Infection and immunity Flashcards
What is an Abscess?
- A collection of pus that has built up within the tissue of the body
- Can develop anywhere in the body
Most commonly in the skin or inside the body, in an organ or in the spaces between organs
What is the aetiology of Abscesses?
- Caused by bacterial infection, parasites, or foreign substances, e.g. aspiration pneumonia
- Bacterial infection is the most common cause, most common causative pathogen is methicillin-resistant Staphylococcus aureus (MRSA)
What are the presenting symptoms of an Abscess?
- Skin abscess:
a. Swollen, pus-filled lump under the surface of the skin
b. Symptoms of an infection, such as fever and chills - Internal abscess:
a. Pain in the affected area
b. Fever
c. Malaise
d. Loss of appetite and weight loss
What are the signs of an Abscess on physical examination?
- Skin abscess:
a. Smooth swelling under skin
b. Pain and tenderness
c. Warmth and erythema
d. White or yellow pus under the skin - Internal abscess:
a. Fever
b. Pain or swelling in the affected area
c. Dependent on the affected area e.g. lung: cough, dyspnoea, liver: jaundice
What are the appropriate investigations for Abscess?
- Bloods:
a. FBC: leukocytosis
b. CRP/ESR: inflammatory markers - Blood culture: positive for organism
- CT/Ultrasound: visualisation of abscess
What is the management for an Abscess?
a. If severe intravenous antibiotics
b. Usually consider percutaneous incision and drainage
c. In very rare cases surgical resection/ debridement
What is Behçet’s disease?
A complex multisystem disorder associated with presumed autoimmune-mediated inflammation of the arteries and veins
What is the triad seen in Behçet’s disease?
- Oral ulcers
- Genital ulcers
- Anterior uveitis
What is the epidemiology of Behçet’s disease?
- More common in the eastern Mediterranean (e.g. Turkey)
- More common in men
- Tends to affect young adults (e.g. 20 - 40 years old)
- Associated with HLA B51
- Around 30% of patients have a positive family history
What are the features of Behçet’s disease?
- Classically: a) oral ulcers b) genital ulcers c) anterior uveitis
- Thrombophlebitis and deep vein thrombosis
- Arthritis
- Neurological involvement (e.g. aseptic meningitis)
- GI: abdo pain, diarrhoea, colitis
- Erythema nodosum
What are the investigations for Behçet’s disease?
- No definitive test
- Diagnosis based on clinical findings
- Positive pathergy test is suggestive (puncture site following needle prick becomes inflamed with small pustule forming)
- Routine bloods, raised inflammatory markers
- Imaging to determine organ involvement e.g. angiography
What is the management of Behçet’s disease?
Immunosuppression: corticosteroids
What is bursitis?
When the fluid-filled sacs (bursa) that cushion the joints become inflamed
What are some examples of bursitis?
- Greater trochanteric pain syndrome (trochanteric bursitis)
- Knees:
a. Infrapatellar bursitis (Clergyman’s knee): Associated with kneeling
b. Prepatellar bursitis (Housemaid’s knee): Associated with more upright kneeling
What are the features of bursitis?
- Pain: usually a dull, achy pain
tender or warmer than surrounding skin - Swollen
- More painful when on movement or pressed on
- May also be erythema
What is the conservative management for bursitis?
- Rest: avoid activities that put pressure on the joint
- Use ice: 10 minutes at a time
- Analgesia
What are the investigations for bursitis?
- Usually clinical
- If suspecting a hot swollen joint:
a. Bloods: inflammatory markers
b. Aspiration for microscopy (gout) and culture (septic arthritis)
c. Refer to secondary care?
What is the medical management of bursitis?
- Antibiotics: usually taken for 7 days if caused by an infection
- Steroid injection: to reduce swelling
- Rarely may need to be drained
What advice can be given to patients to prevent bursitis?
- Maintain a healthy weight
- Warm up properly before exercising
- Use padding when putting a lot of pressure on joints e.g. kneeling
What is Greater trochanteric bursitis?
- Due to repeated movement of the fibroelastic iliotibial band
- Most common in women aged 50-70 years
- Features:
a. Pain over the lateral side of hip/thigh
b. Tenderness on palpation of the greater trochanter
What is cytomegalovirus?
- One of the herpes viruses
- Thought that around 50% of people have been exposed to the CMV virus although it only usually causes disease in the immunocompromised, e.g. people with HIV or those on immunosuppressants following organ transplantation
What is the pathophysiology of CMV?
