الرحمن الله بسمالرحیم
DIAGNOSIS OF MALARIA
By Shervin Ghaffari Hoseini
MD. PhD
Malaria is the world's most important parasitic disease, and kills more people than any other communicable disease except tuberculosis.
Each year 350-500 million cases of malaria occur worldwide, and over one million people die
Laboratory diagnosis of malaria Microscopic Diagnosis
Blood smear Fluorescent Microscopy Quantitative Buffy Coat (QBC ®)
Antigen Detection Immunochromatographic Dipstick: RDT
Serology IFA ELISA
Molecular Diagnosis PCR Real time PCR
Malaria Blood Smear
Remains the gold standard for diagnosis
Blood sample from vein or Puncture from finger pulp
New and clean slide
Both thin and thick films for all patients
Malaria Blood Smear
Thick films: Dry Do not fix but
dehemoglobinate
Stain
Thin films: Dry Fix Stain
Staining methods:Giemsa stainLeishman's stainField’s stain
Malaria Blood Smear
Thick films:
first step: Examination of a thick blood film
20 fold more concentrated species identification difficult minimum of 200 oil immersion fields about 15 minutes for an
experienced observer
Malaria Blood Smear
Thin films:
determine the species entire thin film should be
examined about 20-40 minutes for an
experienced observer
Interpreting Thick and Thin Films
THICK FILM
lysed RBCs larger volume 0.25 μl blood/100
fields more difficult to
diagnose species good screening test
THIN FILM
fixed RBCs, single layer smaller volume 0.005 μl blood/100 fields good species
differentiation requires more time to
read low density infections
can be missed
Calculating Parasite Density - 1
Count the number of parasitized and nonparasitized RBCs in the same fields on thin smear
Count 500-2000 RBCs
% parasitemia = # parasitized RBCs total # of RBCs
X 100
Calculating Parasite Density -2
Count ≥ 200 WBCs on thick film Assume WBC is 8000/l (or count it)
parasites/l =parasites counted WBC counted
X WBC count/l
Estimating Parasite DensityAlternate Method
Count the number of asexual parasites per high-power field (HPF) on a thick blood filmParasites observed Percentage of red cells
parasitized
10-20 per field 1
1-2 per field 0.1
1-2 per 10 fields 0.01
1-2 per 100 fields 0.001
1-2 per 1000 fields 0.0001
1-10 parasites per 100 HPF +
11-100 parasites per 100 HPF ++
1-10 parasites per each HPF +++
> 10 parasites per each HPF ++++
Malaria Blood Smear Prepare smears as soon as possible
Don not fix thick smear
time-honoured peripheral smear study
Identify P. falciparum in a dual infection with P. vivax
Mixed infections are not uncommon.
Malaria Blood Smear
negative test DOES NOT rule out malaria Repeat tests
partial antimalarial treatment sequestration of parasitised cells in
deep vascular beds
malarial pigment in circulating neutrophils and monocytes is
useful
Malaria Blood Smear Advantages Distinguishes between species and
life cycle stages
Parasitemia is quantifiable
Threshold of detection thin film: 100 parasites/ 1 μ lit thick film: 5 -20 parasites/ 1 μ lit
Simple and inexpensive
Malaria Blood Smear
Disadvantages labor-intensive
equipment, training and supervision needed
Fluorescent Microscopy
Fluorescent dyes detect RNA and DNA that is contained in parasites
Nucleic material not normally in mature RBCs
Stain thin film with acridine orange (AO)
Requires special equipment – fluorescent microscope
Staining itself is cheap Sensitivities around 90%
Quantitative Buffy Coat (QBC ®)
Quantitative Buffy Coat (QBC ®)
Advantages Useful for screening large numbers of
samples
Quick, saves time
Due to larger volume of blood observed, method is more sensitive
diagnosis of other diseases such as Babesiosis, Trypanosomiasis and Filariasis is possible
Quantitative Buffy Coat (QBC ®)
Disadvantages Species identification and
quantification difficult: thick/thin films on QBC-positive samples is required
High cost of capillaries and
equipment
Can’t store capillaries for later reference
An adapted light microscope for the viewing of QBC tubes.
Trophozoites of P. falciparum.
Malaria Antigen Detection
Immunologic assays to detect specific antigens
Commercial kits now available as immunochromatographic rapid diagnostic tests (RDTs), used with blood
P. falciparum histidine-rich protein 2 (PfHRP-2) parasite LDH (pLDH)
Mode of action of common malaria RDT format
Malaria Antigen Detection - RDTs
Feature PfHRP-2 tests pLDH tests
Sensitivity/Specificity*
Sensitivity 92-100%Specificity 85- 100%
Sensitivity P.f. 88-98% P.v. 89-94%Specificity P.f. 93-99% P.v. 99-100%
Commercialcost/test**
Approximately US$ 0.60 –1.00 Approximately US$ 2.50
Commercial products
1) PATH falciparum Malaria IC Strip test – Program for Appropriate Technology in Health
2) MAKROmed™3) Orchid ®
1) OptiMAL® - Flow, Inc.2) Binax NOW ®ICT
Malaria - Binax, Inc.
