Parasite and Vector

Malaria in humans is caused by four species of a parasite: Plasmodium vivax, P. falciparum, P. malariae and P. ovale. The Anopheles mosquito is a vector for this parasite. There are 435 known species of the anopheles mosquito, out of which 30-40 species can transmit malaria. In sub-Saharan Africa, the three major species that transmit malaria are: Anopheles gambiae, Anopheles funestus, and Anopheles arabiensis. [1]

Brief Overview of the life cycle [2]

[Picture obtained from www.malariavaccine.org/ mal-what_is_malaria.htm]

Step 1: Infected mosquito bites human host and injects sporozoites into the bloodstream. Sporozoites are haploid cells that are infective.

Step 2: The sporozoites make their way to the liver via blood and lymph and infect human liver cells.

Step 3: In the liver, these cells form infective merozoites or daughter cells, which when released into the bloodstream quickly enter red blood cells inside which they undergo another cycle of replication.

Step 4: RBCs rupture and release the merozoites along with toxins (which cause the symptoms of malaria such as chills and fever) into the bloodstream.

Step 5:

The gametocytes are at a developmental dead end in vertebrates; however, they are the only form of the plasmodium that can infect the mosquito.

Step 6: Another mosquito might take a blood meal from an infected human and receive gametocytes in the blood where they exflagellate to help movement.

Step 7: They enter the insect gut and form a zygote through sexual reproduction.

Step 8: The oocyst that is formed ruptures in the gut releasing many infective sporozoites that travel to the mosquito’s salivary gland, ready to infect the next human it bites.

Symptoms

Major symptoms include fever, chills, sweats, headaches, nausea, vomiting, weakness, body aches. Symptoms specific to P. falciparum include: jaundice, swollen liver and rapid breathing.  Complications that may accompany severe malaria include: irregular breathing, fluid in lungs, anemia, behavioural abnormalities due to infection of the brain, abnormalities in blood coagulation and cardiac problems. [3]

Diagnosis

[Blood cells infected by malaria, from http://www.sciart.org/site/redwet.html]

Methods of diagnosis include microscopy, blood smears, RDT (Rapid Diagnostic Test) that detects antigens to the plasmodium, molecular diagnosis with PCR (Polymerase Chain Reaction),  and serology to detect antibodies to the parasite (uncommon). In sub-Saharan Africa where these diagnostic tools might be inaccessible or costly, fevers are used to diagnose malaria in a presumptive approach to treatment. [4]

Treatment

Historically, quinine from the cinchona bark was used for malaria treatment. Chloroquine with quinine as the active ingredient is a commonly used drug. Artemisinin derivatives are often used overseas though not licensed for use in the United States. Other drugs used are: sulfadoxine-pyrimethamine, mefloquine, atovaquone-proguanil and doxycycline. [5]

References

[1], [2] "Biology", CDC website

[2] David Schneider

[3] "Diesase", CDC website

[4] "Diagnosis", CDC website

[5] "Treatment", CDC website

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