Pathogens and the Host Flashcards
Pathogen
An organism which can cause disease
Commensal
An organism which is part of normal flora
Pathogenesis
Process by which an infection leads to disease
Mechanisms of viral pathogenesis
- Cell destruction following viral infection
- Virus-induced changes to cellular gene expression
- Immunopathogenic disease
The overt disease is often small in comparison to the unapparent.
Innate immunity
Nonspecific defence mechanisms that come into play immediately or within a few hours of an antigens appearance in the body. Includes;
- Epithelial barriers and chemical barriers
- Phagocytic cells; polymorphs (acute - neutrophils, eosinphils, basophils) and macrophages (chronic)
- Dendritic cells (to activate adaptive immune response)
- Natural killer cells
- Complement (antigen/antibody complex triggers cascade)
- Cytokines and chemokines (inflammation, systemic effects, adaptive)
- Anti-microbial substances
Acquired immunity
A specific response obtained by the development of antibodies in response to prior exposure, vaccination or from the transmission of antibodies from mother to fetus or injection of antiserum. Natural and artificial.
Active - own antibodies/ passive - ready-made antibodies.
1. Humeral; B cell converted to plasma cell by CD4+ which makes the antibody. Bacterial and axtra-cellular.
2. Cellular; macrophages converted to T cells which can create CD4/Th2 and CD8/Th1 via cytokines. Viral, fungal, intra-cellular and lymphocytosis.
Antibodies
Immunoglobulins are proteins with antibody activity.
- IgM (primary)
- IgG (secondary)
- IgA (mucosal)
- IgE (allergy and helminth infections)
- IgD (unknown)
Colonisation
When bacteria grow on body sites exposed to the environment without causing any infection
Latent/asymptomatic infection
An infection that is hidden, inactive or dormant e.g. herpes simplex virus
Infection
The presence of microorganisms causing damage to body tissues, usually in the presence of acute inflammation.
Clinical infection
Signs and symptoms; inflammation, pain, pyrexia, tachycardic, rigors, increased WBC count, increased C reactive protein (CRP)
Pathogenicity
The capacity of a microorganism to cause an infection
Infectivity
Ability of a pathogen to establish an infection
Virulence
Ability to cause harmful effects once established. The severity//harmfulness of a disease. Conferred by invasiveness, toxin production and immune invasion
Sites of viral entry
Respiratory tract, alimentary tract, urogenital tract, conjuctiva, arthropod, capillary, skin
Features of acute viral infection
Located to a specific site of the body. There is development of viraemia with widespread infection of tissue. It starts mildly, increases with time and then lessens. E.g influenza A causes respiratory infection, the destruction of respiratory epithelium, altered cytokine production and fever.
Features of enterovirus infection
Acute viral infection. Can cause poliomyelitis, aseptic meningitis, myocarditis, pancreatitis, respiratory infection.
Describe how virus can induce tumours
Retrovirus can lead to lymphomas and leukaemias. E.g. Human T-lymphotrophic virus - 1 (HTLV-1); transmitted by blood or mother to child. It infects T cells and modifies host cell gene expression using a transactivating protein and is directly responsible for tumour.
Papillomaviruses can cause cervical cancer
Humoral immunity
It mainly responds to bacterial infection and is extra-cellular. It causes acute inflammation and neutrophilia, increased WBC count. It results in the production of proteins called immunoglobulins or antibodies from B lymphocytes.
Cell mediated immunity
Macrophages present antigen and stimulate T cells in an intra-cellular response. Cytokines are produced and control the antibody production . CD8 and Th1 cells control antibody production. CD8 and Th1 cells release suppressor and cytotoxic cells. Th1 activate macrophages for phagocytosis whilst CD8 kill infected host cells/foreign cells. It is useful for viruses, bacteria and fungi.
