Microbiology
Summary
Plasmodium spp. are blood protozoa that cause malaria, and are primarily transmitted by the bite of the Anopheles mosquito. Malaria is endemic to regions including Central and South America, Southeast Asia, and sub-Saharan Africa, and often manifests with symptoms such as high-grade fever, chills, flu-like symptoms, hepatosplenomegaly, anemia, jaundice due to intravascular hemolysis, and thrombocytopenia. Among the various Plasmodium species, Plasmodium falciparum is notable for its irregular fever pattern and potential to cause severe malaria complications like cerebral malaria. Erythrocytes infected by this species can lead to renal and hepatic failure, and acute respiratory distress syndrome (ARDS). G6PD deficiency, sickle cell trait, and alpha and beta thalassemia confer relative protection against P. falciparum. On the other hand, Plasmodium vivax and Plasmodium ovale are unique in their ability to produce hypnozoites, dormant forms in the liver that can cause relapses of the disease. Their fever patterns are distinct, with spikes recurring every 48 hours. Another species, Plasmodium malariae, is identified by a fever that recurs every 72 hours. Last, Plasmodium knowlesi is carried by macaques and produces fever spikes every 24 hours.
The Plasmodium life cycle starts when a female mosquito bites and injects sporozoites into the bloodstream, beginning the exoerythrocytic cycle. Sporozoites move to the liver and infect hepatocytes. They divide to form schizonts, each containing multiple merozoites. These schizonts rupture, releasing merozoites into the bloodstream. Sporozoites of P. vivax and P. ovale can become hypnozoites, remaining dormant in hepatocytes before forming schizonts, causing relapses. Merozoites in the bloodstream infect RBCs, starting the erythrocytic cycle. Merozoites develop into ring forms, then mature trophozoites within RBCs. Mature trophozoites become schizonts, which rupture, leading to RBC lysis and merozoite release, causing new infections. Some merozoites differentiate into male and female gametocytes. Microscopic examination of blood smears is the gold standard for diagnosis, showing trophozoites, schizonts, or gametocytes. P. falciparum gametocytes are elongated, P. vivax and P. ovale cause Schu_ffner dots in RBCs.
Lesson Outline
Don't stop here!
Get access to 128 more Microbiology lessons & 13 more medical school learning courses with one subscription!
FAQs
Plasmodium is a genus of blood protozoa that causes malaria in humans. There are several species of Plasmodium that infect humans, but the most deadly is Plasmodium falciparum. Malaria is transmitted to humans through the bite of an infected Anopheles mosquito, which injects the parasites into the bloodstream.
Malaria symptoms can range from mild to severe, and can even be fatal in some cases. Initial symptoms often include fever, headache, and chills. If not treated quickly, the more severe form of the disease (usually caused by P. falciparum) can rapidly progress and cause severe anemia, respiratory difficulties, and organ failure.
The Plasmodium life cycle involves multiple stages both in the mosquito and the human host. Once a mosquito carrying Plasmodium bites a person, the parasite enters the bloodstream and travels to the liver where it matures and reproduces. The next stage occurs when these new parasites re-enter the bloodstream and infect red blood cells, leading to clinical symptoms. Understanding this life cycle is critical in developing treatments and prevention strategies for malaria.
Hemoglobinopathies, like sickle cell trait and thalassemia, can affect the course of a malaria infection. Some studies suggest that these conditions provide a degree of protection against severe malaria. The exact mechanism is not completely understood but it is thought that the abnormal shape or structure of the red blood cells in these conditions makes it harder for the Plasmodium parasite to invade and multiply within the cells.
