Malarial plasmodium: stages, species, pattern of development
The malaria plasmodium causes a dangerous protozoal disease in a person, chronic and recurring, like malaria, from which, according to the World Health Organization, nearly 2 million people die every year.
And today in the list of infectious diseases with fatal outcome in the first place is not AIDS, but malaria.
The only way that malarious plasmodium penetrates the human body is the bite of a mosquito. And from more than three thousand existing in nature species of these dipterous insects, this parasite is transferred only by the malarial mosquito of the anopheles genus (Anopheles superpictus). Moreover, this mosquito must necessarily be a female, since it needs blood as a source of proteins for egg production.
At the time of the bite, the mosquito injects saliva into the human skin (so that blood does not coagulate), and sporozoites of the malarial plasmodium enter the skin with saliva. Sporozoite is the reproductive form of only one stage of the life cycle of this protista. The structure of the malarial plasmodium at the stage of sporozoites has the form of elongated and slightly curved cells measuring no more than 15 μm.
The main host of the malarial plasmodium is the anopheles mosquito, since in its organism the plasmodium is involved in sporogony (sexual reproduction). A person is an intermediate host of a malarial plasmodium, since he uses the organism of Homo sapiens for agamogenesis, that is asexual reproduction. Biologists found that in unicellular genus Plasmodium asexual reproduction has a special form of schizogony, when the original cell is divided into not just two children, but immediately into a set. Thus the reproduction of the malarial plasmodium is adapted to the method of its spreading - from one host to another.
The development cycle of malarial plasmodia
The malarial plasmodium belongs to the simplest microorganisms of the Protista kingdom, the Sporozoa class, the haemosporidia order, the Plasmodium genus.
The types of Plasmodium vivax, Plasmodium malariae, Plasmodium falciparum and Plasmodium ovale malarial plasmodia are dangerous for humans, as they are the cause of malaria. The type of Plasmodium ovale malarial plasmodia is more rare, and it can only be picked up in the African or Asian tropics.
The cycle of malarial plasmodium development: from a mosquito to a human
The cycle of malarial plasmodium development is divided into two practical equal parts, each of which passes in the body of either a mosquito or a human. Let's start with the moment when the sporozoites of the malarious plasmodium penetrate the human body.
Getting into the blood, sporozoite very quickly find themselves in the liver tissue and already here begin asexual reproduction (schizogony), turning into merozoites. These hungry young plasmodia penetrate the red blood cells (erythrocytes) and, while absorbing hemoglobin, continue to asexually multiply in the asexual way. At this stage, the structure of the malarial plasmodium is a cell no larger than 2 μm in size with protoplasm and nucleus, their shape is round or oval (similar to amoeba).
Then the merozoites, destroying the erythrocytes, emerge from them and take the form of rings, and in their protoplasm cavities form - digestive vacuoles, which accumulate nutrients and excrete the products of vital activity: so plasmodia toxins enter the bloodstream of a person.
At this stage, the development of the malarial plasmodium occurs "on schedule" - every 48 hours, and just at the same frequency in a person infected with malaria, attacks of fever with chills and very high fever occur.
Erythrocytic schizogony is cyclically repeated and continues until the amount of merozoites reaches the desired level. And then the cycle of development of malarial plasmodium enters the next stage, and gametocytes are formed by sex cells.
The cycle of malarial plasmodium development: from human to mosquito
To begin sexual reproduction of malarial plasmodium (sporogony), it is necessary to change the host and get into the stomach of the anopheles mosquito. By this time gametocytes are ready for separation into microgametocytes and macrogamethocytes.
And as soon as the mosquito bites the person, sick with malaria, with sucked-up blood, the gametocytes "migrate" to their main host. Here, microgametocytes are transformed into male reproductive cells of plasmodium, and macrogamethocytes into female reproductive cells. Each species of these reproductive cells has a single (haploid) chromosome set. What happens next is easy to guess, and as a result of the merging of gametes of the opposite sex, diploid cells with a complete set of chromosomes - zygotes of malarial plasmodium, having an elongated shape, are obtained.
Zygotes of malarial plasmodia are very mobile and, not mildly, meet between the cells of the muscular wall of the insect stomach, are fixed there and form sporocysts - round cells-incubators covered with a membrane (created, among other things, from mosquito tissues). This cycle of malarial plasmodium development in the mosquito is one of the last. During sporocyst growth, cell mitosis continues under their membrane, and hundreds of sporozoites are formed in each (the structure of which was described above).
There comes a time when the shell is torn, and all these sporozoites are just inside the body of the insect. They have to get closer to the "exit", and mobile sporozoites with this task are doing well, getting into the right place - in the salivary glands of the Anopheles mosquito.
Blood for malarial plasmodia
Blood for malarial plasmodium is taken from the finger on the arm in the usual way, and then a blood smear is made on a sterile slide, which is studied under a microscope.
Since the species of malarial plasmodia differ somewhat in structure, each species has clear diagnostic features.
Experts attribute the structure of the malarial plasmodium to these signs, and the nature of the changes in the affected erythrocytes. As a rule, such red blood cells are enlarged, some change their shape and color, etc.
Prevention of malarial plasmodia
Until today, no one has succeeded in creating a vaccine against malaria, so the prevention of malarial plasmodiums is so important.
In malaria-endemic areas of the world, the prevention of malarial plasmodia, primarily, is aimed at the destruction of Anopheles mosquitoes with the help of insecticides.
For individual protection against malaria mosquito bites, various repellents (liquid, in the form of creams and aerosols) are used, closed clothing and anti-mosquito nets are applied, which are also sprayed with repellents.
There are special pharmaceutical preparations for the prevention of malarial plasmodia. Going to places where malaria is common and there is a chance to pick it up, these funds must be taken in advance.
For example, the anti-malarial drug Delagil (Chlorokhin, Rezokhin) in tablets take 0.5 g twice a week, and then - 0.5 g once a week. The effect of the drug is based on the ability of its active substance, the 4-aminoquinoline derivative, to inhibit the synthesis of nucleic acids and thereby destroy the cells of the malarial plasmodium. This remedy is contraindicated in cases of abnormal kidney and liver function, severe heart failure, a decrease in the hematopoietic function of the bone marrow. It also can not be taken by pregnant women and preschool children. The doctors note that after leaving the malarious dangerous terrain, the drug should be taken at least another month.
How to know what else would Alexander the Great conquer and what Oliver Cromwell would do for England if they were not bitten by a malarial mosquito, and the malarial plasmodium would not cause a fatal disease.
Последнее обновление: 01.06.2018
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Medical expert editor
Portnov Alexey Alexandrovich
Education: Kiev National Medical University. A.A. Bogomolets, Specialty - "General Medicine"
Parasitological diagnosis of malaria is based on the detection of asexual and sexual forms of the pathogen in a microscopic study of blood, which is possible only during its development in the red blood cell.
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