Plasmodium malariae (True Pathogen – Quartan Malaria)
Plasmodium malariae (True Pathogen – Quartan Malaria)
This organism belongs to the phylum Apicomplexa, is a true pathogen, and causes malaria. All forms of the human life cycle will appear in the thick and thin blood films.
Plasmodium malariae ring form
P. malariae band form
P. malariae mature schizont
Within an hour of infection, sporozoites from the mosquito are carried via the blood to the liver, where they penetrate parenchymal cells, thus initiating the preerythrocytic or primary exoerythrocytic cycle. The sporozoites become round or oval and begin dividing, resulting in large numbers of liver merozoites. The merozoites leave the liver and invade the red blood cells (RBCs), initiating the erythrocytic cycle. In P. vivax and P. ovale, a secondary or dormant schizogony occurs from organisms that remain quiescent in the liver until a later time; they are called hypnozoites. Delayed schizogony does not occur in P. falciparum, P. malariae, or P. knowlesi.
P. malariae primarily invades the older RBCs, so the number of infected cells is somewhat limited. The cycle is typically 72 hours, thus it begins again on the 4th day. Splenomegaly occurs during the first few weeks, and the spleen can progress from being soft and palpable to hard during a chronic infection. If therapy is given early, the spleen will return to normal size. Leukopenia is seen; leukocytosis may be present during the febrile episodes. Total plasma proteins are unchanged, although the albumin may be low and the globulin fraction may be elevated due to antibody development. Serum potassium may also be increased.
Bite: female anopheline mosquito; blood, shared needles, congenital infections
Sporadic distribution, mosquito to human, human to human transmission
Early Infection: The incubation period between infection and symptoms may be much longer than that seen with P. vivax or P. ovale malaria, ranging from about 27 to 40 days. Parasites can be found in the bloodstream several days before the initial attack, and the prodromal symptoms may resemble those of P. vivax malaria. A regular periodicity of 72 hours is seen from the beginning, with a more severe paroxysm, including a longer cold stage and more severe symptoms during the hot stage. Collapse during the sweating phase is not uncommon.
Complications: Proteinuria is common in P. malariae infections and in children may be associated with clinical signs of the nephrotic syndrome. It has been suggested that kidney problems may result from deposition within the glomeruli of circulating antigen‑antibody complexes in an antigen‑excess situation seen with a chronic infection. Apparently, the nephrotic syndrome associated with P. malariae infections is unaffected by the administration of steroids. A membranoproliferative type of glomerulonephritis with relatively sparse proliferation of endothelial and mesangial cells is the most common type of lesion seen in quartan malaria. Using immunofluorescence, granular deposits of IgM, IgG, and C3 are seen. Since chronic glomerular disease associated with P. malariae infections is usually not reversible with therapy, genetic and environmental factors may play a role in the nephrotic syndrome. The infection may end with spontaneous recovery, or there may be a recrudescence or series of recrudescences over a long period of years. These patients are left with a latent infection and persisting low‑grade parasitemia for many, many years (can be >40 years).
Blood: Multiple draws (EDTA). Malaria is one of the few parasitic infections considered to be immediately life‑threatening, and a patient with the diagnosis of P. falciparum malaria should be considered a medical emergency because the disease can be rapidly fatal. Any laboratory providing the expertise to identify malarial parasites should do so on a 24‑h basis, 7 days/week. Prepare thick and thin blood films immediately after receipt of the blood.
Although malaria is no longer endemic within the United States, this infection is life threatening, and laboratory requests for blood smear examination and organism identification should be treated as “STAT” requests. Frequently, for a number of different reasons, organism recovery and identification may be more difficult than the textbooks imply. It is very important that this fact be recognized, particularly when one is dealing with a possibly fatal infection with P. falciparum or P. knowlesi. Both thick and thin blood films should be prepared on admission of the patient (clinic, emergency room, in-house), and at least 300 oil immersion fields should be examined on the thick and thin film before a negative report is issued. Since one set of negative films will not rule out malaria, additional blood specimens should be examined over a 36 h time frame. Although Giemsa stain is used for parasitic blood work; the organisms can also be seen with other blood stains such as Wright’s, Wright-Giemsa, or any of the rapid blood stains. Blood collected with EDTA anticoagulant is acceptable; however, if the blood remains in the tube for any length of time, true stippling may not be visible within the infected RBCs (P. vivax as an example), organisms will change their morphology, and some of the parasites will disintegrate (after 4-6 h). Also, it is important to remember that the proper ratio between blood and anticoagulant is necessary for good organism morphology.
Ring Forms: Ring forms of P. malariae tend to be thick, compact (non-ameboid), and may mimic a signet ring with a large stone (nucleus); however, the ring forms can also mimic those of other species. True stippling (Schüffner’s dots) is not seen in P. malariae. It is important to remember than the infected RBCs tend to be normal to small size, often smaller than the uninfected RBCs. Band forms are also very typical in these infections.
Mature Schizont: The mature schizont has been described like a “daisy” head with 8-10 merozoites arranged around the excess pigment.
Gametocyte: The gametocytes are round to oval and tend to fill the entire RBC (smaller than normal infected RBC). Exflagellation of the male gametocytes can occur in the blood if the blood cools and becomes aerated (cap removed – lag time between cooling/cap removal and preparation of the thick and thin blood films.
A number of reports can be relevant – remember to add the appropriate report comments.
Report 1: No Parasites Seen: The submission of a single blood specimen will not rule out malaria; submit additional bloods every 4-6 hours for 3 days if malaria remains a consideration.
Report 2: Plasmodium spp. Seen: Unable to rule out Plasmodium falciparum or Plasmodium knowlesi
Report 3: Plasmodium spp., possible mixed infection: Unable to rule out Plasmodium falciparum or Plasmodium knowlesi
Report 4: Negative for parasites using automated hematology instruments. Automated Hematology instruments will not detect low malaria parasitemias seen in immunologically naïve patients (travelers)
Garcia, L.S. 2007. Diagnostic Medical Parasitology, 5th ed., ASM Press, Washington, D.C.
Improved mosquito control, impregnated bed nets, potential vaccines, prophylaxis
It is important to remember that the malarial parasites remain viable in the tube of blood collected using EDTA. If the blood cools and the cap is removed (blood becomes aerated), the organisms then begin the life cycle seen in the mosquito. Thus exflagellation of the male gametocyte can mimic spirochetes when they separate from the gametocyte (see below):