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Tuesday, 30 April 2019

PALUDISMO POR PARASITACIÓN MIXTA CON PLASMODIUM FALCIPARUM Y PLASMODIUM MALARIAE

Written by Arturo González Raya | Ramón Coca Zúñiga

Figure 1. Microscopic examination (100x) of Wright-Giemsa stained peripheral blood smear from the patient revealed ring forms of Plasmodium parasites. P. falciparum rings have delicate cytoplasm and one or two small chromatin dots.

We present a case of a male from Ghana who lives in Spain and comes back after visiting his country for the first time in 10 years. He received malarial chemoprophylactic treatment for 3 weeks (before and during the trip), but not after the return.
He presented to the emergency department of our Hospital with suggestive symptoms of malaria infection. Microscopic examination of peripheral blood smear revealed many forms morphologically suggestive of Plasmodium falciparum, including trophozoites, gametocytes, ring forms, as well as isolated rounded shape forms with pigmentary accumulations suggestive of P.malariae. A polymerase chain reaction (PCR) assay was performed to rule out mixed infection, detecting P. falciparum and P. malariae in low parasitemia.

FiguraABCD
Figure 2.
Microscopic examination (100x) of Wright-Giemsa stained peripheral blood smear from the patient revealed Ay B) P. falciparum gametocytes presenting a sausage shaped form. C y D) P.malariae gametocytes, presenting a round shape (about the size of red blood cells) and a fine granular appearance.

Malaria is the most common imported tropical disease diagnosed in Spain1, with a mortality of 2-3% frequently related to delays in diagnosis and treatment2. There are 6 known species that can affect humans: P. falciparum, P. vivax, P. ovale (P. ovale wallikeri and P. ovale curtisi), P. malariae and P. knowlesi. There are also a few cases reporting infections from other nonhuman species. The majority of cases of imported severe malaria are caused by P. falciparum, followed distantly by P. vivax and P. knowlesi. The mixed infection is very infrequent. 

The diagnosis of malaria consists of:
  1. Microscopic examination: considered the “gold standard”. At least 3 microscopic examinations in several days should be performed until malaria is definitively excluded from the differential diagnosis, especially with low levels of parasitemia1.
    Thick blood smear.  The examination of a large sample of blood allows parasite quantification and monitoring treatment even with low levels of parasitemia but does not always allow the identification of the species. It is a complex technique that requires highly trained personnel.
    Peripheral thin blood smear. With lower sensitivity but higher specificity. As thick smear, it allows parasite quantification and monitoring treatment. Technique is simpler, and because it does not break the erythrocytes allows the identification of the species and mixed infections.
  2. Rapid diagnostic test: there are several immunochromatographic techniques for the detection of parasite antigens. The principal disadvantages of these methods are that they do not allow parasite quantification, not being useful for evaluation of response to treatment and the possibility of having false negatives in low parasitemias or in very high ones due to prozone effect3.
  3. Nucleic acid detection: most common methods for detection of Plasmodium spp. nucleic acid are PCR-based techniques (conventional and real-time), very sensitive and useful as confirmatory tests for identification of species, mixed and submicroscopic infections4. These are high cost techniques, with long response time (6 to 24h) and are not available in all laboratories5.
  4. Serological techniques: they have no utility in diagnosing acute cases of malaria.
The diagnosis of imported malaria is always urgent, it is recommended to have the result in less than 3 hours in order to avoid a delay in treatment. Malaria symptoms are not always specific, most common are fever, headaches and muscle pains, but some patients do not always present with these. Laboratory testing should be requested as soon as malaria is suspected, whether or not there is a fever. Microscopic examination remains the “gold standard” for the diagnosis, when is not available, a rapid diagnostic test can be used as an initial screening test (never replace).

References
  1. Ramírez-Olivencia G, Herrero MD, Subirats M, de Juanes JR, Pena JM, Puente S. Imported malaria in adults. Clinical, epidemiological and analytical features. Rev Clin Esp. 2012;212:1-9.
  2. Jose Muñoz, Gerardo Rojo-Marcos, Germán Ramírez-Olivencia, Joaquín Salas-Coronas, Begoña Treviño et al. Diagnóstico y tratamiento de la malaria importada en España: recomendaciones del Grupo de Trabajo de Malaria de la Sociedad Española de Medicina Tropical y Salud Internacional (SEMTSI). Enferm Infecc Microbiol Clin. 2015;33(6):e1-e13.
  3. Gillet P, Mori M, van Esbroeck M, van den Ende J, Jacobs J. Assessment of the prozone effect in malaria rapid diagnostic tests. Malar J. 2009;8:271.

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