Plasmodium falciparum is the name given to a single-celled parasite that is an infectious pathogen that can cause the life-threatening tropical disease ‘malaria tropica’ in humans.
What is Plasmodium falciparum?
Infographic on the transmission cycle of malaria by the Anopheles mosquito. Click to enlarge. Plasmodium falciparum belongs to the genus Plasmodia within the Apicomplexa group and maintains a very extensive life cycle. The pathogen is clearly distinguished from the other malaria pathogens by its characteristics. For the unicellular parasite, humans are considered the only natural host. Plasmodium falciparum is transmitted by female Culicidae (mosquitoes), which belong to the Anopheles family. After infection of humans, the malaria pathogen first multiplies within the liver and then in the bloodstream of the human organism. Due to the strong reproduction via the blood, a very high number of parasites can often be detected. The malaria pathogens attach themselves to the cell walls of the blood vessels. This property makes Plasmodium falciparum particularly dangerous, as the parasite has developed special molecular mechanisms of action to bypass the organism’s immune system.
Occurrence, distribution, and characteristics
The malaria tropica pathogen Plasmodium falciparum occurs predominantly in tropical areas and in the southern Sahara. However, the parasite has also established itself in South and Southeast Asia, Papua New Guinea, and the Amazon Basin. About 40% of the world’s population lives in regions with a significantly increased risk of infection. Until the 20th century, the parasite was also detected in the Mediterranean region. In this area, Spain, Italy and the Balkans were predominantly affected. In addition, it has been proven that the pathogen is also widespread in South America. Plasmodium falciparum was probably introduced from Africa to South America through the Atlantic slave trade and spread there. Basically, researchers say that parasites of this species are transmissible within the tropics only up to a sea level of about 1500 meters, but it has been proven several times that transmission is also possible at 2600 – 2800 meters. The Malaria tropica pathogen multiplies in the blood of the human organism, therefore parasitemia is a typical symptom after infection. During the course of the disease, ring-shaped trophocytes are first detected in the blood count. In Plasmodium falciparum, these are smaller than in other malaria pathogens. Mature gametocytes can only be detected long after infection. Frequently, a blood cell is also infected several times. During the course of the disease, the parasites grow and develop. Erythrocytes that exhibit older large ring forms show up with maurerian stains after staining in the laboratory. Later developmental stages are often observed only in small numbers in the blood smear. Through the process of division, the trophozoite later becomes a schizont, which again enlarges and fills most of the red blood cell. Widely developed blood schizonts typically contain 16 merozoites. Immature gametocytes can rarely be detected in peripheral blood. Characteristic of Plasmodium falciparum is the sickle-like shape of the mature gametocytes, which are observed in infected mammals with Plasmodia only in the subgenus Laverania. The macrogametocytes are very thin, the cytoplasm is clearly visible after staining, and the nucleus is relatively compact. Microgametocytes, on the other hand, are roundish in shape, the cytoplasm is not as clearly differentiated after staining, and the nucleus turns out larger and is less compact in shape.
Diseases and disorders
The parasite Plasmodium falciparum is causative for the tropical disease malaria tropica. The main feature of this disease is parasitemia. Parasitemia is defined as an accumulation of parasites in the blood, even when no symptoms of disease are present. Parasitemia is often very pronounced and is accompanied by neurological symptoms and complications. During the course of malaria tropica, rhythmic episodes of fever may occur; if these are not present, infection by Plasmodium falciparum still cannot be ruled out. After a bite by the mosquito, an average of 12 days pass until the outbreak of malaria tropica occurs.If pharmaceutical substances are taken prophylactically, the incubation period may be significantly prolonged. The characteristic symptom of infection by a malaria pathogen is hemorrhagic fever with sweating and chills. However, this symptom is absent in malaria tropica. However, if fever episodes occur, the course of the infection is considered to have a poor prognosis and often results in serious complications with comatose states. Coma and disturbances of consciousness with suddenly changing states of consciousness without signs are typical neurological symptoms of malaria tropica. However, slowly changing disturbances of consciousness, seizures, paralysis, and even death can also be complications. The number of parasites in the blood is always decisive for the diagnosis. It can therefore not only be made on the basis of the symptoms. As a result of infection, anemia also frequently occurs. The more pronounced the parasite infestation, the more severe the anemia. The anemia occurs due to the destruction of red blood cells. Furthermore, the destruction of red blood cells (hemolysis) causes an increase in the level of hemoglobin in the bloodstream. The excess hemoglobin is excreted through the kidney (hemoglobinuria). This process is also known as ‘black water fever’ and can cause acute kidney failure. Due to renal insufficiency, massive edema of the extremities and trunk occurs. In rare cases, edema formation may also occur within the lungs. In addition, an enlarged spleen may result from the breakdown of infected red blood cells. Severe hyperplasia of the spleen may result in mild tissue damage and even complete rupture of the spleen.
