As we already know, the gold standard malaria diagnosing test is the screening of thick and thin blood smears with Romanowsky stain.
Well-stained thin blood film enables the differentiation easy for medical laboratory professionals. Some morphological characteristics of the infected RBCs and parasites can be used to direct the diagnosis towards one of the four Plasmodium species that infect humans, which are, P.vivax, P.falciparum, P.ovale, and P.malariae.
Let’s see how we can differentiate the 4 species using the characteristics of each stages of the life cycle, and features of infected Red blood cells on microscopy.
1. Ring Stage
Ring stage of all Plasmodium species except P. falciparum show large chromatin dot.
falciparum on the contrary, has 1 to 2 small chromatin dots. Also we can see, some chromatin dots are on the surface of the RBC, this is known as applique forms.
The high proportion of infected red blood cells can be examine  here, also  including doubly parasitized cells, is characteristic of Plasmodium falciparum.
Large cytoplasm with occasional pseudopods is seen in vivax ring stage. Remember Plasmodium vivax selectively infects reticulocytes ( immature RBC ), Therefore  we would expect to see a low-grade parasitemia, with ring trophozoites in the biggest red blood cells.
A sturdy cytoplasm is seen in ovale and malariae ring stages. Also P. ovale likes to infect , young red blood cells which bigger than other RBcs .
Therefore ring stage seen inside large reticulocytes are characteristic of Plasmodium ovale infection. RBC infected with P. ovale will reveal the cell’s edges are feathered.
Usually P.malariae infected RBCs smaller than surrounding cells .
2. Trophozoite
Trophozoites of P. falciparum are rarely seen in peripheral blood.
When available, they are seen with compact cytoplasm with dark pigments. Presence of multiple trophozoites in one cell is unique to this species.
Trophozoites of both P. ovale and malariae are compact with a large network of chromatin.
The difference between these two species is that Plasmodium ovale trophozoites have dark brown pigmentation,   These Schuffner’s dots will distort the parasitized RBC into an oval and giving P. ovale its distinctive namesake shape.
In P vivax, large ameboid cytoplasm, large chromatin and fine yellowish-brown pigmentation can be seen within RBC.
But unlike P. ovale infections, these Schuffner’s dots seen in P. vivax don’t distort the red blood cell shape. It stays more rounded without a feathered edge.
while P. malariae trophozoites large chromatin can be occasionally seen in band form with coarse dark brown pigments. This feature  is unique to P. malariae.
3. Schizonts
Schizonts of P. vivax are large and they almost fill the entire red cell. 12-24 merozoites are present in the schizont.
Schizonts of P. falciparum are rarely seen in peripheral blood. 8-24 small merozoites are present in the schizont.
In mature P. ovale and P. malariae schizonts, 6-14 merozoites with large nuclei are present.
malariae schizonts can rarely be present as rosettes. It is mean merozoites lined up around the perimeter of the schizont with pigment in the center.
4. Gametocyte
plasmodium vivax gametocytes are round to oval in shape. They are compact and may almost fill RBCs.
The most definitive finding of P. falciparum is the shape of the gametocytes. Unlike other species of malaria, they are crescent-shaped or banana-shaped
ovale gametocytes are round to oval in shape, compact and may almost fill RBC. They are larger than normal RBC and have a granular appearance as well as Schuffner’s dots.
malariae gametocytes are round to oval in shape, campact and may almost fill RBC.
In all 4 species, chromatin in compact and eccentric in macrogametocyte and diffuse in microgametocyte
Chromatin in a single mass can be seen in P. falciparum macrogametocyte.
5. Size of RBC
RBCs infected with P. vivax are enlarged, to approximately 1.5 times the size of a normal RBC.
Also RBC infected with P.ovale larger compare to the normal RBC.
RBCs infected with P. falciparum are normal in size.
And RBC infected with P.malariae normal or Smaller in size .
6. Schuffner’s dots
Shuffner’s dots are fine invaginations at the surface of the infected reticulocytes. These are present in RBCs infected with P. vivax and P.ovalae.
These characteristics, when considered together, can immensely help in the diagnosis of the specific type of malaria parasite involved in a patient. Therefore, it is a very important topic in medical laboratory technology.
Well friends , I hope you guys enjoyed this video and gain knowledge about how to identify & differentiate these malaria parasites on thin blood smear … So my next video I hope to design as Quiz video for increase your these parasites identification skills …
Thank you.
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