Life Cycle of Malaria

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QUESTION

Why does the malaria parasite first enter the liver?

ANSWER

The malaria parasite enters the liver in order to transform from a sporozoite (which can infect liver cells) to a merozoite, which is capable of infecting red blood cells. Both stages also include a proliferation step, but in the blood, the merozoites are also able to differentiate into gametocytes, which are then taken back up by a mosquito during a blood meal, allowing the malaria parasite to continue its life cycle. If the red blood cell stage were first, followed by the liver, then it would be much harder for the gametocytes to be able to reach a new mosquito host, unless they were to enter the blood a third time.

The blood is also a difficult place for a parasite to survive, since it is the highway of the immune system, whereas the parasite is less easily destroyed when it is hiding out in the hepatocyte cells in the liver. It is also important to note that Plasmodium has a long evolutionary history, and may in some parts of its life cycle be constrained by physiological or life history characteristics of its evolutionary forebears, which may also contribute to our perception of the life cycle as being very complex!

Schizont

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QUESTION

What is a schizont?

ANSWER

A schizont is a malaria parasite which has matured and contains many merozoites, which are the parasite stage that infects red blood cells.

Schizonts can be produces during two separate phases of the life cycle within the human host: first in the hepatocytic cells in the liver (when sporozoites mature) during the exo-erythrocytic cycle and then within the red blood cells during the erythrocytic cycle (when trophozoites mature and divide).

When malaria parasites do not immediately mature into schizonts in the liver (as can be the case with Plasmodium vivax and P. ovale infections), the parasite instead becomes a hypnozoite, which can lay dormant in the liver for many weeks or even months (or, in rare case, years), and produce relapse of infection at a much later date.

Did I have malaria before?

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I am from East Africa. On July 3rd,2011 I had chills and I consulted a doctor, he did a blood test and told me I had malaria and gave me medication.

Then after 10 days I had neck pain and I went again to the doctor, who did another blood test, diagnosed malaria and gave medication. Then after 10 days it repeated.

It’s now the 22nd august,2011. I have pain in my neck and I went to another doctor he told to take blood test and he told for the last one month you didn’t get attacked by malaria. Can I know whether I suffered from malaria for the past 1 month? Also he has told me to take saline with some medicine to flush out that malaria medication. Is it correct? Please advise me.

ANSWER:

One of our collaborating medical doctors has kindly assisted in providing this answer. If recurrent symptoms of malaria were from one exposure to malaria earlier this year, then a drug-resistant strain of Plasmodium vivax is likely. OR, he/she simply needs to take primaquine for 4-6 weeks to eradicate the liver phase. The recurrent blood phase (symptomatic phase) may be due to smoldering infection in the liver. In order to confirm this hypothesis, you would need to know what drugs you were given on your earlier trips to the doctor, as well as the type of malaria the doctor diagnosed, if possible.

 

Malaria After Blood Transfusion

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QUESTION:

How many days does it take to become symptomatic after a blood transfusion of malaria infected blood to patient?

ANSWER:

This depends on the strain and burden of malaria parasites in the blood being transfused. Onset of malaria symptoms can be very rapid if infected red blood cells begin to rupture immediately, say within 24-48 hours, or conversely symptoms can be very delayed (days/weeks/months) if only a few parasites are transfused. Depending on strain, the malaria parasites may need to cycle through the liver to mature before they infect the red cells (such as in the case of Plasmodium vivax or P. ovale).  Then, depending on the strain (P. vivax most commonly), the infected red cell “burden” often needs to approach 0.5 to 1% before synchronized rupture of red cells and release of the parasites is sufficient to produce acute fever and symptoms.


Primaquine for Malaria Treatment

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QUESTION:

In India what is the duration of primaquine therapy in confirmed Malaria infection?

ANSWER:

Primaquine is usually used to kill the hypnozoite stages of Plasmodium vivax or P. ovale. This life stage of the malaria parasite can reside, dormant in the liver’s hepatocyte cells, even after the patient has completed the normal course of treatment for the infection; at this stage, the patient might not have visible malaria parasites in the bloodstream, and thus be considered “cured”. Despite this, the patient is actually potentially at risk from recurrence of malaria if the dormant liver hepatocytes re-enter the blood stream.

For this reason, patients with P. vivax or P. ovale should complete a course of primaquine in addition to the standard malaria treatment offered. The usual adult dosage for primaquine is 15-30mg base, taken orally, once a day for 14 days.