PLASMODIUM FALCIPARUM: CHARACTERISTICS, LIFE CYCLE, SYMPTOMS - BIOLOGY - 2025

Plasmodium falciparum is a unicellular protist of the group of protozoa. The genus Plasmodium has more than 170 described species. Some of these species can become parasites of birds, reptiles and mammals including man.

Four species of Plasmodium parasitize man: Plasmodium falciparum, P. malariae, P. ovale and P. vivax. Plasmodium falciparium was described by Williams H. Welch in 1897 and named it Haematozoon falciparum. Later it was included within the genus Plasmodium.

Plamodium falciparum Taken from pixnio.com

Plamodium falciparum is the cause of malignant tertiary fever. This is one of the most deadly, medically serious types of malaria or malaria. It is the cause of at least 50% of cases of malarial or malarial infections.

characteristics

Plasmodiums are taxonomically located within the Phylum Sporozoa or Apicomplexa. They are characterized by forming spores in their life cycle and by presenting an apical complex. This apical complex secretes molecules that allow entry to the cell to be parasitized.

They also have sexuality by syngamy (fertilization, or fusion of two haploid gametes), do not have cilia and most species are parasitic.

Some of the characteristics that differentiate P. falciparum from other species can be observed in the different stages that they present in the blood. For example, in the ring phase they present a delicate cytoplasm, with 2 color points. In the gametocyte phase, on the other hand, they are shaped like curved rods.

Morphology

Usually

In general, Plasmodiums (which parasitize humans) form four stages of development in man: hepatic schizonts, trophozoites, schizont and gamont or intraerythrocytic gametocytes. They also have three stages of development in mosquitoes: ookinets, oocysts and sporozoites.

In humans

Hepatic schizonts appear as groups of small basophilic bodies located within the host's hepatocytes. They measure between 40-80 μm in diameter when mature.

The intraerythrocytic stages consist of small, ring-shaped trophozoites that are 1–2 μm in diameter. Multinucleated amorphous schizonts are up to 7–8 µm in length. And the micro - (♂) and macro- (♀) gametocytes, which vary in length from 7 to 14 μm.

Other morphological characteristics that distinguish them from other protozoa is that during their development in humans, microgametocytes have a larger and more diffuse nucleus, while macrogametocytes have a darker staining cytoplasm.

In mosquitoes

During the development of Plasmodium in mosquitoes, the microgametes are long and thin, between 15-25 μm in length. Mobile ookinets are 15-20 x 2-5 μm. Oval oocytes can measure up to 50 μm in diameter on the outer surface.

Plasmodium falciparum

The morphology of this species of parasite varies depending on its stage in the blood. In this case, the morphological description of this species will be used when it develops in humans:

- Ring: delicate cytoplasm, with 1-2 small chromatic points, sometimes with lace shapes.

- Trophozoites: they are hardly observed in peripheral blood. At this stage the cytoplasm is compact and has dark pigment.

- Schizonts: schizonts are stem cells that reproduce asexually by merogonia and produce merozoites inside. They are rarely observed in peripheral blood, they present 8-24 small merozoites. They have dark pigment agglutinated in a mass.

- Gametocyte: has the shape of a rod with curved ends, the macrogametocyte presents chromatin in a single mass, while in the microgametocyte it is diffuse and the pigment is dark in color.

Lifecycle

The Plasmodium falciparum protozoan has a fairly complex life cycle. In the human host it presents an asexual phase or schizogony, and in the vector mosquito a brief sexual phase that is mandatory.

Life cycle of Plasmodium spp. Taken from

In humans, infection begins with the bite of an infected female Anopheles mosquito. With the bite, forms of the parasite called sporozoites enter the bloodstream.

These circulate for a short time in the blood, later they penetrate the liver cells and become tissue schizonts. Schizonts cause cellular disruption of hepatocytes. Cell lysis allows the release of between 10,000 and 30,000 merozoites that will infect the red blood cells.

Inside the red blood cells, merozoites mature into the ring, trophozoite, and erythrocytic schizont stages. Once the schizont has matured, it causes the erythrocyte to rupture and releases merozoites.

The released merozoites will invade other red blood cells and some of them will also undergo a process of differentiation into sexual forms. Once differentiation is achieved, they are called microgametocytes and macrogametocytes. The latter are the infective stages for the vector mosquito.

Once micro and macrogametocytes penetrate the Anopheles midgut, they mature and gamete fertilization occurs. The resulting zygote is mobile and is called an ookinet.

The ookinet will transform into an oocyst (cyst of an apicomplex parasite). The oocyst contains the product of the meiotic and mitotic division of a single zygote and gives rise to the sporozoites.

The sporozoites invade the mosquito's salivary glands, from where they can infect a new human when the mosquito feeds.

Symptoms

General

Symptoms appear 8 to 12 days after infection, being vague for 3 to 4 days. The first symptoms to be seen are body pain, moderate headache, fatigue, and anorexia.

Subsequently, the symptoms worsen with fever, severe headache, nausea, vomiting, and epigastric pain. These episodes exhibit a periodicity of less than 48 hours.

Cerebral malaria

Cerebral malaria caused by Plasmodium falciparium occurs when the capillaries and venules of the brain are blocked by infected erythrocytes. These blockages cause small hemorrhages that rapidly increase in size.

Symptoms of this infection include abnormal behavior, bouts of fever, and chills. Changes in the level of consciousness, coma, elevated cerebrospinal fluid (CSF) pressure, and classic decerebrate rigidity associated with hypoglycemia also occur.

There are often neurologic sequelae, such as hemiparesis, cerebral ataxia, cortical blindness, hypotonia, mental retardation, generalized spasticity, or aphasia.

Treatment

Principal

The World Health Organization (WHO) considers that the drug called chloroquine is the indicated treatment to eliminate the blood forms of Plasmodium falciparum. The use of primaquine is also recommended to kill gametocytes of this species.

Chloroquine and primaquine must be administered together for three days. From the fourth to the seventh day, only primaquine should be administered. In cases of mixed infections, the radical cure treatment will be fourteen days.

This treatment consists of chloroquine and primaquine for the first three days. From the fourth to the fourteenth day, only primaquine should be given.

Other medications

Cases of malaria or malaria caused by Plasmodium falciparum showing drug resistance have been consistently reported. This has led to proposing new treatments and adjustments to these.

An example of this is the combination of artesunate and mefloquine in a single tablet for the treatment of uncomplicated infections caused by P. falciparum.

References

1. Comparison of Plasmodium species that cause malaria in humans. Recovered from mcdinternational.org
2. H. Fujioka, M. Aikawa (1999) The malaria parasite and lifecycle. In: M. Wahlgren, P. Perlmann editors. Molecular malaria and clinical aspects. Amsterdam: Harwood Academic Publishers.
3. M. Chavatte, F. Chiron, A. Chabaud, I. Landau (2007) Probable speciations by «host-vector 'fidelisation'»: 14 species of Plasmodium from Magpies. Parasite.
4. J. Zarocostas (2010) Malaria treatment should begin with parasitological diagnosis where possible, says WHO. British Medical Journal.
5. M. Prescott, JP Harley and GA Klein (2009). Microbiology, 7th edition, Madrid, Mexico, Mc GrawHill-Interamericana. 1220 pp.
6. Plasmodium. Recovered from wikipedia.org.
7. Plasmodium. Recovered from parasite.org.au.
8. S. Magali (2011) Studies of avian malaria and Brazil in the international scientific context (1907-1945). History, Sciences, Saúde-Manguinhos.