Flashcards in Infections in the immunocompromised Deck (41)
a micro-organism causing disease
Define primary pathogen
common cause of disease in healthy non-immune hosts e.g. s aureus, s. pneumoniae
Define opportunistic pathogen
rare cause of disease in healthy individuals causes serious disease in compromised hosts e.g. pseudomonas aeruginosa
What is included in host defence?
immunological but also anatomical integrity and physiological defences of the body surfaces e.g peristalsis, muco-ciliary escalator, normal flora, normal urinary flow
What are examples of damage to physical defence mechanisms?
iatrogenic damage e.g. surgery
foreign body insertion
What are some more unusual examples of damage to physiological defence?
antibiotic disturbance of normal flora
cytotoxic damage to the gut
What are the most common infections caused by burns?
pseudomonas aeruginosa and staphylococcus aureus
- spread into bloodstream
- treatment includes topical and systemic agents
prevention of infection
- topical prophylactic use of silver sulfadiazine
- burn wound excision
What are some examples of primary immunodeficiency?
neutrophil defect: CGD
humoral B cell defects
cell-mediated- T cells
severe combined immunodeficiency
What are examples of secondary immunodeficiency?
What pathogens are involved in humoral defects?
- s. pneumoniae
- N. meningitidis
What pathogens are involved in neutrophil defects?
What pathogens are involved in cell mediated defects?
- mycobacteria - salmonella, listeria, legionella
- herpes, respiratory and enteric viruses
fungi and protozoa
- candida aspergilus, pneumocysitis, cryptococcus, cryotosporidium, toxoplasma
What is the management for primary immunodeficiency ?
correct the defect:
- immunoglobulins, cytokines
- gene therapy?
early aggressive antibiotic tx
- daily co-trimoxazole
- penicillin if complement deficiency
- fluoxacillin in some neutrophil disorders
What are the differing presentations of AIDs in HIV- positive individuals in western population compared to africa?
- pre-haart pneumocystitis carinii pneumonia
- TB or slim disease (prolonged diarrhoea with a wasting illness)
How is AIDS diagnosed?
many pathogens are impossible to grow or difficult
some are inaccessible e.g. intracerebral
multiple infections are the rule
antigen detection (PCR DNA probe) + tissue diagnoses may be required
What is an indicator of disease progression in AIDS?
spectrum of infecting organisms relates to disease progression = CD4 count diminshes
CD4 count is boosted by HAART (triple therapy)
rational prophylaxis offered for PCP, MAI, CMV with falling counts
What are the different pathogens that normally infect people with AIDs?
- pneumocystitis carinii
- candida spp
- cryptococcis neoformans
- cerebral toxiplasmosis
- mycobacterium avium
- mycobacterium tuberculosis
What is pneumocystitis carinii?
ubiquitous uncultivable fungus
- 60% of people infected by age 4
- complex life cycle involving cysts and trophozoites
- most common infection in AIDs
- non-productive cough, dyspnoea, fever
- perihilar infiltrates
- may progress to severe respiratory distress
- silver stain/monoclonal antibody detection in BAL or biopsy
What is the treatment for pneumocystitis carinii?
high dose cotrimoxazole
if sulphonamide allergy - pentamidine, dapsone, clindamycin plus primaquine, atovaquone
- cotrimoxazole or inhaled pentamidine
-?? still needed on HAART
What is mycobacterium tuberculosis ?
2-10% annual risk of infection in HIV positive
- worldwide most illness is reactivation of latent infection
in africa 50% of HIV infected are MTB infected
- rapidly progressive disease on primary infection
- extrapulmonary disease more likely as CD4 cells decline
What is mycobacterium avium-intracellulare complex (MAI)?
M. avium- TB in birds
M. intracellulare - atypical human isolate - ubiquitous (soil, water, food, animals)
- pulmonary infection in non-aids pts
- disseminated in advanced AIDS
- fever, night sweats, weight loss, organ infiltration
How is MAI diagnosed and treated?
- culture after 1-4 incubation of sample from a sterile site
- blood culture, bone marrow, lymph node, liver biopsy
- problematic: resistance to antituberculous drugs
- clarithomycin or azithromycin (macrolides) and ethambutol plus rifabulin (+/- clotozamine, rifampicin, ciprofloxacin, amikacin)
- rifabulin at CD4 <0.1x10^9/L
What is cerebral toxoplasmosis?
- protozoal infection, usually asymptomatic (50% infected by middle age) or glandular fever
presentation in aids
- main cause of focal CNS lesions in AIDs
- pneumonitis and chorioretinitis may also occur
Empirical antitoxoplasma therapy if: I. ring enhancing lesions on CT/MRI
What is the treatment for cerebral toxoplasmosis?
pyrimethamine plus folinic acid and sulphadiazine or clindamycin for 3-6 weeks acutely (expert advice needed)
- secondary: prevent realpse pyrimethamine/dapsone
- primary: seropositive patients with low CD4 count
What is cryptococcus neoformans?
capsulate urease-positive yeast
- found in bird droppings
- asymptomatic infection by pulmonary route
leading systemic fungal infection in AIDs
- insidious meningitis - capsule inhibits alternate pathway of complement and little inflammation
- skin and bone infections less common
How is cryptococcus neoformans diagnosed and treated?
microscopy of CSF with india ink
antigen detection by latex agglutination in serum or urine (>90% sensitive)
csf or blood culture
- amphoteracin B or fluconazole
- lifelong fluconazole maintenance therapy required (even with HAART?)
What is cryptosporidiosis?
c.parvum is an apicomplexan protozoan parasite
water borne outbreaks, faecal oral spread esp. farm animals
self-limiting infection (2-3 weeks) in normal children
chronic watery diarrhoea in AIDs can be life-threatening
How is cryptosporidiosis diagnosed and treated?
- modified acid-fast stain
- monoclonal based immunofluorescence
- boil water if at risk
- azithromycin with paromomycin shows promise
What are the common viral infections in AIDs?
HSV - chronic mucocutaneous (oral and anogenital)
VZV - shingles
CMV- retinitis, encephalitis, hepatitis, pneumonia
HHV8 - kaposi's sarcoma