Ring forms

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What is a ring form?

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The earliest stage following red cell invasion has a typical ting form:

• a = chromatin dot
• b = digestive vacuole
• c = parasite cytoplasm

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Description

At the earliest stage of red cell infection parasites of all species have the form of a "ring". Distinction between species at this stage may not be easy (or even possible). However as the parasite mature and develop differences between species become more apparent. In some species the ring appearance is maintained until late stages of maturation, in others there is loss of a typical ring appearance

• P.falciparum: Typically the rings small and delicate, rings tend to persist from early trophozoite until late stages although they may thicken
• P.ovale: Typical rings are large and robust and this shape may persist until late stages of development (contrast with P.vivax)
• P.malariae: Rings are small but more substantial that P.falciparum becomeing solid or bad and losing the ring appearance as they develop
• P.knowlesi: Early forms resemble P.falciparum; as they mature they often extend and become solid or band-like resembling P.malariae
• P.vivax: Early stages appear as rings becoming irregular then eventually taking on a more typical amoeboid appearance at later stages

These changes are illustrated for early and late trophozoite below:

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P.falciparum

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Small and often delicate rings at early stages, these thicken at later stages, although they remain relatively small with a "ring appearance"

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P.ovale

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Robust rings that enlarge during parasite development, although the ring form can often still be distinguished

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P.malariae

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Small but more robust than P.falciparum, the parasites become more solid as they develop and may extend as a band across the cells

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P.knowlesi

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  small or normal P.malariae (round)

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  normal sized P.falciparum (round)

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  ormal or enlarged P.ovale (may become ovoid)

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P.vivax

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  small or normal P.malariae (round)

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  normal sized P.falciparum (round)

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  ormal or enlarged P.ovale (may become ovoid)

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Species significance

These changes can be very helpful in identifying malaria species

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