Plasmodium Vivax: Morphology, Life Cycle And Symptoms

Plasmodium vivax is one of the causative agents of malaria or malaria in humans. This parasite has a very wide geographical distribution and is responsible for most cases of malaria, a tropical disease, considered a major public health problem worldwide.

P. vivax, like all representatives of its genus, has a complex life cycle that includes phases that develop in two hosts. One of the hosts is an invertebrate, where the sexual phase occurs, and the other a vertebrate, where the asexual phase occurs. At least ten species out of more than 175 known species of Plasmodium parasitize humans, four of them causing some form of malaria.

Mosquitoes of the genus Anopheles are the vectors involved in the transmission of P. vivax . There are more than 450 species of anopheles, of which more than 50 have been identified as capable of transmitting any of the four species that cause malaria in humans. Only the female is capable of transmitting the parasite.

Studies by the World Health Organization (WHO) estimate that half of the world’s population is exposed to being infected by the malaria parasite. By 2006, about 250 million cases and one million deaths were registered in the world. Some studies indicate that 2.85 billion people were exposed to some level of risk of transmission during 2009.

Morphology 

P. vivaxit is an irregularly shaped protozoan that does not present locomotive structures. The morphology varies according to each stage.

Young trophozoites are ring-shaped and can occupy up to one-third of the diameter of the erythrocyte . In it you can see a large chromatin point and the cytoplasm .

The mature trophozoite has an amoeboidal shape and is larger, occupying almost the entire erythrocyte. It has 16 merozoites inside, where the chromatin and cytoplasm are appreciated in each of them.

Macrogametocytes can be round or oval and have a homogeneous cytoplasm. Chromatin is small and compact, generally eccentric, with concentrated malarial pigment. While the microgametocyte is smaller, with diffuse and central chromatin, and dispersed malarial pigment.

Schizonts are large, with 12 to 24 large merozoites.

Lifecycle 

When feeding, the female mosquito of the genus Anopheles injects forms of the parasite known as sporozoites into the human skin. These forms reach the liver through the bloodstream.

In liver tissue they become trophozoites, then schizonts. In successive divisions, numerous merozoites are generated, which are dumped back into the bloodstream.

Once in the bloodstream, trophozoites invade erythrocytes or red blood cells. After new divisions of the parasite, the erythrocytes break, releasing more merozoites.

Some of the cells produced develop into gametocytes, which differentiate into two types, microgametocytes and macrogametocytes. Thus, when a mosquito feeds on the infected person again, it removes the gametocytes.

The gametes fuse in the gut of the mosquito to form a zygote that transforms into a mobile form known as an ookinet and then into oocysts. 

The oocysts, after multiple divisions, produce thousands of sporozoites, which migrate to the salivary glands of the insect. When the infected mosquito bites a new victim, it inoculates the infecting forms, starting a new cycle.

Symptoms of the disease

Malaria can be transmitted by the bite of a Plasmodium- infested mosquito , or by the transfusion of blood contaminated with that parasite.

Infection with P. vivax can range from parasitaemia without symptoms or fever without complications, to severe and fatal illness.

The action of the parasite can cause chills followed by intermittent fevers, with a periodicity of 24 to 48 hours. Fever may be accompanied by headache, muscle pain, cough, diarrhea, restlessness, delirium, anemia, heavy sweating, general weakness.

These symptoms alone do not allow a precise differentiation of conditions caused by P. vivax, those caused by other Plasmodiums, or other febrile conditions.

For an accurate diagnosis, parasitological confirmation is required by microscopic examination, which can be a thick smear or peripheral blood smear, or by immunochromatographic tests.

Treatment

Treatment of uncomplicated malaria is based on chloroquine. Primaquine is used to prevent relapse. In cases considered complicated, Quinine is used, supplemented with the antibiotics Doxycycline or Clindamycin.

In the latter cases, the use of intravenous artemisinins has given better results than the administration of intravenous quinine. In pregnant women in highly endemic areas, a prophylactic dose of sulfadoxine-primetamine should be administered to eliminate possible parasites present in the placenta.

With any suspicion of malaria, the patient should be taken to a medical center for parasitological confirmation. Treatments based exclusively on clinical pictures are only indicated in the absence of immediate evidence and its results.

It is advisable to administer antimalarial drugs within the first 24 hours to prevent complications.

Prevention

The World Health Organization establishes the following basic principles for the prevention of malaria:

  • Rapid detection, diagnosis and treatment of all cases of the disease, preferably within 24 hours of onset.
  • The decrease in the transmission of vivax through the eradication and control of its biological vector, that is, the mosquito, through fumigation and elimination of breeding sites.
  • The prevention of new infections in humans through chemoprophylaxis-based treatments.

Given the importance in public health worldwide, the WHO has proposed important strategies and programs. Among which are the Global Technical Strategy against Malaria 2016-2030, a technical framework for all countries where malaria is endemic, and the World Program on Malaria, an instrument that seeks to coordinate global activities linked to the Organization to fight against malaria. malaria, among others.

References

  1. Arboleda, M., Pérez, MF, Fernández, D, Usuga, LY & Meza, M. (2012) Clinical and laboratory profile of patients with Plasmodium vivax malaria  , hospitalized in Apartadó, Colombia. Biomédica vol.32 (suppl); 58-67.
  2. Garnham, PCC (1988). Malaria parasites on man: life-cycles and morphology (excluding ultrastructure). In: Wermsdorfer WH, Mc Gregor I, editors, Malaria: principles and practice of malariology. New York: Churchill Livingstone, vol. I: 61-96.
  3. Guerra CA, Howes RE, Patil AP, Gething PW, Van Boeckel TP, Temperley WH, et al. (2010) The International Limits and Population at Risk of  Plasmodium vivax Transmission in 2009. PLoS Negl Trop Dis 4 (8): e774.
  4. Mueller, I., Galinski, MR, Baird, JK, Carlton, JM, Kochar, DK & Alonso, PL (20099. Key gaps in the knowledge of Plasmodium vivax, a neglected human malaria parasite. The Lancet Infectious Diseases. 9 (9 ): 555–566.
  5. World Health Organization (2008). World Health Organization Global Malaria Program. World Malaria Report 2008. Geneve: WHO.

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