Infected cells have a ‘Owl’s eye’ appearance due to intranuclear inclusion bodies
What are the different types of CMV infection?
- Congenital
- Mononucleosis
- Retinitis
- Encephalopathy
- Pneumonitis
- Colitis
What are the features of congenital CMV infection?
- Growth retardation
- Pinpoint petechial ‘blueberry muffin’ skin lesions
- Microcephaly
- Sensorineural deafness
- Encephalitis (seizures)
- Hepatosplenomegaly
What is CMV mononucleosis?
- Infectious mononucelosis-like illness
- May develop in immunocompetent individuals
What is CMV retintis?
- Common in HIV patients with a low CD4 count (< 50)
- Presents with visual impairment e.g. ‘blurred vision’.
- Fundoscopy shows retinal haemorrhages and necrosis, often called ‘pizza’ retina
- IV ganciclovir is the treatment of choice
What is the most common treatment for CMV?
IV ganciclovir
What is Human immunodeficiency virus (HIV)?
- Caused by a retrovirus that infects and replicates in human lymphocytes and macrophage
- Erodes the integrity of the human immune system over a number of years
- This results in immune deficiency and a susceptibility to a series of opportunistic and other infections as well as the development of certain malignancies
What is the aetiology of Human immunodeficiency virus (HIV)?
- HIV is retrovirus that infects and replicates primarily in human CD4+ T cells and macrophages
- It can be transmitted via blood, blood products, sexual fluids, other fluids containing blood, and breast milk
How is HIV transmitted?
- Sexual contact (most common)
- Before birth or during delivery
- During breastfeeding
- When sharing contaminated needles and syringes (intravenous drug users)
What is the epidemiology of Human immunodeficiency virus (HIV)?
Globally, the HIV incidence rate is believed to have peaked in the late 1990s and to have stabilised subsequently
What are the three phases of Human immunodeficiency virus (HIV)?
- Seroconversion: (4–8 weeks post-infection)
- Early/asymptomatic: (18 months to 15 +years)
- AIDS: Syndrome of secondary diseases reflecting severe immuno deficiency or direct effect
What is HIV seroconversion?
- Typically occurs 3-12 weeks after infection
- Presents as a glandular fever type illness
- Symptomatic in 60-80% of patients
- Increased symptomatic severity is associated with poorer long term prognosis
What are the features of HIV seroconversion?
- Sore throat
- Lymphadenopathy
- Malaise, myalgia, arthralgia
diarrhoea - Maculopapular rash
- Mouth ulcers
- Rarely meningoencephalitis
What is involved in HIV testing?
- After discussion and consent)
- Serum HIV enzyme linked immunosorbent assay: positive/Serum HIV rapid test
- HIV antibodies (usually positive by 12 weeks after exposure)
- p24 antigen: viral core protein
- PCR for viral RNA or incorporated proviral DNA
- Monitor CD4+ count and viral load
What is the standard HIV test?
Combination tests (HIV p24 antigen and HIV antibody):
1. For both diagnosis and screening of HIV
2. If the combined test is positive it should be repeated to confirm the diagnosis
3. Some centres may also test the viral load (HIV RNA levels) at the same time
What is the HIV testing protocol for asymptomatic patients?
- Should be done at 4 weeks after possible exposure
- After an initial negative result when testing for HIV in an asymptomatic patient, offer a repeat test at 12 weeks
What are the early symptoms of HIV?
- Can be asymptomatic for years
- Apparently well
- Some patients may have persistent lymphadenopathy (>1 cm nodes, at 2 + extrainguinal sites for >3 months)
- Progressive minor symptoms, e.g. rash, oral thrush, weight loss, malaise
What is the third stage of HIV and how does this present?
- AIDS: acquired immune deficiency syndrome
- Presents as symptoms of opportunistic infections (linked to CD4 count)
What are the opportunistic infections in a patient with HIV and a CD4 count of 200-500 cells/mm3?
- Oral thrush: Secondary to Candida albicans
- Shingles: Secondary to herpes zoster
- Hairy leukoplakia: Secondary to EBV
- Kaposi sarcoma: Secondary to HHV-8
What is Kaposi sarcoma?
- Caused by HHV-8 (human herpes virus 8)
- Presents as purple papules or plaques on the skin or mucosa (e.g. gastrointestinal and respiratory tract)
- Skin lesions may later ulcerate
- Respiratory involvement may cause massive haemoptysis and pleural effusion
What is the management of Kaposi sarcoma?
