Lecture 17-Bacterial infection-pneumococcal disease Flashcards
how many serotypes identified so far? what are they based on? challenge for treatment
> 90; based on the structural difference in capsule; vaccines that cover all these different types is a challenge
what is pneumococcal disease? (PD)
bacterial infection of URT causing pneumonia, meningitis, sepsis and otitis media
where is PD a major burden?
in areas where vaccine has not been introduced e.g. sub saharan africa, india, china
reasons for child survival gap between ethiopia and germany?
infections left untreated or inadequate prevention/treatment (vaccine)
two types of PD?
non-invasive- e.g. otitis media, pneumonia
invasive e.g. meningitis, sepsis
correlation between disease severity and prevalence
as disease severity increases, prevalence decreases e.g. meningitis most severe but least prevalent compared to otitis media
indigenous population rates
high rates- perhaps genetic factors?
age risk for PD
extremes of age
<5 years
>65 yrs
populations at risk
children in developing countries, indigenous population of developed countries
how does chronic illness affect your risk of PD?
chronic illness (HIV) or the immunocompromised increases your risk
what is the greatest risk factor for getting PD?
recent acquisition of a new virulent strain (when immunocompromised or in a high risk population)–>strain disseminates and cause disease
what type of organism is streptococcus pneumoniae?
ubiquitous organism, even considered a commensal
nasopharyngeal colonisation
prerequisite for disease
- airborne droplets enter nasopharynx, carriage
- local spread to ear (otitis media) or sinus (sinusitis)
- aspiration to alveoli (pneumonia)
what do you want to prevent in disease pathway?
prevent carriage to prevent disease dissemination and spread to someone else
colonisation during early life factors
first days to weeks- asymptomatic
- within 3 years, 50% people colonised, earlier in some settings
colonisation during adult life
relatively stable carriage in older children/adults
streptococcus pneumoniae death rate
11% of deaths in children under 5 years of age worlwide
2 main pneumococcal virulence factors
polysaccharide capsule
pneumolysin
polysaccharide capsule function
inhibits phagocytic clearance and reduce antibiotic exposure (defence mechanisms that enable its survival)
pneumolysin function
pore forming cytotoxin, impair respiratory burst (impair neutrophil function)
other pneumococcal virulence factors
PspC-pneumococcal surface protein C and other proteins
techniques of pneumococcal capsule
level of capsule differs during carriage and invasion
- thick- be away from immune system and protected
-thin- when invading
immune protection based on capsule-specific Ab (IgM, IgG)
what is the basis of current vaccine formulations ?
pneumococcal capsule
host response to pneumococcal infection
- pneumococcus releases toxins to promote growth and survival, spreads into tissues
- Ab deposited, binds to bacteria, facilitates removal through complement mediated phagocytosis
opsonophagocytosis
clearance by complement component and phagocytosis by neutrophils
serotype-specific immunity
host response to pneumococcal infection
-since colonisation is immunising (memory B cells, CD4T cells)
IL-17A
protective against colonisation; helps facilitate removal of bacteria
how is S.pneumoniae detected?
invasive disease detected from sterile site (blood, CSF);; other sites (sputum, urine)- gram stain
- capsule swelling by specific antibody-shows what serotype is causing infection
3 types of pneumonia
- community acquired acute pneumonia (CAP) e.g. strep pneumoniae, H.influenza
- community acquired atypical pneumonia e.g. viruses (A and B), chlamydia
- hospital acquired pneumonia e.g. pseudomonas
what is bacterial pneumonia?
severe CAP- most common cuase of death from infections in developed countries (low fatality, but most common cuase)
what does bacterial pneumonia occur in association with?
other causes of infection- viral infection (e.g. influenza)- co infection
what happens in bacterial pneumonia?
inflammation of lungs accompanied by fluid-filled alveoli and bronchioles- reduce ability to exchange gases and respiratory failure
-described by affected region or organism causing disease e.g. lobar or broncho
is pneumonia invasive or non-invasive?
non-invasive
is meningitis invasive or non-invasive?
invasive
is sepsis invasive or non-invasive?
invasive
is otitis media invasive or non-invasive?
non-invasive
what is the pathogenesis of pneumonia?
