Infective diseases Part 2 Flashcards
(40 cards)
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.
What is Botulism?
Caused by Clostridium botulinum
Food poisoning infection from canned food which has not been processed in a sterile manner
Symptoms
Neurotoxin causes blurred vision, slurred speech, difficulty in swallowing and breathing
Very rare infection in the Developed World
What is viral meningitis?
Viruses can cause acute meningitis:
including enteroviruses, coxsackie virus, cytomegaloviruses & herpes virus
Symptoms
Spectrum of severity of symptoms from mild to severe
They present with similar symptoms to bacterial meningitis but are generally milder illnesses in the immunocompetent patient
What are the 8 types of Herpes?
- Herpes simplex type I (HSV-1).
- Herpes simplex type II (HSV-2).
- Varicella-zoster virus (VZV/HHV-3).
- Epstein-Barr virus (EBV/HHV-4).
- Cytomegalovirus (CMV/HHV-5).
- Herpesvirus type 6 (HBLV/HHV-6).
- Herpesvirus type 7 (HHV-7).
- Kaposi’s sarcoma herpesvirus (KSHV/HHV-8).
What is Herpes Simplex Virus Type 1 & 2 ?
Type 1 - aka ‘Cold Sores”
Type 2 – aka Genital Herpes
very common
Can be asymptomatic or show up as outbreaks of blisters or sores
Spread through intimate contact. e.g kissing, sexual intercourse.
Treatment for herpes infections can lessen the frequency or intensity of breakouts.
In very rare cases, can lead to meningitis
What is Varicella Zoster Virus (type 3)?
Aka “chickenpox”
Spreads through contact with chicken pox blisters
Easily spread through air by infected people
Symptoms
Body Aches
Fever
Fatigue
Irritablity
Blisters over the body
What is Shingles (Herpes Zoster) ?
Same virus which causes chickenpox
After contracting chickenpox, the virus can remain dormant in the dorsal root ganglia
Virus become reactivated in adulthood
Symptoms
Painful skin rash with blisters in a localized area – follows a dermatomal pattern
Rash heals withing 2-4 weeks although some have ongoing nerve pain which can last for months
Postherpetic Neuralgia
What is Epstein- Barr Virus (type 4) ?
Aka Infectious Mononucleosis aka Glandular Fever aka the Kissing Disease
Very common amongst teenagers and students
Spread through saliva by kissing or sharing cutlery.
Incubation periods is about 4-7 weeks
Contagious during the incubation periods and some people may be contagious for as long as 18 months after the infection
Virus remains in the body lifelong
Symptoms
Fever
Lymphadenopathy
Bilateral Posterior cervical Lymphadenopathy (but also other cervical lymph nodes)
Lymph nodes are mildly tender and mobile
Sore Throad (severe)
tonsillar enlargement, ”whitewash” exudate on the tonsils.
Pharyngeal inflammation
General malaise, chills, sweats, anorexia, retro-orbital headache
Splenomegaly
Hepatomegaly
Complications
Hepatitis –
common and self limiting early complication.
Upper airway obstruction –
due to gross enlargement of the tonsil, or peritonsillar abcess (quincy)
Cardiac Complications –
Pericarditis, myocarditis
Renal Complication –
Interstitual nephritis, Acute Kidney Injury
What is PRIONS?
Prions are Proteinaceous Infectious Particles – sometimes spread to humans from infected meat products.
They are an abnormal form of a normally harmless protein found in the brain that is responsible for a variety of fatal neurodegenerative diseases
PrPc are normally folded prions which are non-pathogenic. They function as neurone protection
PrPsc is the mutated and infectious form
Symptoms:
Rapidly developing dementia, Difficulty in walking, Hallucinations, Muscel stiffness, Confusion, Fatiugue, difficulty speaking.
