have the ability to: a) Adherence & colonization: attachment to host epithelial surface. b) Survive ( resist ) host natural defense mechanisms. c) Multiply to large numbers. d) Tissue Destruction:the ability to overcome host defense , invade the tissues and cause destruction to produce clinical disease.  Adherence & Colonization ▪ By adhesins (adherence factors) found on bacterial surfaces. a) Pili b) Other protein surface structures ▪ Host cells structure involved in adhesion include: a) Fibronectin b) Proteins and glycopeptide  Adhesion & tissue destruction What causes bacterial infections Pharmacy for you media/image4.png Tissue destruction by: a) Toxin production ,either: - Exotoxin: produced outside the gram positive and gram negative bacteria eg. Cholera toxin, or - Endotoxin: only found in gram negative bacteria b) Invasion by: - Capsulated , or - Non-capsulated organisms Exotoxin can be: A – B type exotoxins eg. Cholera toxin A :Active unit B :Binding unit for attachment Or,. Membrane active exotoxin eg. Hemolysin of group A Streptococcus Exotoxin Endotoxin  Exotoxin vs Endotoxin Exotoxin Endotoxin 1- Protein Lipopolysaccharide 2- Soluble & Diffusible Part of cell wall 3- Heat Labile Heat stable 4- Pharmacologically specific Non-Specific action Low Immunognicity 5- High Immunogenicity 6- Inactivated by chemicals to Do not form toxoids toxoids 7- No Fever Induce Fever  Tissue distraction by invasion of Capsulated organisms Non capsulated organisms Bacteria that have capsule. Resist intracellular killing Capsules are polysaccharide (except called intracellular ( IC) the capsule of Bacillus anthracis is organisms. polypeptide). Capsule prevents phagocytosis and Examples : capture by immune system..Mycobacterium tuberculosis The organisms are readily killed.Brucella species once phagocytosed. Called.Salmonella typhi extracellular (EC) organisms Example :.Legionella pneumophila.Streptococcus pneumoniae (Pneumococcus) Reference book Sherris Medical Microbiology. An introduction to Infectious Diseases. Latest edition, Kenneth Ryan and George Ray. Publisher : McGraw Hill. Tutor contact address Hanan Habib [email protected]