Infective diseases Part 2 Flashcards
What makes up the Central Nervous System (CNS)?
Brain, protected and enclosed within a rigid, bony skull, and
Spinal Cord, protected within the vertebral canal
Protected by the Blood Brain Barrier
Tell me about the nervous system?
The nervous system has no connection to the outside world
It has no resident microbes
It must depend on other defence mechanisms for protection
The CNS is surrounded by meninges containing cerebrospinal fluid – CSF
The meninges are a potential site of infection
Tell me about The Blood – Brain Barrier (Innate Immunity)?
Is a selective semi-permeable barrier
It controls what substances can enter the CNS
therefore it prevents many potentially toxic metabolites and most pathogens from entering the CNS
However, this means it is difficult to introduce antimicrobial drugs like antibiotics into the CNS
The BBB can however become permeable during inflammation
How do we protect ourselves from pathogens invading our CNS?
The Innate Immune System The Blood brain barrier
selective wall of cells & surrounding vessels that protects the brain from foreign invaders.
However,
Some small pathogens can pass through, but other immune cells cannot
Minimal lymphocytes in CNS, so if the innate barriers are breached, the CNS is very vulnerable
so we have microglial cells!
What cells are the protectors of the brain?
Glial Cells
Also called microglia or neuroglia!
What are the Roles of the Microglial Cells and why is this important?
Microglia remove neurons which aren’t communicating properly & pathogens which have crossed the BBB
They are macrophages of the CNS
Why is this Important?
it ensures that information transfers between neurons is not interrupted.
They also help clean up protein aggregates (abnormal clumps of misshaped proteins that accumulate and are associated with NEURODEGENERATIVE DISEASES:
Alzheimer’s Disease & Parkinson’s Disease (we’ll cover this later in the year in neuro-pathology)
What makes Microglial cells so specialized in this clean up process?
The have long, dynamic arms which allows them to extend and move in all directions
They check the environment the make sure there are no invading pathogen.
If they don’t detect any foreign pathogens they remain in their resting (inactive) state.
What happens when Microglial cells come across a threat?
When microglial cells come across a threat, they will become active
this initiates the process of inflammation
The glial’s shape changes dramatically!
Their arms shorten, and their bodies’ flatten
They then multiply and move to the infected site
Here they engulf the pathogen
ACTIVE microglial cells also have a role in
nutritional support and repair of the neurones and axons
Activatedmicrogliaare thought to participate in the degeneration and regeneration of neuronal cells and to play an important role in the repair of the injured nervous system and are the resident macrophage-like population of the CNS
There are four types of glial cells in the central nervous system. What are they and what are their roles?
Microglial cells - immune system of the brain
ependymal cells - Play a role in cerebrospinal fluid (CSF) homeostasis
oligodendrocytes - Create conditions for the information to be transmitted faster
astrocytes - help communication between neurons
What cells are in the PNS?
Satellite cells
Schwann cells
What is acute bacterial meningitis?
Caused by 4 main bacterial species
Streptococcal pneumoniae, Neisseria meningitidis, Haemophilus influenza & Listeria monocytogenes
Pathway of Infection
Starts as a localised infection
e.g. sinus infection which may invade the epithelium of the nasopharynx and spread to the brain.
Infections can cross the blood brain barrier as the meninges become inflamed & pressure is put on the spinal cord & brain causing characteristic symptoms
Characteristic Symptoms
fever
headache
photophobia
neck stiffness
occasionally diarrhoea & vomiting
Long Term Complications
Can result in lasting disabilities such as deafness, blindness & paralysis
What is Pneumococcal Meningitis?
Streptococcal pneumonia is the cause of 30% of all cases
Pathway of Infection
Infection starts in the ears, nose & lungs before entering the blood and then crossing into the meninges
If untreated there is a high mortality rate
What is Haemophilus meningitis?
Caused by Haemophilus influenzae type B an encapsulated, gram-negative, single-celled, coccobacillus divided into 6 serotypes.
Before the Hib vaccine in 1987 this was the most prevalent bacterial meningitis in children.
What is Meningococcal meningitis?
The most dangerous & highly contagious form of acute bacterial meningitis
Caused by Neisseria meningitidis – a small encapsulated gram-negative diplococcus
Pathway of infection
Spreads from person to person by coughing, kissing or coming into close contact with someone who is ill or is carrying the bacteria.
Symptoms
Classic presentation of symptoms:
Fever, Headache, Neck Stiffness, Photophobia
AND a skin rash that can cause bright red purple patches (purpura)
Vaccinations
Types A, B, C, W, Y and Z (of meningococcal meningitis)
Infants vaccinated for Men B (which causes 90% of meningococcal infections), students for A,C,W and Y
What is Listeriosis?
Caused by Listeria monocytogenes – a small facultative anaerobic, gram-positive rod.
Pathway of Infection
Acquired from contaminated foods - sliced meat, soft cheeses, milk poultry, seafood etc.
The pathogen invades the intestinal lining & enters blood and infects the meninges.
Fatal in 20% of all cases.
What is Tetanus?
Caused by Clostridium tetani – anaerobic gram-positive bacilli & endospore formation
Endotoxin prevents the release of neurotransmitters needed to inhibit muscle contraction
Symptoms:
Produces generalised muscle stiffness especially in the facial, swallowing muscles & causes spasms of jaw muscles = lockjaw
Note – this bacterium produces neurotoxins that affect the peripheral nervous system and not the central nervous system.
