The Human Stage - Initial Infection
The human host experiences two distinct stages of malaria: the liver stage and the blood stage. Initial infection occurs when the bite of a female Anopheles mosquito introduces Plasmodium sporozoites into the host's bloodstream.
The Liver Stage
The sporozoites then infect liver cells. They eventually will mature into schizonts, cell capsules that rupture to release merozoites. The merozoites multiply within the liver. In some forms of the disease, a dormant form of the parasite known as hypnozoites can continue to live in the liver, causing relapses weeks or even years later.
The Blood Stage
The merozoites eventually infect red blood cells. Within the cells, they will become trophozoites. In an intermediary stage known as the ring stage, trophozoites mature into schizonts that rupture, releasing more merozoites, which infect more blood cells. Some of the trophozoites mature into gametocytes that are then ingested by a female mosquito during a blood meal.
The Mosquito Stage
Known as the sporogonic cycle, the ingested gametocytes, both male and female, combine to form zygotes. These eventually become a motile form of the parasite known as an ookinete. The ookinetes move to the mosquito's midgut wall, where they change into oocysts. These grow and rupture, releasing sporozoites. The sporozoites move to the mosquito's salivary glands, starting the infection cycle over again when an infected mosquito bites a host.
Symptoms
Fever and chills are the predominant symptoms of malaria. Headache, muscle and joint pain, vomiting, diarrhea and weakness also can occur. Some forms of the disease can be fatal because of renal failure, anemia, respiratory distress or central nervous system failure.
Diagnosis and Treatment
Diagnosis of malaria should be made by looking for the parasite in a recently collected blood sample. Different forms of Plasmodium require different treatment approaches, so proper identification of the specific form of Plasmodium and the stage of infection is key. Blood tests for antigens also can assist in diagnosing the illness.
The drug of choice for treating malaria is chloroquine. Certain chloroquine-resistant strains of Plasmodium can be treated with either quinine sulfate and doxycycline, tetracycline, clindamycin or atovaquone-proguanil.
Tags: mature into, Anopheles mosquito, blood cells, form parasite, form parasite known