Microbial Infections Flashcards
What is a zoonotic disease and what is an example?
A disease that does not normally circulate within humans, but instead, within an animal reservoir, and afterwards transmitted to humans e.g. Ebola - Hammerhead fruit bat, transmitted by contaminated bush meat
How does the Ebola virus infect humans?
Requires transported Niemann-Pick C1
Why is the animal acting as the animal reservoir not affected?
They have a mutation in that transported (Npc1) hence they get a low grade infection and are carriers of the Ebola virus
What are the 5 main types of infectious agents that cause disease in humans?
- Viruses
- Bacteria
- Fungi
- Protozoa
- Helminths
Features of viruses:
Obligate pathogens - not cells in their own right, only survive inside host cells
Show host specificity - can infect many life forms (including bacteria), but many can only infect particular animals or tissues
Can contain DNA or RNA genetic material
RNA material requires reverse transcriptase to make viral DNA
Uses the host cell’s machinery to synthesise eukaryotic RNA from the viral DNA, and then undergo protein synthesis
Released by budding out of the cell (e.g. come out of the cell wrapped in eukaryotic cell membrane), or cytolysis (bursting out of the host cell - causes severe host cell damage)
Many routes of infection for viruses - oral-faecal, airborne, insect vectors, blood borne
Why can’t the RNA from viruses directly undergo protein synthesis in humans?
Viral RNA is not compatible with the host cell’s machinery, reverse transcriptase is required to synthesis viral DNA, which can be used to synthesise eukaryotic RNA
Which disease has been successfully eradicated?
Smallpox
What virus causes smallpox and who was the last known case?
Variola Virus
Ali Maow Maalin (Somalia - 1977)
Why was it easier to eradicate this disease?
Easy to diagnose - obvious lesions on the body
Efficient vaccine - scarification (scratched onto surface of the skin)
Even with early sign of infection, can still be vaccinated and cured
What were the iron lung chambers used to treat and why?
Polio virus
Negative pressure chambers to help patients breathe - musculature in the thoracic cavity becomes disabled
Why is the polio vaccine easy to distribute?
Oral vaccine - no needles involved therefore can give on a large scale
Features of bacteria:
Prokaryotes - single celled
No internal membranes (except photosynthetic bacteria - but they are not infectious)
Haploid
Unique peptidoglycan cell wall - determines shape
Binary fission - elongates to 2x their size, then splits / divides
Why is having only one copy of chromosomes (haploid) an important characteristic?
Important due to the expression of mutations - any mutation in the genome is immediately expressed and so contributes to the rapid speed of antibiotic resistance / outbreaks
No recessive genotype
Why is the unique peptidoglycan cell wall important?
Target for chemotherapy - e.g. many antibiotics target the synthesis of the cell wall to prevent cell division (and replication)
What are the different shapes bacteria can be?
Rod, coccus (spheres), spirochaete (spirals)
How do bacteria move?
Using a flagellum - often via chemotaxis (e.g. towards food spurces or away from toxins)
What pathogens use the faecal-oral route and an example (+ its features)?
Gut pathogens e.g. shigella
Impacts epithelial cells of the GI tract
Uses host cell components to move within the cytoplasm of the cell (e.g. nucleation of actin within the cells, pushing bacteria between cells)
Spreads e.g. during floods, issues with getting rid of faecal waste, contaminated water supplies
Symptoms = bloody diarrhoea (due to damaged cells and blood released into the contents of the GI tract)
An example of an airborne pathogen (community acquired) and its features?
Neisseria meningitidis (NM)
Vaccination an issue / v. time consuming as it has many serogroups
Many individuals have it e.g. in the nasa pharynx, but it causes no harm (dormant)
Something triggers it to become invasive - into the bloodstream
Medical emergency when it becomes invasive - rapid progression
Initially, non-blanching rash = bleeding into the skin
Further spread - septicimia (other bacteria can enter and circulate the blood)
Further spread - blockage of blood vessels causes loss of digits / limbs
Crossing the blood brain barrier = meningitis (infection of the protective membranes that surround the brain and spinal cord)
What are nosocomial infections and an example (+ its features)?
Hospital acquired infections
e.g. Clostridium Difficile
Has a spore forming stage hence may exist as a spore in hospital (standard disinfectants may not work)
e.g. MRSA
Issue as they are resistant to most standard drugs and do spread more easily
Why does mycobacterium tuberculosis (TB) have such a high mortality rate?
Chronic infection
Difficult to diagnose - need diagnostic tools that can detect TB at earlier stages)
Treatment drugs work well, but take a long time i.e. 6 months
TB vaccine (AKA BKG vaccine) works better in infants than in adults
TB transmitted through adults - need more effective vaccines in adults to reduce transmission
What is myobacterium leprae (leprosy) and its features?
Chronic infection of the skin and nerves
Slow incubation period (i.e. 5 years)
Different forms depending on the patients’ immune response to leprosy
Cell mediated = tuberculoid (skin lesions)
Humoral = lepromatous (numb - cuts / wounds go unnoticed)
What is helicobacter pylori?
Strongly linked to peptic ulcers and gastric cancer
What is pathogenic E-coli?
Line gut epithelial cells
Zoonotic - often picked up in petting zoos / farms
Mutations cause them to become pathogenic
Are mutation rates higher in other micro-organims compared to humans?
No, more or less the same in humans, mice, bacteria etc - 10^-8
(viruses a little higher - 10^-4)
