Infectious Diseases Flashcards
What type of organism causes rabies?
RNA rhabdovirus (specifically lyssavirus)
How does rabies result in death?
Causes encephalitis by virus travelling up nerve axons towards CNS in retrograde fashion
What are 4 clinical features of rabies?
- Prodrome: headache, fever, agitation
- Hydrophobia: water-provoked muscle spasms
- Hypersalivation
- Negri bodies: cytoplasmic inclusion bodies in infected neurons
What should be done in the instance of an animal bite in countries at risk of rabies?
- wash wound
- if individual already immunised: 2 further doses of vaccine
- if not previously immunised: give human rabies immunoglobulin (HRIG) + full vaccination course (dose should be administered locally around wound)
What is first line management of syphilis?
IM benzathine penicillin
What are 4 types of clostridia?
- C. perfringens - gas gangrene (myonecrosis)
- C. botulinum - canned foods/honey - flaccid paralysis
- C. difficile - pseudomembranous colitis
- C. tetani - tetanus, spastic paralysis
What type of bacteria are clostridia?
gram positive, obligate anaerobic bacilli
What is C. perfringens?
- produces α-toxin, a lecithinase, causes gas gangrene (myonecrosis) and haemolysis
- features include tender, oedematous skin with haemorrhagic (black) blebs and bullae.
- Crepitus on palpation
Where is C. botulinum classically found?
canned foods and honey
How does C. botulinum produce its effects?
prevents acetylcholine (ACh) release - leads to flaccid paralysis
How does C. tetani produce its effects?
produces exotoxin (tetanospasmin) that prevents the release of glycine from Renshaw cells in the spinal cord, causing spastic paralysis
Which organism is most commonly the cause of malaria in travellers returning to the UK?
Plasmodium falciparum protozoa
What are 6 examples of drugs which are used as malaria prophylaxis?
- atovaquone + proguanil (Malarone)
- chloroquine
- doxycycline
- mefloquine (Lariam)
- Proguanil (Paludrine)
- Proguanil + chloroquine
Which type of malaria prophylaxis is taken weekly? 2 types
- mefloquine (lariam)
- chloroquine
Which type of malaria prophylaxis is contraindicated in epilepsy (2 types)?
- chloroquine
- mefloquine
Which type of malaria prophylaxis is contraindicated in depression?
mefloquine
What is a key side effect of atovaquone + proguanil (malarone)?
GI upset
What is a key side effect of malaria prophylaxis drug chloroquine?
headache
What are 2 key side effects of doxycycline?
- photosensitivity
- oesophagitis
What are 2 key side effects of mefloquine (malaria prophylaxis)?
- dizziness
- neuropsychiatric disturbance
How long after travel should most types of malaria prophylaxis be stopped?
4 weeks (except Malarone - 7 days)
How long before travel should most types of malaria prophylaxis be started?
1 week (Malarone + doxy 1-2 days; mefloquine 2-3 weeks)
Which 2 types of malaria prophylaxis can be used in pregnancy (if travel cannot be avoided)?
- chloroquine
- proguanil - need folate supplementation alongside
What are 2 types of malaria prophylaxis recommended for use in children?
- diethyltoluamide (DEET) 20-50% - to repel mosquitoes (in children >2 months)
- doxycycline - children >12y
How many doses of tetanus-containing vaccine does the childhood vaccination programme give in total?
5
What are 3 groups into which wounds can be classified when decided about tetanus vaccination?
- clean wound - < 6 hours old, non-penetrating, negligible tissue damage
- tetanus prone - puncture-type injuries in contaminated environemnt e.g. garden, foreign bodies, compound fractures, wounds/burns with sepsis, animal bites and scratches
- high-risk tetanus prone - heavy contamination e.g. soil, manure, wounds or burns with extensive devitalised tissue, wounds/burns requiring surgical intervention
In a patient with a wound, what course of action should be taken regarding tetanus vaccination?
