Plasmodium vivax: Morphology

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The early trophozoite

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• PVET-main image.jpg

The earliest ring forms may be indistinguishable from other species, but during this stage the parasite tends to aquire a more irregular forms and to show signs of modification of the erythrocyte (added dots, and altered size and shape).

• erythrocytes begin to show increased size and altered shape
• parasites retain a ring form but may aquire a more irregular form
• parasites are generally large - occupying up to half of the erythrocyte
• cytoplasmic Schüffner's dots may appear at this stage, although pigment uncommon

Click for P.vivax early trophozoite gallery

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The late trophozoite

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The later growth stage:

• Parasites resemble early ring forms, but are thicker and may be slightly larger
• Additional blue/grey dots and clefts are seen in red cell cytoplasm when stained correctly
• These dots have low number a characteristic "dot" or "line" form Maurer's dots and clefts
• Size and shape of infected red cells is usually unaffected, but may become crenated
• The double dot, accolé, and multiple parasite forms remain present

Click for P.falciparum late trophozoite gallery

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The schizont

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The asexual form:

• Do not generally circulate in this species unless overwhelming infection
• The asexually formed developing "merozoites" cluster untidily
• Schizonts develop progressively to form 8-16 merozoites when mature
• In this species the loose malaria pigment may be seen in clumps between the parasites
• Red cell size is generally unaffected but red cells become pale as haemoglobin is metabolised by the parasites

Click for P.falciparum schizont gallery

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The gametocyte

The gametocyte

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The sexual replication form (very distinctive).

• Gametocytes are elongated but are restricted into typical shape by the red cell membrane
• They parasites are rod shaped but the membrane may cause them to curve into a “"banana" form”
• The residual membrane (empty of haemoglobin) is often seen as a "blister" to the side of the parasite
• The single chromatin area is in the centre of the parasite, often has pigment overlying it
• Gametocytes may not be be seen, or may be the only form present (particularly after treatment)

Click for P.falciparum gametocyte gallery

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• erythrocytes begin to increase size and shape of infected red cells enlarged and distorted during this stage *parasites have a ring form this may be quite irregular *parasites are generally large - occupying up to half of the erythrocyte *cytoplasmic schu8c3bcffneru8e28099s dots may appear at this stage but malaria pigment is not usually seen

the late trophozoite file pvlt.jpg leftt 200px link filepath pvlt.jpg *infected erythrocytes are clearly significantly enlarged and lose their regular outline *parasites are noticeably irregular becoming amoeboid in form *numerous purple schu8c3bcffneru8e28099s dots are seen in the cytoplasm *pigment is often present with irregular distribution

the schizont file pvs.jpg leftt 200px link filepath pvs.jpg *a range of maturing schizonts will generally be present within enlarged red cells *mature schizonts generally contain 16-24 separate merozoites *schu8c3bcffneru8e28099s dots can be detected in any residual cytoplasm of the erythrocyte *pigment is visible in irregularly distributed clumps over the schizont surface

the gametocyte file pvg.jpg leftt 200px link filepath pvg.jpg *very large with ovoid or distorted forms *macrogametocytes female may entirely fill the erythrocyte *microgametocytes male may have a thin cytoplasmic rim with visible schu8c3bcffneru8e28099s dots *pigment is clumped over the surface of the gametocyte