Radiotherapy and resection
What are the opportunistic infections in a patient with HIV and a CD4 count of 100-200 cells/mm3?
- Cryptosporidiosis: The disease is usually self-limiting and similar to that in immunocompetent hosts
- Cerebral toxoplasmosis
- Progressive multifocal leukoencephalopathy: Secondary to the JC virus
- Pneumocystis jirovecii pneumonia
- HIV dementia
What is Pneumocystis jiroveci pnuemonia?
- A unicellular eukaryote, generally classified as a fungus but some authorities consider it a protozoa
- PCP is the most common opportunistic infection in AIDS
all patients with a CD4 count < 200/mm³ should receive PCP prophylaxis
What are the features of Pneumocystis jiroveci pnuemonia?
- Dyspnoea
- Dry cough
- Fever
- Very few chest signs
What is a common complication of Pneumocystis jiroveci pnuemonia?
Pneumothorax
What are the extra-pulmonary features of Pneumocystis jiroveci pnuemonia?
- Rare (1-2%)
- Hepatosplenomegaly
- Lymphadenopathy
- Choroid lesions
What are the investigations for Pneumocystis jiroveci pnuemonia?
- CXR:
a. Typically shows bilateral interstitial pulmonary infiltrates
b. Can present with other x-ray findings e.g. lobar consolidation
c. May be normal - Exercise-induced desaturation
- Bronchoalveolar lavage (BAL) often needed to demonstrate PCP (silver stain shows characteristic cysts)
a. Sputum often fails to show PCP
What is the management of Pneumocystis jiroveci pnuemonia?
- Co-trimoxazole
- IV pentamidine in severe cases
- Steroids if hypoxic (if pO2 < 9.3kPa then steroids reduce risk of respiratory failure by 50% and death by a third)
What are the opportunistic infections in a patient with HIV and a CD4 count of 50-100 cells/mm3?
- Aspergillosis: Secondary to Aspergillus fumigatus
- Oesophageal candidiasis: Secondary to Candida albicans
- Cryptococcal meningitis
- Primary CNS lymphoma: Secondary to EBV
What is oesophageal candidiasis in HIV patients?
- The most common cause of oesophagitis in patients with HIV
- It is generally seen in patients with a CD4 count of less than 100
- Typical symptoms include dysphagia and odynophagia
- Fluconazole and itraconazole are first-line treatments
What are the opportunistic infections in a patient with HIV and a CD4 count of 50-100 cells/mm3?
- Cytomegalovirus retinitis: Affects around 30-40% of patients with CD4 < 50 cells/mm³
- Mycobacterium avium-intracellulare infection
What are the neurocomplications of HIV?
- Toxoplasmosis (50%)
- Primary CNS lymphoma (30%)
- TB
- Others:
a. Encephalitis
b. Cryptococcus
c. Progressive multifocal leukoencephalopathy
d. AIDS dementia complex
What is Toxoplasmosis in HIV patients?
- Opportunistic infection when CD4 count is between 100-200 cells/mm3
- Accounts for 50% of cerebral lesions in HIV patients
- Features: constitutional symptoms, headache, confusion, drowsiness
- On CT: usually single or multiple ring enhancing lesions, mass effect may be seen
- Management: sulfadiazine and pyrimethamine
What is primary CNS lymphoma in HIV patients?
- Secondary to EBV when CD4 count is between 50-100 cells/mm3
- Accounts for 30% of cerebral lesions in HIV patients
- CT: single or multiple homogenous enhancing lesions
- Treatment:
a. Steroids (may significantly reduce tumour size), chemotherapy (e.g. methotrexate) + with or without whole brain irradiation
b. Surgical may be considered for lower grade tumours
What are the differences in toxoplasmosis and primary CNS lymphoma in HIV patients?
- Toxoplasmosis:
a. Multiple lesions
b. Ring or nodular enhancement
c. Thallium SPECT negative - Primary CNS lymphoma:
a. Single lesion
b. Solid (homogenous) enhancement
c. Thallium SPECT positive
How does TB present on CT in patients with HIV?
- Much lesson common than toxoplasmosis and lymphoma
- Single enhancing lesion
What is the most common fungal infection of the CNS (particularly in HIV)?