- if full course of vaccines with last dose <10 years ago - no vaccine or Ig
- if full course of vaccines with last dose >10 years ago - if tetanus prone, give booster; high-risk: booster +tetanus immunoglobulin
- if vaccination history incomplete / unknown - booster, if tetanus prone / high risk - tetanus immunoglobulin
What is considered the number of tetanus vaccine doses that confers lifelong protection?
5
What causes infectious mononucleosis?
HHV-4: EBV
less frequently CMB and HHV-6
What is the classic triad of symptoms / signs in infectious mononucleosis?
- sore throat
- lymphadenopathy - anterior / posterior triangles of neck
- pyrexia
In addition to the classic triad what are 7 other features of infectious mononucleosis?
- malaise, anorexia, headache
- palatal petechiae
- splenomegaly
- hepatitis, transient ALT rise
- lymphocytosis
- haemolytic anaemia secondary to cold agglutins (IgM)
- maculopapular, pruritic rash when take amoxicillin
How long does it typically take symptoms of infectious mononucleosis to resolve?
2-4 weeks
How is a diagnosis of infectious mononucleosis made?
Monospot test - during 2nd week of illness
When should monospot test be performed during infectious mononucleosis?
2nd week of illness
What is the management of infectious mononucleosis / what advice must be given?
- supportive, analgesia, fluids, avoid alcohol
- avoid contact sports for 4 weeks afterwards - risk of splenic rupture
What is the link with EBV and socioeconomic groups?
- higher rates of seropositivity in lower economic groups
- higher incidence of infectious mononucleosis in higher socioeconomic groups - acquire EBV in adolescence rather than early childhood
How long should a child with mumps be excluded from school?
5 days from onset of swollen glands
What are 7 conditions where children don’t need to be excluded from school?
- conjunctivitis
- fifth disease (Slapped cheek)
- roseola
- infectious mononucleosis
- head lice
- threadworms
- hand, foot and mouth
What is the school exclusion advice for scarlet fever?
24h after commencing antibiotics
What is the school exclusion advice for whooping cough?
2 days after commencing abx or 21 days from onset of symptoms if no abx
What is the school exclusion advice for measles?
4 days from onset of rash
What is the school exclusion advice for rubella?
5 days from onset of rash
What is the school exclusion advice for chickenpox?
all lesions crusted over
What is the school exclusion advice for impetigo?
until lesions crusted and healed, or 48h after commencing abx
What is the school exclusion advice for scabies?
until treated
What is the school exclusion advice for influenza?
until recovered
Which virus most often causes the common cold?
rhinovirus
What pathogen is most likely to cause a pneumonia in a 45-year old smoker?
Streptococcus pneumoniae
What is the most common cause of bronchiectasis exacerbations?
Haemophilus influenzae
Which pneumonia is associated with deranged LFTs and hyponatraemia?
Legionella
When should antiretroviral therapy be started in HIV?
should be initiated in all individuals with HIV-1 infection regardless of CD4 count
What is the usual antiretroviral therapy drug regime in HIB?
3 drugs:
* 2x nuceoside reverse transcriptase inhibitors (NRTI)
* protease inhibitor (PI) OR non-nucleoside reverse transcriptase inhibitor (NNRTI)
What are 2 examples of entry inhibitors (drugs for HIV)?
- maraviroc (binds CCR5)
- enfuvirtide (binds gp41)
prevent HIV-1 from entering and infecting immune cells
What are 8 examples of nucleoside analogue reverse transcriptase inhibitors (NRTI)?
- zidovudine (AZT)
- abacavir
- emtricitabine
- didanosine
- lamivudine
- stavudine
- zalcitabine
- tenofovir
What is a side effect commont o many nucleoside analogue reverse transcriptase inhibitors?
peripheral neuropathy
What are 2 adverse effects of tenofovir?
- renal impairment
- osteoporosis
What are 3 adverse effects of zidovudine?
- anaemia
- myopathy
- black nails
What is a key side effect of didanosine?
pancreatitis
What are 2 examples of non-nucleoside reverse transcriptase inhibitors?
- nevirapine
- efavirenz
What are 2 side effects of non-nucleoside reverse transcriptase inhibitors (NNRTI)?
