Malaria Parasite Infections and Misidentification

Malaria Infections

• Plasmodium species present in infected patients:
  • P. knowlesi: 15 cases (0.29%)
  • P. cynomolgi: 21 cases (0.40%)
  • P. inui: 19 cases (0.36%)
  • P. fieldi: 3 cases (0.06%)

Risk Factors for Misidentification

• Common issues leading to misidentification:
  • Poor preparation or staining techniques
  • Deterioration of organisms
  • Insufficient number of parasites present
  • Presence of mixed infections
  • Identification of novel organisms
  • Inexperience of personnel

Detection Methods for Malaria

• Additional testing methods:
  • Rapid Diagnostic Tests (RDTs), PCR, and DNA sequencing
  • Automated analyzers for testing

Rapid Diagnostic Tests (RDTs)

• RDTs use small blood samples (2–50μl) via finger prick or venepuncture.
• Blood specimens are lysed in a buffer solution with malaria-specific antibodies.
• Follow-up testing with thick and thin films on negative results is crucial if clinical signs suggest malaria.
• The effectiveness of RDTs is supported by published studies.

BinaxNOW Malaria Test

• A qualitative immunochromatographic assay for Plasmodium antigens.
• Detects histidine-rich protein II (HRPII) specific to P. falciparum and a pan-malarial antigen common to all human-infecting malaria species.

PCR Testing

• Allows detection of low concentrations of malaria parasites.
• Effective for identifying species in challenging cases.

Haematological Changes in Malaria

• Thrombocytopenia:
  • Common in P. vivax and P. falciparum infections.
  • Results from enhanced splenic clearance and destruction/sequestration.
  • Possible development of DIC in severe cases.
• Leukopenia:
  • Mild in uncomplicated malaria cases.
• Leukocytosis:
  • Often seen in severe P. falciparum infections, potentially TNFα mediated or concurrent with bacteraemia.

Mechanisms of Anaemia in Malaria

• Intravascular and extravascular haemolysis, dyserythropoiesis, and bone marrow insufficiency contribute to anaemia.

Laboratory Diagnosis

• Blood film examination techniques include:
  • Thin and thick film preparations.
  • Thick films used for screening; thin films for confirmation.

Blood Film Preparation

• Blood should be collected when the patient's temperature rises.
• Thick films should be prepared without fixing, while thin films need to be air-dried and fixed before staining.

Staining Techniques

• Thick films stained with a 10% Giemsa solution and require air drying.
• Thin films stained with May-Grünwald & Giemsa stain using a slightly alkaline (pH 7.2) solution to enhance visibility of parasites.

Quiz on the prevalence of different Plasmodium species in infected patients and risk factors for misidentification using morphology. Based on a research study published in 2022.