Cryptococcus:
1. Headache, fever, malaise, nausea/vomiting, seizures, focal neurological deficit
2. CSF:
a. high opening pressure
b. elevated protein
c. reduced glucose
d. normally a lymphocyte predominance but in HIV white cell count many be normal
e. India ink test positive
3. CT:
a. meningeal enhancement
b. cerebral oedema
c. meningitis is typical presentation but may occasionally cause a space-occupying lesion
What are the common causes of diarrhoea in HIV patients?
- May be due to the effects of the virus itself (HIV enteritis) or opportunistic infections
- Possible causes:
a. Cryptosporidium + other protozoa (most common)
b. Cytomegalovirus
c. Mycobacterium avium intracellulare
d. Giardia
What is the management of HIV?
- Antiretroviral therapy (ART): involves a combination of at least three drugs
- Typically two nucleoside reverse transcriptase inhibitors (NRTI) and either a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI)
- This combination both decreases viral replication but also reduces the risk of viral resistance emerging
When should ART be started in HIV patients?
As soon as they have been diagnosed with HIV
What are Nucleoside analogue reverse transcriptase inhibitors (NRTIs)?
- E.g. zidovudine (AZT), abacavir, lamivudine, zalcitabine, tenofovir
- General NRTI side-effects: peripheral neuropathy
- Tenofovir: (recommended regime of two NRTIs), adverse effects include renal impairment and ostesoporosis
- Zidovudine: anaemia, myopathy, black nails
What is the third drug involved in ART for HIV management (after 2 NRTIs)?
- Non-nucleoside reverse transcriptase inhibitors (NNRTI):
a. e.g. nevirapine, efavirenz, b. P450 enzyme interaction (nevirapine induces), rashes - Protease inhibitors (PI):
a. e.g. indinavir, nelfinavir, ritonavir, saquinavir
b. SEs: diabetes, hyperlipidaemia, buffalo hump, central obesity, P450 enzyme inhibition, renal stones - Integrase inhibitors:
a. block the action of integrase, a viral enzyme that inserts the viral genome into the DNA of the host cell
b. e.g. raltegravir, elvitegravir, dolutegravir
What is Infective Endocarditis?
Infection involving the endocardial surface of the heart, including the valvular structures, the chordae tendineae, sites of septal defects, or the mural endocardium
What is the most common cause of infective endocarditis?
Staphylococcus aureus (particularly in the acute presentation and IVDU)
What is the aetiology of Infective Endocarditis?
The endocardium can be colonized by virtually any organism, but the most common are:
1. Streptococci: Mainly a-haemolytic
2.Staphylococci: Staphylococcus aureus (most common)
3. Enterococci (20%)
4. Historical sources of bacteraemia should be considered, such as indwelling vascular catheters, recent dental work, and intravenous drug use
What are the different causative organisms of infective endocarditis associated with?
- Staphylococcus aureus: IVDU (and acute presentatin)
- Streptococcus viridans: found in the mouth, poor dental hygiene or following a dental procedure
- Staphylococcus epidermidis: commonly colonize indwelling lines, most common in prosthetic valves (< 2 months, after which returns to Staph A)
- Streptococcus bovis: associated with colorectal cancer
What are the non-infective causes of infective endocarditis?
- Systemic lupus erythematosus (Libman-Sacks)
- Malignancy: marantic endocarditis
What are the risk factors for infective endocarditis?
- Previously normal valves (50%, typically acute presentation), the mitral valve is most commonly affected
- Rheumatic valve disease (30%)
- Prosthetic valves
- Congenital heart defects
- Intravenous drug users (IVDUs) e.g. typically causing tricuspid lesion)
- Others: recent piercings
What are the presenting symptoms of Infective Endocarditis?
- Fever with sweats/chills/rigors (may be relapsing and remitting)
- Malaise
- Fatigue
- Weight loss
- Headache
- Arthralgia
- Myalgia
- Dyspnoea
- Confusion (particularly in elderly)
- Skin lesions
What are the signs of infective endocarditis on examination?
- Petechiae particularly on retinae (Roth’s spots)
- Pharyngeal and conjunctival mucosa vasculitic lesions
- Janeway lesions (painless palmar macules, which blanch on pressure)
- Osler’s nodes (tender nodules on finger/toe pads)
- Splinter haemorrhages (nail-bed haemorrhages)
What are the investigations for Infective Endocarditis?