- P450 enzyme interaction
- rashes
What are 4 examples protease inhibitors?
- indinavir
- nelfinavir
- ritonavir
- saquinavir
What are 5 side effects of protease inhibitors?
- diabetes
- hyperlipidaemia
- buffalo hump
- central obesity
- P450 enzyme inhibition
What are 2 side effects specific to indinvair (PI)?
- renal stones
- asymptomatic hyperbilirubinaemia
What is a key side effect specific to ritonavir (PI)?
potential P450 inhibitor
What is the mechanism of action of integrase inhibitors?
block action of integrase, viral enzyme that inserts viral genome into DNA of host cell
What are 3 examples of integrase inhibitors?
- raltegravir
- elvitegravir
- dolutegravir
In the absence of the erythema migrans rash, what is the first line test to diagnose Lyme disease?
ELISA to Borrelia burgdorferi
What should be done if ELISA to Borrelia burgdorferi is negative and Lyme disease is still suspected?
- repeat ELISA 4-6 weeks later
- if still suspected in patients with symptoms 12 weeks or more - immunoblot test
What are 4 causes of brain abscess?
- extension of sepsis from middle ear or sinuses
- trauma or surgery to the scalp
- penetrating head injuries
- embolic events from endocarditis
What is the management of a brain abscess?
- craniotomy + abscess cavity debridement
- IVAB e.g. 3rd generation cephalosporin + metronidazole
- ICP management e.g. dexamethasone
What organism most commonly causes scarlet fever?
Streptococcus pyogenes - caused by Group A haemolytic streptococci
What are the typical features of scarlet fever?
- fever
- malaise
- headache
- nausea / vomiting
- sore throat
- strawberry tongue
- rash - fine punctate erythema (pinhead) first on torso (spares palms and soles) - sandpaper
What is the treatment for scarlet fever (+ if pen allergic)?
- 10 days penicillin V
- allergy: azithromycin
What are 6 complications of scarlet fever?
- otitis media
- rheumatic fever
- acute glomerulonephritis
- bacteraemia
- meningitis
- necrotising fasciitis
What is the most common complication of scarlet fever?
otitis media
When does rheumatic fever tend to occur after scarlet fever infection?
20 days after infection
Which antibiotic should be prescribed after both human and animal bites?
co-amoxiclav
doxycycline + metronidazole if pen allergic
What is the management of puncture wounds from animal bites?
should not be sutured closed unless cosmesis at risk
What is the most common isolated bacteria from animal bites?
Pasteurella mutocida (but generally polymicrobial)
What are 4 things that can triger bright red cheeks for several months after parvovirus B19 (erythema infectiosum) has resolved?
- warm bath
- sunlight
- heat
- fever
What are the school exclusion rules for parvovirus B19 / slapped cheek diesase and why?
school exclusion not necessary because no longe rinfectious by the time rash occurs
What is the guidance for a pregnant woman exposed to parvovirus B19 / slapped cheek in first 20 weeks?
seek prompt advice from provider of antenatal care - maternal IgM and IgG need to be checked
When are patients with parvovirus B19 infection infectious?
3 - 5 days before appearance of rash
What can parvovirus B19 infection cause in adults?
acute arthritis
What can parvovirus B19 infection in pregnancy cause in the unborn fetus?
hydrops fetalis - causes severe anaemia due to viral suppression of fetal erythropoiesis, leading to heart failure secondary to severe anaemia, leads to accumulation fo fluid in fetal serous cavities e.g. asites, pleural and pericardial effusions
What are 10 acute phase proteins?
- CRP
- procalcitonin
- ferritin
- fibrinogen
- alpha-1 antitrypsin
- caeruloplasmin
- serum amyloid A
- serum amyloid P component
- haptoglobin
- complement
At what level is raised CRP after surgery suggestive of evolving complications?
150 at 48h post op
What are 5 substances in serum that decrease in the acute phase response?
