Pathology - Infectious Disease Flashcards
What type of organism is clostridia and what diseases do they cause
gram positive
anaerobic
bacillus
spore-producing
1) perfringens: cellulitis, gas gangrene, food poisoning
2) tetani: spastic paralysis
3) botulinum: flaccid paralysis
4) difficile: pseudomembranous colitis
How does botulism toxin cause disease
-causes release of exotoxin which is a neurotoxin that blocks ACh, leading to flaccid paralysis
-the A fragment cleaves the protein synaptobrevin which is needed for fusion of NT vesicles
What is the pathogenesis of gas gangrene
-C. perfringens release both enzymes and toxins
1) enzymes: hyaluronidase, collagenase = degrade extracellular matrix proteins
2) toxins: alpha toxin - zinc metallophospholipse mimicking phospholipase C. Degrades lecithin, destroys RBC/platelets/muscles, nerve damage
How does neisseria meningitidis cause infection and what are the clinical consequences
(gram neg, encapsulated, aerobic, diplococci, coffee bean shaped, high LPS)
- common coloniser of oropharynx
- spread by respiratory droplets
- most people develop immunity and clear it, protected against later infection by the specific serotype
- invasive when new serotype is encountered
- invades respiratory epithelium, then blood stream
- capsule allows evasion of immune response by preventing opsonisation and complement destruction
- mortality 10% despite abx treatment
Consequences: death, sepsis, meningitis, CVA, necrotising vasculitis, seizures, SIADH, hydrocephalus, sensorineural hearing loss, cognitive impairment
What are 2 clinically significant neisseria
1) menigitides: causes meningococcal disease, meningitis and sepsis
2) gonorrhoeae: causes urethritis, prostatitis, PID, septic arthritis, blindness
What causes meningitis
S pneumoniae
N meningitidis
H influzenzae
GBS
E coli (neonates)
Listeria (old)
enterovirus
measles
TB
auto-immune
Infectious and non-infectious. Ultimately, the exact etiology can only be identified in 30-65% of the cases. The rest of the cases of unknown etiology are labeled "idiopathic." In terms of infectious causes, these include viruses, bacteria, fungi, and parasites, the most common agent being viral. Viral: non-polio enteroviruses (more than 1/2, Coxsackie and ECHO viruses), HSV2, VZV, respiratory viruses (adenovirus, influenza virus, rhinovirus), mumps virus, arbovirus, HIV, and lymphocytic choriomeningitis Bacterial: S. pneumoniae, N. meningitidis, GBS, H. influenzae, L. monocytogenes (others: SA, TB, TP, EC) Fungal: Candida, Aspergillus, Cryptococcus Parasites: Toxoplasma gondii, naegleria, neurocysticercosis, trichinosis, and Hartmannella. For the non-infectious causes of aseptic meningitis, etiologies can be classified into three main groups: Systemic diseases with meningeal involvement (e.i sarcoidosis, Behçet's disease, Sjögren's syndrome, systemic lupus erythematosus and granulomatosis with polyangiitis) Drug-induced aseptic meningitis (most commonly reported with non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics (sulfamides, penicillins), intravenous immunoglobulin, and monoclonal antibodies) Neoplastic meningitis (that could be related to either solid cancer metastasis or lymphoma/leukemia. Aseptic meningitis secondary to certain vaccines has also been described, such as measles, mumps, rubella vaccine primarily, but also varicella vaccine, yellow fever vaccine, rabies vaccine, pertussis vaccine, and the influenza vaccine. Some even describe it after vaccination with the meningococcal vaccine.
What are the virulence factors of staph aureus
-surface proteins - host cell adherence
-secrete enzymes - degrade proteins
-secrete toxins that damage host (alpha, beta, delta, gamma, leukocidin)
-contain a capsule that allows attachment
-secrete lipase that degrades lipids on skin surface
What diseases are caused by staph aureus
skin infections (abscess, cellulitis, impetigo)
osteomyelitis
pneumonia
endocarditis
food poisoning
TSS
What are some conditions caused by the different types of staph infections
1) staph aureus: skin infections, osteomyelitis, pneumonia
2) staph epidermidis: most common cause of infective endocarditis in prosthetic valves
3) staph saprophyticus: UTI
What are the risk factors for toxic shock syndrome and what are it’s features
Condition caused by bacterial toxins, usually strep or staph infections
risks: use of tampons, post operation wound infections, post partum, nasal packs, staph or strep skin infections
features: hypotensive shock, acute renal failure, coagulopathy, respiratory failure, soft tissue necrosis, rash
Name some bacteria that cause wound infections
staph aureus
strep pyogenes
clostridium perfringens
pseudomonas aeruginosa
clostridium tetani
Describe streptococci and name some different types of streptococci and what infections they cause
Gram positive cocci that grow in chains or pairs
1) alpha haemolytic strep
- S. pneumoniae: CAP, meningitis
2) beta haemolytic strep
- S. pyogenes (Group A): pharyngitis, scarlet fever, impetigo, nec fas, rheumatic fever, TSS, glomerulonephritis
- S. agalactiae (Group B): neonatal sepsis, pneumonia, meningitis (extreme ages)
3) viridans group
- S. viridans: endocarditis (damaged valves)
- S. mutans: dental caries
What are some post-infectious syndromes caused by streptococci infections
Associated with group A strep infection:
RF
PSGN
PSRA (reactive arthritis)
Scarlet Fever
Erythema Nodosum
PANDAS (Paediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections)
What are virulence factors of streptococcus infections
- capsules - resist phagocytosis
- M proteins that inhibit complement activation
- exotoxins that cause fever and rash
- pneumolysin/streptolysin that destroys cell membranes
What is the pathological sequelae of HIV infection and what are the modes of transmission
-infects CD4+ T cells causing immunosuppression and leading to opportunistic infections and neoplasms
-transmission: 75% sexual (globally heterosexual is more common), IVDU, mother to infant in utero, breastmilk
Describe the structure of the influenza virus
-single stranded RNA virus bound by nucleoprotein that determines type (A, B, C)
type A: infects humans, pigs, horses, birds
type B and C: only infects humans, more common in children who then develop antibodies
- envelope made of lipid bilayer that contains surface glycoproteins haemagglutinin and neuraminidase that determine subtypes
What is the pathological basis for pandemics and epidemics
-pandemics only occur in flu a, epidemics occur in flu a and flu b
1) Epidemic = disease that affects a large number of people within a community
-caused by antigenic drift when virus acquires mutations in H or N to escape antibodies
2) Pandemic = epidemic that is spread over multiple countries or continents
-caused by antigenic shift when H and N are replaced by recombination of RNA segments with an animal virus
What organisms cause malaria and describe the pathogenesis
Plasmodium, spread by anopheles mosquitos
-5 types of plasmodium = falciparum, vivax, ovale, knowles, malariae
1) mosquito salivary glands to human blood (sporozoite)
2) taken up into liver cells, where they multiply (sporozoite)
3) liver cells rupture and release asexual haploid form (merozoite)
4) merozoite invades RBC, where they grow
5) tropozoite matures in RBC to become a schizont and finally a merozoite
6) lysis of RBC causes release of merozoites and infection of more RBCs