- Bloods:
a. FBC (leukocytosis, normocytic anaemia)
b. Raised ESR and CRP
c. U&Es: mildly elevated urea
d. Rheumatoid factors: may be positive (minor criteria for diagnosis)
e. Complement levels: decreased - Blood culture: At least three sets 1h apart: bacteraemia or fungaemia
- ECG: progression of the infection may lead to conduction system disease
- Echocardiography:
a. Should be performed in all cases of suspected IE
b. Detection of vegetations and valve abscess
c. Diagnosis of prosthetic valve endocarditis and assessment of embolic risk
What is the criteria for the diagnosis of Infective Endocarditis?
- Pathological criteria positive, or
- 2 major criteria, or
- 1 major and 3 minor criteria, or
- 5 minor criteria
Also known as Modified Duke criteria
What is the pathological criteria for the diagnosis of Infective Endocarditis?
- Positive histology or microbiology of pathological material obtained at autopsy or cardiac surgery
- E.g. valve tissue, vegetations, embolic fragments or intracardiac abscess content
What is the Major Modified Duke criteria for Infective Endocarditis?
- Positive blood cultures
- Evidence of endocardial involvement e.g. positive echocardiogram or new valvular regurgitation
What is the criteria regarding positive blood cultures for infective endocarditis diagnosis?
- Persistent bacteraemia from two blood cultures taken > 12 hours apart or
- Three or more positive blood cultures where the pathogen is less specific such as Staph aureus and Staph epidermidis
What is the Minor Modified Duke criteria for Infective Endocarditis?
- Predisposing heart condition or IVDU
- Microbiological evidence does not meet major criteria
- Fever > 38ºC
- Vascular phenomena: major emboli, splenomegaly, clubbing, splinter haemorrhages, Janeway lesions, petechiae or purpura
- Immunological phenomena: glomerulonephritis, Osler’s nodes, Roth spots
What is the management for infective endocarditis whilst blood cultures have not come back?
- Native valve: amoxicillin, consider adding low-dose gentamicin
- If penicillin allergic, MRSA or severe sepsis: vancomycin + low-dose gentamicin
- If prosthetic valve: vancomycin + rifampicin + low-dose gentamicin
What is the management of Infective Endocarditis caused by staphylococci?
- Native valve:
a. Flucloxacillin
b. If pen allergic or MRSA: vancomycin + rifampicin - Prosthetic valve:
a. Flucloxacillin + rifampicin + low-dose gentamicin
b. If pen allergic or MRSA: vancomycin + rifampicin + low-dose gentamicin
What is the management of Infective Endocarditis cause by streptococci (e.g. viridans)?
- Fully sensitive:
a. Benzylpenicillin
b. If penallergic: vancomycin + low-dose gentamicin - If less sensitive:
a. Benzylpenicillin + low-dose gentamicin
b. If pen allergic: vancomycin + low-dose gentamicin
What are the indications for surgical management of Infective Endocarditis?
- Severe valvular incompetence
- Aortic abscess (often indicated by a lengthening PR interval)
- Infections resistant to antibiotics/fungal infections
- Cardiac failure refractory to standard medical treatment
- Recurrent emboli after antibiotic therapy
What are the poor prognostic factors for Infective Endocarditis?
- Staphylococcus aureus infection
- Prosthetic valve (especially ‘early’, acquired during surgery)
- Culture negative endocarditis
- Low complement levels
What are the causes of culture negative Infective Endocarditis?
- Prior antibiotic therapy
- Coxiella burnetii
- Bartonella
- Brucella
- HACEK: Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, Kingella)
What is the mortality of Infective Endocarditis based on causative organism?
- Staphylococci - 30%
- Bowel organisms - 15%
- Streptococci - 5%
What are the complications of Infective Endocarditis?
- Valve incompetence
- Intracardiac fistulae or abscesses
- Aneurysm formation
- Heart failure
- Renal failure
- Glomerulonephritis
- Arterial emboli from the vegetations (brain, kidneys, lungs, spleen)
- Fatal if untreated
What is Malaria?
- A parasitic infection caused by protozoa of the genus Plasmodium
- Five species are known to infect humans; Plasmodium falciparum is the most life-threatening
What is the aetiology of Malaria?
- It is naturally transmitted to humans through a bite by an infected female Anopheles mosquito
- May potentially be transmitted by blood transfusion or organ transplantation
What are the presenting symptoms of Malaria?
- High degree of clinical suspicion in any feverish traveller:
a. incubation up to 1 year, but usually 1–2 weeks - Cyclical symptoms of high fever, flulike symptoms, severe sweating and shivering cold/rigors