MALARIA AND DIAGNOSIS OF MALARIA

Malaria remains a disease of global health importance with 3.3 billion people in 97 countries at risk, leading to an estimated 200 million cases and around 600,000 deaths.  Malaria is a disease caused by a plasmodium parasite, transmitted by the bite of infected mosquitoes. A German physician, Johann Friedrich Meckel, must have been the first to see P. Falciparum. In 1847 he reported the presence of black pigment granules from the blood and spleen of a patient who died of malaria. The French Army physician Charles Louis Alphonse Laveran, while working at Bone Hospital, correctly identified the parasite as a causative pathogen of malaria in 1880 and named as Oscillaria Malariae. Six plasmodial species present a significant health threat for human; especially Plasmodium falciparum is considered the most important in terms of death.  Plasmodium vivax is a major cause of illness across large parts of the world, and it is increasingly argued that death due to this parasite, have been underestimated. P. Ovale curtisi, P.  Ovale wallikeri and P. Malariae are much fewer common causes of significant disease. Recently the simian parasite P. Knowlesi has emerged as a local but important cause of disease in Malaysia and other areas of Southeast Asia where it is predominantly a zoonosis, with no definite evidence of primary human-to-human transmission. Plasmodium falciparum is a unicellular protozoan parasite of human, and the deadliest species of Plasmodium that causes malaria in human. The parasite is transmitted through the bite of a female Anopheles mosquito and causes malaria.

 Diagnosis of Malaria

1)    Thick and Thin Smear

A well-prepared blood smear is important to produce good results on analysis after doing a Giemsa stain, in identifying blood cells or/and demonstrating the presence of parasites in a sample. Below, we discuss the procedures for preparing both thin and thick smear for Giemsa staining technique, Importance, and applications of blood smears, in detail. 

Blood smears are mostly done for Differential Leukocyte count (DLC) i.e. it quantifies the white blood cells and specifies the morphologies of each leukocyte. Normally, peripheral blood is used to prepare smears and depending on the function of the smear, two types of smears can be prepared.

a. Thin blood smear – for demonstration and differentiation of leukocytes. 

b. Thick blood smear – for diagnosis of blood protozoan parasites and blood abnormalities eg- anaemia. 

2) Rapid Antigen Test

                 

Although the peripheral blood smear examination that provides the most comprehensive information on a single test format has been the “gold standard” for the diagnosis of malaria, the immunochromatographic tests for the detection of malaria antigens, developed in the past decade, have opened a new and exciting avenue in malaria diagnosis. However, their role in the management and control of malaria appears to be limited at present. 

Immunochromatographic tests are based on the capture of the parasite antigens from the peripheral blood using either monoclonal or polyclonal antibodies against the parasite antigen targets. Currently, immunochromatographic tests can target the histidine rich protein 2 of P. falciparum, a pan malarial Plasmodium aldolase, and the parasite specific lactate dehydrogenase. These RDTs do not require a laboratory, electricity, or any special equipment.

3)    Molecular Test (PCR)

The polymerase chain reaction is a laboratory method that amplifies the parasite’s DNA and allows detection and identification of the Plasmodium species. This test can be used to confirm the diagnosis in laboratories where there is a lack of training and experience in the microscopic examination for malaria. 

It can also be used to determine the Plasmodium species if the results of a blood smear are unclear. Likewise, it is useful for cases in which the number of malaria parasites in the blood is low or when there are different types causing the infection (mixed) and examination using a microscope may be less accurate. The cost of these molecular testing techniques limits their use in many regions where malaria is endemic.

4)    Antibody Test (Serology)

Serology tests detect antibodies in the blood that are produced by the body in response to a malaria infection.  They cannot diagnose an acute infection but help determine if a person was previously exposed. These tests are not routinely used in the U.S. since a diagnosis can be made sooner by detecting the parasite under the microscope or it’s DNA instead of waiting for an immune response to develop weeks later.

5)    Susceptibility Testing

Some malarial parasites have become resistant to the drugs commonly used to treat the infections. Some specialized laboratories can test the parasites from an infected person to determine their drug susceptibility.  This can be done either by growing the parasites in the presence of increasing amounts of the drug and observing the effect of the drug on the parasite or by testing the DNA of the parasite to detect markers that indicate resistance. This latter method is still being evaluated.

 CHANDANI VOHRA