Malaria assay (Plasmodium malaria in the blood)

Plasmodium in the blood smear in healthy people is absent. Malarial plasmodia alternately parasitize in 2 hosts: in the body of a female mosquito of the genus Anopheles, where sexual reproduction occurs, sporogony, and in the human body where asexual reproduction occurs, schizogony. The initial phase of schizogony occurs in hepatocytes (extraerythrocytic schizogonia), followed by erythrocytes (erythrocytic schizogony). Developing in erythrocytes, plasmodia feed on hemoglobin and destroy the affected erythrocytes. All pathological manifestations of malaria [fever attacks, anemia, splenomegaly, central nervous system (CNS) damage in the tropical form of malaria] are associated with erythrocytic schizogony.

There are 4 types of plasmodia:

• P. falciparum - the causative agent of tropical fever, the most dangerous form of malaria, which requires urgent treatment. At P. falciparum erythrocytic schizogony begins in the peripheral bloodstream, and ends in the central, due to the delay of the affected red blood cells in the capillaries of internal organs. As a result, at the onset of infection, only young trophozoites ("rings") are present in blood preparations. The gametocytes after maturation in the capillaries of internal organs are found in the peripheral blood on the 10th -12th day of the disease. Detection in the peripheral blood of adult trophozoites or schizonts of any age indicates the onset of a malignant course of tropical malaria and a near fatal outcome, unless urgent measures are taken. In other types of malaria, erythrocytic schizogony flows entirely in the peripheral blood stream. Gametocytes P. falciparum, in contrast to other species of plasmodia, are not round, but oblong, and differ in a long period of life. They die within 2-6 weeks (other - within 1-3 days), so the detection of gametocytes P. falciparum for many days after the cure of the patient (cessation of erythrocytic schizogony) due to the action of schizoticidal drugs is a common phenomenon that is not considered an indicator of ineffective therapy.
• P. vivax is the causative agent of a three-day malaria.
• P. malariae - the causative agent of four-day malaria
• P. ovale - the causative agent of malaria oval (type three-day).

Erythrocyte schizogony cycle is repeated in the P. falciparum, P. vivax and P. ovale every 48 h in P. malariae - 72 h. Malarial seizures develop at that phase of the cycle of erythrocytic schizogony, when the bulk of the affected red blood cells is destroyed and the daughter plasmodia (merozoites) that have emerged from them invade intact erythrocytes.

To establish the species belonging to malarial parasites, the following matters: the presence of polymorphism of the age stages or one leading, their combination with gametocytes; morphology of different age stages, their size in relation to the affected erythrocyte; nature, size of the nucleus and cytoplasm; intensity of pigment, its shape, size of grains / granules; the number of merozoites in mature schizonts, their size and location with respect to the accumulation of pigment; the propensity of the parasite to attack the erythrocytes of a certain age (tropism); tendency to multiple lesions of individual erythrocytes by several parasite individuals and its intensity; the size of the affected erythrocytes in relation to the uninjured, the shape of the affected erythrocytes, the presence of azurophilic granularity in the affected erythrocytes; form of gametocytes.

At acute attacks of a malaria the certain regularity of changes of a blood is traced. During the chill appears neutrophilic leukocytosis with a shift to the left. During the period of fever, the number of leukocytes decreases somewhat. When sweat appears and with apyrexia, monocytosis builds up. In the future, after 2-4 attacks, anemia develops, which is especially early and develops rapidly with tropical fever. Anemia is mainly hemolytic in nature and is accompanied by an increase in the content of reticulocytes. In blood smears, there are poikilocytosis, anisocytosis, and polychromatophilia of erythrocytes. With the addition of bone marrow depression, the amount of reticulocytes decreases. Sometimes there is a picture of pernicious anemia. ESR in malaria is significantly increased.

In the interictal (febrile) period in the blood for all forms of malaria, in addition to the tropical, adult trophozoites predominate. During this period of the disease, certain stages of the plasmodia are present in the blood constantly, up to the complete cessation of erythrocytic schizogony. In this regard, there is no need to take blood for research only at the height of a malarial attack, but you can examine it at any time. The absence of plasmodium of malaria in blood smears and a thick drop of a patient with malaria reflects only the thoroughness of the research conducted and the professional competence of the laboratory specialist.

Account for a total of asexual and sexual forms, except when assessing the intensity of parasitaemia P. falciparum. The intensity of parasitemia is evaluated by a "thick drop" in the calculation for 1 μl of blood. The number of parasites in relation to a certain number of leukocytes is counted. When 10 or more parasites are detected for 200 white blood cells, the count is over. If 9 or less parasites are detected per 200 leukocytes, counting is continued to determine the number of parasites per 500 leukocytes. When single parasites are detected in a "thick drop" of blood, their number per 1000 leukocytes is counted. The determination of the number of parasites in 1 μl of blood is carried out according to the following formula: X = A × (B / C), where: X - the number of parasites in 1 μl of blood; A - counted number of parasites; B - the number of leukocytes in 1 μl of blood; C - counted number of leukocytes.

In those cases when it is not possible to determine the number of leukocytes in a given patient, their number in 1 μl is conventionally taken on the recommendation of WHO to be 8,000.

Control over the effectiveness of treatment is carried out by examining a thick drop of blood with counting parasites in 1 μl of blood. The study should be performed daily from the 1st to the 7th day from the beginning of chemotherapy. With the disappearance of parasites during this period, further blood tests are performed on the 14th, 21st and 28th days from the start of treatment. When resistance is detected (assessed by the level of parasitemia) and accordingly ineffective treatment, the antimalarial drug is replaced with a specific drug of another group and the blood test is carried out according to the same scheme.

For patients who have suffered tropical malaria, they establish a follow-up medical examination for 1-2 months, with a parasitological examination of blood at intervals of 1-2 weeks. Clinical examination of patients who had malaria caused by P. vivax, P. ovale and P. malariae, should be carried out for 2 years. With any increase in body temperature, these individuals need a laboratory blood test to detect malarial plasmodia.

[1], [2], [3], [4], [5], [6],