Polymerase Chain Reaction (PCR): Using the
non-isotopically labelled probe following PCR amplification, it is possible to detect
malaria parasites. In travelers returning to developed countries, studies based on PCR
have been found to be highly sensitive and specific for detecting all 4 species of
malaria, particularly in cases of low level parasitemia and mixed infections. The PCR test
is reportedly 10-fold more sensitive than microscopy, with one study reporting a
sensitivity to detect 1.35 to 0.38 parasites/µL for P. falciparum and 0.12
parasites/µL for P. vivax. The PCR test has also been found useful in unraveling
the diagnosis of malaria in cases of undiagnosed fever.
Detection
Of Antimalarial Antibodies:
Antibodies to the
asexual blood stages appear a few days after malarial infection, increase in titer over
the next few weeks, and persist for months or years in semi-immune patients in endemic
areas, where re-infection is frequent. In non-immune patients, antibodies fall more
rapidly after treatment for a single infection and are undetectable in 3-6 months.
Re-infection/relapse induces a secondary response with a rapidly increasing antibody
titer.
Malarial antibodies can
be detected by immunofluorescence or enzyme immuno assay. It is useful in epidemiological
surveys, for screening potential blood donors and occasionally for providing evidence of
recent infection in non-immunes. In future, detection of protective antibodies will be
important in assessing the response to malaria vaccines.
Intraleucocytic malaria pigment: Intraleucocytic
malaria pigment has been suggested as a measure of disease severity in malaria. In a study
of 146 children aged 6 months to 14 years in 4 categories - cerebral malaria, mild
malaria, asymptomatic malaria and 'no malaria'- in Ibadan, Nigeria, an area of intense
malaria transmission in Africa, the proportion of pigment-containing neutrophils showed a
clear rise across the spectrum no malaria--asymptomatic malaria--mild malaria--cerebral
malaria (median values 2.0%, 6.5%, 9.0% and 27.0%, respectively; P < 0.0001). The
proportion of pigment-containing monocytes did not differ significantly between the mild
malaria, asymptomatic malaria and no malaria groups but the cerebral malaria group had a
higher median value than the other 3 groups. The ratio of pigment-containing neutrophils
to pigment-containing monocytes showed the same trend across the groups of subjects as was
observed with the number of pigment-containing neutrophils. The study concluded that the
pigment-containing neutrophil count is a simple marker of disease severity in childhood
malaria in addition to the parasite count. (Amodu OK, Adeyemo AA, Olumese PE, Gbadegesin
RA. Intraleucocytic malaria pigment and clinical severity of malaria in children. Trans
R Soc Trop Med Hyg. 1998 (Jan-Feb); 92(1):54-56)
Flowcytometry:
Flowcytometry and
automated hematology analyzers have been found to be useful in indicating a diagnosis of
malaria during routine blood counts. In cases of malaria, abnormal cell clusters and small
particles with DNA fluorescence, probably free malarial parasites, have been seen on
automated hematology analyzers and it is suggested that malaria can be suspected based on
the scatter plots produced on the analyzer. Automated detection of malaria pigment in
white blood cells may also suggest a possibility of malaria with a sensitivity of 95% and
specificity of 88%. On flow cytometric depolarized side scatter, the average relative
frequency of pigment carrying monocytes was found to differ among semi-immune, non-immune
and malaria negative patients.
-
Hanscheid T, Melo-Cristino J, Pinto BG.
Automated detection of malaria pigment in white blood cells for the diagnosis of malaria
in Portugal. Am J Trop Med Hyg. 2001 May-Jun;64(5-6):290-2
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Ben-Ezra J, St. Louis M, Riley RS.
Automated malarial detection with the Abbott Cell-Dyn 4000 hematology analyzer. Lab
Hematol. 2001;7:61-64
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Kramer B, Grobusch MP, Suttorp N et al.
Relative frequency of malaria pigment-carrying monocytes of nonimmune and semi-immune
patients from flow cytometric depolarized side scatter. Cytometry. 2001 Oct
1;45(2):133-40.
Mass spectrometry:
A novel method for
the in vitro detection of the malarial parasite at a sensitivity of 10 parasites/µL of
blood has been recently reported. It comprises a protocol for cleanup of whole blood
samples, followed by direct ultraviolet laser desorption time-of-flight mass spectrometry.
Intense ion signals are observed from intact ferriprotoporphyrin IX (heme), sequestered by
malaria parasites during their growth in human red blood cells. The laser desorption mass
spectrum of the heme is structure-specific, and the signal intensities are correlated with
the sample parasitemia. Many samples could be prepared in parallel and measurement per
sample may not take longer than a second or so. However, the remote rural areas without
electricity are not hospitable for existing high-tech mass spectrometers. Future
improvements in the equipment and technique can make this method deployable and useful.
-
Demirev PA, Feldman AB, Kongkasuriyachai D
et al. Detection of malaria parasites in blood by laser desorption mass spectrometry. Anal
Chem 2002 Jul 15;74(14):3262-6
-
Mann M. Mass tool for diagnosis. Nature
2002 Aug 15;418(6899):731-2
Other investigations: Total and
differential count, hemoglobin, blood glucose, serum bilirubin, serum creatinine, BUN,
AST, ALT, Prothrombin time, urine analysis etc. may be done as needed.
Widal test
may be positive, even up to a dilution of 1:320 for 'O' and H' and at lower titres for
'AH' and 'BH'. Any or all the four may be positive, suggesting a non-specific response. A
positive Widal test in a patient with confirmed malaria should not
therefore be considered as suggestive of typhoid fever.
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