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Advantages of microscopy, serology, antigen tests and molecular techniques for diagnosis of
parasitic infections
Tom van Gool, MD Section Clinical Parasitology Academic Medical Center, Amsterdam
Clinical parasitology in western hospitals: the essentials
Severe illness, potential lethal Effective treatment available when early diagnosed What do we need for diagnosis: Speed (result < 1h after having received bloodsample)
Species determination: P. falciparum, P. vivax, P. ovale, P. malariae, P. knowlesi Parasitaemia of P. falciparum
• ICT Now good test: beware of lower sensitivity of P. vivax, P. ovale, P. malariae!
• Before reporting negative thick smear: study 200 – 400 (1000x) fields • Thin smear stand alone reasonable/good sensitivity! (5 min. sens 93 %)
• Diagnosis at night shifts: make thick smear, thin smear and antigen test Study: antigen test and thin smear (5-10 min): combined good sensitivity and no major clinical mistakes. Study, as good as possible, thick smear. Repeat exam in early morning by experienced technicians!!
• Low parasitemia: no microscopical discrimination possible. (start malarone..)
• P. malariae and P. knowlesi morphologically similar
M Ag MD
L. Link, A. Bart, N. Verhaar, T. van Gool, M. Pronk, V. Scharnhorst (submitted) Case-report: Molecular diagnosis of Plasmodium knowlesi in a Dutch traveler by real-time PCR.
Molecular diagnosis • Limited number of molecular targets • Ongoing research, especially in tropics • Little data evaluation in travellers • Replacement microscopy by multiple PCR’s for all
helminth infections most likely not cost effective
• Improved microscopic diagnosis. Triple Feces Test TFT), multiple sampling, use of fixative: strongly improved sensitvity of microscopy, compared to exam. of one, non fixed sample.
• Antigen test for giardia and cryptosporidium: fast and useful
MD M Ag
Triple-Feces-Test (TFT)
Increaded yield TFT* • G. lamblia, E. histolytica / dispar : 25 - 30% • Dientamoeba fragilis: 100% (10% of all patients pos) • Blastocystis spp: 98% (25% of all patients pos) * compared to microscopy of Ridley concentrate of one, non fixed sample
Some matters in ongoing debate • T: are all positive PCRs, especially also the low positive ones, of clinical significance?
• T: DNA persists long in stools, difficult for monitoring effect treatment?
• P: Should PCR’s be regarded good screening methods and used in combination with microscopy or is /should it be the aim (multiple) multiplex PCR’s replace all microscopy (also for helminths)?
• In AIDS: major role “clinical suspicion”, serology (IgG pos/neg), radiography (CT, MRI), and effectiveness treatment. PCR of little importance • In transplant patients: serology (repeats!) and molecular diagnosis both of value, but importance of findings strongly dependant of
clinical findings at the time. Microscopy of i.e. CSF or BAL can be very useful !
Frequently observed Often not recognised as CL From all over world, also Mediterranean area Military personnel frequent South American infections potentially spread to mucous membranes
Biopsy taken from lesion Diagnostic method Sensitivity Microscopy 69% Culture 84% Microscopy + culture 90% Mini Exon Repeat-PCR 98% fast typing possible
• Microscopy, molecular methods, serology, antigen tests and culture all have a place in diagnosis of parasitic infections in western hospitals
• Don’t think dogmatic about techniques: not one is the best, combinations which combine strengths of different techniques make good diagnosis!
• Think over carefully before what you want to do yourself in your own lab.
• Diagnosis of parasitic infections is an art, as with bacteriology and virology It is not performing one test !
• Outsourcing tests which are difficult or less frequently done is not a shame.
• When decided to do proper parasitic diagnosis, select a motivated small (er) team. Do give them proper training and place them in an high level quality control scheme.
Acknowledgements Dr. A. Bart, Dept. Clinical Parasitology, AMC Dr. P. van Thiel, Dept. Infectious Diseases, AMC Technicians, Dept. Clinical Parasitology, AMC Dr. J. van Hellemond, Harbour Hospital, Rotterdam R. Koelewijn, Harbour Hospital, Rotterdam