How is it diagnosed

Suspected malaria cases : All fever cases unless other wise proved.

Probable malaria cases (Clinically Diagnosed) : Fever cases without the following associated symptoms and not subjected to microscopic examination will be reported separately as clinical malaria.

1. Cough - Acute respiratory infections.

2. Cold with running nose.

3. Skin rash suggestive of eruptive illness.

4. Burning micturition

5. Skin infections e.g. boils, abscess, infected wounds.

6. Painful swelling of joints.

7. Ear discharge.

Seriously sick malaria cases : The Seriously sick malaria cases are those who present with following sign & symptoms.

Cerebral malaria : Case of unarousable coma not attributable to any other cause in a patient with p.falciparum infection. Other cases, with hyperpyrexia, convulsions, severe anaemia, pregnancy with fever, pulmonary oedema in p. falciparum infection, hyper parasitaemia and malaria haemoglobinuria.

Death due to malaria : Deaths due to malaria are only due to p.falciparum infection.

Deaths are very common in Cerebral Malaria Cases.

If any fever case having sign and symptoms cited above dies without microscopic confirmation, the death can be attributed to malaria.

Confirmed malaria death : Death of microscopically confirmed p. falciparum infected patient due to any of the complications mentioned above.

Laboratory Diagnosis

There are four species of the genus plasmodium responsible for the malarial parasite infections that commonly infect man, P.falciparum, P.vivax, P.malariae and P.ovale. The most important of these is P.falciparum because it can be rapidly fatal and is responsible for the majority of malaria related deaths.

In Maharashtra, P.vivax & P falciparum are more common species of malaria. Peripheral smear examination for malarial parasite is the gold standard in confirming the diagnosis of malaria. Thick & Thin smears prepared from the peripheral blood are used for the purpose.

Examination of a thick blood film should be the first step since this has the advantage of concentrating the parasites by 20 fold in comparison to a thin film, although the parasites may appear distorted making species identification difficult. If parasites are seen then the species should be confirmed by the examination of a thin film. Ideally blood should be collected when the patient's temperature is rising.

Under the microscope examine the thick film first, using an oil immersion or high dry lens to determine if parasites are present. Be aware of the patient's platelet and leucocyte counts. Malaria is usually associated with a normal or reduced leucocyte numbers. A leucocytosis is only found in terminal cases. Platelet numbers are moderately or markedly reduced in some 80% of patients with malaria. Parasites may appear distorted if the patient has been treated or has had inadequate or ineffective prophylaxis.

Mixed infections are not uncommon.

Typical Plasmodium Vivax

Salient features are:

· Developing and thick (signet) ring forms

· Enlarged red cells

Diagnostic points:-

1. Red Cells are not enlarged.

2. Rings appear fine and delicate and there may be several in one cell.

3. Some rings may have two chromatin dots.

4. Presence of marginal or applique forms.

5. It is unusual to see developing forms in peripheral blood films.

6. Gametocytes have a characteristic crescent shape appearance. However, they do not usually appear in the blood for the first four weeks of infection.

7. Maurer's dots may be present.

Typical Plasmodium Falciparum

Salient features are:

· Numerous fine ring forms

· Double chromatin dots

· Marginal forms

· Red cells are not enlarged.

Diagnostic points:-

1. Red cells containing parasites are usually enlarged.

2. Schuffner's dots are frequently present in the red cells as shown above.

3. The mature ring forms tend to be large and coarse

Typical Plasmodium Ovale

Salient features are:

· Developing form of plasmodium

· "Comet-like" red cells

· Enlarged red cell

Diagnostic points :-

1. Red cells enlarged.

2. Comet forms common (top right)

3. Rings large and coarse.

4. Schuffner's dots, when present, may be prominent.

5. Mature schizonts similar to those of P. malariae but larger and more coarse

Negative of malaria

Salient features are:

No parasites seen in this field

This film would need to be examined for 10 minutes before being called negative. Repeat films should be prepared and examined on at least 2 further occasions, ideally as the temperature peaks, before the presence of Malaria can be excluded.

Suspected Malaria

Salient features are:

· Numerous ring form of Plasmodium can be seen (as indicated by the arrows).

· Note size of neutrophils (for comparison).

The only definitive diagnosis that can be made from this film is that Malaria is present. Thin films would have to be examined for species identification.

Quantitative Buffy Coat (QBC) Test

The QBC Test, developed by Becton and Dickenson Inc., is a new method for identifying the malarial parasite in the peripheral blood. It involves staining of the centrifuged and compressed red cell layer with acridine orange and its examination under UV light source. It is fast, easy and claimed to be more sensitive than the traditional thick smear examination.

The Rapid Malaria Tests: The RDTs have been developed in different test formats like the dipstick, strip, card, pad, well, or cassette; and the latter has provided a more satisfactory device for safety and manipulation. The test procedure varies between the test kits. In general, the blood specimen (2 to 50µL) is either a finger-prick blood specimen, anticoagulated blood, or plasma, and it is mixed with a buffer solution that contains a hemolyzing compound and a specific antibody that is labeled with a visually detectable marker such as colloidal gold. In some kits, labeled antibody is pre-deposited during manufacture and only a lysing/washing buffer is added. If the target antigen is present in the blood, a labeled antigen/antibody complex is formed and it migrates up the test strip to be captured by the pre-deposited capture antibodies specific against the antigens and against the labeled antibody (as a procedural control). A washing buffer is then added to remove the hemoglobin and permit visualization of any colored lines formed by the immobilized antigen-antibody complexes. The pLDH test is formatted to detect a parasitemia of >100 to 200 parasites/µL and some of the PfHRP2 tests are said to detect asexual parasitemia of >40 parasites/µL.

The PfHRP2 test strips have 2 lines, I for the control and the other for the PfHRP2 antigen. The PfHRP2/PMA test strips and the pLDH test strips have 3 lines, 1 for control, and the other 2 for P. falciparum (PfHRP2 or pLDH specific for P. falciparum) and non-falciparum antigens (PMA or pan specific pLDH), respectively. Change of color on the control line is necessary to validate the test and its non-appearance, with or without color changes on the test lines, invalidates the test. With color change only on the control line and without color change on the other lines, the test is interpreted as negative. With the PfHRP2 test, color change on both the lines is interpreted as a positive test for P. falciparum malaria. With the PfHRP2/PMA [The immuno chromatographic test (ICT Malaria P. f. /P.v.test)] and the pLDH tests, color change on the control line and the pan specific line indicates non-fa1ciparum infection and color change on all the 3 lines indicates the presence of P. falciparum infection, either as monoinfection or as a mixed infection with nonfa1ciparum species. Also, if the PfHRP2 line is visible when the PMA line is not, the test is interpreted as positive for P.falciparum infection. Mixed infections of P. falciparum with the non-falciparum species cannot be differentiated from pure P. falciparum infections. However, with regard to the pLDH test, it is claimed that in the presence of P. vivax infection, the genus specific line is much darker and more intense than the species specific line due to the presence of all the stages of the parasite in the blood.