P. falciparum infection is characterised by:

• small ring shapes, sometimes double chromatin specks

• accolé forms (parasites adherent to the membrane of the red blood cell)

• several parasites per red blood cell

• few or no schizonts

• banana-shaped gametocytes (the name "falciparum" comes from L. "falx" = sickle and "pario" = bring forth; they are sickle-shaped). Sometimes the red blood cell also contains inclusions (Garnham’s bodies) as well as the gametocyte.

• High parasitaemia may occur in P. falciparum and is unusual in the other forms (parasitaemia > 2 % is suggestive of P. falciparum).

  P. vivax preferably penetrates young (therefore large) erythrocytes.

  P. ovale is often found in a thin smear preparation in rather oval-shaped, sometimes distorted red blood cells.

  P. malariae trophozoites sometimes have a typical band shape. The mature schizonts have a daisy head appearance.

In well-stained preparations the nuclei of the parasites are always stained red and the cytoplasm blue. The presence of malaria pigment is very characteristic of the older stages of Plasmodium sp. P. falciparum often contains a single black dot. P. vivax often contains countless fine golden yellow/brown specks of malaria pigment. In P. ovale and P. malariae the pigment inclusions are many and brownish black. Countless fine red spots in the red blood cell (Schüffner’s dots) can be seen in P. vivax and P. ovale (the more mature the parasite, the more dots). In P. ovale the dots are sometimes called James’s dots. Sometimes a few flecks can be observed in P. falciparum (Maurer’s dots or clefts). P. malariae almost never exhibits dots (Ziemann’s dots). The visibility of these dots depends to a great extent on the acidity (pH) with which the thin slide preparation is stained (slightly alkaline: pH = 8 is best). The acidity is important because blood smears are usually stained for haematological tests with a slightly acid pH. With such a stain, the dots will not be seen clearly if at all.

Category: Medicine Notes