Pathogens and Hosts Flashcards
What characterises a clinical infection?
- Inflammation
- Pain
- Pyrexia
- Tachycardia
- Rigors
- Increased white cell count
- Increased C reactive protein (CRP)
What is a pathogen?
An organism which can cause disease
What is a commensal?
An organism which is part of normal flora e.g E.coil in the gut, Staph aureus in the nose
Define pathogenicity
The capacity of a micro-organism to cause an infection
What are the requirements of pathogenicity?
Infectivity
Virulence
Define infectivity
Ability to become established on or within a host
Define virulence
Capacity to cause harmful effects (disease) once established.
What is virulence conferred by?
Conferred by virulence factors.
- Genetically determined microbial components
- Invasiveness
- Toxin production
- Evasion of immune system
What is virulence specific to?
Strains, not species
What are exotoxins?
A toxin secreted by bacteria
How are exotoxins released?
Exotoxins are released extracellularly by the micro-organisim
What are endotoxins?
The main component of the outer membrane of the cell wall of Gram-negative bacteria.
What do enterotoxins act on?
Enterotoxins are exotoxins which act on the GI tract
Define colonisation
The presence of bacteria on a body surface(like on the skin, mouth, intestines or airway) without causing disease in the person.
Define latent (aka asymptomatic) infection
An infection that usuallydoes not cause symptomsand can last a long period of time before becoming active and causing symptoms.
When does an infection occur?
When a microorganism enters a person’s body and causes harm.
What are the mechanisms of the innate immune system?
Physical
Physiological
Chemical
Biological
What are examples of physical barriers of the innate immune system?
Skin - Tears, urine, saliva, bile, pancreatic secretions, mucus and sebaceous secretions
Mucous membranes of respiratory, gastrointestinal and urinary tracts
What is the role of bronchial cilia?
Move microbes and debris up and out of the airways.
What are examples of physiological barriers?
Diarrhoea
Vomiting
Coughing
Sneezing
How does low pH act as a chemical barrier to pathogens?
The relativelylow pH in certain parts of the body prevents pathogen growth.
What are examples of structures with low pH?
Skin–pH 5.5
Gastricacid–pH 1-3
Vagina–pH 4.4
What is the main biological barrier to pathogens?
Normal flora found in the body
Where can body flora be found?
Nasopharynx
Mouthand throat
Skin
GI tract
Vagina
What are the mechanisms of the adaptive immune system?
Cell mediated immunity
Humoral immuity
What is cell mediated immunity mediated by?
T lymphocytes against intracellular pathogens
What is humoral immunity mediated by?
Antibodies
Discuss cell mediated immunity
An immune response that does not involve antibodies.
Rather, phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
What is humoral immunity based on?
Serum antibodies that are produced by plasma cells and bind to antigens in order to assist with their elimination.
What is cell mediated immunity based on?
The action of cytotoxic cells that activate other immune cells andhelp eliminate pathogens and infected host cells.
What is humoral immunity also known as?
Antibody-mediated immunity.
With assistance from helper T cells, B cells will differentiate into plasma B cells that can produce antibodies against a specific antigen.
What does the humoral immune system deal with?
Antigens from pathogens that are freely circulating, or outside the infected cells.
What are common sites of viral entry?
Mucosal linings of the respiratory, alimentary, and urogenital tracts
The outer surface of the eye
The skin
What is antigenic drift?
Minor changes (natural mutations) in the genes of flu viruses occurs gradually over time to generate antigenic variants
What is antigenic shift?
Abrupt major changes in virus antigenic structure due to combination of different strains from different hosts
What does influenza A virus infect?
Cells of respiratory system
Destruction of respiratory epithelium - secondary bacterial infections
What causes fever in influenza A virus?
Alterned cytokine expression leading to fever
e.g interleukin-1 and interferon - Avian influenza virus (H5N1) causes cytokine storm
What are enteroviruses?
Viruses that are:
- Small
- Icosahedral shaped
- Non-envelope
Virons are relatively simple, consisting of a:
Protein capsid surrounding a single-stranded, positive sense RNA genome.
What can enterovirus cause?
- Croup (breathing difficulty and harsh cough)
- Mouth sores.
- Skin rashes.
- Sore throat.
- Chest pain if the infection affects the heart muscle or sac-like covering around the heart (pericarditis)
What are examples of enteroviruses?
- Poliovirus
- Respiratory infections (many enteroviruses)
- Myocarditis (coxsackie B viruses)
What can viruses turn into?
When viruses cause an infection, they spread their DNA, affecting healthy cells’ genetic makeup and potentially causing them to turn into cancer.
What are the mechanisms in which a virus can turn into cancer?
- Directly damage DNA in host cells, resulting in cancer.
- Altering the immune system
- Chronic inflammation.
- Disrupting the body’s normal regulation of cell division.
What can papillomaviruses and HPV infections casue?
Cervical carcinoma
What can retroviruses cause?
Lymphomas and leukemias
