Pathogens and the Host

Question 1

Pathogen

Answer 1

An organism which can cause disease

Question 2

Commensal

Answer 2

An organism which is part of normal flora

Question 3

Pathogenesis

Answer 3

Process by which an infection leads to disease

Question 4

Mechanisms of viral pathogenesis

Answer 4

1. Cell destruction following viral infection
2. Virus-induced changes to cellular gene expression
3. Immunopathogenic disease
   The overt disease is often small in comparison to the unapparent.

Question 5

Innate immunity

Answer 5

Nonspecific defence mechanisms that come into play immediately or within a few hours of an antigens appearance in the body. Includes;

1. Epithelial barriers and chemical barriers
2. Phagocytic cells; polymorphs (acute - neutrophils, eosinphils, basophils) and macrophages (chronic)
3. Dendritic cells (to activate adaptive immune response)
4. Natural killer cells
5. Complement (antigen/antibody complex triggers cascade)
6. Cytokines and chemokines (inflammation, systemic effects, adaptive)
7. Anti-microbial substances

Question 6

Acquired immunity

Answer 6

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.

Question 7

Antibodies

Answer 7

Immunoglobulins are proteins with antibody activity.

• IgM (primary)
• IgG (secondary)
• IgA (mucosal)
• IgE (allergy and helminth infections)
• IgD (unknown)

Question 8

Colonisation

Answer 8

When bacteria grow on body sites exposed to the environment without causing any infection

Question 9

Latent/asymptomatic infection

Answer 9

An infection that is hidden, inactive or dormant e.g. herpes simplex virus

Question 10

Infection

Answer 10

The presence of microorganisms causing damage to body tissues, usually in the presence of acute inflammation.

Question 11

Clinical infection

Answer 11

Signs and symptoms; inflammation, pain, pyrexia, tachycardic, rigors, increased WBC count, increased C reactive protein (CRP)

Question 12

Pathogenicity

Answer 12

The capacity of a microorganism to cause an infection

Question 13

Infectivity

Answer 13

Ability of a pathogen to establish an infection

Question 14

Virulence

Answer 14

Ability to cause harmful effects once established. The severity//harmfulness of a disease. Conferred by invasiveness, toxin production and immune invasion

Question 15

Sites of viral entry

Answer 15

Respiratory tract, alimentary tract, urogenital tract, conjuctiva, arthropod, capillary, skin

Question 16

Features of acute viral infection

Answer 16

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.

Question 17

Features of enterovirus infection

Answer 17

Acute viral infection. Can cause poliomyelitis, aseptic meningitis, myocarditis, pancreatitis, respiratory infection.

Question 18

Describe how virus can induce tumours

Answer 18

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

Question 19

Humoral immunity

Answer 19

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.

Question 20

Cell mediated immunity

Answer 20

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.