Plasmodium falciparum
Etiology/Bacteriology
Taxonomy
| Domain = Eukarya | Kingdom = Chromalveolata | Phylum = Apicomplexa | Class = Aconoidasida | Order = Haemosporida | Family = Plasmodiidae | Genus = Plasmodium | Species = P. falciparum
Description
Pathogenesis
Transmission
Transmission of P. falciparum occurs between humans and Anopheles mosquitos. Malaria is passed by vectors such as Anopheles gambiae, Anopheles albimanus, Anopheles freebomi, Anopheles maculatus, and Anopheles stephensi which transfer from host to host. The parasite can infect the mosquitos through the in take of human blood or a human by the mosquitos injection of saliva into the human. Once the mosquito becomes infected with Plasmodium falciparum it transfers the disease to each new host it penetrates. Humans can rarely transfer the parasite between each other. There have been rare cases of contaminated transfused blood infecting the recipient, but seldom does this occur because of screening that takes place pre-blood donation. Mothers can also pass P. falciparum to their child during birth, this is also a seldom occurrence.
Infectious Dose, Incubation, Colonization
Symptoms of Malaria typically begin 8-25 days following infection, in few cases it can take up to a year. The late onset of incubation is due to taking an inadequate amount of anti-malaria medication. The infectious dose is not precisely known, but it is understood to be a very low number. Malaria can be observed months to years after first set of symptoms are observed. This is due to the parasites ability to lie dormant in liver cells until the environment is right for a relapse. This is mainly seen in P.vivax and P. ovale, other strains of Malaria, rather then P. falciparum. The parasite colonizes in the liver and is then released into the blood stream and attached to erythrocytes.
Epidemiology
The key to Malaria-endemic is Anopheles mosquitos ability to live in an area. Temperature is also important having to stay above 20 degrees Celsius. The main areas of P. falciparum are South America, Africa, India, and few parts of Indonesia. The best possible location is along the equator in a warmer region. Transmission will not occur in high altitudes, colder seasons, and deserts. Malaria is thought to have been around since the beginning of mankind, but was first discovered in blood in 1880 and found to be transmitted by mosquitos in 1889. There are four common species of Malaria of which P. falciparum is the most severe. Plasmodium falciparum continues to increase in drug-resistant populations and insecticide-resistant mosquitos leading to the prediction that the disease will only worsen over time.
Virulence Factors
PfEMP1, P.falciparum erythrocye membrane protein 1, is an adhesive ligand protein which is created inside of a P. falciparum infected erythrocyte and presented on the surface. PfEMP1 is known as a knob and is encoded by the multigene segment, Var. Sequestration occurs when the parasite infected blood cells adhere to vascular endothelium which leads to further adherence of P. falciparum in deep microvasculature of tissues and organs. Each Plasmodium falciparum has roughly 50 versions of PfEMP1 with which it can alter its appearance by changing to another PfEMP1 when the immune system begins to create antibodies for the original PfEMP1 in a process known as antigenic variation. Changing of adherence molecules also means a change in the receptor on the epithelial. The change in receptor is hypothesized to possible change the disease outcome.
RIFIN, repetitive interspersed family, is considered the most abundant multigene family. PfEMP1 along with RIFIN is considered a crucial cornerstones for the virulence of Plasmodium falciparum mainly due to its ability to avoid immune response through antigenic variability and ultimately colonizing and replicating in the liver and erythrocytes. RIFIN is also presented on the outer membrane of an parasite infected erythrocye as an adherence factor.
Rosettes are uninfected red blood cells that form clumps with Malaria-infected erythrocytes. Clumping occurs when particularly sticky PfEMP1 attach to other red blood cells. Only a minority of P. falciparum actually creates rosettes, but when they do they are known to be linked to severe malaria.
Malaria pigment (hemozoin)
Clinical features
Symptoms
Malaria can come in two forms, uncomplicated or severe. In most occurrence the severe case is observed showing symptoms such as cerebral malaria, which cause abnormal behavior, seizures, coma, or impairment of consciousness. Severe symptoms also present anemia due to destruction of red blood cells, hemoglobinuria, acute respiratory distress, low blood pressure, acute kidney failure, metabolic acidosis, and hypoglycemia. These are all due to organ failure and abnormalities in patient's blood or metabolism.
During a rare uncomplicated infection, symptoms appear flu-like. The attack lasts roughly 6-10 hours presenting a cold stage, hot stage, and sweat stage. During these stages one shows symptoms of fever, chills, sweats, headache, nausea, vomiting, body ached, and malaise.
Morbidity and Mortality
Diagnosis
Treatment
Prevention
Risk Avoidance
Immunization
Host Immune Response
References
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