Malaria Parasite Test Procedure, Principle, Results Interpretation

Malaria Parasite Test Procedure, Principle, Results Interpretation

Malaria Parasite Test Procedure, Principle, Results Interpretation

Malaria is a major vector-borne disease in India. Climatic conditions, high genetic diversity of malaria parasites, drug resistance and increasing resistance towards insecticides makes India home to a large number of malaria cases every year. The word ‘Malaria’ is derived from two Italian words, mal (bad) and aria (air). Malaria is an acute febrile illness caused by a protozoan parasite called Plasmodium.

In humans, four different species of Plasmodium can cause malarial infections. These are

1. Plasmodium falciparum

2. Plasmodium vivax

3. Plasmodium ovale

4. Plasmodium malaria

  • The incubation period for malaria varies from 9 to 30 days. Clinical features of infection with Plasmodium vivax and ovale may also develop several months later.
  • Plasmodium falciparum is responsible for more severe forms of malaria infection with serious complications if left untreated.
  • Plasmodium vivax and ovale tend to remain in the liver in dormant forms and may cause relapsing infections several months or years after exposure.
  • Latent blood infection with Plasmodium malaria may be present in the blood for several years and it rarely causes relapses and severe illness.

Transmission of Infection

  • The infection is transmitted to humans by the bite of female Anopheles mosquito.
  • It can also be transmitted via blood transfusions and the use of contaminated syringes.
  • A pregnant woman can transmit the malarial infection to her unborn child through the placenta.

Signs And Symptoms of Malaria Include

  • Fever with chills
  • A headache
  • Body ache or malaise
  • Joint pains and muscular aches
  • Generalized weakness
  • Gastro-intestinal disturbances such as loss of appetite, nausea, vomiting, and diarrhea.
  • Abdominal pain or fullness due to enlarged liver and spleen in prolonged infection
  • Severe complications include organ failure, convulsions, coma, and even death.

Initial signs and symptoms of malaria are often misdiagnosed as influenza. Once the possibility of malaria is suspected, your doctor will advise you to undergo a set of blood routine tests and a test for the malaria parasite.

What Is Malaria Parasite Test?

Various methods for detecting malaria parasite in blood are

1. Peripheral Blood Smear Examination Under Light Microscopy

  • When peripheral blood smear is used for diagnostic purpose, thick film smear yields more accurate results as compared to thin film and enables easier detection of the malaria parasite.
  • On the other hand, thin film enables identification of malaria parasite species and identification of malarial pigments in white blood cells.

2. Fluorescence Microscopy

This method enhances detection of parasites in peripheral blood smears by using fluorescent dyes.

  • Fluorescence microscopy enables rapid and quantitative analysis of a peripheral blood smear by staining white blood cells and malarial parasites separately.

3. Non Microscopic Rapid Diagnostic Test for Malaria Parasite (RMP)

  • Rapid diagnostic test for malaria is useful where microscopic detection is not available.
  • Detection of malaria parasite using test kits is easier to perform and provides results in nearly 15 minutes.
  • This test helps in differentiating malaria from malaria-like febrile illnesses.
  • This test is also used during the course of illness to assess the severity of the parasitic infection.

Principle of Malaria Parasite Test

  • Rapid diagnostic test for malaria parasite is done by using the method of the lateral-flow immunochromatographic assay (Dipstick Technology).
  • The immunochromatographic assay relies on the migration of liquid or blood across the surface of a nitrocellulose membrane test strip which has been impregnated with antibodies.
  • Two types of antibodies are used in these test kits – capture antibody and detection antibody which can be monoclonal or polyclonal.
  • Capture antibodies are bound to a narrow section of the test strip in the immobile phase. They function to extract and bind parasite antigen from the flowing sample of liquid.
  • Detection antibodies are bound to an indicator such as gold chloride in the mobile phase. The complex formed by the indicator and parasite antigen spread across the strip until it gets bound to capture antibodies.
  • Migration of antigen-antibody complex during the mobile phase along the test strip allows the antigen to be captured by antibodies present in the immobile phase. This produces a visible cherry red or purplish colored line.
Blood samples for malaria parasite test procedure are collected before beginning anti-malarial medications and preferably during a fever spike.

Malaria Parasite Test Procedure

Blood samples for malaria test procedure are collected before beginning anti-malarial medications and preferably during a fever spike.

Procedures For Detection Of Malaria Parasite On Peripheral Blood Smear

  • After collection of a blood sample, a drop of blood is taken on a sample and a thick or thin film is spread in the form of a square.
  • This smear is stained with Leishman’s or Giemsa. Giemsa staining is preferred for diagnostic purposes in India. Field’s stain is commonly used for staining thin film. Fluorescent staining is used if fluorescence microscopy is to be used.
  • The smear film is observed under the microscope for detection of the malaria parasite.

Procedure For Detecting Malaria Parasite Using Rapid Diagnostic Test

  • The first step is to collect blood and mix it with a lysing agent (an agent which causes breakdown of blood products).
  • By lysing, red blood cells are broken down and parasite antigens are released.
  • Detection antibodies are present at the nitrocellulose section of the strip (this portion appears like a small plastic well where a small amount of lysed blood is dropped).
  • As the fluid flows along the test strip, if malaria antigen is present, some parasite antigen-detection antibody complex will get accumulated at the test strip portion. Excess detection-antibodies accumulate at the control line.

Malaria Parasite Test Results And Interpretation

Interpretation of thick and thin films is done by examining the same under light microscopy or fluorescence microscopy.

Interpreting rapid diagnostic test kit for malaria parasite

  • After putting a drop of lysed blood into the strip, the intensity of the test band varies according to the amount of malaria antigens present.
  • The control band intensity decreases if the parasite density is high.
  • False-negative or false-positive results may be observed if the quantity of buffer or lysing solution is incorrect.

Rapid diagnostic test for malaria parasite has been proved to have higher sensitivity as compared to microscopic methods. It is also beneficial in detecting low levels of malarial infection.

Reviewed By:

Dr. Kaushal M. Bhavsar (MBBS, MD)

Assistant Professor in Pulmonary Medicine, GMERS Medical College, Ahmedabad