- albumin
- transthyretin (formerly prealbumin)
- transferrin
- retinol binding protein
- cortisol binding protein
What is PEP For hepatitis A exposure?
human normal immunoglobulin (HNIG) or hepatitis A vaccine
What PEP is given for hepatitis B in a HBsAg positive source?
- booster dose of HBV if known responder
- non-responder: hepatitis B immune globulin + booster vaccine
What PEP is given for hepatitis B in an unknown source?
- known responders to HBV vaccine: booster dose of vaccine
- if in process of having vaccine or non-responder - hepatitis B immune globulin (HBIG) + vaccine
What are the PEP Guidelines for hepatitis C?
monthly PCR - if seroconversion, interferon +- ribavirin
What is given for PEP for HIV?
combination of oral antiretrovirals e.g. tenofovir, emtricitabine, lopinavir, ritonavir - ASAP (within 1-2 hours, up to 72h) for 4 weeks
When should further testing be performed after HIV PEP is given?
12 weeks following completion of PEP
When should VZIG be given?
pregnant women without IgG / immunosuppressed
What is the classical route for spread of leptospirosis?
contact with infected rat urine
What are 5 groups who are at risk of leptospirosis?
- sewage workers
- farmers
- vets
- work in abattoir
- recent travel to tropics
What is Weil’s disease?
leptspirosis
What are the 2 phases of leptospirosis?
- early phase - bacteraemia: fever, flu-like sx, subconjunctival suffusion / haemorrhage
- second immune phase (Weil’s disease): AKI, hepatitis, aseptic meningitis
What are 3 investigations to perform in suspected leptospirosis?
- serology - antibodies to Leptospira
- PCS
- culture - takes several weeks
What is the management of leptospirosis?
high dose benzylpenicillin or doxycycline
How long is the course of doxycycline in Lyme disease?
14-21 days
What type of bacteria are the Salmonella group?
aerobic, gram-negative rods (not normally present as commensals in the gut)
What organisms cause typhoid and paratyhpoid?
- typhoid: Salmonella typhia
- paratyphoid: Salmonelal paratyphia (types A, B and C)
How is typhoid transmitted?
faecal-oral route & in contaminated food + water
What are 5 features of the presentation of typhoid / paratyphoid?
- systemic upset - headache, fever, arthralgia
- relative bradycardia
- abdominal pain, distension
- constipation > diarrhoea
- rose spots on trunk
What are 5 complications of typhoid / paratyphoid?
- osteomyelitis
- GI bleed / perforation
- meningitis
- cholecystitis
- chronic carriage
What is the management of toxoplasmosis?
immunocompetent - no treatment
immunocompromised e.g. HIV: 6 weeks pyrimethamine + sulphadiazine
How is toxoplasmosis diagnosed?
serology
What is the commonest cause of meningitis in adults?
Streptococcus pneumoniae
Which organism tends to cause severe malaria?
P Falciparum
What is the criterion standard investigation for malaria?
Giemsa-stained thick and thin peripheral blood films/smears
What are the features of the first, second and third week of typhoid, and fourth if patient survives?
- 1st: GI (abdo pain, constipation from inflamed Peyer patches), and truncal maculopapules
- 2nd: soft splenomegaly, bradycardia
- 3rd: abdo distension, pea soup diarrhoea, bowel perf / peritonitis from necrotic Peyer’s patches
- 4th: fever, mental state + abdo distension improve over a few days
What is the gold standard investigation to diagnose typhoid?
culture isolation - 100% specific - blood + bone
culture of bone marrow 90% sensitive - very painful however
What is a sensitive and specific symptom which is an indicator for dengue fever?
facial flushing
What are 6 features of dengue?
- high fever +- saddleback fever (abates for day then returns)
- facial flushing
- myalgias / arthralgias
- haemorrhagic manifestations: bleeding from nose / gums, melaena, menorrhagia, haematemesis
- abdo pain - if restless, confused, hypothermic + thrombocytopenic –> dengue haemorrhagic fever
- cardiomyopathy
What investigation is used to make a diagnosis of dengue?
serodiagnosis - rise in antibody titre in paired IgG or IgM specimens
