Plasmodia are known as malaria pathogens and are transmitted by the Anopheles mosquito to a host in which they multiply parasitically. Plasmodium vivax is one of four causative agents of malaria. The form of malaria caused by the parasite is known as malaria tertiana, which is considered a milder form of the disease.
What is Plasmodium vivax?
Plasmodia belong to the class Sporozoa. The new systematics assigns the pathogens to the phylum Apicomplexa. All plasmodia can be transmitted by the so-called Anopheles mosquito. The protozoa correspond to malaria pathogens. As parasites, they colonize the red blood cells of the host and feed on hemoglobin, the red blood pigment. The hemoglobin becomes hemozoin during the course of infection. This transformation shows up in infected blood cells as a blackish brown pigment. As erythrocytes (red blood cells) break down, toxic breakdown products are released. These toxins cause the characteristic febrile seizures of malaria. Plasmodium vivax corresponds to one of a total of four unicellular organisms Plasmodia family. The unicellular organism is associated with malaria tertiana. Distribution of the pathogen is mainly in tropical areas and in subtropical areas. In prehistoric times, Plasmodium vivax was also common in Germany and was associated with marsh fever at that time. Malaria tertiana caused by the pathogen corresponds to a rather benign form of malaria, which can be distinguished from malaria tropica in its course and is generally not life-threatening. However, infections with Plasmodium vivax or infections with Malaria tertiana are relatively common. The prevalence is approximately 100 to 400 million new cases per year.
Occurrence, distribution, and characteristics
Like all other malaria parasites, Plasmodium vivax is transmitted with the bite of female Anopheles mosquitoes. Plasmodium vivax occurs as a malaria parasite primarily in the western Pacific region, but is equally common in South America. A characteristic of all plasmodia is the alternation of sexual and asexual reproduction, which is titled with the term alternation of generations. Host alternation occurs. The first of the developmental phases in human infection is the phase of schizogony. The malaria pathogens reach the body of their host in the form of so-called sporozoites. They settle in the liver tissue, where they become schizonts in hepatocytes. After the schizonts decay, the pathogens are present in the form of merozoites, which reach the blood from the liver and colonize the red blood cells there. Within the erythrocytes, the pathogens become further merozoites via the blood schizonts stage. A certain proportion of these merozoites do not reach the survival state of schizonts, but develop into microgametocytes and macrogametocytes. These individual gamonts are transferred back to the insect during a repeated mosquito bite, in whose gut they mature into full gametes and fuse as part of sexual reproduction. A zygote then infiltrates the mosquito’s intestinal wall and gives rise to an oocyst. This oocyst matures. Now asexually dividing, 10,000 sporozoites can arise from the oocyst. Oocysts release the sporozoites by bursting. From the salivary glands of the female mosquito, the sporozoites are transferred back to a human or animal host. Similar to all plasmodia, Plasmodium vivax thus undergoes different stages of development. In the form of liver schizonts, the pathogens carry roundish or oval shapes and measure up to 50 micrometers. In the course of multiplication in a host organism, plasmodial pathogens usually infect a single cell several times, giving rise to trophozoites. At this stage of development, the host’s erythrocytes swell. In addition to the characteristic increase in size, the blood cells undergo other changes and acquire a typical coloration, also known as Schüffner’s stippling. The color change is negligible in infections with Malaria Tertiana. In other forms of malaria, the stippling is much more noticeable. Trophozoites are endowed with amoeboid cytoplasm. More than 15 merozoites are located in each of mature blood schizonts. Immature gametocytes of Plasmodium vivax are not equipped with ameboid cytoplasm.
Diseases and ailments
Plasmodia of the species vivax are described as obligate human pathogens and thus necessarily cause malaria tertiana. The incubation period is up to three weeks after the bite of an infected mosquito. With chemoprophylaxis, incubation periods of months occur. At the beginning of the infection, patients suffer from cyclic fever episodes with a three-day fever rhythm. Between fever days there is one fever-free day. A fever attack is opened by the so-called freezing phase, which usually lasts for an hour. The patient’s body temperature rises sharply during this stage. The subsequent heat phase often lasts for four hours and is accompanied by burning of the skin, nausea, fatigue and vomiting. In many cases, the patient’s body temperatures exceed 40 degrees Celsius. Sweating sets in during the third phase of infection. This last phase usually lasts for about three hours. The affected person’s temperature gradually normalizes during this phase. The patient recovers slowly. After a fever-free day, the next bout of fever sets in. As a rule, patients of malaria tertiana do not suffer from life-threatening general conditions. A prophylactic vaccination against Malaria tertiana does not yet exist. Therefore, travel to high-risk areas of malaria is generally not recommended. If travel is undertaken to the relevant areas, chemoprophylaxis is required. Antimalarial drugs can be carried in case of infection, such as quinine. Quinine acts on the schizonts in the blood, killing the pathogens and stabilizing the affected person. Synthetic agents are also available against malaria pathogens. Meanwhile, however, the pathogens have developed immunity to the synthetic drugs manifold.
