Plasmodium falciparum is the most serious and deadly of the Plasmodium. >5% of red blood cells can become infected and subsequently destroyed during one paroxysm. Parasitemia in other Plasmodium spp. is usually around <2%. The manifestations of Plasmodium falciparum infections have resulted in various names given to an infection (Black Water Fever, Fatal Malaria).
Disease / Pathogenesis
Plasmodium falciparum is the most the most deadly of the Plasmodium. The malaria that it causes is most deadly in small children where, as an example, in Africa nearly 80% of the total deaths due malaria are due to Plasmodium falciparum. 95% of the cases of Plasmodium falciparum infections occur in Africa. And the Sub-Saharan Africa is especially hit the hardest with almost 100% of malarial cases attributed to Plasmodium falciparum.
Plasmodium falciparum is the species of Plasmodium most responsible for malarial deaths. The overwhelming infection of red blood cells is due to the organism’s nondiscriminatory infection of the red blood cells. In other words, whereas the other Plasmodium spp. will infect either young red blood cells or old red blood cells preferentially, Plasmodium falciparum will infect red blood cells in all stages of development. The paroxysms are associated with massive amounts of red blood cell destruction leading to severe anemia; the massive release of merozoites from the infected red blood cells leading to the acute immunological response of the host; the generation of toxic degenerative end products that induce adverse immunologic reactions in the host; a strain on kidneys due to nephrotic damage; capillary obstruction leading to hypoxic damage to various organs; and the added risk of strokes especially when the brain is involved. The organism has also been found to predispose individuals to blood cancer, specifically Burkitts Lymphoma.
The release of the merozoites after lysis of the red blood cells is called the paroxysm and is accompanied by a high fever. The fever has a characteristic hot , cold, and sweating stage. The symptoms that occur are headaches; fever; muscle pain; nausea; vomiting; mild diarrhea, and dizziness. An increased heart rate, and pallor can also be noted. There is involvement of the spleen and liver (splenomegaly or/and hepatomegaly).
The organism has the ability to produce at least 2,000 cell membrane antigens that give it the ability it to elude the host immune system. It will have a 48-hour cycle of periodicity but the host will frequently exhibit irregular bouts of fever due to the diverse stages of red blood cells infected.
As mentioned previously, when the brain is involved the risk of strokes is of great concern. Cerebral malaria is the most dangerous condition leading to death in a host infected with Plasmodium falciparum. Plasmodium falciparum sequestration is the mechanism by which infected cells are clustered and in so doing they stick to the inner surface of blood vessels. This can lead to strokes, and can also lead to the obstruction of capillaries resulting in the damage to organs including the brain. The merozoites in the brain will cause brain damage of varying degrees. Survivors of cerebral malaria due to Plasmodium falciparum will many times have neurological damage that is irreversible (behavioral problems, intellectual impairment, and epilepsy). More complications of malaria can also be hypoglycemia and low blood pressures caused by cardiovascular collapse.
Location in the Host
Plasmodium falciparum infects all stages of red blood cells and infects all areas of the reticuloendothelial system. It can also enter the brain and cause cerebral malaria which can lead to coma and death.
Plasmodium falciparum is the most prevalent malaria species in Africa while Plasmodium vivax is the most common in the world. Plasmodium falciparum is the deadliest of the malaria. Plasmodium falciparum is also found in South-East Asia, Eastern Mediterranean, Western Pacific, Central and Northern South America.
Morphology & Diagnosis
Plasmodium falciparum parasitemia as mentioned before can be >5%. The red blood cells infected are of all developmental stages.
The ring trophozoites in the red blood cells are many times described as “ear-phone” shaped and more than one trophozoite may be seen in the cell. In addition there are appliqué forms that can be seen on the periphery of red blood cells that is characteristic of Plasmodium falciparum. Characteristic gametocyte forms can sometimes be seen and they will have an elongated shape that is described as banana or crescent shaped. When schizonts are seen they will contain 8-24 merozoites and the mature schizont will generally fill about 2/3 of the infected cell. Schizonts are generally not seen in the peripheral blood except for severe cases.