- pneumococcus invades airspace–>interactions between bug and receptors (TLRs on alveolar macrophages)
- response–>cytokine production (in most conditions enough to clear infection)
- chronic doses–>infiltrates of neutrophils doesnt actually clear infection–>accumulation in air space–>overwhelmed, leakage–>invasion into bloodstream (due to increased permeability)–>severe
histopathology of pneumonia
- alveoli filled with inflammatory cells
- thickened alveolar wall
- congested blood vessels (RBCs)
- infected part of lung doesnt function if not treated within time
clinical features of pneumonia
onset of severe illness is abrupt (fever, cough, chest pain, chills, productive sputum, dyspnoea)
untreated pneumonia–>
acute respiratory failure, septic shock, multi-organ failure
two major signs for pneumonia in children
fast breathing
chest in drawing
diagnosis of pneumonia
chest x-ray- determine consolidation
pleural effusion
systemic features (fever)
what is meningitis?
infection of the subarachnoid space with meningeal involvement (leptomeningeal inflammation surrounding brain and spinal cord)
bacterial causes of meningitis?
most common (S.pneumoniae, N.meningitidis)
other infectious causes of meningitis?
viral, fungal, malaria, mycoplasma, rickettsiae
non infectious causes of meningitis
malignancy, SLE, lead/mercury poisoning
what is the pathogenesis of meningitis?
- translocation across BBB- facilitated by upregulation of receptors on endothelial cells during infection
- bacteria multiply–>engage with APCs–>produce cytokines (TNF-alpha, IL-1, IL-6)–>causes inflammation and recruitment of neutrophils–>increase BBB permeability–>intracranial pressure, oedema
pathological features of meningitis
inflammatory infiltrate (lymphocytic blood vessels due to increase BBB permeability), oedema
clinical signs and symptoms of meningitis
- common- severe headache, high fever, stiff neck, nausea, vomiting
- clearer indications- numbness, loss of feelings, light sensitivity, confusion, seizures, rash
what is otitis media?
inflammation of the middle ear cavity
clinical types of otitis media
many
- acute
- recurrent
- OM with effusion (glue ear)
- chronic suppurative OM
major consequences of otitis media
hearing loss, developmental problems
pathogenesis of otitis media
nasopharyngeal carriage (prerequisite)
- accumulation of fluid in eustachian tube (links nasopharynx to middle ear)
- leads to otorrhoea (fluid drainage), tympanic membrane perforation, hearing loss
acute OM
follows a cold–>leading to active infection and pain
- ear drum can rupture, pus discharge, inflammation, swelling (self-limiting within 2-4 weeks)
chronic suppurative OM
initial episode of AOM–> becomes persistent
- usually up to 3 months duration, can spread to brain causing meningitis, hearing loss
first line treatment
antibiotics esp penicillin (as we enter resistance, need to find new drugs)
two major types of vaccines
conjugate vaccines (PCVs) polysaccharide vaccine (PPV)
conjugate vaccines (PCVs)
in infancy, up to 13 serotypes
- take polysaccharide structure from different serotypes, conjugate into protein, makes them immunogenic and long-lasting
polysaccharide vaccine (PPV)
older children and adults. 23 serotypes
probiotics
alternative strategy to prevent/reduce colonisation
what do PCVs produce?
highly functional serotype-specific IgG- protects against IPD, less effective for mucosal disease
what impacts efficacy of PCV?
geographic differences in serotype distribution
what is serotype replacement?
introduce vaccine —>severe decline in serotype e.g. 7–>rise in non7 type (replacement)–>e.g. 19A increased –>therefore make vaccine for that serotype
*vaccine efficacy against IPD
19A
most common serotype replacement disease in australia
vaccine efficacy of PCV against pneumonia
- non-invasive
- correlates of protection less understood
- immune response generated by these vaccines may not provide same protection as for invasive
nutrition role in disease
undernourished children at increased risk of death
- maternal and child nutrition important
- zinc, vitamins A/D important (prevent respiratory infections); weakened respiratory muscles, reduce ability to clear infection
breastfeeding role in disease
highly protective
- exclusive breastfeeding until 6 months until 2 years (developed countries)
- developing countries- low rates
indoor air pollution role in disease
open stove (high risk), smoke for heating enters child’s lungs (increase susceptibility to pneumococcal infection and transmission)