* Compared to microscopy, results from multiple studies** Varies by size of order and vendor
Detection of Plasmodium antigens
A: HRP-2 (histidine-rich protein 2) (ICT) B: pLDH (parasite lactate dehydrogenase)(Flow)C: HRP-2 (histidine-rich protein 2) (PATH)
Antigen DetectionMalaria Immunochromatographic Dipstick
OptiMAL Assay
ControlPlasmodium pan specificmonoclonal antibody
P. falciparum specificmonoclonal antibody
Malaria Antigen Detection - RDTs
Disadvantages The use of the RDT does not
eliminate the need for malaria microscopy Cannot detect mixed infections may not be able to detect infections
with lower parasitemia Cannot detect P. ovale and P. malariae microscopy is needed to quantify
parasitemia
Application of RDTs
Potential uses Epidemics and emergencies Inadequate or absent lab services,
unskilled staff Mobile clinics self-diagnosis by travelers entering
endemic areas outbreak investigation and surveys of
parasite prevalence
Para Sight F test
Malaria Serology – antibody detection
Methods IFA ELISA
Not practical for routine diagnosis of acute malaria because: Delaied development of antibody persistence of antibodies
Serology does not detect current infection but rather measures past experience
Malaria Serology
Valuable epidemiologic tool in some settings
Useful for Identifying infective donor in transfusion-
transmitted malaria Investigating congenital malaria, esp. if
mom’s smear is negative Retrospective confirmation of empirically-
treated non-immunes
Indirect fluorescent antibody (IFA) test. The fluorescence indicates that the patient serum being tested contains antibodies that are reacting with the antigen preparation (here, Plasmodium falciparum parasites).
Polymerase Chain Reaction (PCR)
Molecular technique to identify parasite genetic material
Uses whole blood collected in anticoagulated tube (200 µl) or directly onto filter paper (5 µl)
Polymerase Chain Reaction (PCR)
Advantages PCR is a reference method. It is at least
10-fold more sensitive than microscopy. Threshold of detection
0.1 parasite/µl if whole blood in tube 2 parasites/µl if using filter paper
more reliable for determining species in a mixed infection.
Can identify mutations – try to correlate to drug resistance
May have use in epidemiologic studies
Polymerase Chain Reaction (PCR)
Disadvantages
Parasitemia not quantifiable
Requires specialized equipment, reagents, and training
analysis of a PCR diagnostic test for species-specific detection of Plasmodium DNA. PCR was performed using nested primers
Real-Time PCR
potential to quantify parasitemia,
may detect multiple wavelengths in same tube identifying multiple species in one run
Needs further research and validation for malaria
Real-Time PCR
Quantitative Real-Time PCR
BCSH Guidelines for Quality Control
All malaria films should be examined by two observers
All new batches of Giemsa stain should be tested with a known P. vivax infection ensure that Schüffner’s dots are stained parasitised cells are decolourised. Blood films for this purpose can be
sealed in plastic slide boxes and frozen
BCSH Guidelines for Quality Control continue
All laboratories must ensure that new staff are adequately trained and maintain their skills: Sets of mixed positive and negative
thick and thin films should be available for examination
reference laboratories can often provide spare films for training purposes.
High quality photographs of malaria parasites should be available for reference
BCSH Guidelines for Quality Control continue
Websites can be used for on-going training. www.dpd.cdc.gov/dpdx/HTML/
Image_Library.htm (Centres for Disease Control and Prevention, USA)
www.rph.wa.gov.au (Royal Perth Hospital, West Australia, click on malaria information for learn and test yourself site)
Plasmodium falciparum
Rings: double chromatin dots; appliqué forms;multiple infections in same red cell
Gametocytes: mature (M)andimmature (I) forms (I is rarelyseen in peripheral blood)
Trophozoites: compact(rarely seen in
peripheral blood)
Schizonts: 8-24 merozoites(rarely seen in peripheral blood)
Infected erythrocytes: normal size
M I
Plasmodium vivax
Trophozoites: ameboid; deforms the erythrocyte
Gametocytes: round-oval Schizonts: 12-24 merozoites
Rings
Infected erythrocytes: enlarged up to 2X; deformed; (Schüffner’s dots)
Plasmodium ovaleInfected erythrocytes: moderately enlarged (11/4 X); fimbriated; oval; (Schüffner’s dots)
“malariae - like parasite in vivax - like erythrocyte”
Rings
Trophozoites: compact
Schizonts: 6-14 merozoites; dark pigment; (“rosettes”)
Gametocytes: round-oval
Infected erythrocytes: size normal to decreased (3/4X)
Plasmodium malariae
Trophozoite:compact
Trophozoite:typical band form
Schizont:6-12 merozoites;coarse, dark pigment
Gametocyte:round; coarse,dark pigment