1. Specimen: blood

• Blood is collected from finger tips or ear lobe in older children and adults. In case of infants blood is collected from great toe.
• Smear should be examined atleast twice daily until parasite is detected.

2. Methods of examination:

i. Light microscopy:

• After blood collected from capillary, smear is prepared and stained with Romanwsky’s stain.
• Thick smear is used for detecting the parasite, quantitating parasitaemia, demonstrating malarial pigments.
• Thin smear is used for detecting parasites and also for determining the species.
• Diagnostic of falciparum is
  • –detection of multiple rings in a single RBC with accole form
  • Presence of maurer’s dots in RBC containing large ring
  • Presence of characteristics banana shaped gametocyte

ii. Fluorescence microscopy:

• Kawanoto technique is a fluorescent staining method for demonstrating malarial parasites.
• In this method, blood smears are prepared on a slide and are stained with acridine orange. This is a differential staining. Nuclear DNA stained green and cytoplasmic RNA stained red.
• The stained slide is examined with fluorescence microscope for identification of parasite.

iii. Quantitative buffy coat (QBC):

• This is a sensitive method for detection of malarial parasite.
• It is based on the ability of acridine orange to stain nucleic acid of parasite.
• In this method, blood is collected in a capillary tube coated with fluorescent dye and is subjected to microhaematocrit centrifugation in a specialized centifuse.
• After centrifugation the buffy coat in the tube is examined directly under a fluorescence microscope. Parasite appear brilliant green.
• QBC is more sensitive than thick smear preparation.

iv. Serology:

• IHA, IFA and ELISA

v. Dipstick test:

• It is a rapid diagnostic test extremely useful for rapid diagnosis of cerebral malaria.
• This is an enzyme immunoassay which detects histidine rich protein 2 (pf HRP-2) antigen, a metabolic product specifically produced by falciparum.
• Monoclonal antibodies produced against pfHRO-2 antigen is employed in the test to detect antigen in serum or urine.
• Dipstick test is only useful for detecting falciparum

vi. Molecular diagnosis:

• DNA probe is high;y sensitive. It can detect even a low parasitaemia (<10 parasite/ µl of blood). It is useful to detect drug resistant parasites.
• PCR is highly sensitive and can detect a single P. falciparum in 20µl of blood using PBRK1 primer.
• PCR can be used for identification of malarial parasite

vii. Biochemical diagnosis:

• A normochromic, normocytic haemolytic anaemia
• Leucopenia
• High Erythrocyte sedimentation rate
• Prolonged prothrombin and partial thromboplastin time in severe infection
• Normal plasma concentration of electrolytes, blood and urea nitrogen in uncomplicated malaria
• Decreased anti-thrombin II levels is mild infection
• Metabolic acidosis
• Hypergamma-globulinaemia
• Normal urine analysis
• Biological false positive reaction with VDRL test

Laboratory diagnosis of malarial parasite

The post Laboratory diagnosis of malarial parasite appeared first on Online Biology Notes.