pathogens and the host mw% + Flashcards
Define the terms pathogen and commensal?
- A pathogen is an organism which can cause an infection.
- Commensal is an organism which is part of a normal flora such as E.coli in the gut.
Describe the features of clinical infection?
Characterised by signs and symptoms:
- Inflammation
- Pain
- Pyrexia
- Increased white cell count
- Increased C reactive protein (CRP)
What is pathogenicity?
- The capacity of a micro-organism to cause an infection
What are the requirements of pathogenicity?
- Infectivity: Ability to become established
- Virulence: Ability to cause harmful effects once established
Give examples of infectivity?
- Attachment- E. coli
- Acid resistance
Virulence is conferred by virulence factors, what are they?
- These are Genetically determined microbial components e.g
- Invasiveness
- Toxin production
- Evasion of immune system
Examples of invasiveness?
- Streptococcus pyogenes (Group A streptococci)
- Connective tissue breakdown
- Fibrinolysis- Streptokinase
What are the 3 types of toxins?
- Exotoxins are released extracellularly by the micro-organism
- Enterotoxins are exotoxins which act on the GI tract
- Endotoxin is structurally part of the Gram negative cell wall
Give an example of Enterotoxin?
Cholera
1.Vibrio cholerae
Colonises small intestine
2. Enterotoxin production
Increases cAMP levels- Inhibits uptake of Na+ and Cl- ions
3. Causes death by dehydration
4. Treated by rehydration
Give an example of endotoxin?
- Component of the Gram-negative bacterial cell wall- Lipopolysaccharide
- E. coli and other Gram-negative bacilli
- Induces severe uncontrolled host response - Cytokine production
List the sites of viral entry?
- Skin
- Respiratory tract
- Alimentary (digestive) tract
- Urinogenital tract
- Capillary and conjunctiva (the mucous membrane that covers the front of the eye and lines the inside of the eyelids.)
Describe the features of acute viral infections with the use of examples?
- Localised to affected sites of the body
- Development of vireamia(the presence of viruses in the blood) with widespread infection of tissues.
- The amount of virus spreads quickly as time increases until it reaches its maximum where the pateint shows symptoms and then the numbers decrease rapidly.
- Influenza A virus infects cells of the respiratory tract and destroys respiratory epithelium.
How is generation of novel influenza viruses achived?
- Antigenic DRIFT: Minor changes (natural mutations) in the genes of flu viruses, occurs gradually over time to generate antigenic variants
- Antigenic SHIFT: Abrupt major changes in virus antigenic structure
Describe the features of enterovirus infection with the use of examples?
- This infection mainly happens in the gastrointestinal tract. An example is poliomyelitis which causes the poliovirus.
- The general principal is that the virus infection occurs in the gut, after this it can go in two paths.
- The virus is either excreted in the feaces or there is the development of vireamia, and then the virus travels to the non or neural tissues and they both lead to paralysis
Note: Enteroviruses are a genus of positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. Enteroviruses are named by their transmission-route through the intestine (enteric meaning intestinal).
Describe how a virus can induce tumours with the use of examples?
- Cervical sarcinoma.
- The virus infects the cell first, virus nucleic acid integrates into the cellular genome.
- Viruses then cause changes in the cellulur gene expression which lead to uncontrolled multiplication and tumour formation.