Microbiology, parasitology & COVID-19


Plasmodium malariae

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PubMed Search: Plasmodium malariae[TI] full text[sb]

Haind Fadel, M.D.
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Cite this page: Fadel H. Plasmodium malariae. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parasitologypmalariae.html. Accessed December 7th, 2022.
Definition / general
  • Four species of plasmodia causing human malaria are Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae and Plasmodium ovale
  • Malaria (from the Italian "mal' aria," meaning "bad air") is an acute and sometimes chronic infection of the bloodstream characterized clinically by fever, anemia and splenomegaly and caused by apicomplexan parasites of the genus Plasmodium
  • P. malariae occurs worldwide but with a lower incidence than P. falciparum or P. vivax
  • Disease generally occurs between 45° N and 40° S (WHO: World Malaria Report 2014 [Accessed 9 January 2018])
  • Plasmodium knowlesi: usually causes malaria in monkeys (Lancet 2004;363:1017, Trends Parasitol 2008;24:406, Emerg Infect Dis 2008;14:1434)
Pathophysiology / etiology
  • Can be maintained at low infection rates because it can remain in a human host for an extended period of time and still remain infectious to mosquitoes
  • Spread exclusively by female anopheline mosquitoes
  • Fever paroxysm occurs over 6 - 10 hours and is initiated by the synchronous rupture of erythrocytes with the release of new infectious blood stage forms known as merozoites
  • Transfusion induced malaria may occur when blood donors have subclinical malaria and may prove fatal for the recipient
  • Similarly, congenital malaria may occur in infants born to mothers from endemic areas
  • Infant acquires the infection at birth as a result of rupture of placental blood vessels with maternal fetal transfusion
  • Neither transfusion nor congenital malaria is expected to relapse because exoerythrocytic schizogony does not occur
Diagrams / tables

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Life cycle

Clinical features
  • Causes a chronic infection that can last a lifetime (Wikipedia: Plasmodium malariae [Accessed 9 January 2018])
  • Usually considered to have a low morbidity rate
  • In the early stages of the disease, febrile episodes occur irregularly but eventually become more synchronous, assuming the usual tertian (P. vivax, P. falciparum and P. ovale) or quartan (P. malariae) periodicity
  • Patients with malaria may develop anemia and may have other manifestations, including diarrhea, abdominal pain, headache and muscle aches and pains
  • Persons with P. falciparum and P. malariae infection may have symptom free periods but suffer from sporadic recrudescences owing to persisting low grade parasitemia
  • Schüffner stippling is not seen in P. malariae or P. falciparum infection
  • Identification of malarial parasites on thin blood films requires a systematic approach
  • Three major factors should be considered: appearance of infected erythrocytes, appearance of parasites and stages found
  • P. vivax and P. ovale parasites primarily infect young erythrocytes, whereas P. malariae infects older erythrocytes and P. falciparum infects erythrocytes of all ages
  • Appearance of RBC size: normal
  • Schüffner stippling: Ziemann dots rarely seen
  • Parasite cytoplasm: rounded, compact trophozoites with dense cytoplasm; band form trophozoites occasionally seen
  • Appearance of parasite pigment: dark brown, coarse, conspicuous
  • Number of merozoites: 6 - 12; average is 8; "rosette" schizonts occasionally seen
  • Stages found in circulating blood: all stages; wide variety of stages usually not seen; relatively few rings or gametocytes generally present
  • Laboratory evaluation of patients suspected of having malaria continues to rely on timely examination of thick and thin blood films to demonstrate the intraerythrocytic parasites
  • More advanced laboratory methods include acridine orange staining and detection of parasite specific DNA
Life cycle
  • Malarial parasites undergo a sexual phase (sporogony) in Anopheles mosquitoes that results in the production of infectious sporozoites, as well as an asexual stage (schizogony) in humans that results in the production of schizonts and merozoites
  • In the bloodstream, some merozoites eventually differentiate into gametocytes (gametogony), which when ingested by female anopheline mosquitoes, mature into male microgametes and female macrogametes
  • Fusion of a microgamete and a macrogamete results in the formation of the motile ookinete, which migrates to the outside of the stomach wall and forms an oocyst
  • Within the oocyst, numerous spindle shaped sporozoites are formed
  • Mature oocyst ruptures into the body cavity, releasing sporozoites, which then migrate through the tissues to the salivary glands, from which they are injected into the vertebrate host as the mosquito feeds
  • Time required for development in the mosquito ranges from 8 - 21 days
  • Sporozoites injected into the vertebrate host reach the hepatic parenchymal cells within minutes and initiate the proliferative phase known as exoerythrocytic schizogony
  • Release of merozoites from ruptured hepatic schizonts initiates the bloodstream infection or erythrocytic schizogony and eventually the clinical symptoms of malaria
  • P. vivax and P. ovale differ from P. falciparum and P. malariae in that true disease relapses of the former species may occur weeks to months following subsidence of previous attacks; this occurs due to renewed exoerythrocytic and eventually erythrocytic schizogony from latent hepatic sporozoites, which are known as hypnozoites
  • Recurrences of disease due to P. falciparum or P. malariae, called recrudescences, arise from increased numbers of persisting blood stage forms to clinically detectable levels, not from persisting liver stage forms
  • Liver cells are infected only by sporozoites from the mosquito; thus, transfusion acquired P. vivax or P. ovale infection does not relapse
  • Merozoites released from infected hepatocytes subsequently infect erythrocytes
  • Following amplification of parasites in the bloodstream for a period of time and the development of synchrony in their appearance, clinical attacks of malaria occur
  • Morphologic stages seen in erythrocytes include trophozoites (growing forms), schizonts (dividing forms) and gametocytes (sexual forms)
  • Species causing infection in 1987 were P. vivax (44%), P. falciparum (43%), P. malariae (4%), P. ovale (3%) and undetermined (6%)
Case reports
  • 35 year old man with first case of Plasmodium knowlesi infection in a Japanese traveller (Malar J 2013;12:128)
  • 39 year old woman with first case of Plasmodium cynomolgi infection (from monkeys to mosquitos) (Malar J 2014;13:68)
  • 59 year old woman with transfusion transmitted Plasmodium malariae (Malar J 2013;12:439)
  • No widespread evidence of chloroquine resistance in P. malariae and P. knowlesi species; therefore, chloroquine (or hydroxychloroquine) may still be used for both of these infections
  • In addition, any regimens for chloroquine resistant malaria may be used for P. malariae and P. knowlesi infections
Clinical images

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Adult of Anopheles freeborni

Peripheral smear images

Contributed by Bobbi Pritt, M.D.

Malaria parasites in human red blood cells

Differential diagnosis
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